The Experts below are selected from a list of 5928 Experts worldwide ranked by ideXlab platform
F Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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modelling the interaction of Electron Clouds and microwaves
International Conference on Electromagnetics in Advanced Applications, 2012Co-Authors: Eden Sorolla, F Zimmermann, Michael MattesAbstract:This paper deals with the interaction of Electron Clouds with microwaves inside beam-pipes like the one of the LHC in CERN. The details of the model and recent results are presented during the conference.
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interactions of microwaves and Electron Clouds
2009Co-Authors: Friedhelm Caspers, F ZimmermannAbstract:The modification of microwave signals passing through an Electron cloud can be used as a diagnostic tool for detecting its presence and as a measure for its effective density. This observation method was demonstrated in pioneering measurements at the CERN SPS in 2003 with protons and at PEP-II in 2006 with positron beams in the particle accelerator field. Results and applications of this technique are discussed as well as limitations and possible difficulties. A strong enhancement of the Electron related signals due to cyclotron resonance is theoretically predicted and has been observed in different machines. The application of this method can also be extended to space applications and to plasma physics where microwave diagnostics is known and used since many years. The dynamics of Electron-cloud behavior in strong RF and microwave fields will be addressed. An Electron cloud may also emit microwaves itself, either incoherently or coherently, and the intensity of this emission depends on external parameters such as the electrical bias field and resonator frequencies such as trapped modes resonances in a beam-pipe.
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space charge and Electron Clouds issues
2007Co-Authors: G Franchetti, G Rumolo, I Hofmann, M Giovannozzi, E Shaposhnikova, T Linnecar, Gianluigi Arduini, E Benedetto, E Metral, F ZimmermannAbstract:We present here the relevant space charge issues for long-term beam storage. The impact on the choice of the working point along with the prediction of the beam loss is discussed for the example of the SIS100. We present a first estimate on the effect of self consistency and discuss the equivalence of space charge, and Electron Clouds induced ”quasi” incoherent effect.
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incoherent effects of Electron Clouds in proton storage rings
Physical Review Letters, 2006Co-Authors: G Franchetti, E Benedetto, F ZimmermannAbstract:Electron Clouds in the beam pipe of high-energy proton or positron storage rings can give rise to significant incoherent emittance growth, at densities far below the coherent-instability threshold. We identify two responsible mechanisms: namely, (1) a beam particle periodically crosses a resonance and (2) a beam particle periodically crosses a region of the bunch where its motion is linearly unstable. Formation of halo or beam-core blow up, respectively, are the result. Key ingredients for both processes are synchrotron motion and Electron-induced tune shift. The mechanisms considered provide a possible explanation for reduced beam lifetime and emittance growth observed at several operating accelerators. Similar phenomena are likely to occur in other two-stream systems.
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maps for Electron Clouds application to lhc
2006Co-Authors: T Demma, G Rumolo, Stefania Petracca, F Ruggiero, F ZimmermannAbstract:In this communication we show that the cubic map formalism introduced in [1] to model Electron cloud in RHIC is also reliable in the range of typical LHC parameters.
P A Seidl - One of the best experts on this subject based on the ideXlab platform.
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self consistent simulations of heavy ion beams interacting with Electron Clouds
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: J L Vay, M A Furman, P A Seidl, R H Cohen, A Friedman, D P Grote, Kireeff M Covo, A W Molvik, Peter Stoltz, Seth VeitzerAbstract:Electron-Clouds and rising desorbed gas pressure limit the performance of many existing accelerators and, potentially, that of future accelerators including heavy-ion warm-dense matter and fusion drivers. For the latter, self-consistent simulation of the interaction of the heavy-ion beam(s) with the Electron-cloud is necessary. To this end, we have merged the two codes WARP (HIF accelerator code) and POSINST (high-energy e-cloud build-up code), and added modules for neutral gas molecule generation, gas ionization, and Electron tracking algorithms in magnetic fields with large time steps. The new tool is being benchmarked against the High-Current Experiment (HCX) and good agreement has been achieved. The simulations have also aided diagnostic interpretation and have identified unanticipated physical processes. We present the ''roadmap'' describing the different modules and their interconnections, along with detailed comparisons with HCX experimental results, as well as a preliminary application to the modeling of Electron Clouds in the Large Hadron Collider.
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simulating Electron Clouds in high current ion accelerators with solenoid focusing
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: W M Sharp, P A Seidl, R H Cohen, A Friedman, D P Grote, Jeanluc Vay, P K Roy, J E Coleman, Julien Armijo, I HaberAbstract:Contamination from Electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high-energy density physics (HEDP). These Electrons are produced directly by beam ions hitting lattice elements and intercepting diagnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the solenoid transport experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to include the physics needed to simulate Electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and Electrons.
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simulating Electron Clouds in high current ion accelerators with solenoid focusing
Lawrence Berkeley National Laboratory, 2006Co-Authors: W M Sharp, P A Seidl, R H Cohen, A Friedman, D P Grote, Jeanluc Vay, P K Roy, J E Coleman, Julien Armijo, I HaberAbstract:HIFAN 1539 LBNL-61683 Simulating Electron Clouds in High-Current Ion Accelerators with Solenoid Focusing* W. M. Sharp, D. P. Grote, R. H. Cohen, A. Friedman Lawrence Livermore National Laboratory J.-L. Vay, P. A. Seidl, P. K. Roy, J. E. Coleman, J. Armijo Lawrence Berkeley National Laboratory I. Haber University of Maryland, College Park abstract Contamination from Electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high- energy-density physics (HEDP). These Electrons are produced directly by beam ions hitting lattice elements and intercepting disgnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the Solenoid Transport Experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to included the physics needed to simulate Electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and Electrons. 1. Introduction The Solenoid Transport Experiment (STX) is a scaled experiment to study emittance and envelope characteristics of a space-charge-dominated ion beam confined transversely by solenoids [1]. An important aspect of this project is determining how the beam transverse emittance and envelope parameters evolve during solenoid transport, and how these parameters are affected by stray Electrons in the system. The expectation is that a comparison of STX results with findings from the High-Current Experiment (HCX) will guide the choice of the transport lattice for projected experiments in High-Energy Density Physics (HEDP) and Heavy-Ion Fusion (HIF). The STX is presently undergoing commissioning, with two of the planned four solenoids being tested. The remaining solenoids will be added during the remainder of FY2006. The two-solenoid layout consists of a 300 kV diode producing a K + beam with a 0.3 mm-mrad emittance, a pair of 2.5-T solenoids, each 51.1 cm in length and separated by 8.9 cm, and last, a box with intercepting diagnostics to characterize the beam. Negatively biased rings or “traps” are situated at both ends of the solenoids to restrict Electron movement toward the source, and an aperture plate may be inserted midway along the upstream trap to reduce beam current by about half. To date, the beam has been characterized by placing the diagnostics box in three locations: (1) immediately after the aperture and first Electron trap, without the solenoids in place, (2) immediately after the second solenoid, with the second Electron trap placed partly inside the last solenoid, and (3) 29 cm beyond the last solenoid. Characterization of the beam in the first configuration, without solenoids and with a 1-cm-radius aperture plate in place, shows a 25 mA flattop of the beam that continues for about 10 µs, and slit-plate scans verify that the transverse emittance is about 14 mm-mrad. With the aperture removed, the current is 45 mA, and the emittance, 22 mm-mrad. A diagnostic measurement that is used repeatedly in the work reported here is the current from the final Electron trap to ground through a 50-Ω resistor when a slit plate intercepts the beam 5-10 mm beyond the trap. The trap current in the case without solenoids is exactly what is expected. There is an initial positive current pulse of about 50 mA, balancing the image charge as the beam head enters the Electron trap, followed by a gradually increasing positive current and finally a second capacitive pulse as the beam tail leaves the trap. The
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new simulation capabilities of Electron Clouds in ion beams withlarge tune depression
39th ICFA Advanced Beam Dynamics Workshop HighIntensity High Brightness Hadron Beams HB2006 EPOCHAL InternationalCongress Center Tsukuba Japan May 29-, 2006Co-Authors: J L Vay, P A Seidl, R H Cohen, A Friedman, D P Grote, A W Molvik, Seth Veitzer, M Kireeffcovo, P H Stoltz, J P VerboncoeurAbstract:The authors have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and Electron Clouds (e-Clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D ''slice'' e-cloud code POSINST, as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new ''drift-Lorentz'' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with Electron Clouds in the High-Current Experiment (HCX). They describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-Clouds in the Large Hadron Collider (LHC).
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new experimental measurements of Electron Clouds in ion beams with large tune depression
Presented at: 39th ICFA Advanced Beam Dynamics Workshop High Intensity Highh Brightness Hadron Beams (HB2006) Tsukuba Japan May 29 - Jun 02 2006, 2006Co-Authors: A W Molvik, P A Seidl, R H Cohen, A Friedman, F M Bieniosek, M K Covo, C Leister, J L VayAbstract:We study Electron Clouds in high perveance beams (K = 8E-4) with a large tune depression of 0.2 (defined as the ratio of a single particle oscillation response to the applied focusing fields, with and without space charge). These 1 MeV, 180 mA, K+ beams have a beam potential of +2 kV when Electron Clouds are minimized. Simulation results are discussed in a companion paper [J-L. Vay, this Conference]. We have developed the first diagnostics that quantitatively measure the accumulation of Electrons in a beam [1]. This, together with measurements of Electron sources, will enable the Electron particle balance to be measured, and Electron-trapping efficiencies determined. We, along with colleagues from GSI and CERN, have also measured the scaling of gas desorption with beam energy and dE/dx [2]. Experiments where the heavy-ion beam is transported with solenoid magnetic fields, rather than with quadrupole magnetic or electrostatic fields, are being initiated. We will discuss initial results from experiments using electrode sets (in the middle and at the ends of magnets) to either expel or to trap Electrons within the magnets. We observe Electron oscillations in the last quadrupole magnet when we flood the beam with Electrons from an end wall. These oscillations, of order 10 MHz, are observed to grow from the center of the magnet while drifting upstream against the beam, in good agreement with simulations.
R H Cohen - One of the best experts on this subject based on the ideXlab platform.
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self consistent simulations of heavy ion beams interacting with Electron Clouds
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: J L Vay, M A Furman, P A Seidl, R H Cohen, A Friedman, D P Grote, Kireeff M Covo, A W Molvik, Peter Stoltz, Seth VeitzerAbstract:Electron-Clouds and rising desorbed gas pressure limit the performance of many existing accelerators and, potentially, that of future accelerators including heavy-ion warm-dense matter and fusion drivers. For the latter, self-consistent simulation of the interaction of the heavy-ion beam(s) with the Electron-cloud is necessary. To this end, we have merged the two codes WARP (HIF accelerator code) and POSINST (high-energy e-cloud build-up code), and added modules for neutral gas molecule generation, gas ionization, and Electron tracking algorithms in magnetic fields with large time steps. The new tool is being benchmarked against the High-Current Experiment (HCX) and good agreement has been achieved. The simulations have also aided diagnostic interpretation and have identified unanticipated physical processes. We present the ''roadmap'' describing the different modules and their interconnections, along with detailed comparisons with HCX experimental results, as well as a preliminary application to the modeling of Electron Clouds in the Large Hadron Collider.
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simulating Electron Clouds in high current ion accelerators with solenoid focusing
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: W M Sharp, P A Seidl, R H Cohen, A Friedman, D P Grote, Jeanluc Vay, P K Roy, J E Coleman, Julien Armijo, I HaberAbstract:Contamination from Electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high-energy density physics (HEDP). These Electrons are produced directly by beam ions hitting lattice elements and intercepting diagnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the solenoid transport experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to include the physics needed to simulate Electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and Electrons.
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simulating Electron Clouds in high current ion accelerators with solenoid focusing
Lawrence Berkeley National Laboratory, 2006Co-Authors: W M Sharp, P A Seidl, R H Cohen, A Friedman, D P Grote, Jeanluc Vay, P K Roy, J E Coleman, Julien Armijo, I HaberAbstract:HIFAN 1539 LBNL-61683 Simulating Electron Clouds in High-Current Ion Accelerators with Solenoid Focusing* W. M. Sharp, D. P. Grote, R. H. Cohen, A. Friedman Lawrence Livermore National Laboratory J.-L. Vay, P. A. Seidl, P. K. Roy, J. E. Coleman, J. Armijo Lawrence Berkeley National Laboratory I. Haber University of Maryland, College Park abstract Contamination from Electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high- energy-density physics (HEDP). These Electrons are produced directly by beam ions hitting lattice elements and intercepting disgnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the Solenoid Transport Experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to included the physics needed to simulate Electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and Electrons. 1. Introduction The Solenoid Transport Experiment (STX) is a scaled experiment to study emittance and envelope characteristics of a space-charge-dominated ion beam confined transversely by solenoids [1]. An important aspect of this project is determining how the beam transverse emittance and envelope parameters evolve during solenoid transport, and how these parameters are affected by stray Electrons in the system. The expectation is that a comparison of STX results with findings from the High-Current Experiment (HCX) will guide the choice of the transport lattice for projected experiments in High-Energy Density Physics (HEDP) and Heavy-Ion Fusion (HIF). The STX is presently undergoing commissioning, with two of the planned four solenoids being tested. The remaining solenoids will be added during the remainder of FY2006. The two-solenoid layout consists of a 300 kV diode producing a K + beam with a 0.3 mm-mrad emittance, a pair of 2.5-T solenoids, each 51.1 cm in length and separated by 8.9 cm, and last, a box with intercepting diagnostics to characterize the beam. Negatively biased rings or “traps” are situated at both ends of the solenoids to restrict Electron movement toward the source, and an aperture plate may be inserted midway along the upstream trap to reduce beam current by about half. To date, the beam has been characterized by placing the diagnostics box in three locations: (1) immediately after the aperture and first Electron trap, without the solenoids in place, (2) immediately after the second solenoid, with the second Electron trap placed partly inside the last solenoid, and (3) 29 cm beyond the last solenoid. Characterization of the beam in the first configuration, without solenoids and with a 1-cm-radius aperture plate in place, shows a 25 mA flattop of the beam that continues for about 10 µs, and slit-plate scans verify that the transverse emittance is about 14 mm-mrad. With the aperture removed, the current is 45 mA, and the emittance, 22 mm-mrad. A diagnostic measurement that is used repeatedly in the work reported here is the current from the final Electron trap to ground through a 50-Ω resistor when a slit plate intercepts the beam 5-10 mm beyond the trap. The trap current in the case without solenoids is exactly what is expected. There is an initial positive current pulse of about 50 mA, balancing the image charge as the beam head enters the Electron trap, followed by a gradually increasing positive current and finally a second capacitive pulse as the beam tail leaves the trap. The
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new simulation capabilities of Electron Clouds in ion beams withlarge tune depression
39th ICFA Advanced Beam Dynamics Workshop HighIntensity High Brightness Hadron Beams HB2006 EPOCHAL InternationalCongress Center Tsukuba Japan May 29-, 2006Co-Authors: J L Vay, P A Seidl, R H Cohen, A Friedman, D P Grote, A W Molvik, Seth Veitzer, M Kireeffcovo, P H Stoltz, J P VerboncoeurAbstract:The authors have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and Electron Clouds (e-Clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D ''slice'' e-cloud code POSINST, as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new ''drift-Lorentz'' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with Electron Clouds in the High-Current Experiment (HCX). They describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-Clouds in the Large Hadron Collider (LHC).
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new experimental measurements of Electron Clouds in ion beams with large tune depression
Presented at: 39th ICFA Advanced Beam Dynamics Workshop High Intensity Highh Brightness Hadron Beams (HB2006) Tsukuba Japan May 29 - Jun 02 2006, 2006Co-Authors: A W Molvik, P A Seidl, R H Cohen, A Friedman, F M Bieniosek, M K Covo, C Leister, J L VayAbstract:We study Electron Clouds in high perveance beams (K = 8E-4) with a large tune depression of 0.2 (defined as the ratio of a single particle oscillation response to the applied focusing fields, with and without space charge). These 1 MeV, 180 mA, K+ beams have a beam potential of +2 kV when Electron Clouds are minimized. Simulation results are discussed in a companion paper [J-L. Vay, this Conference]. We have developed the first diagnostics that quantitatively measure the accumulation of Electrons in a beam [1]. This, together with measurements of Electron sources, will enable the Electron particle balance to be measured, and Electron-trapping efficiencies determined. We, along with colleagues from GSI and CERN, have also measured the scaling of gas desorption with beam energy and dE/dx [2]. Experiments where the heavy-ion beam is transported with solenoid magnetic fields, rather than with quadrupole magnetic or electrostatic fields, are being initiated. We will discuss initial results from experiments using electrode sets (in the middle and at the ends of magnets) to either expel or to trap Electrons within the magnets. We observe Electron oscillations in the last quadrupole magnet when we flood the beam with Electrons from an end wall. These oscillations, of order 10 MHz, are observed to grow from the center of the magnet while drifting upstream against the beam, in good agreement with simulations.
A Friedman - One of the best experts on this subject based on the ideXlab platform.
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self consistent simulations of heavy ion beams interacting with Electron Clouds
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: J L Vay, M A Furman, P A Seidl, R H Cohen, A Friedman, D P Grote, Kireeff M Covo, A W Molvik, Peter Stoltz, Seth VeitzerAbstract:Electron-Clouds and rising desorbed gas pressure limit the performance of many existing accelerators and, potentially, that of future accelerators including heavy-ion warm-dense matter and fusion drivers. For the latter, self-consistent simulation of the interaction of the heavy-ion beam(s) with the Electron-cloud is necessary. To this end, we have merged the two codes WARP (HIF accelerator code) and POSINST (high-energy e-cloud build-up code), and added modules for neutral gas molecule generation, gas ionization, and Electron tracking algorithms in magnetic fields with large time steps. The new tool is being benchmarked against the High-Current Experiment (HCX) and good agreement has been achieved. The simulations have also aided diagnostic interpretation and have identified unanticipated physical processes. We present the ''roadmap'' describing the different modules and their interconnections, along with detailed comparisons with HCX experimental results, as well as a preliminary application to the modeling of Electron Clouds in the Large Hadron Collider.
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simulating Electron Clouds in high current ion accelerators with solenoid focusing
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007Co-Authors: W M Sharp, P A Seidl, R H Cohen, A Friedman, D P Grote, Jeanluc Vay, P K Roy, J E Coleman, Julien Armijo, I HaberAbstract:Contamination from Electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high-energy density physics (HEDP). These Electrons are produced directly by beam ions hitting lattice elements and intercepting diagnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the solenoid transport experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to include the physics needed to simulate Electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and Electrons.
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simulating Electron Clouds in high current ion accelerators with solenoid focusing
Lawrence Berkeley National Laboratory, 2006Co-Authors: W M Sharp, P A Seidl, R H Cohen, A Friedman, D P Grote, Jeanluc Vay, P K Roy, J E Coleman, Julien Armijo, I HaberAbstract:HIFAN 1539 LBNL-61683 Simulating Electron Clouds in High-Current Ion Accelerators with Solenoid Focusing* W. M. Sharp, D. P. Grote, R. H. Cohen, A. Friedman Lawrence Livermore National Laboratory J.-L. Vay, P. A. Seidl, P. K. Roy, J. E. Coleman, J. Armijo Lawrence Berkeley National Laboratory I. Haber University of Maryland, College Park abstract Contamination from Electrons is a concern for the solenoid-focused ion accelerators being developed for experiments in high- energy-density physics (HEDP). These Electrons are produced directly by beam ions hitting lattice elements and intercepting disgnostics, or indirectly by ionization of desorbed neutral gas, and they are believed responsible for time dependence of the beam radius, emittance, and focal distance seen on the Solenoid Transport Experiment (STX) at Lawrence Berkeley National Laboratory. The electrostatic particle-in-cell code WARP has been upgraded to included the physics needed to simulate Electron-cloud phenomena. We present preliminary self-consistent simulations of STX experiments suggesting that the observed time dependence of the beam stems from a complicated interaction of beam ions, desorbed neutrals, and Electrons. 1. Introduction The Solenoid Transport Experiment (STX) is a scaled experiment to study emittance and envelope characteristics of a space-charge-dominated ion beam confined transversely by solenoids [1]. An important aspect of this project is determining how the beam transverse emittance and envelope parameters evolve during solenoid transport, and how these parameters are affected by stray Electrons in the system. The expectation is that a comparison of STX results with findings from the High-Current Experiment (HCX) will guide the choice of the transport lattice for projected experiments in High-Energy Density Physics (HEDP) and Heavy-Ion Fusion (HIF). The STX is presently undergoing commissioning, with two of the planned four solenoids being tested. The remaining solenoids will be added during the remainder of FY2006. The two-solenoid layout consists of a 300 kV diode producing a K + beam with a 0.3 mm-mrad emittance, a pair of 2.5-T solenoids, each 51.1 cm in length and separated by 8.9 cm, and last, a box with intercepting diagnostics to characterize the beam. Negatively biased rings or “traps” are situated at both ends of the solenoids to restrict Electron movement toward the source, and an aperture plate may be inserted midway along the upstream trap to reduce beam current by about half. To date, the beam has been characterized by placing the diagnostics box in three locations: (1) immediately after the aperture and first Electron trap, without the solenoids in place, (2) immediately after the second solenoid, with the second Electron trap placed partly inside the last solenoid, and (3) 29 cm beyond the last solenoid. Characterization of the beam in the first configuration, without solenoids and with a 1-cm-radius aperture plate in place, shows a 25 mA flattop of the beam that continues for about 10 µs, and slit-plate scans verify that the transverse emittance is about 14 mm-mrad. With the aperture removed, the current is 45 mA, and the emittance, 22 mm-mrad. A diagnostic measurement that is used repeatedly in the work reported here is the current from the final Electron trap to ground through a 50-Ω resistor when a slit plate intercepts the beam 5-10 mm beyond the trap. The trap current in the case without solenoids is exactly what is expected. There is an initial positive current pulse of about 50 mA, balancing the image charge as the beam head enters the Electron trap, followed by a gradually increasing positive current and finally a second capacitive pulse as the beam tail leaves the trap. The
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new simulation capabilities of Electron Clouds in ion beams withlarge tune depression
39th ICFA Advanced Beam Dynamics Workshop HighIntensity High Brightness Hadron Beams HB2006 EPOCHAL InternationalCongress Center Tsukuba Japan May 29-, 2006Co-Authors: J L Vay, P A Seidl, R H Cohen, A Friedman, D P Grote, A W Molvik, Seth Veitzer, M Kireeffcovo, P H Stoltz, J P VerboncoeurAbstract:The authors have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and Electron Clouds (e-Clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D ''slice'' e-cloud code POSINST, as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new ''drift-Lorentz'' particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with Electron Clouds in the High-Current Experiment (HCX). They describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-Clouds in the Large Hadron Collider (LHC).
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new experimental measurements of Electron Clouds in ion beams with large tune depression
Presented at: 39th ICFA Advanced Beam Dynamics Workshop High Intensity Highh Brightness Hadron Beams (HB2006) Tsukuba Japan May 29 - Jun 02 2006, 2006Co-Authors: A W Molvik, P A Seidl, R H Cohen, A Friedman, F M Bieniosek, M K Covo, C Leister, J L VayAbstract:We study Electron Clouds in high perveance beams (K = 8E-4) with a large tune depression of 0.2 (defined as the ratio of a single particle oscillation response to the applied focusing fields, with and without space charge). These 1 MeV, 180 mA, K+ beams have a beam potential of +2 kV when Electron Clouds are minimized. Simulation results are discussed in a companion paper [J-L. Vay, this Conference]. We have developed the first diagnostics that quantitatively measure the accumulation of Electrons in a beam [1]. This, together with measurements of Electron sources, will enable the Electron particle balance to be measured, and Electron-trapping efficiencies determined. We, along with colleagues from GSI and CERN, have also measured the scaling of gas desorption with beam energy and dE/dx [2]. Experiments where the heavy-ion beam is transported with solenoid magnetic fields, rather than with quadrupole magnetic or electrostatic fields, are being initiated. We will discuss initial results from experiments using electrode sets (in the middle and at the ends of magnets) to either expel or to trap Electrons within the magnets. We observe Electron oscillations in the last quadrupole magnet when we flood the beam with Electrons from an end wall. These oscillations, of order 10 MHz, are observed to grow from the center of the magnet while drifting upstream against the beam, in good agreement with simulations.
K Ohmi - One of the best experts on this subject based on the ideXlab platform.
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Simulation of the synchro-betatron sideband instability caused by Electron Clouds at KEKB
2007 IEEE Particle Accelerator Conference (PAC), 2007Co-Authors: E Benedetto, J W Flanagan, K OhmiAbstract:Electron Clouds cause a fast head-tail instability above a threshold density. Experiments at KEKB revealed the presence of a synchro-betatron sideband above the beam blow-up threshold, which indicates the presence of the head-tail instability. The sideband appears near nuy + knus, where 1 < k < 2, which differs from ordinary instability seen near nuy - nus. We study the origin of the sideband using a computer simulation.
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Betatron Sidebands due to Electron Clouds Under Colliding Beam Conditions
Proceedings of the 2005 Particle Accelerator Conference, 2005Co-Authors: J W Flanagan, K Ohmi, H Fukuma, S Hiramatsu, M Tobiyama, Y. Funakoshi, H. Ikeda, S. Uehara, S. Uno, E A PerevedentsevAbstract:Recently, we have observed vertical betatron sidebands in the transverse beam spectra of positron bunches at the KEKB LER which are associated with the presence of Electron Clouds.[1] When the LER is operating in single-beam mode (no colliding bunches in the HER), these sidebands are sharply peaked. When the bunches are in collision for physics running, the sidebands are still present but are found to be smeared out. The bunch-by-bunch specific luminosity is lower for bunches with sidebands than for those without sidebands. In this paper, the behavior of the sidebands in collision and the effects on luminosity are discussed.
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observation of vertical betatron sideband due to Electron Clouds in the kekb low energy ring
Physical Review Letters, 2005Co-Authors: J W Flanagan, K Ohmi, H Fukuma, S Hiramatsu, M Tobiyama, E A PerevedentsevAbstract:The effects of Electron Clouds on positively charged beams have been an active area of research in recent years at particle accelerators around the world. Transverse beam-size blowup due to Electron Clouds has been observed in some machines and is considered to be a major limiting factor in the development of higher-current, higher-luminosity Electron-positron colliders. The leading proposed mechanism for beam blowup is the excitation of a fast head-tail instability due to short-range wakes within the Electron cloud. We present here observations of betatron oscillation sidebands in bunch-by-bunch spectra that may provide direct evidence of such head-tail motion in a positron beam.
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head tail instability caused by Electron Clouds in positron storage rings
Physical Review Letters, 2000Co-Authors: K Ohmi, F ZimmermannAbstract:In positron or proton storage rings with many closely spaced bunches, a large number of Electrons can be generated in the vacuum chamber due to photoemission or secondary emission. The density of this ‘Electron cloud’ increases along a bunch train, until the growth saturates under the influence of its own space charge field. In this report, we discuss the possibility of a single-bunch two-stream instability driven by the Electron cloud, where any initial head-tail perturbation of the bunch is amplified by the coherent motion of cloud Electrons near the beam. Depending on the strength of the beam-Electron interaction, the chromaticity and the synchrotron oscillation frequency, this instability either resembles a linac beam break up, or a head-tail instability. We present computer simulations of beam break up and headtail instabilities for the Low Energy Ring of the KEK B factory, and compare the simulation results with analytical estimates.