CERN, Geneva
UMAN, Manchester
For the REX-ISOLDE upgrade a superconducting linac based on 101.28 MHz Quarter Wave Resonators (QWRs) is foreseen downstream the normal conducting (NC) linac. Currently the REX-ISOLDE linac can accelerate ions with a mass to charge ratio in the range of 3 < A/q < 4.5 and up to an energy of 3 MeV/u. The upgrade aims to reach a final beam minimum energy of 10 MeV/u for A/q=4.5 in two main stages. The first stage consists of installing two cryomodules loaded with 10 cavities able to reach 5.5 MeV/u at the end of the present linac and the second consists of replacing part of the existing NC linac and adding further cryomodules. We report here on a beam dynamics study of the accelerator for the two installation stages and the transport line to the experimental station.
Fermilab, Batavia
Recently high power tests of the room temperature cross-bar H-type resonators (CH resonators) and high gradient tests of a superconducting single spoke resonator (SSR) have been performed under the High Intensity Neutrino Source (HINS) project at Fermilab. The resonators have shown a tendency of having multipacting at various levels of input power and therefore longer processing time. To provide insights for the problem, detailed numerical simulations of multipacting for these resonators have become necessary. New generation of accelerating structures like superconducting spoke resonators and room temperature CH resonators need a full 3D treatment. Simulations and study of multipacting in the resonators have been carried out using CST Particle Studio. The problematic regions and power levels have been identified for both types of resonators. This presentation will give the result of simulations and comparison with experimental data.
CEA, Bruyeres-le-Chatel
A 15 MeV accelerator scheme based on a dc photo-injector and a rf superconducting linac as been proposed as a new facility for radiography applications. The overall beam dynamics simulation process based on SUPERFISH and PARMELA codes will be reviewed. We present the results for the following beam operating conditions; acceleration of limited number of bunches, up to twenty electron micro-pulses of 100 ps time duration and 200 nC bunch charge, at 352 MHz repetition rate.
GANIL, Caen
IPN, Orsay
CEA, Gif-sur-Yvette
After a detailed design study phase (2003-2004), the SPIRAL2 project at GANIL (Caen, France) was officially approved in May 2005, and is now in its phase of construction, with a project group including the participation of many French laboratories (CEA, CNRS) and international partners. The SPIRAL2 facility is composed of a multi-beam driver accelerator (5 mA/40 Mev deuterons, 5 mA/33 Mev protons, 1 mA/14.5 M ev/u heavy ions), a dedicated building for the production of Radiactive Ion Beams, the existing cyclotron CIME for the post acceleration of the RIBs, and new experimental areas. In this presentation we focus on the beam dynamics studies dedicated to the SPIRAL2 accelerator part of the project, from the ECR sources to the High Energy Beam Lines which have been recently updated. Various tuning examples will be presented for a variety of ions at different final energies, including error studies and beam losses evaluation. Accent is also put on the way we tune the accelerator with the computing code TRACEWIN, by using 3D electromagnetic maps and diagnostics corresponding to the real machine.
CEA, Gif-sur-Yvette
The purpose of the IFMIF-EVEDA (International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities) demonstrator is to accelerate a 125 mA cw deuteron beam up to 9 MeV. Therefore, the project requires that the ion source and the low energy beam transport (LEBT) line deliver a 140 mA cw deuteron beam with an energy of 100 keV and an emittance of 0.25 π .mm.mrad (rms normalized) at the entrance of the RFQ. The deuteron beam is extracted from a 2.45 GHz ECR source based on the SILHI design*. A LEBT with a two solenoids focusing system is foreseen to transport and adapt the beam for the RFQ injection. In order to validate the LEBT design, intensive beam dynamics simulations have been carried out using a parallel implementation of a particle-in-cell 3D code which takes into account the space charge compensation of the beam induced by the ionisation of the residual gas. The simulations results (in particular from the emittance growth point of view) performed under several conditions of gas species or gas pressure in the beam line are presented.
*R. Gobin et al, Rev. Sci. Instrum. 79, 02B303 (2008).
CEA, Gif-sur-Yvette
INFN/LNL, Legnaro, Padova
CIEMAT, Madrid
One major subsystem of IFMIF (International Fusion Materials Irradiation Facility) is its accelerator facility, consisting of two 175 MHz CW accelerators, each accelerating a deuteron beam of 125 mA to the energy of 40 MeV. This high power beam, 10 MW, induces challenging issues that lead to plan a first phase called EVEDA (Engineering Validation and Engineering Design Activity), where only the portion up to 9 MeV of one accelerator will be constructed and tested. For these accelerators, the Parameter Design phase is about to be completed. This paper presents the status of these studies. Due to the very high beam intensity, particular efforts have been dedicated to minimise the space charge effect that can strongly increase the beam size via the halo, and the losses that can prohibit the requested hand-on maintenance. For that, Beam Dynamics simulations have been performed with 106 macro-particles, and a great vigilance has been granted to the emittance growth and the particles on the beam edge. Several possible solutions are presented, for which advantages and drawbacks to fulfil the specifications are discussed.
LAL, Orsay
A growing number of experiments require low emittance ultra-short electron bunches in the 100 fs range (rms value) for the production of coherent light or the injection in plasma for laser-plasma acceleration. Especially in the last case it is highly desirable to have a compact accelerator; hence a strong experimental activity is carried out to get such a beam directly from a photo-injector. We have performed beam dynamic simulations using the PARMELA code to study the performances of the alphaX photo-injector installed in the University of Strathclyde in UK. This rf gun is aimed to produce electron bunches of 100 pC bunch charge, 100 fs bunch length and 1 mmmrad transverse emittance. We will show the results of systematic parametric studies as a function of charge and laser pulse duration as well as the natural evolution of the beam phase space as a function of the distance from the photo-cathode.
GSI, Darmstadt
ORNL, Oak Ridge, Tennessee
CEA, Gif-sur-Yvette
Funding: CARE, contract number RII3-CT-2003-506395) European Community INTAS Project Ref. no. 06-1000012-8782
Transverse emittance growth along the Alvarez DTL section is a major concern with respect to the preservation of beam quality of high current beams at the GSI UNILAC. In order to define measures to reduce this growth appropriate tools to simulate the beam dynamics are indispensable. This paper is on benchmarking of three beam dynamics simulation codes, i.e. DYNAMION, PARMILA, and PARTRAN against systematic measurements of beam emittance growth for different machine settings. Experimental set-ups, data reduction, the preparation of the simulations, and the evaluation of the simulations will be described. It was found that the mean value of final horizontal and vertical rms-emittances can be reproduced well by the codes.
TEMF, TU Darmstadt, Darmstadt
TU Darmstadt, Darmstadt
Funding: This work was partially funded by DESY Hamburg and DFG (SFB 634).
At the Superconducting DArmstadter LINear Accelerator (S-DALINAC) a new 100 keV polarized electron source is currently being installed. Therefore, a new low energy injection concept has to be designed. One of the main components of the injector are a polarized electron source, an alpha magnet and a Wien filter used for spin rotation as well as various beam forming elements. Fast beam dynamics simulations can advantageously assist the design process because of the flexible parameter variations combined with nearly simultaneous solution responses. Based on the moment approach a fast tracking code named V-Code has been implemented at TEMF. In order to simulate the entire injector an alpha magnet model was added to the V-Code database of beam line elements. In this paper a summary of issues regarding the implementation complemented with simulation results will be provided.
INFN/LNL, Legnaro, Padova
Soreq NRC, Yavne
IPN, Orsay
CEA, Gif-sur-Yvette
TRIUMF, Vancouver
Funding: We acknowledge the financial support of the European Community under the FP6 "Research Infrastructure Action-Structuring the European Research Area" EURISOL DS Project Contract No. 515768 RIDS.
A 1 GeV, 5 mA cw superconducting proton/H- linac, with the capability of supplying cw primary beam to up to four targets simultaneously by means of a new beam splitting scheme, is under study in the framework of the EURISOL DS project which aims to produce an engineering-oriented design of a next generation European Radioactive beam facility. The EURISOL driver accelerator would be able to accelerate also a 100 muA 3He beam up to 2 GeV, and a 5 mA deuteron beam up to 200 MeV. The linac characteristics and the status of the beam dynamics studies will be presented.
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
KEK, Ibaraki
JAEA, Ibaraki-ken
KEK/JAEA, Ibaraki-Ken
In the design of the very high intensity proton beam of the J-PARC LINAC, precise control of transverse beam dynamics is extremely important for suppression of beam loss. We present results of transverse beam matching and orbit corrections. The linac has 7 matching sections, each of which consists of 4 quadrupole magnets and 4 wire scanners. At 5 matching sections, beam widths at wire scanners are designed to agree with each other. This condition is used in the newly developed algorithm of quadrupole field correction based on a transport model, XAL. Excellent matching performance has been achieved with mismatch factor less than 5% at beam current of 5 to 30 mA. Control of beam parameters from linac into RCS is important for RCS paint injection. Beam studies and comparison to a model have been performed with linac wire scanners combined with multi-wire proportional monitors in the injection line. Orbit corrections with dipole steering magnets based on XAL model have been performed. Orbit deviations were suppressed within 1 mm in horizontal and vertical directions in the whole linac. For these measurements, detailed comparisons to a multi-particle simulation will be shown.
Kyoto ICR, Uji, Kyoto
ILL, Grenoble
RIKEN, Wako, Saitama
KEK, Ibaraki
University of Tokyo, Tokyo
JAEA, Ibaraki-ken
Kyoto University, Kyoto
ICEPP, Tokyo
We are developing a modulating permanent magnet sextupole lens to focus pulsed cold neutrons. It is based on the extended Halbach configuration to generate stronger magnetic field. In order to adjust the strength, the magnet is divided into two nested co-axial rings, where the inner ring is fixed and the outer ring can be rotated. Synchronizing the modulation with neutron beam pulse suppresses the chromatic aberration. These devices largely improve the utilization efficiency of neutrons, which makes even small linac based neutron sources practical. We have fabricated a half-scale model and studied its strength, torque and temperature rise during the operation. The main causes of the temperature rise are eddy-current loss in the poles made of soft magnetic material in inner ring and hysteresis loss. A laminated structure reduced the eddy-current loss. The temperature rise was suppressed to about half of the former model. We now study their B-H curve to optimize the thickness of the sheet. Annealing of the material is supposed to reduce the hysteresis loss, which will be tested soon. The experimental results of very-cold neutrons focusing with the half-scale model are also described.
MEPhI, Moscow
RAS/INR, Moscow
A new computer code for 3D simulation of multipacting phenomenon in axisymmetric and non-axisymmetric rf structures is presented. The goal of the simulation is to determine resonant electron trajectories and electron multiplication in rf structure. Both SW and TW structures of normal- and superconductivity have been studied. Simulation results are compared with theoretical calculations and experimental measurements.
MEPhI, Moscow
ScanTech, Atlanta, Georgia
MSU, Moscow
Introscan, Moscow
Analysis of input coupler asymmetry influence on beam dynamics in superconducting cavities of Energy Recovery Linac (ERL) injector is presented. Both coaxial and waveguide, single and twin input couplers were analyzed. Using computer simulation electromagnetic fields distribution in accelerating cavity was obtained and recalculated to the transverse-kick to the bunch passing the coupler. Also calculation of external coupling was done. RTMTRACE code was adapted for particle beams dynamic simulation. Acceptable transverse emittance growth was achieved for twin-coaxial (4%) and waveguide (5%) input coupler designs.
NIIEFA, St. Petersburg
Saint-Petersburg State University, Saint-Petersburg
AN Krylov SRI, St. Petersburg
Funding: Rosatom corp.
We present results of calculations of the neutron generation processes in metal targets induced by protons with energies up to 1 GeV using GEANT4 framework. Results on the neutron yield in large targets and neutron generation as a function of target's dimensions are presented. Energy deposit in the target is also given. The obtained results are to be used for multiplying blanket ADS target design.
CERN, Geneva
CEA, Gif-sur-Yvette
Linac4 is a normal conducting H- linac to be built at CERN as a new injector to the PS Booster and later on as a front end of a Superconducting Proton Linac (SPL). The layout consists of a H- rf source, a magnetic LEBT, a RFQ (accelerating the beam from 45 keV to 3 MeV), a chopper line, a conventional Drift Tube Linac (from 3 MeV to 50 MeV), a Coupled Cavity Drift Tube Linac (from 50 MeV to 100 MeV) and a pi-mode structure (PIMS, from 100 to 160 MeV), all operating at a frequency of 352 MHz. End-to-end beam dynamics simulations have been carried out in parallel with the codes PATH and TRACEWIN to optimise the design and performance of the accelerator and at the same time to guarantee a cross-check of the results found. An extensive statistical campaign of longitudinal error studies (static and dynamic) was then launched for validation of the proposed design and to assess the maximum level of RF jitter/inaccuracies (in both phase and amplitude) the system can tolerate before beam quality at injection in the PS Booster - and later in the SPL- is compromised.
IPM, Tehran
University of Oslo, Oslo
CERN, Geneva
The aim of the CLIC Test Facility CTF3, built at CERN by an international collaboration, is to address the main feasibility issues of the CLIC electron-positron linear collider technology by 2010. One key-issue studied in CTF3 is the generation of the very high current drive beam, used in CLIC as the rf power source. It is particularly important to simulate and control the drive beam longitudinal dynamics in the drive beam generation complex, since it directly affects the efficiency and stability of the rf power production process. In this paper we describe the ongoing effort in modelling the longitudinal evolution of the CTF3 drive beam and compare the simulations with experimental results.
Imperial College of Science and Technology, Department of Physics, London
University of Warwick, Coventry
STFC/RAL/ISIS, Chilton, Didcot, Oxon
STFC/RAL/ASTeC, Chilton, Didcot, Oxon
In order to contribute to the development of high power proton accelerators in the MW range, to prepare the way for an ISIS upgrade and to contribute to the UK design effort on neutrino factories, a front end test stand (FETS) is being constructed at the Rutherford Appleton Laboratory (RAL) in the UK. The aim of the FETS is to demonstrate the production of a 60 mA, 2 ms, 50 pps chopped beam at 3 MeV with sufficient beam quality. The results of numerical simulations of the particle dynamics from the charge separation dipole behind the ion source to the end of the MEBT will be presented. Previous measurements showed that the emittance of the beam delivered by the ion source exceeded our expectations by more than a factor of 3. Since then various changes in the beam extraction/post accelerator region reduced the beam emittance by a factor of 2. Simulations of the particle dynamics in the FETS based on distributions gained from recent measurements of the transversal beam emittance behind the ion source will be presented and the results for different input distributions discussed.
UMAN, Manchester
Higher order modes (HOMs) are simulated with finite element and finite difference computer codes for the ILC superconducting cavities currently under investigation for the ILC. In particular, HOMs in KEK's Ichiro type of cavity and Cornel University's Re-entrant design are focussed on in this work. The aim, at these Universities and laboratories, is to achieve an accelerating gradient in excess of 50 MV/m in 9-cell superconducting cavities whilst maintaining a high quality and stable electron beam. At these high gradients, electrical breakdown is an important cause for concern and the wakefields excited by the energetic electron beams are also potentially damaging to the beam's emittance. Here we restrict the analysis to performing detailed simulations, on emittance dilution due to beams initially injected with realistic offsets from the electrical centre of the cavities and due to statistical misalignments of the cavities. We take advantage of the latest beam dynamics codes in order to perform these simulations.
UMAN, Manchester
The globalised scattering matrix (GSM) method provides an efficient means of obtaining the electromagnetic field in interconnected multi-cavity structures. In the proposed XFEL at DESY and the ILC facilities, energetic electron beams can readily excite higher order modes which if left unchecked can dilute the emittance of the beams. The GSM in conjunction with finite element modelling of the scattering matrices of the linac cavities is used to enable the characteristic eigenmodes to be rapidly obtained and the potential for trapped modes is investigated. This characteristic eigensystem allows the wakefield experienced by the beam to be analysed and the consequences on beam quality ascertained. The impact of fabrication errors on the transverse electromagnetic field and corresponding resonant frequencies of the modes is also explored in detailed simulations.
ANL, Argonne
ORNL, Oak Ridge, Tennessee
Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC-02-06CH11357.
In an effort to simulate the SNS linac using the beam dynamics code TRACK and to benchmark the results against the recent commissioning data, we have started updating TRACK to support SNS-type elements such as DTL's and CCL's. After successfully implementing and simulating the DTL section of the SNS linac*, we have implemented the CCL section and the high energy superconducting (SC) section up to 1 GeV. Results from end-to-end simulations of the SNS linac using TRACK will be presented and compared to simulations using other codes and to the recent commissioning data.
*"First TRACK Simulations of the SNS linac", B. Mustapha et al., in Proceedings of Linac-06 Conference, Knoxville, Tennessee, August 21-25, 2006.
ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
We present a Monte-Carlo method implemented in the code elegant for simulating Touschek scattering effects in a linac beam. The local scattering rate and the distribution of scattered particles can be obtained from the code. In addition, scattered particles can be tracked to the end of the beam line and the local beam loss rate and beam halo information recorded. This information can be used for beam collimation system design.
ANL, Argonne
Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Intrabeam scattering (IBS) may become an issue for linac-based fourth-generation light sources such as X-ray free-electron lasers and energy recovery linacs (ERLs), both of which use high-brightness electron beams with extremely small emittance and energy spread. Any degradation of the extremely high beam quality could significantly reduce the X-ray performance. We present here a strategy first used in the code elegant for simulating IBS effects for high brightness linac beams. We also present an application to a possible ERL upgrade of the Advanced Photon Source.
Northern Illinois University, DeKalb, Illinois
Funding: Work supported by the Department of Defense under contract N00014-06-1-0587 with Northern Illinois University.
Numerical simulations of charged particle beams require an approximation to the particle distribution being simulated. Depending on the flavor of the N-body code, these approximations suffer from different computational difficulties. We briefly outline these difficulties, and present approximations to particle distributions using orthogonal functions. We discuss two different types of orthogonal functions, new in the context of beam simulations: wavelets and scaled Gauss-Hermite basis. On the wavelet side, we present the wavelet-based Poisson equation solver we recently devised for use in particle-in-cell beam simulations, and report on some important enhancements being implemented as a part of an ongoing project. On scaled Gauss-Hermite basis side, we report preliminary results in efficiently approximating discrete particle distributions in an orthogonal basis in which the corresponding potential and forces are directly and easily found from the expansion coefficients of the distribution. Finally, we discuss application of these particle distribution representations in simulation of coherent synchrotron radiation.
G.H. Gillespie Associates, Inc., Del Mar, California
A specialized software package has been developed that enables the rapid implementation of custom beam optics modules that run in the Particle Beam Optics Laboratory (PBO Lab). PBO Lab is a commercially available software application that supports a suite of accelerator codes for design, operations, and personnel education. The intuitive and easy-to-use graphic user interface (GUI) is largely responsible for the popularity of PBO Lab. The Open Architecture Software Integration System, or OASIS, builds upon the capability of PBO Lab to host a suite of different codes, and provides an innovative framework that allows users to readily integrate their own optics programs into PBO Lab. The OASIS GUI can be used to readily create new PBO Lab modules without writing or compiling any source code. OASIS has been used to develop several new modules for PBO Lab. This paper presents a summary of the OASIS framework and describes some of the features used in creating the new PBO Lab modules for several popular optics codes.
G.H. Gillespie Associates, Inc., Del Mar, California
A new graphic user interface (GUI) has been created for the PARMILA 2 program. PARMILA 2 is an advanced version of the historical PARMILA program originally developed to design and model drift tube linear (DTL) accelerators. PARMILA 2 expands upon that capability to support the design and simulation of coupled cavity linear (CCL) accelerator structures, coupled-cavity drift tube linac (CCDTL) structures, superconducting accelerator structures, as well as DTL structures and transport lines that can include magnetic, radiofrequency and electrostatic beam optics elements. The Open Architecture Software Integration System, or OASIS, has been used to develop a custom module for the PARMILA 2 program that runs along with a suite of other optics codes in the Particle Beam Optics Laboratory (PBO Lab). OASIS development tools were utilized to define the innovative GUI for the PARMILA 2 module. Existing PARMILA 2 executables, including Parmila.exe, Lingraf.exe and readdst.exe, have been implemented via GUI commands utilizing other OASIS tools without any compilation or linking required. This paper presents an overview of the PARMILA 2 module and illustrates some of the GUI features.
CLASSE, Ithaca, New York
BNL, Upton, Long Island, New York
CERN, Geneva
Evolution of short intense electron bunches passing through bunch-compressing beamlines is simulated using the UAL (Unified Accelerator Libraries) string space charge formulation. Excellent agreement is obtained with results obtained experimentally at CTF-II, the CERN "Compact Linear Collider'' test facility. The 40 MeV energy of these data is low enough for Coulomb and Biot-Savart forces to be important and high enough for coherent synchrotron radiation and centrifugal space charge forces to be important. UAL results are also compared with CSRtrack results for emittance growth in a 40 MeV 'standard' chicane. Vertical space charge forces are found to be important in this (low energy) case.
LANL, Los Alamos, New Mexico
NSTec, Los Alamos, New Mexico
Voss Scientific, Albuquerque, New Mexico
SAIC, Los Alamos, New Mexico
Funding: Work supported by USDOE under contract DE-AC52-06NA25396
The DARHT-II linear induction accelerator (LIA) accelerates a 2 kA electron beam to more than 17 MeV. The beam pulse has a greater than 1.5-microsecond flattop region over which the electron kinetic energy is constant to within 1%. The beam dynamics are diagnosed with 21 beam-position monitors located throughout the injector, accelerator, and after the accelerator exit, where we also have beam imaging diagnostics. I will discuss the tuning of the injector and accelerator, and I will present data for the resulting beam dynamics. Beam motion at the accelerator exit is undesirable for its application as a bremsstrahlung source for multi-pulse radiography of explosively driven hydrodynamic experiments. I will discuss the tuning procedures and other methods we use to minimize beam motion, and to suppress the beam-breakup (BBU) and ion-hose instabilities*.
*"Long-pulse beam stability experiments on the DARHT-II linear induction accelerator", Carl Ekdahl, et al., IEEE Trans. Plasma. Sci. Vol. 34, 2006, pp. 460-466.
LANL, Los Alamos, New Mexico
Funding: This work has benefited from the use of the LANSCE at LANL. This facility is funded by the US DOE and operated by LANS for NSSA under Contract DE-AC52-06NA25396. LA-UR-08-03585.
Tuning particle accelerators is time consuming and expensive, with a number of inherently non-linear interactions between system components. Conventional control methods have not been successful in this domain, and the result is constant and expensive monitoring of the systems by human operators. This is particularly true for the start-up and conditioning phase after a maintenance period or an unexpected fault. In turn, this often requires a step by step restart of the accelerator. Surprisingly few attempts have been made to apply intelligent accelerator control techniques to help with beam tuning, fault detection, and fault recovery problems. The reason for that might be that accelerator facilities are rare and difficult to understand systems that require detailed expert knowledge about the underlying physics as well as months if not years of experience to understand the relationship between individual components, particularly if they are geographically disjoint. This paper will give an overview about the research effort in the accelerator community that has been dedicated to the use of artificial intelligence methods for accelerator beam line tuning.
SLAC, Menlo Park, California
Funding: Work supported by DOE contract DE-AC02-76SF00515.
SLAC's Advanced Computations Department (ACD) has developed the first high-performance parallel Finite Element 3D Particle-In-Cell code, Pic3P, for simulations of rf guns and other space-charge dominated beam-cavity interactions. As opposed to standard beam transport codes, which are based on the electrostatic approximation, Pic3P solves the complete set of Maxwell-Lorentz equations and thus includes space charge, retardation and wakefield effects from first principles. Pic3P uses advanced Finite Element methods with unstructured meshes, higher-order basis functions and quadratic surface approximation. A novel scheme for causal adaptive refinement reduces computational resource requirements by orders of magnitude. Pic3P is optimized for large-scale parallel processing and allows simulations of realistic 3D particle distributions with unprecedented accuracy, aiding the design and operation of the next-generation of accelerator facilities. Applications to the Linac Coherent Light Source (LCLS) rf gun are presented.
SLAC, Menlo Park, California
UMAN, Manchester
The CLIC linear collider aims at accelerating multiple bunches of electrons and positrons and colliding them at a center of mass energy of 3 TeV. These bunches are accelerated through X-band linacs operating at an accelerating frequency of 12 GHz. Each beam readily excites wake-fields in the accelerating cavities of each linac. The transverse components of the wake-fields, if left unchecked, can dilute the beam emittance. The present CLIC design relies on heavy damping of these wake-fields in order to ameliorate the effects of the wake-fields on the beam emittance. Here we present initial results on simulations of the long-range wakefields in these structures and on beam dynamics simulations. In particular, detailed simulations are performed, on emittance dilution due to beams initially injected with realistic offsets from the electrical centre of the cavities and due to statistical misalignments of the cavities.
ORNL, Oak Ridge, Tennessee
GSI, Darmstadt
The 4ν=1 resonance of a linac is found when the depressed tune is around 90 deg. It is observed that this fourth order resonance is dominating over the better known envelope instability and practically replacing it. Simulation study shows a clear emittance growth by this resonance and its stopband. Experimental measurement of the stopband of this resonance is proposed and conducted in early 2008 using the UNILAC at GSI. This study will serve as a excellent benchmarking.
ORNL, Oak Ridge, Tennessee
Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
For a high intensity linac such as the SNS linac, it matters to match adequately to minimize the beam mismatch and potential beam loss. The technique of doing the matching using the wire-scanners in series was employed. It was verified that matching was improved through the matching technique based on the beam profile measurements from wire-scanners in series.
ORNL, Oak Ridge, Tennessee
Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.
The importance of a proper phase law is recognized to tune the synchronous phase of each superconducting cavities of a high intensity proton linac such as the SNS linac. The factors to be optimized are:
- maximizing the longitudinal acceptance
- better matching throughout the linac and
- achieving maximum beam energy.
LLNL, Livermore, California
It has been empirically observed in both experiments and particle-in-cell simulations that space-charge-dominated beams suffer strong growth in emittance and particle losses in alternating gradient quadrupole transport channels when the undepressed phase advance increases beyond about 85 degrees per lattice period. Although this criterion has been used extensively in practical designs of strong focusing intense beam transport lattices, the origin of the limit has not been understood. We propose a mechanism for the transport limit resulting from strongly chaotic classes of halo particle resonances near the core of the beam that allow near-edge particles to rapidly increase in oscillation amplitude when the space-charge intensity and the flutter of the matched beam envelope are both sufficiently large. A core particle model is applied to parametrically analyze this process and the results are compared with extensive particle simulations.
ANL, Argonne
Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC-02-06CH11357.
Accelerator simulations still do not provide everything designers and operators need to deploy a new facility with confidence. This is mainly because of limitations preventing realistic, fast-turnaround, end-to-end simulations of the beam from the source all the way through to a final interaction point and because of limitations in on-line monitoring that prevent a full characterization of the actual beam line. As a result, once a machine is built there can be a gap between the expected behavior of the machine and the actual behavior. This gap often corresponds to enormous work and significant delays in commissioning a new machine. To address the shortcomings of the existing beam dynamics simulation codes, and to fulfill the requirements of future hadron and heavy-ion machines, a starting point for a realistic simulation tool is being developed at ANL that will support detailed design evaluation and also fast turnaround computation to support commissioning and operation of the facility. The proposed simulations will be performed on the fast growing computing facility at ANL with peta-scale capability.