| Paper | Title | Page |
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| WEP003 | A New Correction Scheme to Compensate Depolarizing Integer Resonances at ELSA | 1507 |
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Funding: BMBF Since more than four decades, the University of Bonn supports research at the in-house electron accelerator ELSA. Presently, the polarized electrons gained from an inverted source are accumulated in a stretcher ring and accelerated within a fraction of a second up to 3.2 GeV. During the fast ramping various depolarizing resonances are crossed. By taking several expedient measures (closed orbit correction, tune jumping, etc.) a high polarization degree of up to 65% is reached. One important part of these measures is the harmonic correction of integer resonances. Those resonances are compensated by applying additional horizontal fields, distributed sinusoidally along an one-turn orbit length. In case of an appropriate setting of amplitude and phase, all resonance driving effects should be neutralized completely. First studies have shown that vertical displacements and resulting horizontal fields in the quadrupole magnets, caused by the resonance correction, have to be taken into account as well. With regard to a new correction scheme, the first experimental results confirmed by simulative and theoretical studies will be presented. |
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| WEP005 | Modeling the Low-Alpha-Mode at ANKA with the Accelerator Toolbox | 1510 |
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| The ANKA storage ring is operated frequently with low momentum compaction lattices to produce short bunches for the generation of coherent synchrotron radiation in the THz range. The bunch length can be varied in steps from one centimeter down to the sub millimeter level. These low alpha optics are modeled by using the Matlab based tools, Accelerator Toolbox (AT) and LOCO. The results are compared with measurements such as orbit response matrices, dispersion and chromaticity. This paper provides results of a study on the feasibilities as well as limitations of the measurements and calculations. | ||
| WEP006 | Study of Effects of Failure of Beamline Elements & Their Compensation in CW Superconducting Linac | 1513 |
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| Project-X is the proposed high intensity proton facility to be built at Fermilab, US. The first stage of the Project-X consists of superconducting Linac which will be operated in continuous wave (CW) mode to accelerate the beam from 2.5 MeV to 3 GeV. The operation at CW mode puts high tolerances on the beam line components, particularly on radiofrequency (RF) cavity. The failure of beam line elements at low energy is very critical as it results in mis-match of the beam with the following sections due to different beam parameters than designed parameter. It makes the beam unstable which causes emittance dilution, and ultimately results in beam losses. In worst case, it could affect the reliability of the machine and may lead to the shutdown of the Linac to replace the failed elements. Thus, it is important to study these effects and their compensation to get smooth beam propagation in Linac. This paper describes the results of study performed for the failure of RF cavity & solenoid in SSR0 section. | ||
| WEP007 | Calculation of Acceptance of High Intensity Superconducting Proton Linac for Project-X | 1516 |
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| Project-X is the proposed high intensity proton facility to be built at Fermilab, US. Its Superconducting Linac, to be used at first stage of acceleration, will be operated in continuous wave (CW) mode. The Linac is divided into three sections on the basis of operating frequencies & six sections on the basis of family of RF cavities to be used for the acceleration of beam from 2.5 MeV to 3 GeV. The transition from one section to another can limit the acceptance of the Linac if these are not matched properly. We performed a study to calculate the acceptance of the Linac in both longitudinal and transverse plane. Investigation of most sensitive area which limits longitudinal acceptance and study of influence of failure of beam line elements at critical position, on acceptance are also performed. | ||
| WEP010 | Design of the Bilbao Accelerator Low Energy Extraction Lines | 1519 |
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Funding: European Spallation Source - Bilbao The ESS-Bilbao linac will accelerate H+ and H− beams up to 50 MeV, which need to be transported to three laboratories, where different types of experiments will be conducted. This paper reports on the preliminary design of the transfer line, which is mainly performed based on beam dynamics simulations. |
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| WEP011 | Low Energy Beam Transport Developments for the Bilbao Accelerator | 1522 |
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Funding: European Spallation Source - Bilbao In this work we present a future upgrade of the ESS-Bilbao multi-source Low Energy Transport System (LEBT). It consists of a set of solenoids and steering dipoles used to match the characteristics of both ion source beams i.e., the Electron Cyclotron Resonance (ECR) H+/D+ source and the H− Penning source, to the input specifications of the RFQ. Different configurations of the geometry and magnetic fields are studied in order to minimize the emittance growth along the LEBT, while providing the beam specifications required by the RFQ. |
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| WEP015 | Initial Simulations of Electron and Ion Beam Optics for the ANL EBIS Electron Collector | 1525 |
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Funding: U.S. Department of Energy, Office of Nuclear Physics, under contract number DE-AC02-06CH11357 An Electron Beam Ion Source (EBIS) being developed at the Argonne National Laboratory (ANL) will be used to charge breed rare isotopes from a 1 Ci 252Cf source, the Californium Rare Isotope Breeder Upgrade (CARIBU). Simulations have been performed using commercially available software, TriComp, to ensure the electron collector is properly designed to dissipate the electron beam power and provide adequate acceptance for the injected ion beam. |
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| WEP016 | Evaluating the Dynamic Aperture for the New RHIC 250-GeV Polarized Proton Lattice | 1528 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. To increase luminosity in the Relativistic Heavy Ion Collider’s (RHIC’s) polarized proton 250 GeV operations, we are considering reducing beta* to 0.65 m at the interaction points (IPs), and increasing bunch intensity. The new working point near the 2/3 integer will used on the ramp to preserve polarization. In addition, we plan to adjust the betatron-phase advances between IP6 and IP8 to (k+1/2)*PI so to lower the dynamic beta-beat from the beam-beam interaction. The effects of all these changes will impact the dynamic aperture, and hence, it must be evaluated carefully. In this article, we present the results of tracking the dynamic aperture with the proposed lattices. |
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| WEP017 | Re-Examination of the NSLS-II Magnet Multipole Specifications | 1531 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy The NSLS-II magnet multipole specifications were determined based on analysis of nonlinear beam dynamics. The required field quality does not exceed what was specified for the existing third-generation light sources. While the prototype magnets have met these specifications, the magnets from mass production could potentially have bigger errors which exceed certain tolerances. In this paper we discuss the results of recent calculations to provide further insight into the acceptable range of the magnet multipoles based on the physics requirements. |
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| WEP018 | Optics Error Measurements in the AGS for Polarized Proton Operation | 1534 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. A large distortion of the vertical beta function became evident in the Brookhaven AGS during the 2010 polarized proton run. This paper describes the beam measurements and model calculations made to verify the distortion of the optics, to infer possible sources and to explore correcting strategies. The optics distortion is only apparent when operating with a betatron tune very near the integer (as required for polarization preservation during acceleration in the AGS) and with the lattice chromaticity sextupoles powered. The measurements indicate a small (on the order of millimeters) unexpected systematic horizontal closed orbit displacement in the sextupoles that is not evident in beam position monitor measurements. Motivated especially by these observations a complete survey of the AGS was performed during the 2010 shutdown period.&nb sp; The results of that survey and their impact on the observed optical errors in the AGS are included. |
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| WEP021 | The Effect of Initial Energy Spread on Longitudinal Beam Modulations in an Electron Gun | 1537 |
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| Computer simulations are used to investigate the evolution of longitudinal density and energy modulations of an electron beam in a linear accelerator system. This study examines the effect of initial energy spread on the modulations as the beam is accelerated in the electron gun. | ||
| WEP022 | Status of Low Emittance Tuning at CesrTA | 1540 |
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Funding: Work supported by the National Science Foundation and by the US Department of Energy under contract numbers PHY-0734867 and DE-FC02-08ER41538. We report on the status of emittance tuning techniques at the CESR Test Accelerator CesrTA. The CesrTA experimental program requires the capability to operate in a variety of machine lattices with the smallest possible emittance. We have attempted to minimize the turn-around time of our low emittance tuning procedure. We utilize high bandwidth BPM electronics for fast, precision measurements of orbit, betatron phase, transverse coupling, and dispersion. Turn by turn data is used to measure BPM button electrode gains to a under a percent. Gain-corrected coupling data is utilized to determine BPM tilts to 10mrad, allowing for measurement of vertical dispersion at the level of 10mm. Measurement and analysis of the data for characterizing BPM response takes 5 minutes. Beam based measurement of machine functions, data analysis, and implementing corrections in the machine takes another 5 minutes. An x-ray beam size monitor provides a real time check on the effectiveness of the procedure. A typical correction results in an emittance less than 20pm at 2.1GeV in 1-2 iterations. Sub 15pm has been achieved with adjustment of closed coupling/vertical dispersion bumps and betatron tunes. |
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| WEP024 | Near-ideal Emittance Exchange at the Fermilab Photoinjector | 1543 |
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| The A0 Photoinjector at Fermilab is presently home to an emittance exchange (EEX) experiment. The emittance exchange beamline consists of a 3.9 GHz normal conducting deflecting mode cavity flanked by two doglegs. Electron bunches with charges of 250 pC and energy of 14.3 MeV are routinely sent through the exchanger. Here we present results of a 1:1 transverse and longitudinal emittance exchange. | ||
| WEP030 | Direct Focusing Error Correction with Ring-wide TBT Beam Position Data | 1546 |
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| Turn-By-Turn (TBT) betatron oscillation data is a very powerful tool in studying machine optics. Hundreds and thousands of turns of data are taken in just few tens of milliseconds. With beam in free oscillation and covering all positions and angles at every location focusing error diagnosis can be made almost instantly. This paper describes a new approach that observes focusing error collectively over all available TBT data to find the optimized quadrupole strength, one location at a time. Example will be shown and other issues will be discussed. | ||
| WEP031 | Low-Emittance Lattice Designs for ALS Ultimate Upgrade | 1549 |
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| Based upon the Theoretical Minimum Emittance (TME) technique, a new method has been developed to optimize low-emittance and low-beta lattices for further brightness upgrades at the Advanced Light Source (ALS). The study provides us a different perspective on the lattice design, and confirms results earlier found using both Global Scan of All Stable Settings (GLASS) and Genetic Algorithms (GA) techniques. Since the optimal low-beta lattice may have a dynamic aperture too small to allow off-axis injection, to overcome this problem, an alternating high-low beta lattice could be used for the upgrade. Several options of these high-low beta lattices are investigated using Genetic Algorithms. | ||
| WEP032 | Beam Transport in a Compact Dielectric Wall Accelerator for Proton Therapy | 1552 |
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Funding: This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA2A27344. To attain the highest accelerating gradient in the compact dielectric wall (DWA) accelerator, the accelerating voltage pulses should have the shortest possible duration. To do so, the DWA will be operated in the “virtual” traveling mode*. Since only a short section of HGI wall would be excited, the accelerating field’s axial profile could be non-uniform and time dependent, especially near the entrance and exit of the DWA, which could lead to dispersion in beam acceleration and transport, and eventually emittance growth. The dispersive transverse kick on a short proton bunch at the DWA entrance and its impact on acceptable input proton bunch length will be discussed. Without using any external lenses, the dispersive transverse kicks on the beam can be mitigated. Implementing the mitigations into the transport strategy, we have established a baseline transport case. Results of simulations using 3-D, EM PIC code, LSP** indicate that the DWA transport performance meets the medical specifications for intensity modulation proton treatment. Sensitivity of the transport performance to the switch timing will be presented. * G. J. Caporaso, Y-J Chen and S. E. Sampayan, "The Dielectric Wall Accelerator", Rev. of Accelerator Science and Technology, vol. 2, p. 253 (2009). ** Alliant Techsystems Inc., http://www.lspsuite.com/. |
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| WEP033 | Using an Emittance Exchanger as a Bunch Compressor | 1555 |
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Funding: This work is supported by the U.S. Department of Energy through the LANL/LDRD program. An Emittance EXchanger (EEX), like a chicane, can be used for bunch compression. However, it offers a unique characteristic: the R56 term in an EEX vanishes, which decouples the final longitudinal position from the particles’ energies, thereby suppressing the microbunch instability. Also, it can provide simultaneous compression in both the longitudinal and one transverse dimensions, where, for example, the final longitudinal size is smaller than the initial horizontal size and the final horizontal size is smaller than the initial longitudinal size. In this scheme, there is no dependence on an energy slew needed for compressing the beam, simplifying the rf requirements. A bunch-compression scheme using two EEXs is presented, including CSR calculations. |
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| WEP035 | Intense Sheet Electron Beam Transport in a Periodically Cusped Magnetic Field | 1558 |
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Funding: Acknowledgements: We gratefully acknowledge funding by the Office of Naval Research. We explore periodically cusped magnetic (PCM) fields in the regime of a Ka-Band coupled-cavity travelling wave tube (beam current = 3.5A, voltage = 19.5kV, 10:1 beam aspect ratio). We use finite-element beam optics code MICHELLE to simulate the 3-dimensional beam optics for the beam transport within a PCM field. Realistic 3-dimensional magnetic fields have been considered to determine the practicality of these designs. We present the methodology used to focus and transport a thermal beam from a shielded-cathode, high aspect-ratio electron gun. |
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| WEP036 | Start-to-End Beam Dynamics Simulations for the SRF Accelerator Test Facility at Fermilab | 1561 |
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Funding: LANL Laboratory Directed Research and Development program 20110067DR. U.S. DoE contract No. DE-FG02-08ER41532 Northern Illinois University. Fermi Research Alliance, LLC Contract No. DE-AC02-07CH11359. Fermilab is currently building a superconducting RF (SCRF) linear-accelerator test facility. In addition to testing ILC-spec SCRF accelerating modules for ILC and Project-X, the facility will be capable of supporting a variety of advanced accelerator R&D experiments. The accelerator facility includes a 40-MeV photoinjector capable of producing bunches with variable parameters. In this paper, we present start-to-end simulations of the accelerator beamline. |
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| WEP038 | Physics Design of a Prototype 2-Solenoid LEBT for the SNS Injector | 1564 |
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| To mitigate the operational risks associated with the SNS electrostatic LEBT, an R&D effort is underway to develop a 2-solenoid magnetic LEBT, which should improve the reliability while matching or exceeding the beam dynamic capabilities of the present electrostatic LEBT. This paper discusses the physics design of a prototype 2-solenoid magnetic LEBT. | ||
| WEP039 | Tracking Stripped Proton Particles in SNS Ring Injection Momentum Dump Line | 1567 |
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| 3D computer simulations are performed to study magnetic field distributions and particle trajectories along the SNS ring injection momentum dump line. Optical properties and transfer maps along the dump line are calculated. The stripped proton particle distributions on the dump window are analyzed. The study has provided useful information for the redesign of the SNS ring injection beam dump. | ||
| WEP041 | Weak Resonances Induced by Nonlinear Multipoles in a Quadrupole Doublet Lattice | 1570 |
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Funding: This submission was sponsored by a contractor of the United States Government under contract DE-AC05-00OR22725 with the United States Department of Energy. In this paper we report the effects on beam dynamics from two intrinsic multipole components of a quadrupole magnet – dodecapole and psedu-octupole, in a quadrupole doublet lattice. Weak resonances at transverse phase advances 60°; and 90°; per cell, which may contribute to halo formation and beam loss in a linac, are shown from multi-particle tracking simulations. Although the net effect of the psedu-octupole component alone is very small due to substantial cancellations within the same magnet, its existence may significantly enhance the weak resonances which are induced by the dodecapole component of quadrupole magnets. The combined contributions of these two magnetic field components may not be simply linear-scaled because of the extreme nonlinear nature. |
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| WEP042 | FACET Emittance Growth | 1573 |
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Funding: Work supported by the U.S. Department of Energy under contract number DE-AC02-76SF00515. FACET, the Facility for Advanced Accelerator and Experimental Tests, is a new facility being constructed in sector 20 of the SLAC linac primarily to study beam driven plasma wakefield acceleration. The FACET beamline consists of a chicane and final focus system to compress the 23 GeV, 3 nC electron bunches to ~20μm long and ~10μm wide. Simulations of the FACET beamline indicate the short-duration and large, 1.5% rms energy spread beams may suffer a factor of four emittance growth from a combination of chromaticity, incoherent synchrotron radiation (ISR), and coherent synchrotron radiation (CSR). Emittance growth is directly correlated to head erosion in plasma wakefield acceleration and is a limiting factor in single stage performance. Studies of the geometric, CSR, and ISR components are presented. Numerical calculation of the rms emittance can be overwhelmed by long tails in the simulated phase space distributions; more useful definitions of emittance are given. A complete simulation of the beamline is presented as well, which agrees with design specifications. |
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| WEP044 | Emittance and Phase Space Exchange | 1576 |
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Funding: This work was supported by the US DOE under Contract No. DE-AC02-76SF00515. Alternative chicane-type beamlines are proposed for exact emittance exchange between horizontal phase space (x,x') and longitudinal phase space (z, delta). Methods to achieve exact phase space exchanges, i.e. mapping x to z, x' to delta, z to x and delta to x' are suggested. Some applications of the phase space exchanger and the feasibility of an emittance exchange experiment with the proposed beamline at SLAC are discussed. |
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| WEP045 | Measurement and Manipulation of Beta Functions in the Fermilab Booster | 1579 |
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| In order to meet the needs of Fermilab’s planned post- collider experimental program, the total proton throughput of the 8 GeV Booster accelerator must be nearly doubled within the next two years. A system of 48 ramped corrector magnets has recently been installed in the Booster to help improve efficiency and allow for higher beam intensity without exceeding safe radiation levels. We present the preliminary results of beta function measurements made using these corrector magnets. Our goal is to use the correctors to reduce irregularities in the beta function, and ultimately to introduce localized beta bumps to reduce beam loss or direct losses towards collimators. | ||
| WEP048 | Comparison of RF Cavity Transport Models for BBU Simulations | 1582 |
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| The transverse focusing effect in RF cavities plays a considerable role in beam dynamics for low-energy beamline sections and can contribute to beam breakup (BBU) instability. The purpose of this analysis is to examine RF cavity models in simulation codes which will be used for BBU experiments at Jefferson Lab and improve BBU simulation results. We review two RF cavity models in the simulation codes elegant and TDBBU (a BBU simulation code developed at Jefferson Lab). elegant can include the Rosenzweig-Serafini (R-S) model for the RF focusing effect. Whereas TDBBU uses a model from the code TRANSPORT which considers the adiabatic damping effect, but not the RF focusing effect. Quantitative comparisons are discussed for the CEBAF beamline. We also compare the R-S model with the results from numerical simulations for a CEBAF-type 5-cell superconducting cavity to validate the use of the R-S model as an improved low-energy RF cavity transport model in TDBBU. We have implemented the R-S model in TDBBU. It will cause BBU simulation results to be better matched with analytic calculations and experimental results. | ||
| WEP050 | Advances in Modeling the University of Maryland Electron Ring | 1585 |
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Funding: Work funded by the US Dept. of Energy Offices of Fusion Energy Sciences and High Energy Physics, and by the Dept. of Defense Office of Naval Research and the Joint Technology Office. The University of Maryland Electron Ring (UMER) is a research accelerator designed to operate with extreme space charge. The existence of high-precision experimental measurements of tune, dispersion, chromaticity, response matrix elements, and other parameters*, **, *** has prompted a revision of the models used to describe the machine. Due to the low energy (10 keV) of the electrons, the dipole and quadrupole magnets used are air-core printed-circuit coils whose fields we calculate using a Biot-Savart solver. Different levels of approximations for the magnetic fields have been developed. We present simulation results from the particle-in-cell code WARP, and from the accelerator code, ELEGANT. These are compared both against simpler models as well as experimental results. The improved modeling has significantly reduced the discrepancies between simulation and experiment. * D.F. Sutter, et al., Proc. PAC 2009 ** C. Wu, et al., Proc. PAC 2009 *** S. Bernal, et al., Proc. AAC 2010 |
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| WEP062 | Optimized Sextupole Configurations for Sextupole Magnet Failure in Top-up Operation at the APS* | 1588 |
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Recently there was a situation at the APS when one sextupole power supply failed during top-up operation (all magnets at the APS have separate power supplies). The beam was not lost but the lifetime decreased significantly to the point where it was hard for the injectors to provide enough charge for top-up injections. Luckily, the power supply was able to reset quickly, and the operation was not compromised. One can anticipate similar failures in the future when it would not be possible to reset the power supply. In such a case, the APS would need to operate with lower lifetime until the next intervention period. Here we present an optimization of the sextupole distribution in the vicinity of the failed sextupole that allows us to partially recover the lifetime. A genetic optimization algorithm that involves simultaneous optimization of the dynamic and energy apertures was used*. Experimental tests are also presented. * M. Borland et al., "Application of Direct Methods of Optimizing Storage Ring Dynamic and Momentum Apertures," Proc. ICAP2009, to be published. |
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| WEP063 | Tracking Particles Through A General Magnetic Field | 1591 |
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. A method that tracks particles directly through a general magnetic field described in a 3D field table was added to the code elegant recently. It was realized by converting an arbitrary particle's motion to a combination of free-drift motion and centripetal motion through the coordinate system rotation and using a general linear interpolation tool developed at the Advanced Photon Source (APS). This method has been tested by tracking particles through conventional magnetic elements (dipole, sextupole, etc.) to verify reference coordinate system conversions, tracking accuracy, and long-term tracking stability. Results show a very good agreement between this new method and the traditional method. This method is not designed to replace mature traditional methods that have been used in most tracking codes. Rather, it is useful for magnets with complicated field profiles or for studying edge effects. |
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| WEP064 | Beam Dynamics Study of the Intermediate Energy X-Ray Wiggler for the Advanced Photon Source | 1594 |
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Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. An intermediate-energy x-ray (IEX) helical wiggler is planned for the APS storage ring. Because of its high field and rapid field roll-off, the disturbance to the beam dynamics is large and needs to be well understood before the installation. We present a new method of fitting the magnetic field to an analytical wiggler model, which simplifies the usual nonlinear fitting problem and guarantees the best fit. The fitting method was validated by comparison to an analytical method. |
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| WEP065 | Multiobjective Dynamic Aperture Optimization at NSLS-II | 1597 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. In this paper we present a multiobjective approach to the dynamic aperture (DA) optimization. Taking the NSLS- II lattice as an example, we have used both sextupoles and quadrupoles as tuning variables to optimize both on-momentum and off-momentum DA. The geometric and chromatic sextupoles are used for nonlinear properties while the tunes are independently varied by quadrupoles. The dispersion and emittance are fixed during tunes variation. The algorithms, procedures, performances and results of our optimization of DA will be discussed and they are found to be robust, general and easy to apply to similar problems. |
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| WEP066 | Tracking Code Developement for Beam Dynamics Optimization | 1600 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. Dynamic aperture (DA) optimization with direct particle tracking is a straight forward approach when the computing power is permitted. It can have various realistic errors included and is more close than theoretical estimations. In this approach, a fast and parallel tracking code could be very helpful. In this presentation, we describe an implementation of storage ring particle tracking code TESLA for beam dynamics optimization. It supports MPI based parallel computing and is robust as DA calculation engine. This code has been used in the NSLS-II dynamics optimizations and obtained promising performance. |
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| WEP067 | Cornell ERL Tolerance Simulations | 1603 |
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Funding: Supported by NSF award DMR-0807731 Cornell University is planning to build an Energy Recovery Linac (ERL) hard x-ray lightsource operating at 5 GeV. Simulations of its approximately 3 km of electron beamline that incorporate a host of reasonable alignment and field errors, and their compensation by an orbit correction scheme, are presented. These simulations start with realistic particle distributions just after injection and track them through acceleration, the production of undulator radiation, deceleration (energy recovery), and finally transport to the beam stop. To this realistic model, single error sources are further added with increasing magnitudes in order to establish alignment and field tolerance estimates. |
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| WEP070 | Ring for Test of Nonlinear Integrable Optics | 1606 |
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Funding: Work supported by UT-Battelle, LLC and by FRA, LLC for the U. S. DOE under contracts No. DE-AC05-00OR22725 and DE-AC02-07CH11359 respectively. Nonlinear optics is a promising idea potentially opening the path towards achieving super high beam intensities in circular accelerators. Creation of a tune spread reaching 50% of the betatron tune would provide strong Landau damping and make the beam immune to instabilities. Recent theoretical work* have identified a possible way to implement stable nonlinear optics by incorporating nonlinear focusing elements into a specially designed machine lattice. In this report we propose the design of a test accelerator for a proof-of-principle experiment. We discuss possible studies at the machine, requirements on the optics stability and sensitivity to imperfections. * V. Danilov and S. Nagaitsev, Phys. Rev. ST Accel. Beams 13, 084002 (2010) |
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| WEP072 | Control of Chaotic Particle Motion Using Adiabatic Thermal Beams | 1609 |
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Funding: This work was supported by US Department of Energy, Grant No. DE-FG02-95ER40919 and Grant No. DE-FG02-05ER54835. Charged-particle motion is studied in the self-electric and self-magnetic fields of a well-matched, intense charged-particle beam and an applied periodic solenoidal magnetic focusing field. The beam is assumed to be in a state of adiabatic thermal equilibrium. The phase space is analyzed and compared with that of the well-known Kapchinskij-Vladimirskij (KV)-type beam equilibrium. It is found that the widths of nonlinear resonances in the adiabatic thermal beam equilibrium are narrower than those in the KV-type beam equilibrium. Numerical evidence is presented, indicating almost complete elimination of chaotic particle motion in the adiabatic thermal beam equilibrium. |
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| WEP073 | Adiabatic Thermal Beam Equilibrium in Periodic Focusing Fields | 1612 |
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Funding: This work was supported by US Department of Energy, Grant No. DE-FG02-95ER40919 and Grant No. DE-FG02-05ER54835. Adiabatic thermal equilibrium is an important state of a charged-particle beam. The rigid-rotor thermal beam equilibrium in a uniform magnetic focusing field is established. The equivalent kinetic and warm-fluid theories of adiabatic thermal beam equilibrium in a periodic solenoidal magnetic focusing field are discussed. Good agreement between theories and experiment is found. The warm-fluid theory of adiabatic thermal beam equilibrium in an alternating-gradient quadrupole magnetic focusing field is discussed. For the periodic solenoidal magnetic focusing field, charged-particle dynamics in the adiabatic thermal beam equilibrium are studied numerically and compared with those in the Kapchinskij-Vladimirskij (KV) type beam equilibrium. Numerical evidence is presented, indicating almost complete elimination of chaotic particle motion in the adiabatic thermal beam equilibrium. |
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| WEP074 | Correcting Aberrations in Complex Magnet Systems for Muon Cooling Channels | 1615 |
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Funding: Supported in part by DOE SBIR grant DE-SC0005589 Designing and simulating complex magnet systems needed for cooling channels in both neutrino factories and muon colliders requires innovative techniques to correct for both chromatic and spherical aberrations. Optimizing complex systems, such as helical magnets for example, is also difficult but essential. By using COSY INFINITY, a differential algebra based code, the transfer and aberration maps can be examined to discover what critical terms have the greatest influence on these aberrations. |
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| WEP076 | Masking the Paul Trap Simulator Experiment (PTSX) Ion Source to Modify the Transverse Distribution Function and Study Beam Stability and Collective Oscillations | 1618 |
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Funding: Research supported by the U.S. Department of Energy. A variety of masks were installed on the Paul Trap Simulator Experiment (PTSX) cesium ion source in order to perform experiments with modified transverse distribution functions. Masks were used to block injection of ions into the PTSX chamber, thereby creating injected transverse beam distributions that were either hollow, apertured and centered, apertured and off-center, or comprising five beamlets. Experiments were performed using either trapped plasmas or the single-pass, streaming, mode of PTSX. The transverse streaming current profiles clearly demonstrated centroid oscillations. Further analysis of these profiles also shows the presence of certain collective beam modes, such as azimuthally symmetric radial modes. When these plasmas are trapped for thousands of lattice periods, the plasma quickly relaxes to a state with an elevated effective transverse temperature and is subsequently stable. Both sinusoidal and periodic step function waveforms were used and the resulting difference in the measured transverse profiles will be discussed. |
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| WEP079 | Mathematical Models of Feedback Systems for Control of Intra-Bunch Instabilities Driven by E-Clouds and TMCI | 1621 |
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Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP). The feedback control of intrabunch instabilities driven by E-Clouds or strong head-tail coupling (TMCI) requires sufficient bandwidth to sense the vertical position and drive multiple sections of a nanosecond scale bunch. These requirements impose challenges and limits in the design and implementation of the feedback system. This paper presents models for the feedback subsystems: receiver, processing channel, amplifier and kicker, that take into account their frequency response and limits. These models are included in multiparticle simulation codes (WARP/CMAD/Head-Tail) and reduced mathematical models of the bunch dynamics to evaluate the impact of subsystem limitations in the bunch stabilization and emittance improvement. With this realistic model of the hardware, it is possible to analyze and design the feedback system. This research is crucial to evaluate the performance boundary of the feedback control system due to cost and technological limitations. These models define the impact of spurious perturbations, noise and parameter variations or mismatching in the performance of the feedback system. The models are validated with simulation codes and measurements of lab prototypes. |
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| WEP080 | Spin Tracking with GPUs to 250 GeV in RHIC Lattice | 1624 |
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Funding: Supported by DOE NP grant DE-SC0004432 We have benchmarked UAL-SPINK against Zgoubi and a list of well understood spin physics results. Along the way we addressed issues relating to longitudinal dynamics and orbit bump and distortion handling as well as appropriate slicing necessary for the TEAPOT-SPINK spin orbit integrator. We have also ported this TEAPOT-SPINK algorithm to the GPU’s. We present the challenges associated with this work. |
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| WEP082 | Crab Crossing Consideration for MEIC | 1627 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Crab crossing of colliding electron and ion beams is essential for accommodating the ultra high bunch repetition frequency in the conceptual design of MEIC – a high luminosity polarized electron-ion collider at Jefferson Lab. The scheme eliminates parasitic beam-beam interactions and avoids luminosity reduction by restoring head-on collisions at interaction points. In this paper, we report simulation studies of beam dynamics with crab cavities for MEIC design. The detailed study involves full 3-D simulations of particle tracking through the various configurations of crab cavities for evaluating the performance. To gain insight, beam and RF dominated fields with other parametric studies will be presented in the paper. |
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| WEP084 | Beam Dynamics and Instabilities in MEIC Design | 1630 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. In this paper, we report the first study of beam related instabilities in lepton ring of the proposed electron-ion collider beyond the 12 GeV upgrade of CEBAF at Jefferson lab. The design parameters are consistent with PEP-II. Present studies reveal that coupled bunch and two stream instabilities are important issues and we need feedback system. |
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| WEP085 | Beam Breakup Studies for New Cryo-Unit | 1633 |
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| In this paper, we report the numerical simulations of cumulative beam breakup studies for a new cryo-unit for injector design at Jefferson lab. The system consists of two 1-cell and one 7-cell superconducting RF cavities. The study has been performed using a 2-dimensional time-domain code TDBBU developed in-house. The stability has been confirmed for the present setup of beamline elements with different initial offsets and currents ranging 1 mA - 100 mA. | ||
| WEP087 | Numerical Studies of Non-Linear Dynamics in BEP | 1636 |
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| An analysis of the dependence of experimental captured positron current data from the booster storage ring BEP (VEPP-2000 facility, BINP, Russia) on the working point position on the frequency map has uncovered a great number of different non-linear resonances. The number of captured positrons after a single injection is observed to be much less than the expected value. It is anticipated that the high degree of symmetry in the magnet system of BEP, however, should lead to the suppression of such resonances. To study this discrepancy, numerical simulations of positron beam movement under different perturbations to account for potential errors in magnetic field gradient of non-linear elements and errors in their angular location are used. The findings of this research provide qualitative explanations of the experimental work diagram and answers to two main questions, specifically “Why in the absence of skew-sextupoles in structure and small coupling are strong skew-sextupole resonances observed” and “Why skew-sextupole resonances are stronger than sextupole ones of the same harmonic”. A comparison between simulation results and analytical estimates is also presented. | ||
| WEP090 | Simulation Study of Intrabeam Scattering in Low Emittance Ring | 1639 |
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| HALS(Hefei Advanced Light Source) is under designing dedicated to good coherence and high brightness at 1.5GeV. Low emittance is required to reach the design request. Due to the low energy and emittance with relative high bunch charge, intrabeam scattering effect will be very strong. It is worth accurately calculating to check if the design goal can be reached. Theoretic calculation based on Gaussian beam distribution doesn't warrant in strong IBS regime. In this paper we present the results of particle simulation study of intrabeam scattering effect on a temporary design lattice of HALS ring. | ||
| WEP091 | Implementation of H− Intrabeam Stripping into TRACK | 1642 |
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H− intrabeam stripping has been presented* as potentially harmful to MW scale H− linacs. If not taken properly into account, intrabeam stripping of the H− beam could lead to losses in excess of the 1 W/m limit and result in non-tolerable beamline elements activation. This paper describes the implementation of the H− intrabeam stripping effect into the beam dynamics code TRACK**. Simulations results and numerical applications will be presented for the SNS linac and the FNAL ProjectX.
* V. Lebedev, "Intrabeam Stripping in H− Linacs", LINAC2010 ** P. Ostroumov, "TRACK, The Beam Dynamics Code", PAC2005 |
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| WEP092 | Space Charge Effect of the High Intensity Proton Beam during the Resonance Extraction for the MU2E Experiment at Fermilab | 1645 |
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| The proposed Mu2e experiment to search for direct μ to e conversion at Fermilab plans slow, resonant extraction of a beam with 3× 1012 protons from the Debuncher ring. Space charge of this high intensity beam is a critical factor, since it induces significant betatron tune spread and consequently affects resonance extraction processes, such as spill uniformity and beam losses. This study shows the multi-particle simulation results in the early stages of resonance extraction and spill uniformity in the presence of 2D and 3D space charge effects. | ||
| WEP094 | Space Charge Measurements with a High Intensity Bunch at the Fermilab Main Injector | 1648 |
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| Fermilab Main Injector will be required to operate with 3 times higher bunch intensity than today for Project X. The plan to study the space charge effects at the injection energy with intense bunches will be discussed. | ||
| WEP095 | Analysis of the Beam Loss Mechanism in the Project-X Linac | 1651 |
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| Minimization of the beam losses in a multi-MW H-minus linac of the Project X to the level below 1W/m is a challenging task. Analysis of different mechanisms of beam stripping, including stripping in electric and magnetic fields, residual gas, black-body radiation and intra-beam stripping, is analyzed. Other sources of beam losses are misalignment of beamline elements and errors in RF fields and phase. We presented the requirements for dynamics errors and correction schemes to keep beam losses under control | ||
| WEP096 | Simulations of Space Charge in the Fermilab Main Injector | 1654 |
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| The Fermilab Project X plan for future high intensity running relies on the Main Injector as the engine for delivering protons in the 60-120 GeV energy range. Project X plans call for increasing the number of protons per Main Injector bunch from the current value of 1.0× 1011 to 3.0× 1011. Space charge effects at the injection energy of 8 GeV have the potential to seriously disrupt operations. We report on ongoing simulations with Synergia, our multi-physics process accelerator modeling framework, to model space charge effects in the Main Injector combined with the effects of magnet fringe fields and apertures. | ||
| WEP098 | Formation of High Charge State Heavy Ion Beams with Intense Space Charge | 1657 |
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Funding: This work was performed under the auspices of the U.S Department of Energy by LBNL under contract DE-AC02-05CH11231. High charge-state heavy-ion beams are of interest and used for a number of accelerator applications. Some accelerators produce the beams downstream of the ion source by stripping bound electrons from the ions as they pass through a foil or gas. In other accelerator systems, ions of charge state >1 are produced directly in the ion source. Heavy-ion inertial fusion (HIF) would benefit from low-emittance, high current ion beams with charge state >1. For these accelerators, the desired dimensionless perveance upon extraction from the emitter is ~0.001, and the electrical current of the beam pulse is ~ 1 A. For accelerator applications where high charge state and very high current are desired, space charge effects might present unique challenges. For example, in a stripper, the separation of charge states might create significant nonlinear space-charge forces which would impact the beam brightness. We will report on the particle-in-cell simulation of the formation of such beams for HIF, and review the possible technical approaches. |
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| WEP099 | Numerical Solution for the Potential and Density Profile of a Thermal Equilibrium Sheet Beam | 1659 |
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Funding: This research was performed under the auspices of the US DOE at the Lawrence Livermore and Lawrence Berkeley National Laboratories under contract numbers DE-AC52-07NA27344 and DE-AC02-05CH11231. A one-dimensional Vlasov-Poisson model for sheet beams is presented to provide a simple framework for analysis of space-charge effects. Centroid and rms envelope equations including image charge effects are derived and reasonable parameter equivalences with commonly employed 2D transverse models of unbunched beams are established. This sheet beam model is applied to analyze several problems of fundamental interest. First, a sheet beam thermal equilibrium distribution in a continuous focusing channel is constructed and shown to have analogous properties to two- and three-dimensional thermal equilibrium models in terms of the equilibrium structure and Deybe screening properties. Second, the simpler formulation for sheet beams is exploited to explicitly calculate the distribution of particle oscillation frequencies within a thermal equilibrium beam. It is shown that as space-charge intensity increases, the frequency distribution becomes broad which suggesting robust stability properties for beams with strong space-charge. |
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| WEP100 | Energy Spread Compensation for Multi-Bunch Linac Operation Mode | 1662 |
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Funding: This work was supported under the U.S. Department of Energy contract number: DE-AC02-06CH11357 with Argonne National Laboratory. Higher wakefield gradients can be achieved by increasing the total beam charge which is passed through a dielectric-loaded structure and by reducing the transverse size of the beam. Currently, the Argonne AWA photoinjector operates with electron bunches of up to 100 nC and the goal is to raise the total beam charge to about 1000 nC and to improve the beam focusing to a few 100's microns transverse spot size. The increase of the beam charge can be done by superimposing electron bunches that fill up several consecutive RF buckets. Although the energy stored in a single 7-cell linac is by design large the multi-bunch operation with short bunch trains (~10 ns) is still plagued by large energy spread due to significant beam loading effects. In this paper we present a technique intended to reduce the energy spread for a high charge bunch train by properly choosing the time delay between consecutive bunches. The simulations show that the energy spread can be lowered to about 2.8% from about 6.0% for a 10-bunch train of total charge 1000 nC and kinetic energy of about 70 MeV. |
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| WEP101 | Smooth Approximation of Dispersion with Strong Space Charge | 1665 |
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Funding: This work is funded by the US Dept. of Energy Offices of High Energy Physics and High Energy Density Physics, and by the US Dept. of Defense Office of Naval Research and Joint Technology Office. We apply the Venturini-Reiser envelope-dispersion equations* to a continuous beam in a uniform focusing/bending lattice to study the combined effects of linear dispersion and space charge. Within this simple model we investigate the scaling of average dispersion and the effects on beam dimensions; we also introduce a generalization of the space-charge intensity parameter and apply it to the University of Maryland Electron Ring (UMER) and other machines. In addition, we present results of calculations to test the smooth approximation by solving the Venturini-Reiser original equations and also through simulations with the code ELEGANT. *M. Venturini and M. Reiser, Phys. Rev. Lett. 81, 1, p. 96, 6 July 1998 |
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| WEP102 | Current Dependent Tune Shifts in the University of Maryland Electron Ring UMER | 1668 |
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Funding: Work supported by the U.S. DOE Offices of High Energy Physics and Fusion Energy Sciences and by the U.S. DOD Office of Naval Research and Joint Technology Office. The shift in betatron tunes as a function of space charge has been studied in many accelerators and storage rings. Because of its low operating energy (10 keV, γ = 1.02) and wide range of beam currents (0.6 to 100 mA, corresponding respectively to predicted incoherent tune shifts of 1.2 to 5.2), the University of Maryland electron ring (UMER) provides a unique opportunity to study space charge driven tune shifts over a wide parameter space. Comparisons of predictions and measurements are presented, including a discussion of special factors such as the magnetic penetration of the vacuum chamber walls. |
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| WEP103 | Ion Instability Study for the ILC 3 km Damping Ring | 1671 |
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| The ILC GDE is currently pushing the cost reduction for all subsystems of the ILC project for the Technique Design Phase 1. A short damping ring with circumference of 3.2 km was developed for this purpose. Based on this lattice, we performed a weak-strong simulation study of the ion instability in the electron damping ring for various beam parameters and vacuum pressures. The simulation results are given in this paper. | ||
| WEP104 | Transverse Feedback System and Instability Analysis at HLS | 1674 |
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| In this paper, we introduce the BxB transverse feedback systems at Hefei Light Source (HLS), which employ an analog system and a digital system. The experiment result of two systems. as well as the primary analysis of beam instability in HLS injection and operation are also presented in this paper. | ||
| WEP107 | CSR Shielding Experiment | 1677 |
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| It is well known that the emission of coherent synchrotron radiation (CSR) in a dipole magnets leads to increase in beam energy spread and emittance. At the Brookhaven National Laboratory Accelerator Test Facility (ATF) we study the suppression of CSR emission affect on electron beam in a dipole magnet by two vertically spaced conducting plates. The gap between the plates is controlled by four actuators and could be varied from 0 to 14 mm. Our experimental results show that closing the plates significantly reduces both the beam energy loss and CSR-induced beam energy spread. In this paper we present selected results of the experiment and compare then with rigorous analytical theory. | ||
| WEP108 | Application of Coherent Tune Shift Measurements to the Characterization of Electron Cloud Growth | 1680 |
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Funding: DOE = DE-FC02-08ER41538 NSF = PHY-0734867 Measurements of coherent tune shifts at the Cornell Electron Storage Ring Test Accelerator (CesrTA) have been made for electron and positron beams under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of several electron cloud simulation programs allows the evaluation of important parameters in these models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders. We outline recent improvements to the analysis techniques that should improve the fidelity of the modeling. |
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| WEP109 | Simulations of Electron Cloud Induced Instabilities and Emittance Growth for CesrTA | 1683 |
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Funding: US Department of Energy DE-FC02-08ER41538, National Science Foundation PHY-0734867 We present results of a series of studies obtained using the simulation code CMAD to study how electron clouds affect the dynamics of positron beams in CesrTA. The study complements ongoing experiments dedicated for studying the same phenomena. The simulation involves tracking positrons through the CesrTA lattice and simultaneously computing the force exerted due to space charge of the electrons on each of the tracked positrons. The electrons themselves are allowed to evolve under the influence of the positrons. Several results bear a close resemblance to what has been observed experimentally. |
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| WEP110 | Electron Cloud Modeling for the ILC Damping Rings | 1686 |
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Funding: Support by DOE contract DE-FC02-08ER41538 and NSF contract PHY-0734867 Electron cloud buildup is a primary concern for the performance of the damping rings under development for the International Linear Collider. We have performed synchrotron radiation profile calculations for the 6.4-km DC04 and 3.2-km DSB3 lattice designs using the SYNRAD utility in the Bmad accelerator software library. These results are then used to supply input parameters to the electron cloud modeling package ECLOUD. Contributions to coherent tune shifts from the field-free sections and from the dipole and quadrupole magnets have been calculated, as well as the effect of installing solenoid windings in the field-free regions. For each element type, SYNRAD provides ring occupancy, average beam sizes, beta function values, and beta-weighted photon rates for the coherent tune shift calculation. An approximation to the antechamber design has been implemented in ECLOUD as well, moving the photoelectron source point to the edges of the antechamber entrance and removing cloud particles which enter the antechamber. |
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| WEP111 | Beam Breakup in Dielectric Wakefield Accelerating Structures: Modeling and Experiments | 1689 |
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Funding: Work supported by USDOE SBIR program. Beam breakup (BBU) effects resulting from parasitic wakefields limit considerably the intensity of the drive beam that can be transported through a dielectric accelerating structure and hence the accelerating field that can be achieved. We have been developing techniques to control BBU effects using a quadrupole channel or solenoid surrounding the wakefield device. We report here on the status of simulations and experiments on BBU and its mitigation, emphasizing an experiment at the Argonne Wakefield Accelerator facility using a 26 GHz dielectric wakefield device fitted with a solenoid to control BBU. We present calculations based on a particle-Green’s function beam dynamics code (BBU-3000) that we are developing. The code allows rapid, efficient simulation of BBU effects in advanced linear accelerators. |
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| WEP112 | Accurate Simulation of the Electron Cloud in the Fermilab Main Injector with VORPAL | 1692 |
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| Precision simulations of the electron cloud at the Fermilab Main Injector (MI) have been studied using the plasma simulation code VORPAL. Fully 3D and self consistent solutions that includes Yee-type E.M. field maps, electron spatial distributions and the time evolution of the cloud with respect to the bunch structure in the MI. The microwave absorption experiment has been simulated in detail and the response of the antennas has been derived from the VORPAL's pseudo-potential data. Based on the results of these simulations and the ongoing experimental program, two distinct new experimental techniques are proposed. The first one is based on the use BPM plates placed in dipole fields and that are made of material(s) for which the secondary emission is well characterized. The second technique would be based on the optical, or ultra-violet, detection of the radiation emitted (inverse photo-electric effect) when the cloud interacts with the inner surface of the beam pipe. As the microwave absorption experiment, this techique is non-invasise and has the advantage of providing spatial images of the cloud as well as accurate timing (ns) information. | ||
| WEP113 | Low-Energy Run of Fermilab Electron Cooler's Beam Generation System | 1695 |
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Funding: FNAL is operated by FRA, LLC under Contract No.DE-AC02-07CH11359 with US DoE. BNL is operated by BSA, LLC under Contract No.DE-AC02-98CH10886 with US DoE. In the context of the evaluation of possibly using the Fermilab Electron Cooler for the proposed low-energy RHIC run at BNL, operating the cooler at 1.6 MeV electron beam energy was tested in a short beam line configuration. The main conclusion of this feasibility study is that the cooler's beam generation system is suitable for BNL needs. The beam recirculation was stable for all tested parameters. In particular, a beam current of 0.38 A was achieved with the cathode magnetic field up to the maximum value presently available of 250 G. The energy ripple was measured to be 40 eV. A striking difference with running the 4.3 MeV beam (nominal for operation at FNAL) is that no unprovoked beam recirculation interruptions were observed. |
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| WEP114 | Transverse Instability of the Antiproton Beam In the Recycler Ring | 1698 |
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Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. The brightness of the antiproton beam in Fermilab’s 8 GeV Recycler ring is limited by a transverse instability. This instability has occurred during the extraction process to the Tevatron for large stacks of antiprotons even with dampers in operation. This paper describes observed features of the instability, introduces the threshold phase density to characterize the beam stability, and finds the results to be in agreement with a resistive wall instability model. Effective exclusion of the longitudinal tails from Landau damping by decreasing the depth of the RF potential well is observed to lower the threshold density by up to a factor of two. |
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| WEP115 | The FNAL Injector Upgrade | 1701 |
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| The present FNAL linac H− injector has been operational since the 1970s and consists of two magnetron H− sources and a 750keV Cockcroft-Walton Accelerator. In the upgrade, both slit-type magnetron sources will be replaced with circular aperture sources, and the Cockcroft-Walton with a 200MHz RFQ. Operational experience at BNL (Brookhaven National Laboratory) has shown that the upgraded source and RFQ will be more reliable and require less manpower than the present system. | ||
| WEP116 | Bucket Shaking Stops Bunch Dancing in Tevatron | 1704 |
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Bunches in Tevatron are known to be longitudinally unstable: their collective oscillations stay without any sign of decay. Typically, a feedback damper is used to stop these oscillations. Recently, it was theoretically predicted that the oscillations can be stabilized by means of small bucket shaking*. Detailed measurements in Tevatron have shown that this method does work. In this paper, an essential theory and specific observations of the related process are presented.
* A. Burov, “Dancing Bunches as van Kampen Modes”, this conference. |
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| WEP118 | Planned Experiments on the Princeton Advanced Test Stand | 1707 |
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| The Princeton Advanced Test Stand (PATS) is currently being developed as a compact experimental facility for studying the physics of high perveance ion beams, beam-plasma interactions, and volume plasma sources for use on the Neutralized Drift Compression Experiments NDCX-I/II. PATS consists of a six-foot-long vacuum chamber with numerous ports for diagnostic access and a pulsed capacitor bank and switching network capable of generating 100 keV ion beams. This results in a flexible system for performing experiments on beam neutralization by volume plasma relevant to NDCX-I/II. The PATS beamline will include an aluminosilicate source for producing a K+ beam, focusing optics, a ferroelectric plasma source (FEPS) and diagnostics including Faraday cups, Langmuir probes, and emittance scanners. Planned experiments include studying beam propagation through a tenuous plasma (np < nb). This regime is relevant to final stages of neutralized drift compression when the beam density begins to exceed the plasma density. The experiment will investigate charge neutralization efficiency, effects of plasma presence on beam emittance, and collective instabilities. | ||
| WEP119 | Coherent Radiation in Whispering Gallery Modes | 1710 |
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Funding: Work at SLAC: U.S. Department of Energy Contract No. DE-AC03-76SF00515 Work at CLS: NSERC, NRC, Province of Saskatchewan, U. of Saskatchewan. Theory predicts that CSR in storage rings should appear in whispering gallery modes *, which are resonances of the entire vacuum chamber and are characterized by their high frequencies and concentration of the field near the outer wall of the chamber. The theory assumes that the chamber is a smooth circular torus. We observe that a power spectrum from the NSLS-VUV ring **, which has a vacuum chamber in bends like that of the model, shows a series of sharp peaks with frequencies close to those of the theory. Sharp peaks are also seen in highly resolved spectra at the Canadian Light Source***, and those are invariant in position under large changes in the machine setup (energy, fill pattern, bunch length, CSR bursting or steady, optical beam line, etc.). Invariance of the spectrum suggests that it is due to resonances like whispering gallery modes, but they must be strongly perturbed from the circular case because of large outer wall excursions at the two IR ports. * R. L. Warnock and P. Morton, Part. Accel. 25, 113 (1990). ** G. L. Carr et al., Proc. PAC 2001, Chicago. *** T. May et al., IEEE 33rd Intl. Conf. IR Millimeter and THz Waves, 2008. |
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| WEP123 | Study on Low-Frequency Oscillations in a Gyrotron Using a 3D CFDTD PIC Method | 1713 |
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Funding: Work supported by the U.S. Department of Energy under Grant No. DE-SC0004436. Low-frequency oscillations (LFOs) have been observed in a high average power gyrotron and the trapped electron population contributing to the oscillation has been measured. As high average power gyrotrons are the most promising millimeter wave source for thermonuclear fusion research, it is important to get a better understanding of this parasitic phenomenon to avoid any deterioration of the electron beam quality thus reducing the gyrotron efficiency. 2D Particle-in-cell (PIC) simulations quasi-statically model the development of oscillations of the space charge in the adiabatic trap, but the physics of the electron dynamics in the adiabatic trap is only partially understood. Therefore, understanding of the LFOs remains incomplete and a full picture of this parasitic phenomenon has not been seen yet. In this work, we use a 3D conformal finite-difference time-domain (CFDTD) PIC method to accurately and efficiently study the LFOs in a high average power gyrotron. Complicated structures, such as a magnetron injection gun, can be well described. Employing a highly parallelized computation, the model can be simulated in time domain more realistically. |
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| WEP125 | Higher-order Spin Resonances in 2.1 GeV/c Polarized Proton Beam | 1716 |
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Funding: This research was supported by grants from the German Science Ministry Spin resonances can cause partial or full depolarization or spin-flip of a polarized beam. We studied 1st-, 2nd- and 3rd-order spin resonances with a 2.1 GeV/c vertically polarized proton beam stored in the COSY Cooler Synchrotron. We observed almost full spin-flip when crossing the 1st-order G*gamma=8−nuy vertical-betatron-tune spin resonance and partial depolarization near some 2nd- and 3rd-order resonances. We observed almost full depolarization near the 1st-order G*gamma=8−nux horizontal spin resonance and partial depolarization near some 2nd- and 3rd-order resonances. Moreover, we found that a 2nd-order nux resonance seems about as strong as some 3rd-order nux resonances, while some 3rd-order nuy resonances seem much stronger than a 2nd-order nuy resonance. It was thought that, for flat accelerators, vertical spin resonances are stronger than horizontal, and lower order resonances are stronger than higher order ones. The data suggest that many higher-order spin resonances, both horizontal and vertical, must be overcome to accelerate polarized protons to high energies; the data may help RHIC to better overcome its snake resonances between 100 and 250 GeV/c. |
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| WEP126 | Progress in Experimental Study of Current Filamentation Instability | 1719 |
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Funding: Work supported by Department of Energy and National Science Foundation Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI could play an important role in the generation of magnetic fields and radiation in the after-glow of gamma ray bursts and also in energy transport for the fast-igniter inertial confinement fusion concept. Simulations were conducted with the particle-in-cell code QuickPIC* for e- beam and plasma parameters at the Brookhaven National Laboratory – Accelerator Test Facility, BNL-ATF. Results show that for a 2cm plasma the instability reaches near saturation. An experimental program was proposed and accepted at the BNL-ATF and an experiment is currently underway. There are three components to the experimental program: 1) imaging of the beam density/filaments at the exit from the plasma, 2) measurement and imaging of the transverse plasma density gradient and measurement of the magnetic field and 3) identifying the radiation spectrum of the instability. Preliminary results from phase one will be presented along with the progress and diagnostic design for the following phases of the experiment. * C. Huang et. al. Journal of Computational Physics 217, 2(2006) |
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| WEP130 | Simulation Study of Transverse Spectrum in HIRFL-CSR | 1722 |
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Funding: Work supported by HIRFL-CSR project Particles in a storage ring oscillate in the longitudinal and transverse dimensions. Therefore, the beam parameters, such as tune, momentum spread, emittance and their evolution can be obtained by analyzing the beam signals in frequency domain. In this paper, the simulation result of transverse beam spectrum in HIRFL-CSR is reported, including the influence of electron cooling, power supply ripple and the misalignment between ion and electron beams. Transverse coupling would occur if the longitudinal magnetic field of electron cooling device can not be compensated. And the distribution of ion beam in transverse space is a circle due to the misalignment between ion and electron beams. In this paper, main interest is focused on the effect of power supply ripple. The tune ripple form is the sine ware with the frequency of 50Hz which is equal to that of the industrial frequency in the simulation firstly. And then different forms of current ripple of power supply are simulated for comparative analysis. Tune shift will be induced by the power supply ripple. In this paper, those factors which may affect the accumulation of HIRFL-CSR are simulated in transverse beam spectrum. |
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| WEP131 | A New Approach to Calculate the Transport Matrix in RF cavities | 1725 |
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Funding: Work supported by USDoE A realistic approach to calculate the transport matrix in RF cavities is developed. It is based on joint solution of equations of longitudinal and transverse motion of a charged particle in an electromagnetic field of the linac. This field is a given by distribution (measured or calculated) of the component of the longitudinal electric field on the axis of the linac. New approach is compared with other matrix methods to solve the same problem. The comparison with code ASTRA has been carried out. Complete agreement for tracking results for a TESLA-type cavity is achieved. A corresponding algorithm has been implemented into the MARS15 code. |
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| WEP133 | Adaptive Space-charge Meshing in the General Particle Tracer Code | 1728 |
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| Efficient and accurate space-charge calculations are essential for the design of high-brightness charged particle sources. Space-charge calculations in the General Particle Tracer (GPT) code make use of an efficient multigrid Poisson solver developed for non-equidistant meshes at Rostock University. GPT uses aggressive mesh-adaptation with highly non-equidistant spacing to speed up calcula- tion time, where the mesh line positions are based upon the projected charge density. Here we present a new meshing scheme where the solution of an intermediate step in the multigrid algorithm is used to define optimal mesh line positions. An analytical test case and comparison with a molecular dynamics calculation of an ultrafast electron diffraction experiment demonstrate the capabilities of this new algorithm in the GPT code. | ||
| WEP134 | Depolarization and Beam-beam Effects at Future e+e− Colliders | 1731 |
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| In order to exploit the full potential of proposed future high-energy electron-positron linear colliders, precise knowledge of the polarization state of the beams is required. In this paper we present an updated analysis of the depolarization effects caused by the intense beam-beam interaction, which is expected to be the dominant source of depolarization. The impact of higher-order effects are considered and numerical results from the Guinea-Pig and CAIN simulations are presented for the latest International Linear Collider (ILC) and Compact LInear Collider (CLIC) parameters. | ||
| WEP136 | Modelling of the EMMA ns-FFAG Ring Using GPT | 1734 |
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| EMMA (Electron Machine with Many Applications) is a prototype non-scaling Fixed-Field Alternating Gradient (ns-FFAG) accelerator whose construction at Daresbury Laboratory, UK, was completed in Aug 2010. The energy recovery linac ALICE will serve as an injector for EMMA, within an energy range of 10-20 MeV. The injection line consists of a dogleg to extract the beam from ALICE, a matching section, and tomography section for transverse emittance measurements. This is followed by a transport section to the injection point of the EMMA ring. The ring is composed of forty two cells, each containing one focusing and one defocusing quadrupole. Commissioning of the EMMA ring started in late 2010. A number of different injection energy and bunch charge regimes are planned; for some of the regimes the effects of space charge may be significant. It is therefore necessary to model the electron beam transport in the injection line and the ring using a code capable of both calculating the effect of and compensating for space charge. Therefore the General Particle Tracer (GPT) code has been used. A range of injection beam parameters have been modelled for comparison with experimental results. | ||
| WEP137 | Performance Analysis on the IBM Blue Gene/P for Wakefield Calculations | 1737 |
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| Accurate and efficient simulations will significantly reduce the cost and the risk in the design process for various applications in accelerator design. We improved capability of the Argonne-developed high-fidelity wakefield simulation code, NekCEM, by upgrading pre-setup and communication subroutines for high-performance simulations beyond petascale. We present a detailed study of parallel performance of NekCEM on the IBM Blue Gene/P at Argonne. We demonstrate strong scaling up to P=131,072 cores using up to more than 1.1 billion grid points with the total number of elements up to E=273,000 and N=15 which gives 75% efficiency at 8,530 grid points per core compared to the base case of P =16,384 cores. | ||
| WEP138 | Developing Software Packages for Electromagnetic Simulations | 1740 |
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Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. In addition to previous developments on parallel beam dynamics software packages, our efforts have been extended to electromagnetic simulations. These efforts include developing new software packages solving the Maxwell equations in 2D and 3D. Scalable algorithms have been used for use of ALCF supercomputers. These new solvers are based on high order numerical methods. Comparative studies of structured and unstructured grids, continuous and discontinuous Galerkin methods will be discussed. The effects of bases will also be presented. Efficiency and challenges of new software packages will be presented. Some benchmarking and simulation results will be shown. |
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| WEP139 | Comparison of 1D and 2D CSR Models with Application to the Fermi@Elettra Bunch Compressors | 1743 |
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Funding: Work partially supported by DOE grant DE-FG02-99ER41104 We compare our 2D mean field (Vlasov-Maxwell) treatment of coherent synchrotron radiation (CSR) effects with 1D approximations of the CSR force which are commonly implemented in CSR codes. In our model we track particles in 4D phase space and calculate 2D forces*. The major cost in our calculation is the computation of the 2D force. To speed up the computation and improve 1D models we also investigate approximations to our exact 2D force. Preliminary results are encouraging**. As an application, we present numerical results for the LCLS bunch compressors, where recently detailed measurements of the CSR-induced energy loss and transverse emittance growth have been performed and compared with numerical calculations***. * Phys. Rev. ST Accel. Beams 12, 080704 (2009) ** http://www.lnf.infn.it/conference/uBI10/ *** Phys. Rev. ST Accel. Beams 12, 030704 (2009) |
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| WEP140 | Benchmarking Stepwise Ray-Tracing in Rings in Presence of Radiation Damping | 1746 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. A number of recent machine designs, including ‘‘nano-beams'', sub-millimeter ‘‘low-beta'' IRs, etc., require high accuracy on beam orbit and beam size, reliable evaluation of machine parameters, dynamic apertures, etc. This can only be achieved using high precision simulation tools. Stepwise ray-tracing methods are in this category of tools, stochastic synchrotron radiation and its effects on an electron beam in a storage ring are simulated here in that manner. Benchmarking of the method against analytical model expectations, using a Chasman-Green cell, is presented. |
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| WEP141 | Development of a Stepwise Ray-Tracing Based on-Line Model at AGS | 1749 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. A model of the Alternating Gradient Synchrotron is being developed based on stepwise ray-tracing numerical tools. It provides a realistic representation of the lattice, and accounts for the two helical partial Siberian snake insertions. The aim is to make this stepwise ray-tracing based model an aid for the understanding of the AGS, in matter of both beam dynamics and polarization transmission. |
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| WEP142 | Electron Cloud Modeling Results for Time-resolved Shielded Pickup Measurements at CesrTA | 1752 |
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Funding: Support by DOE contract DE-FC02-08ER41538 and NSF contract PHY-0734867 The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1 meter long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron energy distributions, and the secondary elastic yield value. |
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| WEP146 | A Quasi-3D Model of Electron Cyclotron Resonance Ion Source (ECRIS) | 1755 |
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Funding: Grant supported by DOE office of Nuclear Physics FAR-TECH, Inc is developing a hybrid, quasi-3D model to model charge breeding of an ion beam in an electron cyclotron resonance ion source. The model is a combination of 3D mapping of the plasma background calculated by GEM1D* and 3D tracking of the ion trajectories with MCBC**. The 3D electron distribution function and electric field of the background plasma are calculated self-consistently. The test beam ions are then tracked in it using MCBC which includes Coulomb, ionization and charge exchange collisions. The exact ion trajectories in the plasma and steady state 3D ion distribution at the extraction aperture are predicted and compared with previous simulations and experiments. * D. H. Edgell et al., Rev. Sci. Instrum. 73, 641, 2002. ** J. S. Kim et al., Rev. Sci. Instrum. 79, 02B906, 2008. |
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| WEP147 | The Effect of Space-charge and Wake Fields in the Fermilab Booster | 1758 |
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Funding: This work was supported by the DOE contracts DE-AC02-07CH11359, DE-AC02-05CH11231 and DE-AC02-06CH11357 and the ComPASS project funded through the SciDAC. We calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between the flat and the circular geometry impedance is presented. We use the wake fields calculated for the Fermilab Booster laminated magnets in realistic beam simulations using the Synergia code. We find good agreement between our calculation of the coherent tune shift at injection energy and the experimental measurements. |
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| WEP149 | Beam Measurement by a Wall Gap Monitor in ALPHA | 1761 |
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| In this report, we present our electron beam measurements with a wall gap monitor (WGM) in ALPHA injection and extraction beam lines. The WGM is first bench mark tested, and then installed in the ALPHA injection line to measure both the macro andμpulse of the injected beam and calibrate the beam current. By scanning the bending magnet before the WGM, and applying a demodulation signal processing scheme, we measured the tomography of the longitudinal phase space of the injected beam. We moved the WGM to extraction beam line and measured the properties of the extracted beam. By comparing the frequency spectrum of injected and extracted beam, we have confirmed the debunching performance of ALPHA. | ||
| WEP150 | GPU Computing for Particle Tracking | 1764 |
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Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 This is a feasibility study of using a modern Graphics Processing Unit (GPU) to parallelize the accelerator particle tracking code. To demonstrate the massive parallelization features provided by GPU computing, a simplified TracyGPU program is developed for dynamic aperture calculation. Performances, issues, and challenges from introducing GPU are also discussed. |
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| WEP151 | HPC Cloud Applied to Lattice Optimization | 1767 |
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Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 As Cloud services gain in popularity for enterprise use, vendors are now turning their focus towards providing cloud services suitable for scientific computing. Recently, Amazon Elastic Compute Cloud (EC2) introduced the new Cluster Compute Instances (CCI), a new instance type specifically designed for High Performance Computing (HPC) applications. At Berkeley Lab, the physicists at the Advanced Light Source (ALS) have been running Lattice Optimization on a local cluster, but the queue wait time and the flexibility to request compute resources when needed are not ideal for rapid development work. To explore alternatives, for the first time we investigate running the Lattice Optimization application on Amazon’s new CCI to demonstrate the feasibility and trade-offs of using public cloud services for science. |
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| WEP152 | Parallel Optimization of Beam-Beam Effects in High Energy Colliders | 1770 |
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Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231. Beam-beam effects limit luminosity in high energy colliders. Parallel beam-beam simulation codes were developed to study those beam-beam effects and to help the collider design. In this paper, we will present a parallel optimization algorithm integrating together with the parallel beam-beam simulation to optimize the luminosity of the colliding beams. This algorithm is based on a differential evolutionary global optimization method and takes advantage of the two-level parallelization in both parallel search and parallel objective function evaluation. This significantly increases the scalability of the simulation on peta-scale supercomputers and reduces the time for finding the optimal working point. |
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| WEP153 | Simulation Results of a Feedback Control System to Damp Electron Cloud Single-Bunch Transverse Instabilities in the CERN SPS | 1773 |
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Funding: Work supported by the US-DOE under Contract DE-AC02-05CH11231 and the US-LHC Accelerator Research Program (LARP). Transverse Single-Bunch Instabilities due to Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model. |
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| WEP154 | Direct Numerical Modeling of E-Cloud Driven Instability of a Bunch Train in the CERN SPS | 1776 |
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Funding: Supported by the US-DOE under Contract DE-AC02-05CH11231, the SciDAC program ComPASS and the US-LHC Accelerator Research Program (LARP). Used resources of NERSC and the Lawrencium cluster at LBNL. Electron clouds impose limitations on current accelerators that may be more severe for future machines, unless adequate measures of mitigation are taken. It has been proposed recently to use feedback systems operating in the GHz range to damp single-bunch transverse coherent electron cloud driven instabilities that may occur in relatively long, ns scale, proton bunches such as those in the CERN SPS. The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the growth rate and frequency patterns in space-time of the electron cloud driven transverse instability for a proton bunch train in the CERN SPS accelerator with, or without, feedback models (with various levels of idealization) for damping the instability. We will present our latest simulation results, contrast them with actual measurements and discuss the implications for the design of the actual feedback system. |
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| WEP156 | GPU-Accelerated 3D Time-Domain Simulation of RF Fields and Particle Interactions | 1779 |
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Funding: This work is supported by the U.S. Office of Naval Research. The numerical simulation of electromagnetic fields and particle interactions in accelerator components can consume considerable computational resources. By performing the same computation on fast, highly parallel GPU hardware instead of conventional CPUs it is possible to achieve a 20x reduction in simulation time for the traditional 3D FDTD algorithm. For structures that are small compared to the RF wavelength, however, or that require fine grids to resolve, the FDTD technique is constrained by the Courant condition to use very small time steps compared to the RF period. To avoid this constraint we have implemented an implicit, complex-envelope 3D ADI-FDTD algorithm for the GPU and demonstrate a further 5x reduction in simulation time, now two orders of magnitude faster than conventional FDTD codes. Recently, a GPU-based particle interaction model has been introduced, for which results will be reported. These algorithms form the basis of a new code, NEPTUNE, being developed to perform self-consistent 3D nonlinear simulations of vacuum electron devices. |
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| WEP157 | An Implementation of the Fast Multipole Method for High Accuracy Particle Tracking of Intense Beams | 1782 |
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| We implement a single level version of the fast multipole method in the software package COSY Infinity. This algorithm has been used in other physics fields to determine high accuracy electrostatic potentials, and is implemented here for charged particle beams. The method scales like NlogN with the particle number and has a priori error estimates, which can be reduced to essentially machine precision if multipole expansions of high enough order are employed, resulting in a highly accurate algorithm for simulation of intense beams without averaging such as encountered in PIC methods. In order to further speed up the algorithm we use COSY Infinity’s innate differential algebraic methods to help with the expansions inherent in this system. Differential algebras allow for fast and exact numerical differentiation of functions that carries through any mathematical transformations performed, and can be used to quickly create the expansions used in the fast multipole method. This can then be combined with moment method techniques to extract transfer maps which include space charge within distributions that are difficult to approximate. | ||
| WEP159 | Improved Algorithms for Multipacting Simulation in the Analyst Code | 1785 |
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Funding: Work funded by the U.S. Dept. of Energy, Office of Science, SBIR Contract No. DE-FG02-05ER84373. Electron multipacting is often deleterious in RF structures and must be controlled via modifications to the geometry, materials, or external fields. Recent improvements to the capabilities for modeling multipacting in the Analyst software package are presented in this paper. A backward difference scheme*, coupled with Newton-Raphson iteration, is used to integrate particle position/momentum, with integrations interrupted at element faces to minimize errors and lost particles. Support for the Furman-Pivi secondary emission model** has been implemented, with separate representations for low energy, re-diffused, and backscattered secondary particles, and multiple emissions per impact based upon a probability distribution. We have also developed a method to prune the tree of secondary particles resulting from an impact that minimizes particle count growth while maintaining important statistical information about the resonance. Finally, we have added support for volumetric sourcing of primaries, wherein the model volume is seeded with a population of particles with random positions and initial velocities. These improvements, along with benchmark calculations, will be presented. * D. Darmofal, et al., Jour. Comp. Phys., 123, 1996, pp. 182-195. ** M. Furman, et al., LBNL-52807, June, 2003. |
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| WEP160 | Inclusion of Surface Roughness Effects in Emission Modeling With the MICHELLE Code | 1788 |
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High-brightness electron beams are needed in millimeter-wave tubes and other high-power RF applications. Cathode surface roughness at the micron scale, commonly due to machining or other effects, can lead to broadening of the velocity distribution of electrons downstream, increasing emittance and lowering beam brightness. In this paper we investigate methods of including surface roughness effects in the MICHELLE code*. Modeling of typical surface imperfections over an entire cathode is not feasible, since it requires representation of features that are 3 to 5 orders of magnitude smaller than the cathode. Moreover, the actual surface imperfections for a given cathode are unknown without a prohibitive microscopic investigation of the surface, and these details vary between cathodes with the same machining history. To avoid these problems we investigated modifications to emission models that can account for these effects in an average sense, allowing the use of a smooth emission surface in a model while retaining the essential effects of the rough surface on the beam. We present the results of this investigation, along with representative solutions for sample structures.
*John Petillo, et al., “Recent Developments in the MICHELLE 2D/3D Electron Gun and Collector Modeling Code”, IEEE Trans. Electron Devices Sci., vol. 52, no. 5, May 2005, pp. 742-748. |
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| WEP161 | Modeling and Simulations of Electron Emission from Diamond-Amplified Cathodes | 1791 |
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Funding: This work is supported by the U. S. Department of Energy under the DE-SC0004431 grant. Emission of electrons from a diamond-amplified cathode was recently demonstrated*. This experiment was based on a promising new concept** for generation of high-current, high-brightness, and low thermal emittance electron beams. The measurements from transmission and emission experiments have shown the potential to realize the diamond-amplified cathode concept. However, the results indicate that the involved physical properties should be understood in greater detail to build diamond cathodes with optical properties. We have already made progress in understanding the secondary electron generation and charge transport in diamond with the models we implemented in the VORPAL computational framework. We have been implementing models for electron emission from diamond and will present results from 3D VORPAL simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, propagation of the charge clouds, and then the emission of electrons into diamond. We will discuss simulation results on the dependence of the electron emission on diamond surface properties. * X. Chang et al., Electron Beam Emission from a Diamond-Amplified Cathodes, to appear in Phys. Rev. Lett. (2010). ** I. Ben-Zvi et al., Secondary emission enhanced photoinjector, Rep. C-A/AP/149, BNL (2004). |
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| WEP162 | Modeling of Diamond Based Devices for Beam Diagnostics | 1794 |
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Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grants DE-SC0004584 (Tech-X Corp.) and DE-FG02-08ER41547 (BNL). Beamlines at new light sources, such as the National Synchrotron Light Source II will operate at flux levels beyond the saturation level of existing diagnostics, necessitating the development of new devices. Currently, there is no detector which can span the entire flux range that is possible even in a second generation light source and will become crucial for next generation light sources. One new approach* is a diamond-based detector that will be able to monitor beam position, flux and timing to much better resolution. Furthermore, this detector also has linear response to flux over 11 orders of magnitude. However, the successful development of the detector requires thorough understanding and optimization of the physical processes involved. We will discuss the new modeling capabilities we have been implementing in the VORPAL 3D code to investigate the effects of charge generation due to absorption of x-ray photons, transport, and charge trapping. We will report results from VORPAL simulations on charge collection and how it depends on applied field, charge trapping, and the energy of absorbed photons. *J. W. Keister, J. Smedley, D. A. Dimitrov, and R. Busby, Charge Collection and Propagation in Diamond X-ray Detectors, IEEE Transactions on Nuclear Science, 57, 2400 (2010). |
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| WEP163 | RF Cavity Characterization with VORPAL | 1797 |
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| When designing a radio frequency (RF) accelerating cavity structure various figures of merit are considered before coming to a final cavity design. These figures of merit include specific field and geometry based quantities such as the ratio of the shunt impedance to the quality factor (R/Q) or the normalized peak fields in the cavity. Other important measures of cavity performance include the peak surface fields as well as possible multipacting resonances in the cavity. High fidelity simulations of these structures can provide a good estimate of these important quantities before any cavity prototypes are built. We will present VORPAL simulations of a simple pillbox structure where these quantities can be calculated analytically and compare them to the results from the VORPAL simulations. We will then use VORPAL to calculate these figures of merit and potential multipacting resonances for two cavity designs under development at Jefferson National Lab for Project X. | ||
| WEP164 | Accelerating Beam Dynamics Simulations with GPUs | 1800 |
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Funding: This work is funded by the DOE/BES Grant No. DE-SC0004585, and by Tech-X Corp. We present recent results of prototyping general-purpose particle tracking on GPUs, discussing our CUDA implementation of transfer maps for single-particle dynamics and collective effects. Our goal being incorporation of the GPU-accelerated tracking into ANL's accelerator code ELEGANT, we used the code's quadrupole and drift-with-LSC elements as test cases. We discuss the use of data-parallel and hardware-assisted approaches (segmented scan and atomic updates) for resolving memory contention issues at the charge deposition stage of algorithms for modeling collective effects. |
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| WEP165 | Advanced Modeling of TE Microwave Diagnostics of Electron Clouds | 1803 |
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Funding: Part of this work is being performed under the auspices of the U.S. Department of Energy as part of the ComPASS SciDAC project, #DE-FC02-07ER41499. Numerical simulations of electron cloud buildup and in particular rf microwave diagnostics provide important insights into the dynamics of particle accelerators and the potential for mitigation of destabilizing effects of electron clouds on particle beams. Typical Particle-In-Cell (PIC) simulations may accurately model cloud dynamics; however, due to the large range of temporal scales needed to model side band production due to ecloud modulation, typical PIC models may not be the best choice. We present here preliminary results for advance numerical modeling of rf electron cloud diagnostics, where we replace kinetic particles with an equivalent plasma dielectric model. This model provides significant speedup and increased numerical stability, while still providing accurate models of rf phase shifts induced by electron cloud plasmas over long time scales. |
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| WEP167 | Searching for the Optimal Working Point of the MEIC at JLab Using an Evolutionary Algorithm | 1805 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Supported in part by SciDAC collaboration. The Medium-energy Electron Ion Collider (MEIC), a proposed medium-energy ring-ring electron-ion collider based on CEBAF at Jefferson Lab. The collider luminosity and stability are sensitive to the choice of a working point – the betatron and synchrotron tunes of the two colliding beams. Therefore, a careful selection of the working point is essential for stable operation of the collider, as well as for achieving high luminosity. Here we describe a novel approach for locating an optimal working point based on evolutionary algorithm techniques. |
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| WEP170 | Inspection Camera for Superconducting Cavity at IHEP | 1808 |
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| The first 1.3GHz low-loss large grain 9-cell superconducting cavity for ILC was fabricated at the Institute of High Energy Physics (IHEP) in April, 2010. The gradient of the cavity reached 20MV/m on the first vertical test in KEK in June, 2010. The gradient was limited by quench and field emission of the ninth-cell of the cavity. To locate the position of defects and improve surface processing, we have developed a high resolution inspection camera for the 1.3GHz 9-cell superconducting cavity of IHEP to check the cavity surface and make comparison. The camera is suitable for single and multi-cell 1.3GHz superconducting cavities. As there are several types of cavity under developing in IHEP, the camera was designed to be suitable for different type and frequency cavities like 500MHz BEPC II superconducting cavity, 1.3GHz TESLA and TESLA-like cavity, 1.3GHz and 650MHz low-beta cavity. | ||
| WEP173 | Numerical Calculations for the SR Characteristics Described in Terms of Quantum Theory: The Case of Weakly Excited Particles. | 1810 |
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| We present the numerical calculations based on the theoretical research of SR characteristics for the weakly excited particles. For a spinless and spinor particle the exploration of effective angles and deviation angles is to be conducted. Comparing the data obtained with its classical analogue , one shows that the quantum theory gives a number of unpredictable results. | ||
| WEP174 | Simulations and Calculations of Cavity-to-cavity Coupling for Elliptical SCRF Cavities in ESS | 1813 |
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| The proton linac of the European Spallation Source (ESS) will rely on two families of superconducting cavities for the medium and high beta regions. Presented here are simulations of various cavity designs for different betas. The simulations are performed using the ACE3P codes developed at SLAC National Accelerator Laboratory, and the simulated eigenmode and R/Q spectrum will be shown for each design. Dangerous modes are identified. Of particular importance is the investigations of multiple cavity (cryomodule) configurations. From this, the simulated cavity-to-cavity coupling within a cryomodule is extracted. A theoretical model of this coupling based on the calculated cutoff frequencies, decay lengths, and resonance conditions, has also been developed, and a comparison made with the results of the simulation. | ||
| WEP176 | Loss Factor of Tapered Structures for Short Bunches | 1816 |
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Funding: Work supported by DOE contract DE-AC02-98CH10886 Using the electromagnetic simulation code ECHO, we have found* a simple phenomenological formula that accurately describes the loss factor for short bunches traversing an axisymmetric tapered collimator. In this paper, we consider tapered collimators with elliptical cross-section and use the GdfidL code to calculate the loss factor dependence on the geometric parameters for short bunches. The results for both axisymmetric and elliptical collimators are discussed. * A. Blednykh and S. Krinsky, Phys. Rev. ST-AB 13, 064401 (2010). |
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| WEP177 | Radial Transmission Line Analysis of Multi-layer Circular Structures | 1819 |
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Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. The analysis of multi-layer beam tubes is a frequent problem and is usually solved with axially propagating waves. This treatment is ill suited to a short multi-layer structure such as the present example of a ferrite covered ceramic break in the beam tube at the ERL photo-cathode electron gun. This paper demonstrates that such structures can better be treated by radial wave propagation. The theoretical method is presented and numerical results are compared with measured network analyser data and Microwave Studio generated simulations. The results confirm the concept of radial transmission lines as a valid analytical method. |
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| WEP178 | Electromagnetic Field Measurement of Fundamental and Higher-order Modes for 7-cell Cavity of PETRA-II | 1822 |
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| The booster synchrotron for NSLS-II will include a 7-cell PETRA cavity, which was manufactured for the PETRA-II project at DESY. The cavity fundamental frequency operates at 500 MHz. In order to verify the impedances of the fundamental and higher-order modes (HOM) which were calculated by computer code, we measured the magnitude of the electromagnetic field of the fundamental acceleration mode and HOM’s, using the bead-pull method. To keep the cavity body temperature constant, we used a chiller system to supply cooling water at 20 degrees C. The bead-pull measurement was automated with a computer. We encountered some issues during the measurement process due to the difficulty in measuring the electromagnetic field magnitude in a multi-cell cavity as compared to a single-cell cavity. We describe the apparatus for the field measurement and the obtained results. | ||
| WEP179 | Calculating Point-Charge Wakefields from Finite Length Bunch Wake-Potentials | 1825 |
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| Starting from analytical properties of high frequency geometric impedance we show how one can accurately calculate short bunch wake-potentials (and even point-charge wakefields) from time domain calculations performed with a much longer bunch. In many practical instances this drastically reduces the need for computer resources, speeds up the calculations, and improves their accuracy. To illustrate this method we give examples for 2D accelerator structures of various complexities. | ||
| WEP181 | Coherent Radiation in Insertion Devices | 1828 |
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Funding: NSF We calculate the coherent radiation in an undulator/wiggler with a vacuum chamber of arbitrary cross section. The backward radiation is a coherent and it has wavelengths about twice the period of the undulator/wiggler. Mostly of coherent radiation is going with the wavelengths approximately the bunch length at small angles however. |
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| WEP184 | Cerenkov Radiator Driven by a Superconducting RF Electron Gun | 1831 |
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Funding: Parts of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The Naval Postgraduate School (NPS), Niowave, Inc., and Boeing have recently demonstrated operation of the first superconducting RF electron gun based on a quarter wave resonator structure. In preliminary tests, this gun has produced 10 ps-long bunches with charge in excess of 78 pC, and with beam energy up to 396 keV. Initial testing occurred at Niowave's Lansing, MI, facility, but the gun and its diagnostic beamline are planned for installation at NPS in the near future. The design of the diagnostic beamline is conducive to the addition of a Cerenkov radiator without interfering with other beamline operations. Design and simulations of a Cerenkov radiator, consisting of a dielectric lined waveguide will be presented. The dispersion relation for the structure is determined and the beam interaction is studied using numerical simulations. The characteristics of the microwave radiation produced in both the long and short bunch regimes will be examined. |
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| WEP185 | Properties of Longitudinally Uniform Beam Waveguides | 1834 |
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Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. Beam waveguide (BWG) geometry with two longitudinally uniform concave reflectors can support quasi-optical transverse resonances of electromagnetic waves and longitudinal power transmission. The quasi-optical resonance in BWG can be treated as a Gaussian beam. The BWG are often known to have high Q-factors while operating in higher order modes. The latest interests on these beam waveguides are the application for microwave or millimeter wave undulators for synchrotron radiation. The general properties of the BWG are discussed with the field solutions and dispersion properties derived with elliptical beam waveguides approximation. Potential applications of BWG for supporting circularly polarized wave are discussed. |
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| WEP186 | Wake Potentials in the ILC Interaction Region | 1837 |
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Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515. The vacuum chamber of the ILC Interaction Region (IR) is optimized for best detector performance. It has special shaping to minimize additional backgrounds due to the metal part of the chamber. Also, for the same reason this thin vacuum chamber does not have water cooling. Therefore, small amounts of power, which may be deposited in the chamber, can be enough to raise the chamber to a high temperature. One of the sources of “heating” power is the electromagnetic field of the beam. This field diffracts by non-regularities of the beam pipe and excites free-propagating fields, which are then absorbed by the pipe wall. In addition we have a heating power of the image currents due to finite conductivity of the metallic wall. We will discuss these effects as updating the previous results. |
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| WEP187 | Simulation and Optimization of Project-X Main Injector Cavity | 1840 |
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| Project-X, a proposed high intensity proton facility to support a world-leading program in neutrino and flavor physics at Fermilab, plans to use the existing FNAL recycler and main injector (MI) complex, but requires upgrading the MI RF system. Currently there are two proposed 53MHz RF cavity designs for 6GeV to 120GeV operation. One design is a straight-line quarter wave resonant cavity, and the other a tapered quarter wave resonant cavity. The electromagnetic (EM) simulations of the two cavity designs are carried out by using SLAC finite element parallel code suit ACE3P. The EM simulation results for the RF parameters and higher-order-mode (HOM) properties have shown that the tapered cavity design has better RF performance than the straight one. The tapered cavity shape will then be optimized for the final design to meet the specified performance requirements for the Project-X. Possible multipacting zones in the cavity will be identified and the use of HOM dampers investigated for the optimized design. | ||
| WEP189 | Compression and Synchronization of an Ultra-short Electron Beam Using a THz Undulator Interaction | 1843 |
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Funding: DOE-BES No. DE-FG02-92ER40693 and DOE-BES No. DE-FG02-07ER46272 Injection of electron beams into laser driven picosecond scale accelerating structures demand highly synchronized electron beams with bunch lengths approaching the femtosecond scale. One-dimensional numerical studies of undulator interactions of 3.5 MeV sub-picosecond electron beams and THz pulse trains produced by optical rectification have shown substantial compression and a reduction in time of arrival jitter with respect to the accelerator drive laser from the scale of hundreds of fs to that of tens of fs. In this paper a THz undulator based compression and synchronization scheme is investigated. |
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| WEP190 | Magnetic Field Expansion Out of a Plane: Application to Cyclotron Development | 1846 |
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| In studies of the dynamics of charged particles in a cyclotron magnetic field, the specified field is generally Bz in the z = 0 midplane where Br and Btheta are zero. Br(r,theta, z) and Btheta (r,theta, z) are usually determined through a linear expansion which assumes that Bz is independent of z. An expansion to only first order may not be sufficient for orbit simulations at small r and large z. This paper reviews the expansion of a specified Bz(r,theta, z = 0) out of the z = 0 midplane to arbitrary order, and shows simple examples worked out to 4th order. | ||
| WEP192 | Simulation Results for a Cavity BPM Design for the APS Storage Ring | 1849 |
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Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. A rectangular cavity BPM / tilt monitor for the APS storage ring has been designed to detect residual vertical-longitudinal tilt caused by the proposed short-pulse x-ray (SPX) project crab cavities. Electromagnetic simulations have been performed to verify the conceptual design and evaluate design alternatives. MAFIA and Microwave Studio have been applied to simulate the device in both time and frequency domains. The device geometry has been optimized to efficiently damp strongly driven lower- and higher-order modes while preserving the tilt-sensitive mode of interest. This mode is coupled out to the processing electronics using a waveguide geometry chosen to maximize isolation from the beam-driven modes. |
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| WEP194 | Measurement Techniques to Characterize Instabilities Caused by Electron Clouds | 1852 |
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Funding: Work is supported by NSF (PHY-0734867) and DOE (DE-FC02-08ER41538) grants. The study of electron cloud-related instabilities for the CESR-TA project has required the development of new measurement techniques. The dynamics of the interaction of electron clouds with trains of bunches has been undertaken employing three basic observations. Measurements of tune shifts of bunches along a train has been used extensively with the most recent observations permitting the excitation of single bunches within the train to avoid collective train motion from driving the ensemble of bunches. Another technique has been developed to detect the coherent self-excited spectrum for each of the bunches within a train. This method is particularly useful when beam conditions are near the onset of an instability. The third method was designed to study bunches within the train in conditions below the onset of unstable motion. This is accomplished by separately driving each bunch within the train for several hundred turns and then observing the damping of its coherent motion. These last two techniques have been applied to study both transverse dipole (centroid) and head-tail motion. We will report on the observation methods and give examples of typical results. |
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| WEP195 | Time Resolved Measurement of Electron Clouds at CesrTA using Shielded Pickups | 1855 |
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Funding: This work is supported by the US National Science Foundation PHY-0734867, and the US Department of Energy DE-FC02-08ER41538. The Cornell Electron Storage Ring has been reconfigured as a Test Accelerator (CesrTA). Shielded pickups have been installed at three locations in CesrTA for the purpose of studying time resolved electron cloud build-up and decay. The pickup design provides electromagnetic shielding from the beam wakefield while allowing cloud electrons in the vacuum space to enter the detector. This paper describes the hardware configuration and capabilities of these detectors at CesrTA, presents examples of measurements, and outlines the interpretation of detector signals with regard to electron clouds. Useful features include time-of-flight measurement of cloud electrons and the use of a solenoidal field for energy measurement of photoelectrons. Measurement techniques include the use of two bunches spaced in multiples of 4ns, where the second bunch samples the decay of the cloud produced by the first bunch. |
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| WEP196 | Single-Shot Longitudinal Phase Space Measurement Diagnostics Beamline Status at the Argonne Wakefield Accelerator | 1858 |
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| A single-shot longitudinal phase space diagnostics experiment is currently being commissioned at Argonne Wakefield Accelerator. The diagnostic beamline consists of two magnetic dipoles that bend the beam horizontally followed by an rf deflecting cavity that streaks the beam vertically. Using this configuration, the incoming longitudinal phase space can be mapped to a final (x,y) plane which can be directly measured, e.g., using a YAG screen. In this paper we discuss the limitations of such longitudinal phase space diagnostics and present some preliminary measurements. | ||
| WEP199 | Estimation of Ecloud and TMCI Driven Vertical Instability Dynamics from SPS MD Measurements - Implications for Feedback Control | 1861 |
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Funding: Work supported by the U.S. Department of Energy under contract # DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP). We present analysis of beam motion data obtained in high intensity SPS MD studies in 2009 and 2010. The single-bunch vertical E-cloud motion seen in parts of the bunch train after injection shows large tune shifts (roughly 0.02 above the 0.185 tune) developing between tail and head of unstable bunches. The unstable vertical motion has spectral content up to roughly 1.2 GHz and a quasi-periodic growth and decoherence relaxation oscillation effect is seen with time scales of hundred turns. Beam slice FFT and RMS techniques are illustrated to extract parameters important for the design of wide-band vertical feedback system, such as a growth rates of unstable motion, tune shifts within a single bunch and characterization of the bandwidth of the unstable structures within a bunch. We highlight the impact of synchrotron motion and injection transients on a proposed vertical processing channel. We present our MD plans including the beam driving process, developments in reduced model / identification techniques to extract dynamics from experimental and simulation data. *J. Fox et al., ‘‘SPS Ecloud Instabilities - Analysis Of Machine Studies And Implications For Ecloud Feedback,'' IPAC'10, WEPEB052 |
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| WEP201 | Status of NSLS-II Booster | 1864 |
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| The National Synchrotron Light Source II is a third generation light source under construction at Brookhaven National Laboratory. The project includes a highly optimized 3 GeV electron storage ring, linac pre-injector and full-energy booster-synchrotron. Budker Institute of Nuclear Physics builds booster for NSLS-II. The booster should accelerate the electron beam continuously and reliably from minimal 170 MeV injection energy to maximal energy of 3.15 GeV and average beam current of 20 mA. The booster shall be capable of multi-bunch and single bunch operation. This paper summarizes the status of NSLS-II booster and the main designed parameters. | ||
| WEP204 | An FFAG Accelerator for Project X | 1867 |
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| The next generation of high-energy physics experiments requires high intensity protons in the multi-GeV energy range for efficient production of secondary beams. The Fermilab long-term future requires an 8 GeV proton source to feed the Main Injector for a 2 MW neutrino beam source in the immediate future and to provide 4 MW pulsed proton beam for a future neutrino factory or muon collider. We note that a 3GeV cw linac matched to a 3–8 GeV FFAG ring could provide beam for both of these mission needs, as well as the cw 3 GeV experiments, and would be a natural and affordable scenario. We present details of possible scenarios and outline future design and research directions. | ||
| WEP205 | A Gap Clearing Kicker for Main Injector | 1870 |
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Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. Fermilab Main Injector has been operating at high Beam Power Levels since 2008 when multi-batch slip stacking became operational. In order to increase the beam power even further we have to address the localized beam loss due to beam left over in the Injection Kicker Gap during slip stacking. A set of Gap Clearing Kickers that kick any beam left in the injection gap to the beam abort have been installed during the summer of 2009 and became operational in October 2010. The kicker performance and its effect on beam losses will be described. |
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| WEP206 | An Accumulator/Pre-Booster for the Medium-Energy Electron Ion Collider at JLab | 1873 |
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| Future nuclear physics facilities such as the proposed electron ion collider (MEIC) will need to achieve record high luminosities in order to maximize discovery potential. Among the necessary ingredients is the ability to generate, accumulate, accelerate, and store high current ion beams from protons to lead ions. One of the main components of this ion accelerator complex for MEIC chain is the accumulator that also doubles as a pre-booster, which takes 200 MeV protons from a superconducting linear accelerator, accumulates on the order of 1A beam, and boosts its energy to 3GeV, before extraction to the next accelerator in the chain, the large booster. This paper describes its design concepts, and summarizes some preliminary results, including linear optics, space charge dynamics, and spin polarization resonance analysis. | ||
| WEP207 | Progress Towards A Novel Compact High Voltage Electrostatic Accelerator | 1876 |
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| A proof-of-principle demonstrator system has been successfully built and tested. It is based on a Cockcroft-Walton (or Greinacher) cascade but has been developed using a different design philosophy and using modern materials. This can then enable this compact accelerator configuration to operate at much higher voltage gradients. This paper explores the progress made to-date and future plans to utilize the technology to develop one such concept for an energy efficient 10 MV, 100 microamp, tandem proton accelerator, with less than a 2 square meter footprint . | ||
| WEP208 | Design of an Antiproton Recycler Ring | 1879 |
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Funding: Work supported by the EU under contract PITN-GA-2008-215080, the Helmholtz Association of National Research Centers (HGF) under contract VH-NG-328, and the GSI Helmholtz Centre for Heavy Ion Research. At present, the only place in the world where experiments utilising low-energy antiprotons can be performed is the AD at CERN. The MUSASHI trap, as part of the ASACUSA collaboration, enables access to antiproton energies in the order of a few hundreds of eV. Whilst MUSASHI produces cutting-edge research, the available beam quality and luminosity is not sufficient for collision experiments on the level of differential cross sections. A small electrostatic ring, and associated electrostatic acceleration section, is being designed and developed by the QUASAR Group. It will serve as a prototype for the future ultra-low energy storage ring (USR), to be integrated at the facility for low-energy antiproton and ion research (FLAIR). This small AD recycler ring will be unique due to its combination of size, electrostatic nature and energy of the circulating particles. In this contribution, the design of the ring is described and details about the injection section are given. |
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| WEP209 | Reliability Study of the AIRIX Induction Accelerator over a Functioning Period of Ten Years (2000-2010) | 1882 |
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| AIRIX is a high current (19 MeV, 2 kA) electron linear induction accelerator used as a 60 ns single shot X-ray source for hydrodynamic experiments. As single shot experiments are performed with the AIRIX facility, the best performances and a high reliability level must be met for each experiment. A high availability is also a key issue for the successful development of hydrotest projects. The AIRIX accelerator has been running for hydroshot experiments since 2000 and several thousands electron and X-ray beams have been produced. This paper outlines the reliability results of the AIRIX accelerator over a functioning period of ten years. Failure rates for each main subsystems are shown : injector, accelerating cells, high voltage generators, and measurement chains. We also give an overview of the most probable faults, with the associated occurrence rates, which can alter the X source of the AIRIX machine over this ten year period. | ||
| WEP210 | Low Energy Beam Measurements Using PHIL Accelerator at LAL, Comparison with PARMELA Simulations | 1885 |
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| PHIL (“PHoto-Injector at LAL") is a new electron beam accelerator at LAL. This accelerator is dedicated to test and characterize electron RF-guns and to deliver electron beam to users. This machine has been designed to produce and characterise low energy (E<10 MeV), small emittance (e<10 p.mm.mrad), high brilliance electrons bunch at low repetition frequency (n<10Hz). The first beam has been obtained on the 4th of November 2009. The current RF-gun tested on PHIL is the AlphaX gun, a 2.5 cell S-band cavity designed by LAL for the plasma accelerator studies performed at the Strathclyde university. This paper will present the first AlphaX RF-gun characterizations performed at LAL on PHIL accelerator, and will show comparisons between measurements and PARMELA simulations. | ||
| WEP212 | Development of a 325 MHz 4-Rod RFQ | 1888 |
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| A 4-Rod RFQ with a frequency of 325 MHz and an output energy of 3 MeV will be build as a part of the FAIR project of GSI. Design studies and model measurements on a short prototype of a 325 MHz 4-Rod RFQ model were made including simulations using CST Microwave Studio. The latest simulation results regarding the dipole field of this structure are presented in this paper. | ||
| WEP213 | New Development of a RFQ Beam Matching Section | 1891 |
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Funding: BMBF Funneling is a method to increase low energy beam currents in multiple stages. The Frankfurt Funneling Experiment is a model of such a stage. The experiment is built up of two ion sources with electrostatic lens systems, a Two-Beam-RFQ accelerator, a funneling deflector and a beam diagnostic system. The two beams are bunched and accelerated in a Two-Beam RFQ. A funneling deflector combines the bunches to a common beam axis. Current work is the construction and beam tests of a new beam transport system between RFQ accelerator and deflector. With extended RFQ-electrodes the drift between the Two-Beam-RFQ and the rf-deflector will be minimized and therefore unwanted emittance growth reduced. First rf-measurements with the improved Two-Beam-RFQ will be presented. |
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| WEP214 | Tuning Studies on 4-Rod RFQs | 1894 |
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| For the optimization of Radio Frequency Quadrupole (RFQ) design parameters, a certain voltage distribution along the electrodes of an RFQ is assumed. Therefore an accurate tuning of the voltage distribution is very important for the beam dynamic properties of an RFQ. A variation can lead to particle losses and reduced beam quality. Our electrode design usually implies a constant longitudinal voltage distribution. For its adjustment tuning plates are used between the stems of the 4-Rod RFQ. Their optimal positions can be found by an iterative process. To structure this tuning process simulations with a NI LabVIEW based Tuning Software and CST Microwave ® are performed and compared to measurements of the ReA3-RFQ of the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The results of this studies are presented in this paper. | ||
| WEP220 | Development of the Dual-Slot Resonance Linac | 1897 |
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Funding: Work supported by DOE Office of High Energy Physics, DOE-SBIR #DE-FG02-08ER85034. We present the development of a novel electron accelerating structure with strong cell-to-cell coupling. The coupling is provided by a pair of resonant slots, separated by a non-resonant void region, located within the wall between adjacent cells. The 10+2/2 cell standing-wave structure, operating in a phase and amplitude stabilized pi/2 mode, will provide an energy gain of 10 MeV. |
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| WEP221 | CW Room-Temperature Bunching Cavity for the Project X MEBT | 1900 |
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| The Project-X, a multi-MW proton source based on superconducting linac, is under development at Fermilab. The front end of the linac contains a CW room temperature MEBT section which comprises ion source, RFQ and high-bandwidth bunch selective chopper. The length of the chopper exceeds 10 m, so four re-bunching cavities are used to support the beam longitudinal dynamics. The RF and mechanical designs of the re-bunching cavity including stress and thermal analysis are reported. | ||
| WEP222 | Low Energy Beam Diagnostic for APEX, the LBNL VHF Photo-injector | 1903 |
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Funding: This work was supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 A high-repetition rate (MHz-class), high-brightness electron beam photo-gun is under construction at Lawrence Berkeley National Laboratory in the framework of the Advanced Photo-injector EXperiment (APEX). The injector gun is based on a normal conducting 187 MHz RF cavity operating in CW mode. In its first operational phase it will deliver short bunches (~ 1 to tens of picoseconds) with energy of 750keV, and bunch charges ranging from 1pC to 1nC. Different high efficiency cathode materials will be tested, and the beam quality will be studied as a function of parameters as charge, initial bunch length and transverse size, focusing strength. Both the laser and electron beam diagnostics have been designed to assure the needed flexibility. In particular a high-resolution electron diagnostic section after the photo-gun provides the necessary dynamical range for scanned beam parameters: energy and energy spread, charge and current, transverse and longitudinal phase spaces, slice properties. The photo-gun electron beam diagnostic layout is presented, and the hardware choices, resolution and achievable dynamical ranges are also discussed. |
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| WEP224 | Operational Status and Life Extension Plans for the Los Alamos Neutron Science Center (LANSCE) | 1906 |
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Funding: Work supported by the U. S. Department of Energy, National Nuclear Security Administration, Contract No. DE-AC52-06NA25396 – Publication Release LA-UR- 10-06556 The Los Alamos Neutron Science Center (LANSCE) accelerator and beam delivery complex generates the proton beams that serve three neutron production sources, a proton radiography facility and a medical and research isotope production facility. The recent operating history of the facility, including both achievements and challenges, will be reviewed. Plans for performance improvement will be discussed, together with the underlying drivers for the ongoing LANSCE Linac Risk Mitigation project. The details of this latter project will be discussed. The status of accelerator-related plans for the MaRIE Project (Matter-Radiation Interactions in Extremes Experimental Project) will also be discussed. Taken together, the LANSCE Linac Risk Mitigation Project and the MaRIE initiative demonstrate a commitment to investment in the ongoing operation and improvement of the facility, and a resurgent interest in the spectrum of science accessible at LANSCE. These plans will assure continued facility operational and scientific vitality well beyond 2020. |
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| WEP225 | H-Mode Accelerating Structures with PMQ Focusing for Low-Beta Beams | 1909 |
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| We report results of the project developing high-efficiency normal-conducting RF accelerating structures based on inter-digital H-mode (IH) cavities and the transverse beam focusing with permanent-magnet quadrupoles (PMQ), for beam velocities in the range of a few percent of the speed of light. The shunt impedance of IH-PMQ structures is 10-20 times higher than that of a conventional drift-tube linac, while the transverse size is 4-5 times smaller. The H-PMQ accelerating structures following a short RFQ can be used both in the front end of ion linacs or in stand-alone applications. Results of the combined 3-D modeling – electromagnetic computations, beam-dynamics simulations with high currents, and thermal-stress analysis – for a full IH-PMQ accelerator tank are presented. The accelerating field profile in the tank is tuned to provide the best propagation of a 50-mA deuteron beam using coupled iterations of electromagnetic and beam-dynamics modeling. Multi-particle simulations with Parmela and CST Particle Studio have been used to confirm the design. Measurement results of a cold model of the IH-PMQ tank are in a good agreement with the calculations and will also be presented. | ||
| WEP226 | Commissioning Results of the ReA RFQ at MSU* | 1912 |
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Funding: Project funded by Michigan State University The Facility for Rare Isotope Beams (FRIB) is currently in the preliminary design phase at Michigan State University (MSU). FRIB consists of a driver LINAC for the acceleration of heavy ion beams, followed by a fragmentation target station and a ReAccelerator facility (ReA3). ReA3 comprises gas stopper systems, an Electron Beam Ion Trap (EBIT) charge state booster, a room temperature radio frequency quadrupole (RFQ), a LINAC using superconducting quarter wave resonators and an achromatic beam transport and distribution line to the new experimental area. Beams from ReA3 will range from 3 MeV/u for heavy ions to about 6 MeV/u for light ions. The ReA3 RFQ, which is of the 4 rod type, is designed to accelerate ions with an Q/A of 0.2 to 0.5 from 12 keV/u to 600 keV/u. The RFQ operates at a frequency of 80.5 MHz and power levels up to 120 kW at 10% duty factor. In this paper we will report on commissioning results from the ReA3 RFQ using a H2+ and He+ beam from an auxiliary ion source. |
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| WEP228 | Effect of Transverse Electron Velocities on the Longitudinal Cooling Force in the Fermilab Electron Cooler | 1915 |
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Funding: FNAL is operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. In Fermilab’s electron cooler, a 0.1A, 4.3MeV DC electron beam propagates through the 20 m cooling section, which is immersed in a weak longitudinal magnetic field. A proper adjustment of 200 dipole coils, installed in the cooling section for correction of the magnetic field imperfections, can create a helix-like trajectory with the wavelength of 1-10 m. The longitudinal cooling force is measured in the presence of such helices at different wavelengths and amplitudes. The results are compared with a model calculating the cooling force as a sum of collisions with small impact parameters, where the helical nature of the coherent angle is ignored, and far collisions, where the effect of the coherent motion is neglected. A qualitative agreement is found. |
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| WEP229 | Status of 2 MeV Electron Cooler for COSY-Julich/HESR | 1918 |
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| The 2 MeV electron cooling system for COSY-Jülich was proposed to further boost the luminosity even in presence of strong heating effects of high-density internal targets. The 2 MeV cooler is also well suited in the start up phase of the High Energy Storage Ring (HESR) at FAIR in Darmstadt. It can be used for beam cooling at injection energy and is intended to test new features of the high energy electron cooler for HESR. The project is funded since mid 2009. The design and construction of the cooler is accomplished in cooperation with the Budker Institute of Nuclear Physics in Novosibirsk, Russia. The technical layout of the 2 MeV electron cooler is described. The infrastructure necessary for the operation of the cooler in the COSY ring (radiation shielding, cabling, water cooling etc.) is established. The electron beam commissioning at BINP Novosibirsk is scheduled to start at the end of 2010. First results are reported. | ||
| WEP231 | TRIUMF Cyclotron Beam Quality Improvement | 1921 |
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| TRIUMF cyclotron for decades operated at 500 MeV. Recently, the two primary beamlines 1A and 2A, have been reconfigured for running at 480 MeV. The objective was to reduce beam losses caused by the electromagnetic stripping by 30%. The radiation losses reduction was confirmed with both online measurements and residual activation field mapping after 8 month of beam production. In order to improve stability of both primary beams, one of the harmonic coils was configured in Bz-mode to compensate for the beam split ratio fluctuations. Br-mode of this coil and two outer radius trim coils was utilized to correct the beam vertical position at extraction. Moreover, to make the beam spot position on the target stable and insensitive to any uncontrolled movement of the stripper foil due to heat distortion, the beamline front end optics was tuned to compensate the cyclotron's inherent dispersion. Details of these developments and improvements are discussed in the paper. | ||
| WEP232 | A Multi Megawatt Ring Cyclotron to Search for CP Violation in the Neutrino Sector | 1924 |
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A new approach to search for CP violation in the neutrino sector* is proposed by the experiment called DAEδALUS (Decay At rest Experiment for cp At Laboratory for Underground Science). DAEδALUS needs three sources of neutrino fluxes, each one located at 1.5, 8 and 20 km from the underground detector. Each source has to be supplied with a proton beam with power higher than 1, 2 and 5 MW respectively. Here we present the study for a Superconducting Ring Cyclotron able to accelerate the H2+ molecules and to deliver proton beam with maximum energy of 800 MeV and the required power. Although the average power for the first 2 sites are 1 and 2 MW, the 20% duty cycle, required by the experiment, has the consequence that the peak power should stay in the range 5-10 MW and a peak current of about 4.5 mA of H2+ is necessary. We present the parameters of the superconducting magnetic sector simulated by the code TOSCA, the isochronous magnetic field produced and the magnetic forces acting on the coils. Some evaluation on the feasibility of the ring cyclotron, the advantages and problems relates with acceleration of the H2+ molecules will be also presented.
* J. Alonso et al., “Expression of Interest for a Novel Search for CP Violation in the Neutrino Sector: DAEδALUS”, Jun 2010. e-Print: arXiv:1006.0260 |
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| WEP234 | Longitudinal Dynamics in the EMMA ns-FFAG | 1927 |
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Funding: Work supported by the Science and Technology Facilities Council UK. Grant Number: ST/G004277/1 EMMA is the first non-scaling FFAG to be constructed, whose use of linear magnets means that the accelerating electron bunch rapidly crosses many resonances. We have modeled the capture and acceleration of bunches in the serpentine channel created by the radio-frequency cavities, and compare it to a proposed experiment in which induction cells allow slow acceleration. Two induction cores each providing ~20kV over 1.65 μs enable a number of resonance crossing experiments. |
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| WEP237 | The Oak Ridge Isochronous Cyclotron Refurbishment Project | 1930 |
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Funding: Managed by UT-Battelle, LLC for the U.S. Department of Energy under contract DE-AC05-00OR22725. The Oak Ridge Isochronous Cyclotron (ORIC) has been in operation for nearly fifty years at the Oak Ridge National Laboratory (ORNL). Presently, it serves as the driver accelerator for the ORNL Holifield Radioactive Ion Beam Facility (HRIBF), where beams are produced using the Isotope Separation Online (ISOL) technique for post-acceleration by the HRIBF 25URC tandem accelerator. Operability and reliability of ORIC are critical issues for the success of HRIBF and have presented increasingly difficult operational challenges for the facility in recent years. Earlier this year, a trim coil failure rendered ORIC inoperable for several months. This presented HRIBF with the opportunity to undertake various repairs and maintenance upgrades aimed at restoring the full functionality of ORIC and improving the reliability to a level better than what had been typical over the previous decade. In this paper, we present details of these efforts, including the replacement of the entire trim coil set and measurements of their radial field profile. Comparison of measurements and operating tune parameters with setup code predictions will also be presented. |
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| WEP241 | Beam Dynamics Simulations and Measurements at the Project X Test Facility | 1933 |
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Funding: Work supported by Fermi Research Alliance, LLC under DE-AC02-07CH11359 with the U.S. DOE Project X, under study at Fermilab, is a multi task SRF beam facility, aiming to provide high intensity protons for rare processes experiments and nuclear physics at low energy, and simultaneously for the production of neutrinos, as well as muon beams in the long term. A beam test facility - former known as High Intensity Neutrino Source (HINS) - is under commissioning for testing critical components of the project, e.g. a beam chopper. In this paper we describe the layout of the test facility and present beam dynamics simulations and measurements. |
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| WEP242 | Project X Functional Requirements Specification | 1936 |
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Funding: Work supported by the Fermi Research Alliance, under contract to the U.S. Department of Energy Project X is a multi-megawatt proton facility being designed to support intensity frontier research in elementary particle physics, with possible applications to nuclear physics and nuclear energy research, at Fermilab. A Functional Requirements Specification has been developed in order to establish performance criteria for the Project X complex in support of these multiple missions. This paper will describe the Functional Requirements for the Project X facility and the rationale for these requirements. |
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| WEP243 | Status of the Neutralized Drift Compression Experiment (NDCX-II) | 1939 |
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Funding: This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344, by LBNL under Contract DE-AC02-05CH11231, and by PPPL under Contract DE-AC02-76CH03073. The Neutralized Drift Compression Experiment (NDCX-II) is an induction accelerator project currently in construction at Lawrence Berkeley National Laboratory for warm dense matter (WDM) experiments investigating the interaction of ion beams with matter at high temperature and pressure. The machine consists of a lithium injector, induction accelerator cells, diagnostic cells, a neutralized drift compression line, a final focus solenoid, and a target chamber. The machine relies on a sequence of acceleration waveforms to longitudinally compress the initial ion pulse from 600 ns to less than 1 ns in ~ 12 meters. Radial confinement of the beam is achieved with 2.5 T solenoids. In the initial hardware configuration, 30-50 nC of Li+ will be accelerated to 1.2 MeV and allowed to drift-compress to a peak current of ~ 20 A. Construction of the accelerator will be completed in the summer of 2011 and will provide a worldwide unique opportunity for ion-driven warm dense matter experiments as well as research related to novel beam manipulations for heavy ion fusion drivers. The basic design of the machine and the current status of the construction project will be presented. |
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| WEP244 | Growth and Characterization of Bialkali Photocathodes for Cornell ERL Injector | 1942 |
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| The requirements of high quantum efficiency in the visible spectral range and that of an increased lifetime as compared to cesiated GaAs can be met by multi-alkali photocathodes, either CsKSb or NaKSb. In this paper we detail the procedures that allow the growth of thin films suitable for the ERL photoinjector operating at Cornell University. Quantum efficiency, spectral response, and surface characterization of deposited samples is presented. A load-locked multi-alkali cathode growth system is also described. | ||
| WEP245 | Optimization of DC Photogun Electrode Geometry | 1945 |
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| DC photoguns that employ electrostatic focusing to obtain lower beam emittance must inherently trade off between focusing strength and the field at the photocathode, and are traditionally pushed to the limits of breakdown voltage. In this paper, we numerically investigate a highly parametrized electrostatic geometry exploring the trade-off between the voltage breakdown condition and electrostatic focusing. We then compare the results to DC gun designs where the focusing is introduced via embedded solenoidal fields. Finally, we present investigations for a multi-anode gun design that seeks to simultaneously achieve both high electric field at the photocathode and high gun voltage without violating the empirical voltage breakdown condition. In the most feasible cases, the electrode geometry is optimized via genetic algorithms. Designs on the optimal front are compared with the current performance of the Cornell ERL prototype DC photogun. | ||
| WEP248 | Overview of the LBNE Neutrino Beam | 1948 |
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Funding: Work supported by Fermi Research Alliance, LLC, under contract DE-AC02-07CH11359 with the U.S. Department of Energy. The Long Baseline Neutrino Experiment (LBNE) will utilize a neutrino beamline facility located at Fermilab. The facility will aim a beam of neutrinos toward a detector placed at the Deep Underground Science and Engineering Laboratory (DUSEL) in South Dakota. The neutrinos are produced in a three step process. First, protons from the Main Injector hit a solid target and produce mesons. Then, the charged mesons are focused by a set of focusing horns into the decay pipe, towards the far detector. Finally, the mesons that enter the decay pipe decay into neutrinos. The parameters of the facility were determined by an amalgam of the physics goals, the Monte Carlo modeling of the facility, and the experience gained by operating the NuMI facility at Fermilab. The initial beam power is expected to be ~700 kW, however some of the parameters were chosen to be able to deal with a beam power of 2.3 MW. |
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| WEP249 | Intense Muon Beams for Experiments at Project X | 1951 |
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Funding: Supported in part by DOE SBIR grant DE-SC00002739 A coherent approach for providing muon beams to several experiments for the intensity-frontier program at Project X is described. Concepts developed for the front end of a muon collider/neutrino factory facility, such as phase rotation and ionization cooling, are applied, but with significant differences. High-intensity experiments typically require high-duty-factor beams pulsed at a time interval commensurate with the muon lifetime. It is challenging to provide large RF voltages at high duty factor, especially in the presence of intense radiation and strong magnetic fields, which may preclude the use of superconducting RF cavities. As an alternative, cavities made of materials such as ultra-pure Al and Be, which become very good - but not super - conductors at cryogenic temperatures, can be used. |
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| WEP251 | Design Studies of Pre-Boosters of Different Circumference for an Electron Ion Collider at JLab | 1954 |
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| The Medium-Energy Electron Ion Collider (MEIC) at JLab comprises a figure-8 shaped pre–booster ring as one of the main components. As it performs for both the accumulation of protons and ions it must have a circumference long enough to accommodate components such as RF cavities, cooling devices, collimation, injection and extraction. The length of the large booster ring in MEIC is suggested to be in the range 1.0-1.2km. Based on preliminary design work, the minimum viable length of the pre-booster in MEIC was identified as 200m. It is clear that the integer multiple of the length of the designed pre-booster should match with that of the large booster in MEIC. In order to cater future requirements of the EIC, the pre-booster in MEIC needs to be designed in different versions featured by different lengths. Thus, three different pre-boosters of lengths 200m, 250m and 300m are designed with various cell structures. This paper summarizes the three variants of the lattice. | ||
| WEP254 | Simulation of H− Beam Chopping in a Solenoid-Based Low-Energy Beam Transport (LEBT) | 1957 |
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Funding: This work is supported by the US DOE Office of Science, Office of Basic Energy Sciences, including grant No. DE-SC0000844. The H- linac for the Spallation Neutron Source (SNS) includes an electrostatic low-energy beam transport (LEBT) subsystem. The ion source group at SNS is developing a solenoid-based LEBT, which will include MHz frequency chopping of the partly-neutralized, 65~keV, 60~mA H- beam. Particle-in-cell (PIC) simulations using the parallel VORPAL framework are being used to explore the possibility of beam instabilities caused by the cloud of neutralizing ions generated from the background gas, or by other dynamical processes that could increase the emittance of the H- beam before it enters the radio-frequency quadrupole (RFQ) accelerator. |
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| WEP256 | Laser-Proton Acceleration as Compact Ion Source | 1960 |
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| Preparatory work is presented in the context of the upcoming LIGHT project, which is dedicated to build up a test stand for injecting laser accelerated protons into conventional accelerator structures, located at GSI Helmholtzcenter for Heavy Ion Research (Darmstadt, Germany). In an experimental campaign in 2010, a beam of 8.4×109 protons with 170 ps pulse duration and (6.7±0.1) MeV particle energy could be focused with the use of a pulsed high-field solenoid. Collimation and transport of a 300 ps proton bunch containing 3×109 protons with (13.5±0.5) MeV particle energy over a distance of 407 mm was also demonstrated. Parallel simulation studies of the beam transport through the solenoid are in good agreement with the experiment. | ||
| WEP257 | Spectroscopic Estimation of Plasma Parameters for ECR Ion Source in the Intense 14-MeV Neutron Generator being developed at IPR | 1963 |
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An accelerator based 14-MeV neutron generator, for fusion neutronics studies is being developed at IPR. ECR ion source is used to generate deuterium plasma. Electron density and temperature in the ECR plasma are measured using non-intrusive spectroscopic methods. Langmuir probes, though conventionally used for estimating local parameters in low-pressure microwave plasmas, are difficult to implement here owing to space constraint and heating of the probe from interaction with standing microwaves. Pure helium (He), He seeded hydrogen and deuterium plasmas are studied. Spectra for entire visible range are recorded for different fill pressures for a constant microwave power and different powers for a constant fill pressure. For optically thin plasmas of low density, line intensity ratio method can be used with appreciable reliability. CR model is used from ADAS (atomic data and analysis structure) to predict plasma parameters from suitable line ratios.
sbanerje@ipr.res.in sudhir@ipr.res.in Institute for Plasma Research |
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| WEP261 | Performance of the New EBIS Preinjector | 1966 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy, and by the National Aeronautics and Space Administration. The construction and initial commissioning phase of a new heavy ion preinjector was completed at Brookhaven in September, 2010, and the preinjector is now operational. This preinjector, using an EBIS source to produce high charge state heavy ions, provided helium and neon ion beams for use at the NASA Space Radiation Laboratory in the Fall of 2010, and gold and uranium beams are being commissioned during the 2011 run cycle for use in RHIC. The EBIS operates with an electron beam current of up to 10 A, to produce mA level currents in 10 to 40 μs beam pulses. The source is followed by an RFQ and IH linac to accelerate ions with q/m > 0.16 to an energy of 2 MeV/amu, for injection into the Booster synchrotron. The performance of the preinjector is presented, including initial operational experience for the NASA and RHIC programs. |
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| WEP263 | A Multiple Cathode Gun Design for the eRHIC Polarized Electron Source | 1969 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The future electron-ion collider eRHIC requires a high average current (~50 mA), short bunch (~3 mm), low emittance (~20 μm) polarized electron source. The maximum average current of a polarized electron source so far is more than 1 mA, but much less than 50 mA, from a GaAs:Cs cathode [1]. One possible approach to overcome the average current limit and to achieve the required 50 mA beam for eRHIC, is to combine beamlets from multiple cathodes to one beam. In this paper, we present the feasibility studies of this technique. |
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| WEP264 | Laser Ion Source With Long Pulse Width for RHIC-EBIS | 1972 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and by the National Aeronautics and Space Administration. The Electron Beam Ion Source (EBIS) at Brookhaven National Laboratory is a new heavy ion-projector for RHIC and NASA Space Radiation Laboratory. Laser Ion Source (LIS) with solenoid can supply many kinds of ion from solid targets and is suitable for long pulse length with low current as ion provider for RHIC-EBIS. In order to understand a plasma behavior for fringe field of solenoid, we measure current, pulse width and total ion charges by a new ion probe. The experimental result indicates that the solenoid confines the laser ablation plasma transversely. |
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| WEP267 | Estimates of the Number of Foil Hits for Charge Exchange Injection | 1975 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. For high intensity circular proton machines, one of the major limitations is the charge exchange injection foil. The number of foil hits due to circulating beam may cause the foil to fail and cause radiation due to multiple nuclear scattering and energy straggling. This paper will describe methods to estimate these quantities without going through lengthy simulations. |
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| WEP268 | Changes in LEBT/MEBT at the BNL 200 MeV Linac | 1978 |
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Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. After reconfiguration of the low energy (35 keV) and the medium energy (750 keV) transport lines in 2009-10, the Brookhaven linac is now delivering the highest intensity beam since it was built in 1970 (~120 μA average current of H− to the Brookhaven Linac Isotope Producer). It is also now delivering lower emittance polarized H− ion beam for the polarized program at RHIC. To increase the intensity further, we are replacing the buncher in the 750 keV line with one with higher Q value, to allow operation at higher power. Also, to improve polarization, we are replacing the magnetic solenoid before the RFQ in the 35 keV line by a solenoid-einzel lens combination. The paper will report on the results of these changes. |
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| WEP270 | A High Current Density Li+ Alumino-silicate Ion Source for Target Heating Experiments | 1981 |
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Funding: This work was performed under the auspices of the U.S Department of Energy by LLNL under contract DE AC52 07NA27344, and by LBNL under contract DE-AC02-05CH11231. The NDCX-II accelerator has been designed for target heating experiments in the warm dense matter regime. It will use a large diameter (≈ 10.9 cm) Li+ doped alumino-silicate source with a pulse duration of 0.5 μs, and beam current of ≈ 93 mA. Characterization of a prototype lithium alumino-silicate sources is presented. Using 6.35 mm diameter prototype emitters (coated and sintered on a ≈ 75% porous tungsten substrate), at a temperature of ≈1275° C, a space-charge limited Li+ beam current density of ≈ 1 mA/cm2 was measured. At higher extraction voltage, the source is emission limited at around ≈ 1.5 mA/cm2, weakly dependent on the applied voltage. The lifetime of the ion source is ≈ 50 hours while pulsing the extraction voltage at 2 to 3 times per minute. Measurements under these conditions show that the lifetime of the ion source does not depend only on beam current extraction, and lithium loss may be dominated by neutral loss or by evaporation. The thickness of the coating does not affect the emission density. It is inferred that pulsed heating, synchronized with the beam pulse rate may increase the life time of a source. |
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| WEP271 | Development of a Permanent-Magnet Microwave Ion Source for a Sealed-Tube Neutron Generator | 1984 |
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Funding: Supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. A microwave ion source has been designed and constructed for use with a sealed-tube, high-yield neutron generator. When operated with a tritium-deuterium gas mixture the generator will be capable of producing 5 · 1011 n/s in non-proliferation applications. Microwave ion sources are well suited for such a device because they can produce high extracted beam currents with a high atomic fraction at low gas pressures of 0.2 − 0.3 Pa required for sealed tube operation. The magnetic field strength for achieving electron cyclotron resonance (ECR) condition, 87.5 mT at 2.45 GHz microwave frequency, was generated and shaped with permanent magnets surrounding the plasma chamber and a ferromagnetic plasma electrode. This approach resulted in a compact ion source that matches the neutron generator requirements. The needed proton-equivalent extracted beam current density of 40 mA/cm2 was obtained at moderate microwave power levels of ∼ 400W. Results on magnetic field design, pressure dependency and atomic fraction measured for different wall materials are presented. |
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| WEP273 | Saddle RF Antenna H− Ion Source Progress | 1987 |
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Funding: Supported in part by USDOE Contract DE-AC05-00OR22725 and STTR Grant DE-SC0002690 In this project we are developing an RF H− surface plasma source (SPS) with saddle (SA) RF antenna which will provide better power efficiency for high pulsed and average current, higher brightness with longer lifetime and higher reliability. Several versions of new plasma generators with a small AlN test chamber and different antennasandmagneticfieldconfigurationsweretestedin the SNS ion source Test Stand. A prototype SA SPS was installed in the Test Stand with a larger, normal-sized SNS AlN chamber that achieved unanalyzed peak currents of up to 67 mA with an apparent efficiency of 1.6 mA/kW. Control experiments with H− beam produced by SNS SPS with internal and external antennas were conducted. A new version of the RF triggering plasma source (TPS) has been designed. A Saddle antenna SPS with water cooling is being fabricated for high duty factor testing. |
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| WEP274 | Broadband Antenna Matching Network Design and Application for RF Plasma Ion Source | 1990 |
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Funding: This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE. The RF ion source at Spallation Neutron Source has been upgraded to meet higher beam power requirement. One important subsystem for efficient operation of the ion source is the 2MHz RF impedance matching network. The real part of the antenna impedance is very small and is affected by plasma density for 2MHz operating frequency. Previous impedance matching network for the antenna has limited tuning capability to cover this potential variation of the antenna impedance since it employed a single tuning element and an impedance transformer. A new matching network with two tunable capacitors has been built and tested. This network can allow precision matching and increase the tunable range without using a transformer. A 5-element broadband matching network also has been designed, built and tested. The 5-element network allows wide band matching up to 50 kHz bandwidth from the resonance center of 2 MHz. The design procedure, simulation and test results are presented. |
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| WEP275 | Highly-Persistent SNS H− Source Fueling 1-MW Beams with 7-9 kC Service Cycles | 1993 |
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Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. Running routinely with ~40-mA, 1-MW beams, the SNS linac is fed from the ion source with ~1ms long, ~50-mA H− beam pulses at 60 Hz. This requires the daily extraction of ~230 C of H− ions, which exceeds the routine daily production of other H− accelerator sources by almost an order of magnitude. The source service cycle has been extended from 2, to 3, to 4, and up to 5.6 weeks without age-related failures. The 7-9 kC of H− ions delivered in single service cycles exceed the service cycle yields of other accelerator sources. The paper discusses the findings as well as the issues and their mitigations, which enabled the simultaneous increase of the beam current, the duty factor, the availability, and the service cycle. |
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| WEP276 | Development of an Advanced Barium Ion Source for a Laser-Induced-Fluorescence (LIF) Diagnostic on the Paul Trap Simulator Experiment (PTSX) | 1996 |
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| The Paul Trap Simulator Experiment (PTSX) is a cylindrical Paul trap that simulates the nonlinear transverse dynamics of intense charged particle beam propagation through an equivalent kilometers-long magnetic alternating-gradient (AG) focusing system. Understanding the collective dynamics and instability excitations of intense charged particle beam is of great importance for a wide variety of accelerator applications. Since the optical spectrum of barium ions is better-suited to the Laser-Induced-Fluorescence (LIF) diagnostic than cesium ions, a barium ion source is being developed to replace the cesium ion source. A Laser-Induced-Fluorescence diagnostic will be able to provide in situ measurement of the radial density profile and, ultimately, the velocity distribution function of the intense charged particle beam. The new barium ion source is expected to increase the ion density as well as minimize the number of neutral barium atoms which enter the PTSX vacuum chamber. The design includes an ionizer, an extractor, and a neutral gas filter scheme. Initial test results of this new barium ion source will be presented. | ||
| WEP277 | Operational Findings and Upgrade Plans on the Superconducting Electron Accelerator S-DALINAC | 1999 |
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Funding: DFG through SFB 634. The S-DALINAC is a superconducting recirculating electron accelerator with a final energy of 130 MeV. It operates in cw at 3 GHz. It accelerates beams of either unpolarized or polarized electrons and is used as a source for nuclear- and astrophysical experiments at the university of Darmstadt since 1987. We will report on the operational findings, recent modifications and on the future upgrade plans: First results from the new digital rf control system, the injector current upgrade and the improved longitudinal working point will be presented. In addition, an overview of the future plans, namely installing an additional recirculation path and two scraper systems will be given. |
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| WEP279 | Improvements on the Design of an Ultra-Low Emittance Injector for a Future X-ray FEL Oscillator | 2002 |
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Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC02-06CH11357. The concept of an ultra-low transverse emittance injector for the X-ray Free-Electron Laser Oscillator* was discussed at PAC09**. Two problems come to mind. A dual-frequency rf chopper for reducing the beam rate from 100 MHz to 1 ~ 3 MHz would limit our choice of the beam repetition rate. The electron back-bombardment could be solved by embedding a three-pole wiggler*** in the nose cone of the gun cavity, but that results in increased emittance. Inspired by the concept of a triode gun, the injector now includes a gated 100 MHz rf gun with thermionic cathode to avoid those limitations. The design has been studied and is capable of producing 40 pC bunches with 0.1 micrometer effective transverse rms emittance. * K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008). ** P.N. Ostroumov et al., Proc. of PAC09, p.461 (2009). *** M. Borland et al., Proc. of LINAC10, to be published. |
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| WEP280 | Development of an Ultra-Low-Emittance RF PhotoInjector for a Future X-Ray FEL Oscillator | 2005 |
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Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC02-06CH11357. The proposed x-ray free-electron laser oscillator* requires continuous electron bunches with ultra-low normalized transverse emittance of less than 0.1 micrometer, a bunch charge of 40 pC, an rms uncorrelated energy spread of less than 1.4 MeV, produced at a rate between 1 MHz to 10 MHz. The bunches are to be compressed to an rms length of ~1 ps and accelerated to the final energy of 7 GeV. In this paper, we discuss a design for an ultra-low-emittance injector based on a 325-MHz room-temperature rf cavity and a Cs2Te photocathode. The results of initial optimizations of the beam dynamics with a focus on extracting and preserving ultra-low emittance will be presented. * K.-J. Kim et al., Phys. Rev. Lett. 100, 244802 (2008). |
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| WEP281 | Beam Imaging of a High-Brightness Elliptic Electron Gun | 2008 |
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Funding: This work was funded in part by the Department of Energy, Grant No. DE-FG02-07ER84910. An innovative research program is being carried out to experimentally demonstrate a high-brightness, space-charge-dominated elliptic electron beam using a non-axisymmetric permanent magnet focusing system. Results of the fabrication, initial testing and beam imaging of an elliptic electron gun are reported. Good agreement is found between the experimental measurements and simulation. |
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| WEP282 | Design of the NSLS-II Linac Front End Test Stand | 2011 |
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Funding: This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The NSLS-II operational parameters place very stringent requirements on the injection system. Among these are the charge per bunch train at low emittance that is required from the linac along with the uniformity of the charge per bunch along the train. The NSLS-II linac is a 200 MeV linac produced by RI Research Instruments GmbH. Part of the strategy for understanding to operation of the injectors is to test the front end of the linac prior to its installation in the facility. The linac front end consists of a 90 keV electron gun, 500 MHz subharmonic prebuncher, focusing solenoids and a suite of diagnostics. The diagnostics in the front end need to be supplemented with an additional suite of diagnostics to fully characterize the beam. In this paper we discuss the design of a test stand to measure the various properties of the beam generated from this section. In particular, the test stand will measure the charge, transverse emittance, energy, energy spread, and bunching performance of the linac front end under all operating conditions of the front end. |
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| WEP283 | Simulations of Transverse Stacking in the NSLS-II Booster | 2014 |
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Funding: This manuscript has been authored by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. The NSLS-II injection system consists of a 200 MeV linac and a 3 GeV booster. The linac needs to deliver 15 nC in 80 - 150 bunches to the booster every minute to achieve current stability goals in the storage ring. This is a very stringent requirement that has not been demonstrated at an operating light source. We have developed a scheme to transversely stack two bunch trains in the NSLS-II booster in order to alleviate the charge requirements on the linac. This scheme has been outlined previously. In this paper we show particle tracking simulations of the tracking scheme. We show that the booster lattice has sufficient orbit correction and dynamic aperture at injection to maintain the charge and emittance of the first beam while it circulates waiting for the next train to arrive. We also show simulations of the booster ramp with a stacked beam for a variety of lattice errors and injected beam parameters. In all cases the performance of the proposed stacking method is sufficient to reduce the required charge from the linac. For this reason the injection system of the NSLS-II booster is being designed to include this feature. |
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| WEP284 | Performance Study of K2CsSb Photocathode inside a DC High Voltage Gun | 2017 |
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Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grant DE-FG02-08ER41547. In the past decade, there has been considerable interest in the generation of tens of mA average current in a photoinjector. Until recently, GaAs:Cs cathodes and K2CsSb cathodes have been tested successfully in DC and RF injectors respectively for this application. Our goal is to test the GaAs:Cs in RF injector and the K2CsSb cathode in the DC gun in order to widen our choices. Since the multialkali cathode is a compound with uniform stochiometry over its entire thickness, we anticipate that the life time issues seen in GaAs:Cs due surface damage by ion bombardment would be minimized with this material. Hence successful operation of the K2CsSb cathode in DC gun could lead to a relatively robust electron source capable of delivering ampere level currents. In order to test the performance of K2CsSb cathode in a DC gun, we have designed and built a load lock system that would allow the fabrication of the cathode at BNL and its testing at JLab. In this paper, we will present the design of the load-lock system, cathode fabrication, and the cathode performance in the preparation chamber and in the DC gun. |
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| WEP287 | Field Emission Measurements from Niobium Electrodes | 2020 |
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| Increasing the operating voltage of a DC high voltage photogun serves to minimize space charge induced emittance growth and thereby preserve electron beam brightness, however, field emission from the photogun cathode electrode can pose significant problems: constant low level field emission degrades vacuum via electron stimulated desorption which in turn reduces photocathode yield through chemical poisoning and/or ion bombardment and high levels of field emission can damage the ceramic insulator. Niobium electrodes (single crystal, large grain and fine grain) were characterized using a DC high voltage field emission test stand at maximum voltage -225kV and electric field gradient > 10MV/m. Niobium electrodes appear to be superior to diamond-paste polished stainless steel electrodes. | ||
| WEP288 | Optimizing the CEBAF Injector for Beam Operation with a Higher Voltage Electron Gun | 2023 |
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| Recent developments in the DC gun technology used at CEBAF have allowed an increase in operational voltage from 100kV to 130kV. In the near future this will be extended further to 200kV with the purchase of a new power supply. The injector components and layout at this time have been designed specifically for 100kV operation. It is anticipated that with an increase in gun voltage and optimization of the layout and components for 200kV operation, that the electron bunch length and beam brightness can be improved upon. This paper explores some upgrade possibilities for a 200kV gun CEBAF injector through beam dynamic simulations. | ||
| WEP289 | The Impact of Laser Polarization in Multiphoton Photoemission from a Copper Cathode | 2026 |
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Multiphoton photoemission from a copper cathode has been recently demonstrated to be a simple and efficient method to generate high quality electron beams. To further improve this scheme to achieve higher charge yielding efficiency and lower intrinsic emittance, we explored the effects of laser polarization at oblique incidence. Charge yields of s and p polarization from coated and uncoated cathodes were measured. The vectorial photoelectric effect was observed on the uncoated cathode but much less evident on the coated one, suggesting that surface properties are critical to the vectorial effect and in general important in photoemission. The results not only are useful in the optimization of an rf photoinjector, but also allow deeper understanding of the photoemission physics.
* P. Musumeci et al., Phys. Rev. Lett. ZeHn4, 084801 (2010). ** P. Musumeci et al., Phys. Rev. Lett. ZeHn0, 244801 (2008). |
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| WEP290 | A Novel Electron Gun for Off-axis Beam Injection | 2029 |
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| For certain type of electron accelerators injection from an off-axis cathode is required. This is the case of a race-track microtron (RTM), in which the beam passes several times through the accelerating structure, or of a high power standing wave electron linac, for which the lifetime of an on-axis cathode would be strongly reduced by the electron back-bombardment. The standard solution with the beam injection via a dipole magnet from an electron gun placed off-axis is too bulky, moreover in case of RTMs it requires special compensating dipoles. An annular ring cathode gun used in some accelerators leads to large beam emittance and divergence. As a new solution we describe a 3D on-axis electron gun with an off-axis cathode and a central hole for the beam passage. Results of the design optimization and performance of an electron gun built for a miniature 12 MeV RTM for medical applications are presented. We also discuss results of the beam parameters measurements and estimates of the beam emittance. | ||
| WEP293 | Design and Fabrication of the Lithium Beam Ion Injector for NDCX-II | 2032 |
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Funding: This work is performed under the auspices of the U.S. Department of Energy by LBNL under contract DE-AC02-05CH11231. A 130 keV injector is developed for the NDCX-II facility. It consists of a 10.9 cm diameter lithium doped alumina-silicate ion source heated to ~1300 °C and 3 electrodes. Other components include a segmented Rogowski coil for current and beam position monitoring, a gate valve, pumping ports, a focusing solenoid, a steering coil and space for inspection and maintenance access. Significant design challenges including managing the 3-4 kW of power dissipation from the source heater, temperature uniformity across the emitter surface, quick access for frequent ion source replacement, mechanical alignment with tight tolerance, and structural stabilization of the cantilevered 27” OD graded HV ceramic column. The injector fabrication is scheduled to complete by May 2011, and assembly and installation is scheduled to complete by the beginning of July. |
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| WEP295 | Status of Laser Stripping at the SNS | 2035 |
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Funding: This work was supported by SNS through UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 for the U.S. Department of Energy. This paper presents an overview of experimental and theoretical studies on laser stripping that have been conducted up to the present time in the SNS project. The goal of this work is to develop techniques to achieve the experimental preconditions necessary for the successful realization of a future intermediate experiment on laser stripping. The experimental work consists of the tuning and measurement of H־ beam parameters in readiness for the intermediate experiment, and also takes into account the features and possibilities of the SNS accelerator. |
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| WEP296 | Effects of Errors of Velocity Tilt on Maximum Longitudinal Compression During Neutralized Drift Compression of Intense Beam Pulses | 2038 |
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Funding: Research supported by the U.S. Department of Energy. Neutralized drift compression offers an effective means for particle beam focusing and current amplification. In neutralized drift compression, a linear longitudinal velocity tilt is applied to the beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam intensity can increase more than a factor of 100 in the longitudinal direction. We have performed an analytical study of how errors in the velocity tilt acquired by the beam in the induction bunching module limits the maximum longitudinal compression. It is found in general that the compression ratio is determined by the relative errors in the velocity tilt. That is, one-percent errors may limit the compression to a factor of one hundred. However, part of pulse where the errors are small may compress to much higher values determined by the initial thermal spread of the beam pulse. Examples of slowly varying and rapidly varying errors compared to the beam pulse duration are studied. |
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| WEP297 | A Conceptual Design of the 2+ MW LBNE Beam Absorber | 2041 |
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Funding: This work is supported by the U.S. Department of Energy. The Long Baseline Neutrino Experiment (LBNE) will utilize a neutrino beamline facility located at Fermilab. The facility will aim a beam of neutrinos, produced by 60-120 GeV protons from the Fermilab Main Injector, toward a detector placed at the Deep Underground Science and Engineering Laboratory (DUSEL) in South Dakota. Secondary particles that do not decay into muons and neutrinos as well as any residual proton beam must be stopped at the end of the decay region to reduce noise/damage in the downstream muon monitors and reduce activation in the surrounding rock. This goal is achieved by placing an absorber structure at the end of the decay region. The requirements and conceptual design of such an absorber, capable of operating at 2+ MW primary proton beam power, is described. |
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