OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), May 1, 2005
Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-l... more Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment, theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP and the electron cloud code POSINST, with additional functionalities. The development of the new capability follows a "roadmap" describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electron and ion motion, a module to generate neutrals desorbed by beam ion impacts at the wall, and a module to track impact ionization of the gas by beam ions or electrons. Example applications of the new capability to the modeling of electron effects in the High Current Experiment (HCX) are given.
The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consis... more The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consistent with an Ecloud driven instability. We present recent MD data from the SPS, details of the instrument technique and spectral analysis methods which help reveal complex vertical motion that develops within a subset of the injected bunch trains. The beam motion is detected via wide-band exponential taper striplines and delta-σ hybrids. The raw sum and difference data is sampled at 50 GHz with 1.8 GHz bandwidth. Sliding window FFT techniques and RMS motion techniques show the development of large vertical tune shifts on portions of the bunch of nearly 0.025 from the base tune of 0.185. Results are presented via spectrograms and rms bunch slice trajectories to illustrate development of the unstable beam and time scale of development along the injected bunch train. The study shows that the growing unstable motion occupies a very broad frequency band of 1.2 GHz. These measurements are comp...
One of the options under consideration for a future upgrade of the LHC injector complex includes ... more One of the options under consideration for a future upgrade of the LHC injector complex includes the replacement of PS with PS2 (a longer circumference and higher energy ring). Efforts are currently underway to design the new machine and characterize the beam dynamics. Electron cloud effects represent a potentially serious limitation to the achievement of the upgrade goals. We report on ongoing numerical studies aiming at estimating the e-cloud density threshold for the occurrence of single bunch instabilities or significant degradation of the beam emittance. We present selected results obtained in the more familiar quasi-static approximation and/or in the Lorentz-boosted frame.
Retarding field analyzers (RFAs) provide an effective measure of the local electron cloud density... more Retarding field analyzers (RFAs) provide an effective measure of the local electron cloud density and energy distribution. Proper interpretation of RFA data can yield information about the behavior of the cloud, as well as the surface properties of the instrumented vacuum chamber. However, due to the complex interaction of the cloud with the RFA, particularly in regions of high magnetic field, understanding these measurements can be nontrivial. This paper will examine different methods for interpreting RFA data via cloud simulation programs. Possible techniques include postprocessing the output of a simulation code to predict the RFA response, and incorporating an RFA model into the program itself.
We have integrated the electron-cloud code POSINST with WARP [2]-a 3-D parallel Particle-In-Cell ... more We have integrated the electron-cloud code POSINST with WARP [2]-a 3-D parallel Particle-In-Cell accelerator code developed for Heavy Ion Inertial Fusion-so that the two can interoperate. Both codes are run in the same process, communicate through a Python interpreter (already used in WARP), and share certain key arrays (so far, particle positions and velocities). Currently, POSINST provides primary and secondary sources of electrons, beam bunch kicks, a particle mover, and diagnostics. WARP provides the field solvers and diagnostics. Secondary emission routines are provided by the Tech-X package CMEE.
Lawrence Berkeley National Laboratory, Apr 18, 2008
The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ... more The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ILC positron damping ring wiggler. WARP is a parallelized, 3D particle-in-cell code which is fully self-consistent for all species. The POSINST models for the production of photoelectrons and secondary electrons are used to calculate electron creation. Mesh refinement and a moving reference frame for the calculation will be used to reduce the computer time needed by several orders of magnitude. We present preliminary results for cloud buildup showing 3D electron effects at the nulls of the vertical wiggler field. First results from a benchmark of WARP-POSINST vs. POSINST are also discussed.
We provide a detailed description of a model and its computational algorithm for the secondary el... more We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel.
Proceedings of the 2005 Particle Accelerator Conference
Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-l... more Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment, theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP and the electron cloud code POSINST, with additional functionalities. The development of the new capability follows a "roadmap" describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electron and ion motion, a module to generate neutrals desorbed by beam ion impacts at the wall, and a module to track impact ionization of the gas by beam ions or electrons. Example applications of the new capability to the modeling of electron effects in the High Current Experiment (HCX) are given.
PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)
This paper presents new simulation results for the power deposition from the electron cloud in th... more This paper presents new simulation results for the power deposition from the electron cloud in the beam screen of the Large Hadron Collider (LHC). We pay particular attention to the sensitivity of the results to certain low-energy parameters of the secondary electron (SE) emission. Most of these parameters, which constitute an input to the simulation program, are extracted from recent measurements at CERN and SLAC.
Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation ... more Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation in the ILC-DR. We report on simulations carried out using an augmented version of POSINST, accounting for e-cloud dynamics in the presence of grooves, and make contact with previous estimates of an effective secondary electron yield for grooved surfaces.
We provide a detailed description of a model and its computational algorithm for the secondary el... more We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel. We also present details of the electron-cloud simulation code POSINST that are relevant to the secondary emission process. This note expands on our previously published article .
Physical Review Special Topics - Accelerators and Beams, 2002
In this paper we present a new approach, based on a shifted Green function, to evaluate the elect... more In this paper we present a new approach, based on a shifted Green function, to evaluate the electromagnetic field in a simulation of colliding beams. Unlike a conventional particle-mesh code, we use a method in which the computational mesh covers only the largest of the two colliding beams. This allows us to study long-range parasitic collisions accurately and efficiently. We have implemented this algorithm in a new parallel strong-strong beam-beam simulation code. As an application, we present a study of a beam sweeping scheme for the LBNL luminosity monitor of the Large Hadron Collider.
The 31 st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects "ECLOUD'04" was held Apr... more The 31 st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects "ECLOUD'04" was held April 19-23, 2004 at Napa, CA, USA. A broad range of current topics in this field were illuminated by 53 talks in 7 sessions plus 6 session summaries at the final summary session. These covered a variety of experimental methods and results, along with progress on understanding of the topic obtained from simulations and analytic theory, and evaluations of the effectiveness of various methods/mechanisms for mitigation of the adverse impact on accelerator performance. In addition, a panel discussion was held on "Future Needs and Future Directions". A summary of progress on the major themes covered at ECLOUD'04 is presented.
A replacement for the PS storage ring is being considered, in the context of the future LHC accel... more A replacement for the PS storage ring is being considered, in the context of the future LHC accelerator complex upgrade, that would likely place the new machine (the PS2) in a regime where the electron-cloud (EC) effect might be an operational limitation. We report here our present understanding of the ECE build-up based on simulations. We focus our attention on the bending magnets and the field-free regions, and consider both proposed bunch spacings of 25 and 50 ns. The primary model parameters exercised are the peak secondary emission yield (SEY) delta_{m}ax, and the electron-wall impact energy at which SEY peaks, E_{m}ax. By choosing reasonable values for such quantities, and exploring variations around them, we estimate the range for the EC density n_{e} to be expected in nominal operation. We present most of our results as a function of bunch intensity N_{b}, and we provide a tentative explanation for a curious non-monotonic behavior of n_{e} as a function of N_{b}. We explore ...
In studies with positron beams in the Advanced Photon Source, a dramatic amplification was observ... more In studies with positron beams in the Advanced Photon Source, a dramatic amplification was observed in the electron cloud for certain bunch current and bunch spacings. In modeling presented previously, we found qualitative agreement with the observed beam-induced multipacting condition, provided reasonable values were chosen for the secondary electron yield parameters, including the energy distribution. In this paper, we model and discuss the build-up and saturation process observed over long bunch trains at the resonance condition. Understanding this saturation mechanism in more detail may have implications for predicting electron cloud amplification, multipacting, and instabilities in future rings.
We present recent simulation results for the main features of the electron cloud in the storage r... more We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code.
Proceedings of the 2005 Particle Accelerator Conference
We present initial results for the self-consistent beamcloud dynamics simulations for a sample LH... more We present initial results for the self-consistent beamcloud dynamics simulations for a sample LHC beam, using a newly developed set of modeling capability based on a merge [1] of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP [2] and the electron-cloud code POSINST . Although the storage ring model we use as a test bed to contain the beam is much simpler and shorter than the LHC, its lattice elements are realistically modeled, as is the beam and the electron cloud dynamics. The simulated mechanisms for generation and absorption of the electrons at the walls are based on previously validated models available in POSINST .
Lawrence Berkeley National Laboratory, Jun 19, 2002
We present an update of computer simulation results for some features of the electron cloud at th... more We present an update of computer simulation results for some features of the electron cloud at the Large Hadron Collider (LHC) and recent simulation results for the Super Proton Synchrotron (SPS). We focus on the sensitivity of the power deposition on the LHC beam screen to the emitted electron spectrum, which we study by means of a refined secondary electron (SE) emission model recently included in our simulation code.
Lawrence Berkeley National Laboratory, Jul 8, 2002
We present recent simulation results for the main features of the electron cloud in the storage r... more We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), May 1, 2005
Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-l... more Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment, theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP and the electron cloud code POSINST, with additional functionalities. The development of the new capability follows a "roadmap" describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electron and ion motion, a module to generate neutrals desorbed by beam ion impacts at the wall, and a module to track impact ionization of the gas by beam ions or electrons. Example applications of the new capability to the modeling of electron effects in the High Current Experiment (HCX) are given.
The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consis... more The SPS at high intensities exhibits transverse single-bunch instabilities with signatures consistent with an Ecloud driven instability. We present recent MD data from the SPS, details of the instrument technique and spectral analysis methods which help reveal complex vertical motion that develops within a subset of the injected bunch trains. The beam motion is detected via wide-band exponential taper striplines and delta-σ hybrids. The raw sum and difference data is sampled at 50 GHz with 1.8 GHz bandwidth. Sliding window FFT techniques and RMS motion techniques show the development of large vertical tune shifts on portions of the bunch of nearly 0.025 from the base tune of 0.185. Results are presented via spectrograms and rms bunch slice trajectories to illustrate development of the unstable beam and time scale of development along the injected bunch train. The study shows that the growing unstable motion occupies a very broad frequency band of 1.2 GHz. These measurements are comp...
One of the options under consideration for a future upgrade of the LHC injector complex includes ... more One of the options under consideration for a future upgrade of the LHC injector complex includes the replacement of PS with PS2 (a longer circumference and higher energy ring). Efforts are currently underway to design the new machine and characterize the beam dynamics. Electron cloud effects represent a potentially serious limitation to the achievement of the upgrade goals. We report on ongoing numerical studies aiming at estimating the e-cloud density threshold for the occurrence of single bunch instabilities or significant degradation of the beam emittance. We present selected results obtained in the more familiar quasi-static approximation and/or in the Lorentz-boosted frame.
Retarding field analyzers (RFAs) provide an effective measure of the local electron cloud density... more Retarding field analyzers (RFAs) provide an effective measure of the local electron cloud density and energy distribution. Proper interpretation of RFA data can yield information about the behavior of the cloud, as well as the surface properties of the instrumented vacuum chamber. However, due to the complex interaction of the cloud with the RFA, particularly in regions of high magnetic field, understanding these measurements can be nontrivial. This paper will examine different methods for interpreting RFA data via cloud simulation programs. Possible techniques include postprocessing the output of a simulation code to predict the RFA response, and incorporating an RFA model into the program itself.
We have integrated the electron-cloud code POSINST with WARP [2]-a 3-D parallel Particle-In-Cell ... more We have integrated the electron-cloud code POSINST with WARP [2]-a 3-D parallel Particle-In-Cell accelerator code developed for Heavy Ion Inertial Fusion-so that the two can interoperate. Both codes are run in the same process, communicate through a Python interpreter (already used in WARP), and share certain key arrays (so far, particle positions and velocities). Currently, POSINST provides primary and secondary sources of electrons, beam bunch kicks, a particle mover, and diagnostics. WARP provides the field solvers and diagnostics. Secondary emission routines are provided by the Tech-X package CMEE.
Lawrence Berkeley National Laboratory, Apr 18, 2008
The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ... more The self-consistent code suite WARP-POSINST is being used to study electron cloud effects in the ILC positron damping ring wiggler. WARP is a parallelized, 3D particle-in-cell code which is fully self-consistent for all species. The POSINST models for the production of photoelectrons and secondary electrons are used to calculate electron creation. Mesh refinement and a moving reference frame for the calculation will be used to reduce the computer time needed by several orders of magnitude. We present preliminary results for cloud buildup showing 3D electron effects at the nulls of the vertical wiggler field. First results from a benchmark of WARP-POSINST vs. POSINST are also discussed.
We provide a detailed description of a model and its computational algorithm for the secondary el... more We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel.
Proceedings of the 2005 Particle Accelerator Conference
Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-l... more Electron clouds and gas pressure rise limit the performance of many major accelerators. A multi-laboratory effort to understand the underlying physics via the combined application of experiment, theory, and simulation is underway. We present here the status of the simulation capability development, based on a merge of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP and the electron cloud code POSINST, with additional functionalities. The development of the new capability follows a "roadmap" describing the different functional modules, and their inter-relationships, that are ultimately needed to reach self-consistency. Newly developed functionalities include a novel particle mover bridging the time scales between electron and ion motion, a module to generate neutrals desorbed by beam ion impacts at the wall, and a module to track impact ionization of the gas by beam ions or electrons. Example applications of the new capability to the modeling of electron effects in the High Current Experiment (HCX) are given.
PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)
This paper presents new simulation results for the power deposition from the electron cloud in th... more This paper presents new simulation results for the power deposition from the electron cloud in the beam screen of the Large Hadron Collider (LHC). We pay particular attention to the sensitivity of the results to certain low-energy parameters of the secondary electron (SE) emission. Most of these parameters, which constitute an input to the simulation program, are extracted from recent measurements at CERN and SLAC.
Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation ... more Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation in the ILC-DR. We report on simulations carried out using an augmented version of POSINST, accounting for e-cloud dynamics in the presence of grooves, and make contact with previous estimates of an effective secondary electron yield for grooved surfaces.
We provide a detailed description of a model and its computational algorithm for the secondary el... more We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel. We also present details of the electron-cloud simulation code POSINST that are relevant to the secondary emission process. This note expands on our previously published article .
Physical Review Special Topics - Accelerators and Beams, 2002
In this paper we present a new approach, based on a shifted Green function, to evaluate the elect... more In this paper we present a new approach, based on a shifted Green function, to evaluate the electromagnetic field in a simulation of colliding beams. Unlike a conventional particle-mesh code, we use a method in which the computational mesh covers only the largest of the two colliding beams. This allows us to study long-range parasitic collisions accurately and efficiently. We have implemented this algorithm in a new parallel strong-strong beam-beam simulation code. As an application, we present a study of a beam sweeping scheme for the LBNL luminosity monitor of the Large Hadron Collider.
The 31 st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects "ECLOUD'04" was held Apr... more The 31 st ICFA Advanced Beam Dynamics Workshop on Electron-Cloud Effects "ECLOUD'04" was held April 19-23, 2004 at Napa, CA, USA. A broad range of current topics in this field were illuminated by 53 talks in 7 sessions plus 6 session summaries at the final summary session. These covered a variety of experimental methods and results, along with progress on understanding of the topic obtained from simulations and analytic theory, and evaluations of the effectiveness of various methods/mechanisms for mitigation of the adverse impact on accelerator performance. In addition, a panel discussion was held on "Future Needs and Future Directions". A summary of progress on the major themes covered at ECLOUD'04 is presented.
A replacement for the PS storage ring is being considered, in the context of the future LHC accel... more A replacement for the PS storage ring is being considered, in the context of the future LHC accelerator complex upgrade, that would likely place the new machine (the PS2) in a regime where the electron-cloud (EC) effect might be an operational limitation. We report here our present understanding of the ECE build-up based on simulations. We focus our attention on the bending magnets and the field-free regions, and consider both proposed bunch spacings of 25 and 50 ns. The primary model parameters exercised are the peak secondary emission yield (SEY) delta_{m}ax, and the electron-wall impact energy at which SEY peaks, E_{m}ax. By choosing reasonable values for such quantities, and exploring variations around them, we estimate the range for the EC density n_{e} to be expected in nominal operation. We present most of our results as a function of bunch intensity N_{b}, and we provide a tentative explanation for a curious non-monotonic behavior of n_{e} as a function of N_{b}. We explore ...
In studies with positron beams in the Advanced Photon Source, a dramatic amplification was observ... more In studies with positron beams in the Advanced Photon Source, a dramatic amplification was observed in the electron cloud for certain bunch current and bunch spacings. In modeling presented previously, we found qualitative agreement with the observed beam-induced multipacting condition, provided reasonable values were chosen for the secondary electron yield parameters, including the energy distribution. In this paper, we model and discuss the build-up and saturation process observed over long bunch trains at the resonance condition. Understanding this saturation mechanism in more detail may have implications for predicting electron cloud amplification, multipacting, and instabilities in future rings.
We present recent simulation results for the main features of the electron cloud in the storage r... more We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code.
Proceedings of the 2005 Particle Accelerator Conference
We present initial results for the self-consistent beamcloud dynamics simulations for a sample LH... more We present initial results for the self-consistent beamcloud dynamics simulations for a sample LHC beam, using a newly developed set of modeling capability based on a merge [1] of the three-dimensional parallel Particle-In-Cell (PIC) accelerator code WARP [2] and the electron-cloud code POSINST . Although the storage ring model we use as a test bed to contain the beam is much simpler and shorter than the LHC, its lattice elements are realistically modeled, as is the beam and the electron cloud dynamics. The simulated mechanisms for generation and absorption of the electrons at the walls are based on previously validated models available in POSINST .
Lawrence Berkeley National Laboratory, Jun 19, 2002
We present an update of computer simulation results for some features of the electron cloud at th... more We present an update of computer simulation results for some features of the electron cloud at the Large Hadron Collider (LHC) and recent simulation results for the Super Proton Synchrotron (SPS). We focus on the sensitivity of the power deposition on the LHC beam screen to the emitted electron spectrum, which we study by means of a refined secondary electron (SE) emission model recently included in our simulation code.
Lawrence Berkeley National Laboratory, Jul 8, 2002
We present recent simulation results for the main features of the electron cloud in the storage r... more We present recent simulation results for the main features of the electron cloud in the storage ring of the Spallation Neutron Source (SNS) at Oak Ridge, and updated results for the Proton Storage Ring (PSR) at Los Alamos. In particular, a complete refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has been included in the simulation code.
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Papers by Miguel Furman