2011 Particle Accelerator Conference - List of Keywords (damping)

Paper	Title	Other Keywords	Page
MOOCS2	Numerical Verification of the Power Transfer and Wakefield Coupling in the CLIC Two-beam Accelerator	wakefield, simulation, dipole, coupling	51
	A.E. Candel, K. Ko, Z. Li, C.-K. Ng, V. Rawat, G.L. Schussman SLAC, Menlo Park, California, USA A. Grudiev, I. Syratchev, W. Wuensch CERN, Geneva, Switzerland
	The Compact Linear Collider (CLIC) provides a path to a multi-TeV accelerator to explore the energy frontier of High Energy Physics. Its two-beam accelerator concept envisions large complex 3D structures, which must be modeled to high accuracy so that simulation results can be directly used to prepare CAD drawings for machining. The required simulations include not only the fundamental mode properties of the accelerating structures but also the Power Extraction and Transfer Structure (PETS), as well as the coupling between the two systems. Time-domain simulations will be performed to understand pulse formation, wakefield damping, fundamental power transfer and wakefield coupling in these structures. Applying SLAC's parallel finite element code suite, these large-scale problems will be solved on some of the largest supercomputers available. The results will help to identify potential issues and provide new insights on the design, leading to further improvements on the novel two-beam accelerator scheme.
	Slides MOOCS2 [286.042 MB]

MOODS4	Dancing Bunches as van Kampen Modes	impedance, synchrotron, injection, proton	94
	A.V. Burov Fermilab, Batavia, USA
	Theory of van Kampen modes is applied to bunch longitudinal motion. Case of inductive impedance domination is studied in more details. Threshold for loss of Landau damping is found to be very sensitive to fine structure of the distribution function. Good agreement with the Tevatron's "dancing bunches" is obtained.
	Slides MOODS4 [0.408 MB]

MOP064	Asymmetric Laser Radiant Cooling in Storage Rings	electron, laser, photon, simulation	229
	E.V. Bulyak NSC/KIPT, Kharkov, Ukraine J. Urakawa KEK, Ibaraki, Japan F. Zimmermann CERN, Geneva, Switzerland
	Laser pulses with small spatial and temporal dimensions can interact with a fraction of the electron bunches circulating in Compton storage rings. We studied synchrotron dynamics of such bunches when laser photons scatter off from the electrons with energy higher than the synchronous energy. In this case of ‘asymmetric cooling', as shown theoretically, the stationary energy spread is much smaller than under conditions of regular scattering; the oscillations are damped faster. Coherent oscillations of large amplitude may be damped in one synchrotron period, which makes this method feasible for injection the bunches into a ring in the longitudinal phase space. The theoretical results are validated with simulations.

MOP266	Stripline Kicker Design for NSLS2 Storage Ring	impedance, kicker, pick-up, feedback	603
	W.X. Cheng, A. Blednykh, S. Krinsky, O. Singh BNL, Upton, Long Island, New York, USA
	In the NSLS2 storage ring, there are four stripline kickers/pickups. Two long striplines with electrode length of 30cm will be used as bunch-by-bunch transverse feedback actuators. Two short stripline kickers/pickups with 15cm length will mainly used for tune measurement excitation or signal pickup for the beam stability monitor. High shunt impedance of the long stripline kickers is demanded to produce 200μs damping time. Meanwhile the beam impedance should be minimized. The design work for these two types of stripline is discussed in this paper.

MOP298	Commisioning Results from the Recently Upgraded RHIC LLRF System	LLRF, controls, cavity, feedback	678
	K.S. Smith, M. Harvey, T. Hayes, G. Narayan, F. Severino, S. Yuan, A. Zaltsman BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy During RHIC Run 10, the first phase of the LLRF Upgrade was successfully completed. This involved replacing the aging VME based system with a modern digital system based on the recently developed RHIC LLRF Upgrade Platform, and commissioning the system as part of the normal RHIC start up process. At the start of Run 11, the second phase of the upgrade is underway, involving a significant expansion of both hardware and functionality. This paper will review the commissioning effort and provide examples of improvements in system performance, flexibility and scalability afforded by the new platform.

TUOCN1	Accurate Computation of Transfer Maps for Realistic Beamline Elements from Surface Data	wiggler, dipole, multipole, electron	742
	C.E. Mitchell NRL, Washington, DC, USA A. Dragt UMD, College Park, Maryland, USA
	The behavior of orbits in charged-particle beam transport systems, including both linear and circular accelerators as well as final focus sections and spectrometers, can depend sensitively on nonlinear fringe-field and high-order-multipole effects in the various beam-line elements. The inclusion of these effects requires a detailed and realistic model of the interior and fringe fields, including their high spatial derivatives. A collection of surface fitting methods has been developed for extracting this information accurately from 3-dimensional field data on a grid, as provided by various 3-dimensional finite-element field codes. Based on these realistic field models, Lie or other methods may be used to compute accurate design orbits and accurate transfer maps about these orbits. This talk will provide a description of the methods along with example applications. An exactly-soluble but numerically challenging model field is used to provide a rigorous collection of performance benchmarks.
	Slides TUOCN1 [1.630 MB]

TUP052	HOM Damping Properties of Fundamental Power Couplers in the Superconducting Electron Gun of the Energy Recovery LINAC at Brookhaven National Laboratory	cavity, HOM, gun, simulation	901
	L.R. Hammons, H. Hahn BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. Among the accelerator projects under construction at the Relativistic Heavy Ion Collider (RHIC) is an R&D energy recovery LINAC (ERL) test facility. The ERL includes both a five-cell superconducting cavity as well as a superconducting, photoinjector electron gun. Because of the high-charge and high-current demands, effective higher-order mode (HOM) damping is essential, and several strategies are being pursued. Among these is the use of the fundamental power couplers as a means for damping some HOMs. Simulation studies have shown that the power couplers can play a substantial role in damping certain HOMs, and this presentation will discuss these studies along with measurements.

TUP053	Ferrite HOM Load Surrounding a Ceramic Break	HOM, gun, dipole, cavity	904
	L.R. Hammons, H. Hahn BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. Several future accelerator projects at the Relativistic Heavy Ion Collider are being developed using a super-conducting electron energy recovery LINAC along with a superconducting electron gun as the source. All of the projects involve high-current, high-charge operation and require effective higher-order mode (HOM) damping to achieve the performance objectives. Among the HOM designs being developed is a waveguide-type HOM load for the electron gun consisting of a ceramic break surrounded by ferrite tiles. This design is innovative in its approach and achieves a variety of ends including broadband HOM damping and protection of the superconducting cavity from potential damage to the ferrite tiles. Furthermore, the ceramic is an effective thermal transition. This design may be useful in various applications since it readily allows for replacement of the ferrite tiles with other materials and may also be useful for testing the absorbing properties of these materials. In this paper, the details of the design will be discussed along with current modelling and testing results as well as future plans.

TUP097	Fundamental and HOM Coupler Design for the Superconducting Parallel-Bar Cavity	cavity, HOM, impedance, coupling	1015
	S.U. De Silva, J.R. Delayen ODU, Norfolk, Virginia, USA S.U. De Silva JLAB, Newport News, Virginia, USA
	The superconducting parallel-bar cavity is currently being considered as a deflecting system for the Jefferson Lab 12 GeV upgrade and as a crabbing cavity for a possible LHC luminosity upgrade. Currently the designs are optimized to achieve lower surface fields within the dimensional constraints for the above applications. A detailed analysis of the fundamental input power coupler design for the parallel-bar cavity is performed considering beam loading and the effects of microphonics. For higher beam loading the damping of the HOMs is vital to reduce beam instabilities generated due to the wake fields. An analysis of threshold impedances for each application and impedances of the modes that requires damping are presented in this paper with the design of HOM couplers.

TUP099	Design of Superconducting Parallel-bar Deflecting/Crabbing Cavities with Improved Properties	cavity, HOM, higher-order-mode, superconductivity	1021
	J.R. Delayen, S.U. De Silva ODU, Norfolk, Virginia, USA J.R. Delayen JLAB, Newport News, Virginia, USA
	The superconducting parallel-bar cavity is a deflecting/crabbing cavity with attractive properties, compared to other conventional designs, that is being considered for a number of applications. All designs to-date have been based on straight loading elements and rectangular outer conductors. We present new designs of parallel-bar cavities using curved loading elements and circular or elliptical outer conductors, with significantly improved properties such as reduced surface fields and wider higher-order mode separation.

TUP183	Self-optimizing High Dynamic Power Supply Control	controls, power-supply, feedback	1175
	X.H. Ke, F. Jenni FHNW, Windisch, Switzerland H. Jäckle PSI, Villigen, Switzerland
	Funding: Paul Scherrer Institute, Switzerland In 1999, the first fully digitally controlled magnet power supplies were put into operation at PSI (Paul Scherrer Institute, Switzerland). Today, approximately 1000 are in use at PSI and a multiple of that worldwide. This project aims at developing a high performance control scheme for a better dynamic behavior of today's magnet powers supplies, without reducing their excellent static behaviors. The resulting control strategy, an in situ identification based observer, combined with state space and proportional integral (SS-PI) control, leads to a significantly improved dynamic behavior of the existing power supplies. The whole commissioning, including system identification, as well as control parameter determination and optimization, is done automatically on the DSP with support of a PC. The control strategy has been implemented on the existing PSI controller and a 10A-corrector power supply, together with various magnets, by updating the software and/or firmware only. Currently, the new control strategy is being implemented and tested at PSI on a second generation Digital Power Electronic Control System (DPC) controller card.

TUP236	Progress of a Gradient Damping Wiggler of the ALPHA Storage Ring	dipole, wiggler, storage-ring, electron	1265
	C.W. Huang, D.J. Huang NTHU, Hsinchu, Taiwan S.D. Chen NCTU, Hsinchu, Taiwan M.-H. Huang, C.-S. Hwang, C.Y. Kuo, F.-Y. Lin, Y.T. Yu NSRRC, Hsinchu, Taiwan S.-Y. Lee IUCF, Bloomington, Indiana, USA
	The main purpose of a gradient damping wiggler (GDW) to be installed in the Alpha storage ring in Indiana University is to correct the momentum-compaction factor and the damping partition in the Alpha storage ring. One middle pole and two outer poles in one set of the GDW are installed on the same girder. Two sets of GDW will be installed in the two short straight sections. The dipole and gradient-field strengths of the middle (outer) pole are 0.67 T (-0.67 T) and 1.273 T m^-1 (1.273 T m^-1), respectively. One completed set of GDW is already fabricated; we shall add an end shim to improve the region of effective good field within which the middle and outer poles along the transverse x-axis (△B/B = 0.1 %) are ±50 and ±40 mm respectively. We used a trim coil on the three poles to adjust the first and second integral fields to zero. Here we discuss the integral magnetic field features along the straight trajectory and the ideal orbital trajectory with a Hall probe mapping system, and present an analysis of the magnetic field.

TUP283	Inductively Coupled, Compact HOM Damper for the Advanced Photon Source	impedance, HOM, coupling, diagnostics	1358
	G.J. Waldschmidt, D. Horan, L.H. Morrison ANL, Argonne, USA
	Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 The Advanced Photon Source requires damping of higher-order modes in the storage ring rf cavities in order to prevent beam instability at beam currents in excess of 100 mA proposed for the APS Upgrade. Due to constraints imposed by available space and by existing 35-mm pick-up ports on the cavity, a compact design has been analyzed with a quarter-wave rejection filter of the fundamental mode. Separate broadband, low-frequency and high-frequency dampers are utilized to span the frequency range from 500 MHz to 1500 MHz. The dampers have been designed to reject the fundamental cavity mode, couple strongly to HOM’s, utilize an external rf load, minimize the overall size, and incorporate rf diagnostics. In addition, the mechanical design has been optimized to simplify construction, improve mechanical stability, and reduce thermally induced stresses.

WEODN1	Overview of System Specifications for Bunch by Bunch Feedback Systems	feedback, kicker, controls, coupling	1475
	D. Teytelman Dimtel, San Jose, USA
	Bunch-by-bunch feedback control of coupled-bunch instabilities has become a ubiquitous feature of storage rings, light sources and colliders. Specifying the requirements for these systems demands knowledge of the instability sources and the accelerator operating parameter space. System requirements include the necessary loop gain and bandwidth, kick voltage, and the overall noise floor. Based on these specifications one can select the system BPMs, processing algorithms, power amplifiers and kickers and make tradeoffs of system cost against necessary performance. Through the use of analytical and experimental techniques this talk will illustrate practical and intelligent choices in this specification process. The approach involves experimental characterization of the accelerator at low or moderate beam currents. Measurements are used to calibrate a parameterized analytical beam dynamics model which can be then extrapolated to nominal beam currents with confidence. The speaker will present example results from several recent installations, highlighting the measurements, the model predictions, and the achieved system performance.
	Slides WEODN1 [1.755 MB]

WEP065	Multiobjective Dynamic Aperture Optimization at NSLS-II	lattice, sextupole, quadrupole, dipole	1597
	L. Yang, W. Guo, S. Krinsky, Y. Li BNL, Upton, Long Island, New York, USA
	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.

WEP066	Tracking Code Developement for Beam Dynamics Optimization	lattice, simulation, wiggler, dynamic-aperture	1600
	L. Yang BNL, Upton, Long Island, New York, USA
	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.

WEP085	Beam Breakup Studies for New Cryo-Unit	HOM, simulation, cavity, linac	1633
	S. Ahmed, F.E. Hannon, A.S. Hofler, R. Kazimi, G.A. Krafft, F. Marhauser, B.C. Yunn JLAB, Newport News, Virginia, USA I. Shin University of Connecticut, Storrs, Connecticut, USA
	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.

WEP103	Ion Instability Study for the ILC 3 km Damping Ring	ion, simulation, vacuum, emittance	1671
	G.X. Xia MPI-P, München, Germany
	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	feedback, injection, octupole, resonance	1674
	J.H. Wang, Y.B. Chen, W. Li, L. Liu, M. Meng, B.G. Sun, L. Wang, Y.L. Yang, Z.R. Zhou USTC/NSRL, Hefei, Anhui, People's Republic of China
	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.

WEP114	Transverse Instability of the Antiproton Beam In the Recycler Ring	antiproton, extraction, emittance, bunching	1698
	L.R. Prost, C.M. Bhat, A.V. Burov, J.L. Crisp, N. Eddy, M. Hu, A.V. Shemyakin Fermilab, Batavia, USA
	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.

WEP116	Bucket Shaking Stops Bunch Dancing in Tevatron	synchrotron, simulation, impedance, dipole	1704
	A.V. Burov, C.-Y. Tan Fermilab, Batavia, USA
	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.

WEP140	Benchmarking Stepwise Ray-Tracing in Rings in Presence of Radiation Damping	emittance, radiation, lattice, synchrotron	1746
	F. Méot BNL, Upton, Long Island, New York, USA
	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.

WEP177	Radial Transmission Line Analysis of Multi-layer Circular Structures	impedance, cavity, simulation, gun	1819
	H. Hahn, L.R. Hammons BNL, Upton, Long Island, New York, USA
	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.

WEP192	Simulation Results for a Cavity BPM Design for the APS Storage Ring	cavity, simulation, storage-ring, linac	1849
	X. Sun, G. Decker ANL, Argonne, USA
	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.

WEP194	Measurement Techniques to Characterize Instabilities Caused by Electron Clouds	electron, feedback, dipole, betatron	1852
	M.G. Billing, G. Dugan, M.J. Forster, R.E. Meller, M.A. Palmer, G. Ramirez, J.P. Sikora, H.A. Williams CLASSE, Ithaca, New York, USA R. Holtzapple CalPoly, San Luis Obispo, California, USA K.G. Sonnad Cornell University, Ithaca, New York, USA
	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.

THOBS2	Optimization of Magnet Stability and Alignment for NSLS-II	alignment, storage-ring, emittance, ion	2082
	S.K. Sharma, L. Doom, A.K. Jain, P.N. Joshi, F. Lincoln, V. Ravindranath BNL, Upton, Long Island, New York, USA
	Funding: This work was supported by Department of Energy contract DE-AC02-98CH10886 The high-brightness design of NSLS-II requires uncorrelated vertical RMS motion of the multipole magnets on a girder to be less than 25 nm. Also, the highly nonlinear lattice requires alignment of the multipole magnets to 30 microns. The speaker will describe the stability of the girder-magnets assembly and the factors affecting it, such as ambient ground motion and temperature fluctuations in the storage ring. Technical solutions to achieve the desired stability will be presented as well.
	Slides THOBS2 [4.431 MB]

THP056	Near Real-time ORM Measurements and SVD Matrix Generation for 10 Hz Global Orbit Feedback In RHIC	feedback, dipole, ion, injection	2226
	C. Liu, R.L. Hulsart, W.W. MacKay, A. Marusic, K. Mernick, R.J. Michnoff, M.G. Minty BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy. To reduce the effect of trajectory perturbations due to vibrations of the final focusing quadrupoles at RHIC, global orbit feedback was successfully prototyped during run-10. The system was tested using transfer functions between the beam position monitors and correctors obtained from the online optical model and a correction algorithm based on singular value decomposition (SVD). In run-11 we plan to self-calibrate the system using SVD matrices derived from orbit response matrix (ORM) measurements acquired real-time using the new FPGA-based signal processing. Comparisons between measurement and model and of feedback performance with the two methods are presented.

THP083	Fabrication and Design of the Main Linacs for CLIC with Damped and Detuned Wakefield Suppression and Optimised Surface Electromagnetic Fields	wakefield, dipole, linac, HOM	2291
	R.M. Jones, A. D'Elia, V.F. Khan UMAN, Manchester, United Kingdom A. Grudiev, G. Riddone, W. Wuensch CERN, Geneva, Switzerland
	Funding: Research leading to these results has received funding from the European commission under the FP7 research infrastructure grant no. 227579. We report on the suppression of long-range wakefields in the main linacs of the CLIC collider. This structure operates with a 120 degree phase advance per cell. The wakefield is damped using a combination of detuning the frequencies of beam-excited higher order modes and by light damping, through slot-coupled manifolds. This serves as an alternative to the present baseline CLIC design which relies on heavy damping. Detailed simulations of both the optimised surface fields resulting from the monopole mode, and from wakefield damping of the dipole modes, are discussed. We report on fabrication details of a structure consisting of 24 cells, diffusion bonded together. This design, known as CLIC_DDS_A, takes into practical mechanical engineering issues and is the result of several optimisations since the earlier CLIC_DDS designs. This structure is due to be tested for its capacity to sustain high gradients at CERN.

THP105	Final Design of ILC RTML Extraction Line for Single Stage Bunch Compressor	extraction, sextupole, kicker, septum	2321
	S. Seletskiy BNL, Upton, Long Island, New York, USA N. Solyak Fermilab, Batavia, USA
	The use of single stage bunch compressor (BC) in the International Linear Collider (ILC) [1] Damping Ring to the Main Linac beamline (RTML) requires new design for the extraction line (EL). The EL located downstream of the BC will be used for both an emergency abort dumping of the beam and the tune-up continuous train-by-train extraction. It must accept both compressed and uncompressed beam with energy spread of 3.54% and 0.15% respectively. In this paper we report the final design that allowed minimizing the length of such extraction line while offsetting the beam dumps from the main line by 5m distance required for acceptable radiation level in the service tunnel. Proposed extraction line can accommodate beams with different energy spreads at the same time providing the beam size suitable for the aluminum ball dump window.

THP119	Potential Two-fold Reduction of Advanced Photon Source Emittance using Orbit Displacement	lattice, emittance, quadrupole, sextupole	2339
	M. Borland ANL, Argonne, USA
	Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The Advanced Photon Source (APS) is a 7-GeV electron storage ring light source that operates with an effective emittance of 3.1 nm using optics with distributed dispersion. Lower emittance is desirable for some x-ray experiments, but is difficult using conventional optics adjustments because of the required strength of quadrupoles and sextupoles. Changing the damping partition number by changing the rf frequency is another approach, but is incompatible with distributed dispersion because it would require simultaneous realignment of all APS beamlines. In this paper, we evaluate a new approach to changing the damping partition number using a systematic orbit bump in all sectors.

THP129	Emittance Reduction Approaches for NSLS-II	emittance, lattice, wiggler, dipole	2363
	W. Guo, F.J. Willeke BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy NSLS-II is a third generation light source that is under construction at the Brookhaven National Laboartory. The 3GeV 792m long 30-cell storage ring will be commissioned in 2014. The emittance is lowered from 2nm to 1nm by three 7m damping wigglers. This paper will discuss the future emittance reduction approaches for NSLS-II. One option is installing more damping wigglers; an alternative solution is to manipulate the damping partition by shifting the chromatic quadrupoles horizontally. Both methods can lower the emittance effectively; however, the second method does not occupy the user straights. When the quarupoles are moved, the orbit and thus the vacuum chamber need to be redesigned, and beam dynamics could be affected. In the paper we will compare the lattice properties for the two options, and address the potential issues.

THP193	Study of Single and Coupled-Bunch Instabilities for NSLS-II	simulation, wakefield, cavity, dipole	2483
	G. Bassi, A. Blednykh BNL, Upton, New York, USA
	We study single and coupled-bunch instabilities for the NSLS-II storage ring with a recently developed parallel tracking code. For accurate modelling of the coupled-bunch instability, we investigate improvements to current point-bunch models to take into account finite bunch-size effects.

THP212	Superconducting Cavity Design for Short-Pulse X-Rays at the Advanced Photon Source	cavity, HOM, cryomodule, coupling	2516
	G.J. Waldschmidt, B. Brajuskovic, R. Nassiri ANL, Argonne, USA G. Cheng, J. Henry, J.D. Mammosser, R.A. Rimmer, H. Wang JLAB, Newport News, Virginia, USA
	Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Superconducting cavities have been analyzed for the short-pulse x-ray (SPX) project at the Advanced Photon Source (APS). Due to the strong damping requirements in the APS storage ring, single-cell superconducting cavities have been designed. The geometry has been optimized for lower-order and higher-order mode damping, reduced peak surface magnetic fields, and compact size. The integration of the cavity assembly, with dampers and waveguide input coupler, into a cryomodule will be discussed.

FROBS6	High Current SRF Cavity Design for SPL and eRHIC	cavity, HOM, dipole, electron	2589
	W. Xu, I. Ben-Zvi, R. Calaga, H. Hahn, E.C. Johnson, J. Kewisch BNL, Upton, Long Island, New York, USA
	Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy In order to meet the requirements of high average current accelerators, such as the Superconducting Proton Linac (SPL) at CERN and the electron–ion collider (eRHIC) at BNL, a high current 5-cell SRF cavity, called BNL3 cavity, was designed. The optimization process aimed at maximizing the R/Q of the fundamental mode and the geometry factor G under an acceptable RF field level of Bpeak/Eacc or Epeak/Eacc. In addition, a pivotal consideration for the high current accelerators is efficient damping of dangerous higher-order modes (HOM) to avoid inducing emittance degradation, cryogenic loading or beam-breakup (BBU). To transport the HOMs out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs but not the fundamental mode. Moreover, concerning the BBU effect, the BNL3 cavity is aimed at low (R/Q)Qext for dangerous modes, including dipole modes and quadrupole modes. This paper presents the design of the BNL3 cavity, including the optimization for the fundamental mode, and the BBU limitation for dipole and quadrupole modes. The BBU simulation results show that the designed cavity is qualified for high-current, multi-pass machines such as eRHIC.
	Slides FROBS6 [2.577 MB]

Paper

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MOOCS2

Numerical Verification of the Power Transfer and Wakefield Coupling in the CLIC Two-beam Accelerator

wakefield, simulation, dipole, coupling

51

A.E. Candel, K. Ko, Z. Li, C.-K. Ng, V. Rawat, G.L. Schussman
SLAC, Menlo Park, California, USA
A. Grudiev, I. Syratchev, W. Wuensch
CERN, Geneva, Switzerland

The Compact Linear Collider (CLIC) provides a path to a multi-TeV accelerator to explore the energy frontier of High Energy Physics. Its two-beam accelerator concept envisions large complex 3D structures, which must be modeled to high accuracy so that simulation results can be directly used to prepare CAD drawings for machining. The required simulations include not only the fundamental mode properties of the accelerating structures but also the Power Extraction and Transfer Structure (PETS), as well as the coupling between the two systems. Time-domain simulations will be performed to understand pulse formation, wakefield damping, fundamental power transfer and wakefield coupling in these structures. Applying SLAC's parallel finite element code suite, these large-scale problems will be solved on some of the largest supercomputers available. The results will help to identify potential issues and provide new insights on the design, leading to further improvements on the novel two-beam accelerator scheme.

Slides MOOCS2 [286.042 MB]

MOODS4

Dancing Bunches as van Kampen Modes

impedance, synchrotron, injection, proton

94

A.V. Burov
Fermilab, Batavia, USA

Theory of van Kampen modes is applied to bunch longitudinal motion. Case of inductive impedance domination is studied in more details. Threshold for loss of Landau damping is found to be very sensitive to fine structure of the distribution function. Good agreement with the Tevatron's "dancing bunches" is obtained.

Slides MOODS4 [0.408 MB]

MOP064

Asymmetric Laser Radiant Cooling in Storage Rings

electron, laser, photon, simulation

229

E.V. Bulyak
NSC/KIPT, Kharkov, Ukraine
J. Urakawa
KEK, Ibaraki, Japan
F. Zimmermann
CERN, Geneva, Switzerland

Laser pulses with small spatial and temporal dimensions can interact with a fraction of the electron bunches circulating in Compton storage rings. We studied synchrotron dynamics of such bunches when laser photons scatter off from the electrons with energy higher than the synchronous energy. In this case of ‘asymmetric cooling', as shown theoretically, the stationary energy spread is much smaller than under conditions of regular scattering; the oscillations are damped faster. Coherent oscillations of large amplitude may be damped in one synchrotron period, which makes this method feasible for injection the bunches into a ring in the longitudinal phase space. The theoretical results are validated with simulations.

MOP266

Stripline Kicker Design for NSLS2 Storage Ring

impedance, kicker, pick-up, feedback

603

W.X. Cheng, A. Blednykh, S. Krinsky, O. Singh
BNL, Upton, Long Island, New York, USA

In the NSLS2 storage ring, there are four stripline kickers/pickups. Two long striplines with electrode length of 30cm will be used as bunch-by-bunch transverse feedback actuators. Two short stripline kickers/pickups with 15cm length will mainly used for tune measurement excitation or signal pickup for the beam stability monitor. High shunt impedance of the long stripline kickers is demanded to produce 200μs damping time. Meanwhile the beam impedance should be minimized. The design work for these two types of stripline is discussed in this paper.

MOP298

Commisioning Results from the Recently Upgraded RHIC LLRF System

LLRF, controls, cavity, feedback

678

K.S. Smith, M. Harvey, T. Hayes, G. Narayan, F. Severino, S. Yuan, A. Zaltsman
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
During RHIC Run 10, the first phase of the LLRF Upgrade was successfully completed. This involved replacing the aging VME based system with a modern digital system based on the recently developed RHIC LLRF Upgrade Platform, and commissioning the system as part of the normal RHIC start up process. At the start of Run 11, the second phase of the upgrade is underway, involving a significant expansion of both hardware and functionality. This paper will review the commissioning effort and provide examples of improvements in system performance, flexibility and scalability afforded by the new platform.

TUOCN1

Accurate Computation of Transfer Maps for Realistic Beamline Elements from Surface Data

wiggler, dipole, multipole, electron

742

C.E. Mitchell
NRL, Washington, DC, USA
A. Dragt
UMD, College Park, Maryland, USA

The behavior of orbits in charged-particle beam transport systems, including both linear and circular accelerators as well as final focus sections and spectrometers, can depend sensitively on nonlinear fringe-field and high-order-multipole effects in the various beam-line elements. The inclusion of these effects requires a detailed and realistic model of the interior and fringe fields, including their high spatial derivatives. A collection of surface fitting methods has been developed for extracting this information accurately from 3-dimensional field data on a grid, as provided by various 3-dimensional finite-element field codes. Based on these realistic field models, Lie or other methods may be used to compute accurate design orbits and accurate transfer maps about these orbits. This talk will provide a description of the methods along with example applications. An exactly-soluble but numerically challenging model field is used to provide a rigorous collection of performance benchmarks.

Slides TUOCN1 [1.630 MB]

TUP052

HOM Damping Properties of Fundamental Power Couplers in the Superconducting Electron Gun of the Energy Recovery LINAC at Brookhaven National Laboratory

cavity, HOM, gun, simulation

901

L.R. Hammons, H. Hahn
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Among the accelerator projects under construction at the Relativistic Heavy Ion Collider (RHIC) is an R&D energy recovery LINAC (ERL) test facility. The ERL includes both a five-cell superconducting cavity as well as a superconducting, photoinjector electron gun. Because of the high-charge and high-current demands, effective higher-order mode (HOM) damping is essential, and several strategies are being pursued. Among these is the use of the fundamental power couplers as a means for damping some HOMs. Simulation studies have shown that the power couplers can play a substantial role in damping certain HOMs, and this presentation will discuss these studies along with measurements.

TUP053

Ferrite HOM Load Surrounding a Ceramic Break

HOM, gun, dipole, cavity

904

L.R. Hammons, H. Hahn
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Several future accelerator projects at the Relativistic Heavy Ion Collider are being developed using a super-conducting electron energy recovery LINAC along with a superconducting electron gun as the source. All of the projects involve high-current, high-charge operation and require effective higher-order mode (HOM) damping to achieve the performance objectives. Among the HOM designs being developed is a waveguide-type HOM load for the electron gun consisting of a ceramic break surrounded by ferrite tiles. This design is innovative in its approach and achieves a variety of ends including broadband HOM damping and protection of the superconducting cavity from potential damage to the ferrite tiles. Furthermore, the ceramic is an effective thermal transition. This design may be useful in various applications since it readily allows for replacement of the ferrite tiles with other materials and may also be useful for testing the absorbing properties of these materials. In this paper, the details of the design will be discussed along with current modelling and testing results as well as future plans.

TUP097

Fundamental and HOM Coupler Design for the Superconducting Parallel-Bar Cavity

cavity, HOM, impedance, coupling

1015

S.U. De Silva, J.R. Delayen
ODU, Norfolk, Virginia, USA
S.U. De Silva
JLAB, Newport News, Virginia, USA

The superconducting parallel-bar cavity is currently being considered as a deflecting system for the Jefferson Lab 12 GeV upgrade and as a crabbing cavity for a possible LHC luminosity upgrade. Currently the designs are optimized to achieve lower surface fields within the dimensional constraints for the above applications. A detailed analysis of the fundamental input power coupler design for the parallel-bar cavity is performed considering beam loading and the effects of microphonics. For higher beam loading the damping of the HOMs is vital to reduce beam instabilities generated due to the wake fields. An analysis of threshold impedances for each application and impedances of the modes that requires damping are presented in this paper with the design of HOM couplers.

TUP099

Design of Superconducting Parallel-bar Deflecting/Crabbing Cavities with Improved Properties

cavity, HOM, higher-order-mode, superconductivity

1021

J.R. Delayen, S.U. De Silva
ODU, Norfolk, Virginia, USA
J.R. Delayen
JLAB, Newport News, Virginia, USA

The superconducting parallel-bar cavity is a deflecting/crabbing cavity with attractive properties, compared to other conventional designs, that is being considered for a number of applications. All designs to-date have been based on straight loading elements and rectangular outer conductors. We present new designs of parallel-bar cavities using curved loading elements and circular or elliptical outer conductors, with significantly improved properties such as reduced surface fields and wider higher-order mode separation.

TUP183

Self-optimizing High Dynamic Power Supply Control

controls, power-supply, feedback

1175

X.H. Ke, F. Jenni
FHNW, Windisch, Switzerland
H. Jäckle
PSI, Villigen, Switzerland

Funding: Paul Scherrer Institute, Switzerland
In 1999, the first fully digitally controlled magnet power supplies were put into operation at PSI (Paul Scherrer Institute, Switzerland). Today, approximately 1000 are in use at PSI and a multiple of that worldwide. This project aims at developing a high performance control scheme for a better dynamic behavior of today's magnet powers supplies, without reducing their excellent static behaviors. The resulting control strategy, an in situ identification based observer, combined with state space and proportional integral (SS-PI) control, leads to a significantly improved dynamic behavior of the existing power supplies. The whole commissioning, including system identification, as well as control parameter determination and optimization, is done automatically on the DSP with support of a PC. The control strategy has been implemented on the existing PSI controller and a 10A-corrector power supply, together with various magnets, by updating the software and/or firmware only. Currently, the new control strategy is being implemented and tested at PSI on a second generation Digital Power Electronic Control System (DPC) controller card.

TUP236

Progress of a Gradient Damping Wiggler of the ALPHA Storage Ring

dipole, wiggler, storage-ring, electron

1265

C.W. Huang, D.J. Huang
NTHU, Hsinchu, Taiwan
S.D. Chen
NCTU, Hsinchu, Taiwan
M.-H. Huang, C.-S. Hwang, C.Y. Kuo, F.-Y. Lin, Y.T. Yu
NSRRC, Hsinchu, Taiwan
S.-Y. Lee
IUCF, Bloomington, Indiana, USA

The main purpose of a gradient damping wiggler (GDW) to be installed in the Alpha storage ring in Indiana University is to correct the momentum-compaction factor and the damping partition in the Alpha storage ring. One middle pole and two outer poles in one set of the GDW are installed on the same girder. Two sets of GDW will be installed in the two short straight sections. The dipole and gradient-field strengths of the middle (outer) pole are 0.67 T (-0.67 T) and 1.273 T m^-1 (1.273 T m^-1), respectively. One completed set of GDW is already fabricated; we shall add an end shim to improve the region of effective good field within which the middle and outer poles along the transverse x-axis (△B/B = 0.1 %) are ±50 and ±40 mm respectively. We used a trim coil on the three poles to adjust the first and second integral fields to zero. Here we discuss the integral magnetic field features along the straight trajectory and the ideal orbital trajectory with a Hall probe mapping system, and present an analysis of the magnetic field.

TUP283

Inductively Coupled, Compact HOM Damper for the Advanced Photon Source

impedance, HOM, coupling, diagnostics

1358

G.J. Waldschmidt, D. Horan, L.H. Morrison
ANL, Argonne, USA

Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
The Advanced Photon Source requires damping of higher-order modes in the storage ring rf cavities in order to prevent beam instability at beam currents in excess of 100 mA proposed for the APS Upgrade. Due to constraints imposed by available space and by existing 35-mm pick-up ports on the cavity, a compact design has been analyzed with a quarter-wave rejection filter of the fundamental mode. Separate broadband, low-frequency and high-frequency dampers are utilized to span the frequency range from 500 MHz to 1500 MHz. The dampers have been designed to reject the fundamental cavity mode, couple strongly to HOM’s, utilize an external rf load, minimize the overall size, and incorporate rf diagnostics. In addition, the mechanical design has been optimized to simplify construction, improve mechanical stability, and reduce thermally induced stresses.

WEODN1

Overview of System Specifications for Bunch by Bunch Feedback Systems

feedback, kicker, controls, coupling

1475

D. Teytelman
Dimtel, San Jose, USA

Bunch-by-bunch feedback control of coupled-bunch instabilities has become a ubiquitous feature of storage rings, light sources and colliders. Specifying the requirements for these systems demands knowledge of the instability sources and the accelerator operating parameter space. System requirements include the necessary loop gain and bandwidth, kick voltage, and the overall noise floor. Based on these specifications one can select the system BPMs, processing algorithms, power amplifiers and kickers and make tradeoffs of system cost against necessary performance. Through the use of analytical and experimental techniques this talk will illustrate practical and intelligent choices in this specification process. The approach involves experimental characterization of the accelerator at low or moderate beam currents. Measurements are used to calibrate a parameterized analytical beam dynamics model which can be then extrapolated to nominal beam currents with confidence. The speaker will present example results from several recent installations, highlighting the measurements, the model predictions, and the achieved system performance.

Slides WEODN1 [1.755 MB]

WEP065

Multiobjective Dynamic Aperture Optimization at NSLS-II

lattice, sextupole, quadrupole, dipole

1597

L. Yang, W. Guo, S. Krinsky, Y. Li
BNL, Upton, Long Island, New York, USA

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.

WEP066

Tracking Code Developement for Beam Dynamics Optimization

lattice, simulation, wiggler, dynamic-aperture

1600

L. Yang
BNL, Upton, Long Island, New York, USA

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.

WEP085

Beam Breakup Studies for New Cryo-Unit

HOM, simulation, cavity, linac

1633

S. Ahmed, F.E. Hannon, A.S. Hofler, R. Kazimi, G.A. Krafft, F. Marhauser, B.C. Yunn
JLAB, Newport News, Virginia, USA
I. Shin
University of Connecticut, Storrs, Connecticut, USA

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.

WEP103

Ion Instability Study for the ILC 3 km Damping Ring

ion, simulation, vacuum, emittance

1671

G.X. Xia
MPI-P, München, Germany

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

feedback, injection, octupole, resonance

1674

J.H. Wang, Y.B. Chen, W. Li, L. Liu, M. Meng, B.G. Sun, L. Wang, Y.L. Yang, Z.R. Zhou
USTC/NSRL, Hefei, Anhui, People's Republic of China

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.

WEP114

Transverse Instability of the Antiproton Beam In the Recycler Ring

antiproton, extraction, emittance, bunching

1698

L.R. Prost, C.M. Bhat, A.V. Burov, J.L. Crisp, N. Eddy, M. Hu, A.V. Shemyakin
Fermilab, Batavia, USA

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.

WEP116

Bucket Shaking Stops Bunch Dancing in Tevatron

synchrotron, simulation, impedance, dipole

1704

A.V. Burov, C.-Y. Tan
Fermilab, Batavia, USA

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.

WEP140

Benchmarking Stepwise Ray-Tracing in Rings in Presence of Radiation Damping

emittance, radiation, lattice, synchrotron

1746

F. Méot
BNL, Upton, Long Island, New York, USA

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.

WEP177

Radial Transmission Line Analysis of Multi-layer Circular Structures

impedance, cavity, simulation, gun

1819

H. Hahn, L.R. Hammons
BNL, Upton, Long Island, New York, USA

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.

WEP192

Simulation Results for a Cavity BPM Design for the APS Storage Ring

cavity, simulation, storage-ring, linac

1849

X. Sun, G. Decker
ANL, Argonne, USA

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.

WEP194

Measurement Techniques to Characterize Instabilities Caused by Electron Clouds

electron, feedback, dipole, betatron

1852

M.G. Billing, G. Dugan, M.J. Forster, R.E. Meller, M.A. Palmer, G. Ramirez, J.P. Sikora, H.A. Williams
CLASSE, Ithaca, New York, USA
R. Holtzapple
CalPoly, San Luis Obispo, California, USA
K.G. Sonnad
Cornell University, Ithaca, New York, USA

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.

THOBS2

Optimization of Magnet Stability and Alignment for NSLS-II

alignment, storage-ring, emittance, ion

2082

S.K. Sharma, L. Doom, A.K. Jain, P.N. Joshi, F. Lincoln, V. Ravindranath
BNL, Upton, Long Island, New York, USA

Funding: This work was supported by Department of Energy contract DE-AC02-98CH10886
The high-brightness design of NSLS-II requires uncorrelated vertical RMS motion of the multipole magnets on a girder to be less than 25 nm. Also, the highly nonlinear lattice requires alignment of the multipole magnets to 30 microns. The speaker will describe the stability of the girder-magnets assembly and the factors affecting it, such as ambient ground motion and temperature fluctuations in the storage ring. Technical solutions to achieve the desired stability will be presented as well.

Slides THOBS2 [4.431 MB]

THP056

Near Real-time ORM Measurements and SVD Matrix Generation for 10 Hz Global Orbit Feedback In RHIC

feedback, dipole, ion, injection

2226

C. Liu, R.L. Hulsart, W.W. MacKay, A. Marusic, K. Mernick, R.J. Michnoff, M.G. Minty
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
To reduce the effect of trajectory perturbations due to vibrations of the final focusing quadrupoles at RHIC, global orbit feedback was successfully prototyped during run-10. The system was tested using transfer functions between the beam position monitors and correctors obtained from the online optical model and a correction algorithm based on singular value decomposition (SVD). In run-11 we plan to self-calibrate the system using SVD matrices derived from orbit response matrix (ORM) measurements acquired real-time using the new FPGA-based signal processing. Comparisons between measurement and model and of feedback performance with the two methods are presented.

THP083

Fabrication and Design of the Main Linacs for CLIC with Damped and Detuned Wakefield Suppression and Optimised Surface Electromagnetic Fields

wakefield, dipole, linac, HOM

2291

R.M. Jones, A. D'Elia, V.F. Khan
UMAN, Manchester, United Kingdom
A. Grudiev, G. Riddone, W. Wuensch
CERN, Geneva, Switzerland

Funding: Research leading to these results has received funding from the European commission under the FP7 research infrastructure grant no. 227579.
We report on the suppression of long-range wakefields in the main linacs of the CLIC collider. This structure operates with a 120 degree phase advance per cell. The wakefield is damped using a combination of detuning the frequencies of beam-excited higher order modes and by light damping, through slot-coupled manifolds. This serves as an alternative to the present baseline CLIC design which relies on heavy damping. Detailed simulations of both the optimised surface fields resulting from the monopole mode, and from wakefield damping of the dipole modes, are discussed. We report on fabrication details of a structure consisting of 24 cells, diffusion bonded together. This design, known as CLIC_DDS_A, takes into practical mechanical engineering issues and is the result of several optimisations since the earlier CLIC_DDS designs. This structure is due to be tested for its capacity to sustain high gradients at CERN.

THP105

Final Design of ILC RTML Extraction Line for Single Stage Bunch Compressor

extraction, sextupole, kicker, septum

2321

S. Seletskiy
BNL, Upton, Long Island, New York, USA
N. Solyak
Fermilab, Batavia, USA

The use of single stage bunch compressor (BC) in the International Linear Collider (ILC) [1] Damping Ring to the Main Linac beamline (RTML) requires new design for the extraction line (EL). The EL located downstream of the BC will be used for both an emergency abort dumping of the beam and the tune-up continuous train-by-train extraction. It must accept both compressed and uncompressed beam with energy spread of 3.54% and 0.15% respectively. In this paper we report the final design that allowed minimizing the length of such extraction line while offsetting the beam dumps from the main line by 5m distance required for acceptable radiation level in the service tunnel. Proposed extraction line can accommodate beams with different energy spreads at the same time providing the beam size suitable for the aluminum ball dump window.

THP119

Potential Two-fold Reduction of Advanced Photon Source Emittance using Orbit Displacement

lattice, emittance, quadrupole, sextupole

2339

M. Borland
ANL, Argonne, USA

Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
The Advanced Photon Source (APS) is a 7-GeV electron storage ring light source that operates with an effective emittance of 3.1 nm using optics with distributed dispersion. Lower emittance is desirable for some x-ray experiments, but is difficult using conventional optics adjustments because of the required strength of quadrupoles and sextupoles. Changing the damping partition number by changing the rf frequency is another approach, but is incompatible with distributed dispersion because it would require simultaneous realignment of all APS beamlines. In this paper, we evaluate a new approach to changing the damping partition number using a systematic orbit bump in all sectors.

THP129

Emittance Reduction Approaches for NSLS-II

emittance, lattice, wiggler, dipole

2363

W. Guo, F.J. Willeke
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
NSLS-II is a third generation light source that is under construction at the Brookhaven National Laboartory. The 3GeV 792m long 30-cell storage ring will be commissioned in 2014. The emittance is lowered from 2nm to 1nm by three 7m damping wigglers. This paper will discuss the future emittance reduction approaches for NSLS-II. One option is installing more damping wigglers; an alternative solution is to manipulate the damping partition by shifting the chromatic quadrupoles horizontally. Both methods can lower the emittance effectively; however, the second method does not occupy the user straights. When the quarupoles are moved, the orbit and thus the vacuum chamber need to be redesigned, and beam dynamics could be affected. In the paper we will compare the lattice properties for the two options, and address the potential issues.

THP193

Study of Single and Coupled-Bunch Instabilities for NSLS-II

simulation, wakefield, cavity, dipole

2483

G. Bassi, A. Blednykh
BNL, Upton, New York, USA

We study single and coupled-bunch instabilities for the NSLS-II storage ring with a recently developed parallel tracking code. For accurate modelling of the coupled-bunch instability, we investigate improvements to current point-bunch models to take into account finite bunch-size effects.

THP212

Superconducting Cavity Design for Short-Pulse X-Rays at the Advanced Photon Source

cavity, HOM, cryomodule, coupling

2516

G.J. Waldschmidt, B. Brajuskovic, R. Nassiri
ANL, Argonne, USA
G. Cheng, J. Henry, J.D. Mammosser, R.A. Rimmer, H. Wang
JLAB, Newport News, Virginia, USA

Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Superconducting cavities have been analyzed for the short-pulse x-ray (SPX) project at the Advanced Photon Source (APS). Due to the strong damping requirements in the APS storage ring, single-cell superconducting cavities have been designed. The geometry has been optimized for lower-order and higher-order mode damping, reduced peak surface magnetic fields, and compact size. The integration of the cavity assembly, with dampers and waveguide input coupler, into a cryomodule will be discussed.

FROBS6

High Current SRF Cavity Design for SPL and eRHIC

cavity, HOM, dipole, electron

2589

W. Xu, I. Ben-Zvi, R. Calaga, H. Hahn, E.C. Johnson, J. Kewisch
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy
In order to meet the requirements of high average current accelerators, such as the Superconducting Proton Linac (SPL) at CERN and the electron–ion collider (eRHIC) at BNL, a high current 5-cell SRF cavity, called BNL3 cavity, was designed. The optimization process aimed at maximizing the R/Q of the fundamental mode and the geometry factor G under an acceptable RF field level of Bpeak/Eacc or Epeak/Eacc. In addition, a pivotal consideration for the high current accelerators is efficient damping of dangerous higher-order modes (HOM) to avoid inducing emittance degradation, cryogenic loading or beam-breakup (BBU). To transport the HOMs out of the cavity, the BNL3 cavity employs a larger beam pipe, allowing the propagation of HOMs but not the fundamental mode. Moreover, concerning the BBU effect, the BNL3 cavity is aimed at low (R/Q)Qext for dangerous modes, including dipole modes and quadrupole modes. This paper presents the design of the BNL3 cavity, including the optimization for the fundamental mode, and the BBU limitation for dipole and quadrupole modes. The BBU simulation results show that the designed cavity is qualified for high-current, multi-pass machines such as eRHIC.

Slides FROBS6 [2.577 MB]