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| MOBP03 | Upgrade of BNL Accelerator Facility | luminosity, ion, proton, heavy-ion | 29 | ||
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A number of upgrades are planned for the Brookhaven accelerator facility that is primarily made of RHIC and its injector, the AGS. The RHIC luminosity and proton polarization are to evolve towards the Enhanced Design parameters by 2008. A new Electron Beam Ion Source is under development, and commissioning is expected in 2009. The aim of the RHIC II upgrade is to increase the heavy ion luminosity by an order of magnitude, through electron cooling in store. With the addition of an electron ring, the high-luminosity electron-ion collider proposal eRHIC can be realized. Studies have also been done for a new injector to the AGS replacing the present Booster for an upgrade of the beam average power to 1 MW at 28 GeV. The new injector to match the AGS repetition rate can be either a 1.5-GeV SCL or a FFAG accelerator. With the upgrade of the injector complex, neutrino superbeams could be produced.
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| MOCP04 | LHC Upgrade Options and CARE-HHH Activities | luminosity, simulation, dipole, quadrupole | 49 | ||
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The European Accelerator Network on High Energy High Intensity Hadron Beams (CARE HHH) is developing scenarios for luminosity and energy upgrades of the Large Hadron Collider (LHC). The LHC upgrade options under consideration differ in terms of beam parameters, electron-cloud effects, beam-beam compensation, use of crab cavities, and interaction-region layout. Complementary investigations concern injector upgrades, novel magnet technologies, advanced collimation schemes, and ultimate intensity limitations. Flanking these upgrade studies, an accelerator-physics code web repository has been set up, and an extensive simulation-code benchmarking campaign is being prepared.
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| TUAX01 | Accumulation of High Intensity Beam and First Observations of Instabilities in the SNS Accumulator Ring* | impedance, kicker, extraction, lattice | 59 | ||
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The Spallation Neutron Source accumulator ring, designed to accumulate up to 1.5·1014 protons per pulse, was commissioned in January of 2006. During the run, over 1.·1014 protons were accumulated in the ring in the natural chromaticity state without any sign of instabilities. The first beam instabilities were observed for a high intensity coasting beam with zero chromaticity. Preliminary analysis of data indicates instabilities related to extraction kicker impedances, and electron-proton instability. Here we review the background theory and design philosophy of the ring, as it relates to instabilities, and compare the pre-commissioning predictions with the experimental measurements.
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| TUAX03 | Beam loss, emittance growth and halo formation due to the pinched electron cloud | emittance, simulation, synchrotron, resonance | 84 | ||
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Electron cloud can cause beam losses and emittance growth in proton or positron storage rings. If the electron density exceeds a certain threshold value, a strong head-tail instability manifests itself, characterized by a rapid beam-size blow-up with a rise time comparable to the synchrotron period. However, even for densities below the coherent-instability threshold, the electron-cloud can give rise to a significant emittance growth. We identified the mechanism for this incoherent growth as one caused by the combined effect of the beam particles synchrotron motion and the longitudinal variation of the tune shift, which is proportional to the pinched electron-cloud distribution along the bunch. This can give rise to the periodic crossing of a resonance, in analogy to halo formation in space-charge dominated beams, or eventually, if the tune shift is sufficiently large, to the crossing of bunch regions where the single-particle motion is linearly unstable.
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| TUAX04 | Test of a prototype active damping system for the e-p instability at the LANL PSR | feedback, damping, kicker, impedance | 94 | ||
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Our collaboration from LANL, SNS, LBNL and SLAC has developed and successfully tested a prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold (as measured by the RF buncher voltage) by ~30%. Beam leakage into the gap at lower RF buncher voltage and resulting higher growth rates from more trapped electrons is the likely cause of this limitation. We will describe the system configuration and results of several experimental tests of system performance. We will also discuss our studies and analysis of the factors limiting system performance.
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| TUAX05 | Studies of e-cloud build up for the FNAL main injector and for the LHC | dipole, simulation, cryogenics, injection | 102 | ||
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We present a summary of recent simulation studies of the electron-cloud (EC) build-up for the FNAL Main Injector and for the LHC. In the first case we pay particular attention to the dependence on bunch intensity (Nb) at injection energy, and we focus on the dipole magnets and field-free regions. The saturated value of the average EC density shows a clear threshold in Nb beyond which the beam will be approximately neutralized on average. For the case of the LHC we limit our discussion to arc dipoles at collision energy, and bunch spacings tb=25 ns or tb=75 ns. The main variables exercised in this study are Nb and the peak value of the secondary emission yield (dmax). For tb=25 ns we conclude that the EC power deposition is comfortably below the available cooling capacity of the cryogenic system if dmax is below ~1.2 at nominal Nb. For tb=75 ns, the EC power deposition is insignificant. As a byproduct of this exercise, we reach a detailed understanding of the significant role played by the backscattered secondary electrons.
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| TUAX06 | Electron cloud and single-bunch instabilities in the Relativistic Heavy Ion Collider | beam-losses, vacuum, emittance, ion | 117 | ||
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Electron cloud is one of the leading mechanisms that limit the performance of high intensity circular accelerators and colliders. Electron cloud in RHIC is in an intermediate regime sharing features of both the long-bunch (PSR) and short-bunch (photon factories) machines. Vacuum-pressure rises, transverse tune shifts, and electron flux are observed at injection, upon transition crossing, and at top energy. Transverse emittance growth, fast instabilities, and beam loss also occur upon transition crossing. Mitigation measures are implemented both to reduce the production of electron cloud and to control the beam stability. This paper summarizes the observation and initial analysis of the electron-cloud effects at RHIC.
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| TUAZ01 | Overview of recent halo diagnosis and non-destructive beam profile monitoring | synchrotron, laser, diagnostics, radiation | 54 | ||
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Beam profile (emittance) and beam halo are characteristic properties of high-intensity and high energy beams that might limit the performance of the adjacent accelerator. Therefore a reliable measurement and determination of these parameters is most helpful for understanding, tuning and improvement of the whole accelerator chain to achieve the best (at least the design-) performance. This talk will give an overview over recent instruments used for non-destructive beam profile and halo monitoring and will discuss their limits, experiences and latest improvements.
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| TUAZ05 | Comparison of Graphite and Diamond Structured Carbon Stripper Foils under Operational Conditions at the Los Alamos PSR | proton, injection, radiation, beam-losses | 112 | ||
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In the Los Alamos Proton Storage Ring H–Ions merge with circulating protons in a bending magnet and are stripped of their two electrons in a carbon stripper foil. The circulating protons continue to interact with the foil. Despite efforts to minimize the number of these foil hits, like “painting” of the vertical phase space, they can not totally be eliminated. As a result foil heating and radiation damage limit the lifetime of these foils. In recent years LANL has collaborated with KEK to improve the graphite foils in use at PSR and these foils now last typically for two months. Recently an alternative in the form of diamond structured carbon foils has been proposed for use at SNS. Depending on the grain size these are referred to as microcrystalline or nanocrystalline foils. Both types have been tested in PSR, with quite different results. While the microcrystalline foil failed catastrophically before production beam currents were reached the nanocrystalline foil was successfully used in normal operation for several weeks. Advantages of the diamond foil concept as well as some noteworthy differences that we observed with respect to the LANL graphite foils will be discussed here.
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| TUBZ01 | The Beam Diagnostics System for J-PARC Synchrotrons | proton, injection, beam-losses, pick-up | 128 | ||
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The beam diagnostics system for J-PARC synchrotrons (RCS and MR) will be presented. The design of the system will be described for high current machines. Some test results will be reported.
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| WEAX03 | Space charge neutralization and its dynamic effects | space-charge, linac, simulation, proton | 187 | ||
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High-power accelerators are being studied for several projects including accelerator driven neutron or neutrino sources. The low energy part of these facilities has to be carefully optimized to match the beam requirements of the higher energy parts. In this low energy part, the space charge self force, induced by a high intensity beam, has to be carefully controlled. This nonlinear force can generate a large and irreversible emittance growth of the beam. To reduce the space charge (SC), neutralization of the beam charge can be done by capturing some particles of the ionised residual gas in the vacuum chamber. This space charge compensation (SCC) regime complicates the beam dynamics study. This contribution aims to modelize the beam behavior in such a regime and to give order of magnitude to the linac designer for the neutralization rise time and the induced emittance growth.
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| WEAY01 | New advances in beam cooling | ion, storage-ring, beam-cooling, antiproton | 162 | ||
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New developments in beam cooling since ICFA’2004 seminar are presented with concentration on trends in electron cooling, stochastic cooling, muon cooling and beam crystallization - the trends, which, as one can expect, will mark the future in the cooling methods applications.
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Keywords: particle storage rings, cooling methods, electron beam, Schottky noise. |
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| WEAY02 | Electron cooling of 8 GeV antiprotons at Fermilab’s Recycler: Results and operational implications | antiproton, emittance, extraction, beam-losses | 182 | ||
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Electron cooling of 8 GeV antiprotons at Fermilab’s Recycler storage ring is now routinely used in the collider operation. It requires a 0.1-0.5 A, 4.3 MeV DC electron beam that reduces the longitudinal phase-space of the circulating antiproton beam. This paper first describes the characteristics of the electron beam that was achieved to successfully cool antiprotons as well as its necessary stability. Then, results from various cooling force measurements along with comparison to a simple non-magnetized model will be presented. Finally, operational aspects of the implementation of electron cooling at the Recycler will be discussed, such as regulation of the cooling rate and the influence of the electron beam on the antiprotons lifetime.
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| WEAY03 | Experimental studies of stability issues at HIMAC cooler | ion, resonance, feedback, injection | 197 | ||
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We have investigated coherent transverse instability when high-density circulating-ion beam was obtained with cool-stacking injection in the HIMAC synchrotron. By using a cooled beam and the Oxygen gas-sheet beam profile monitor, further, we have observed a particle trapping in resonance crossing. We will report these experimental studies at the HIMAC synchrotron.
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| WEAY04 | Analysis of the magnetized friction force | ion, simulation, plasma, interaction-region | 210 | ||
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A comprehensive examination of theoretical models for the friction force, in use by the electron cooling community, was performed. Here, we present our insights about the models gained as a result of comparison between the friction force formulas and direct numerical simulations, as well as studies of the cooling process as a whole.
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| WEAY05 | New experimental results on electron cooling at COSY-Juelich | proton, injection, ion, scattering | 223 | ||
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Recent electron cooling results of a proton beam at COSY – Juelich are summarized. The influence of residual gas ions trapped in the electron beam on the cooled beam stability as well as methods to suppress the instabilities are described. Results on the numerical simulation for the formation of a crystalline proton beam in COSY using the BETACOOL code and results of experimental investigations of the cooling process at extremely low proton beam intensity are reported. Future plans are briefly addressed.
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| WEAZ07 | Shock wave propagation near 7 TeV proton beam in LHC collimator materials | proton, target, coupling, radiation | 241 | ||
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A study is presented to estimate the influence of the impact of a 7 TeV proton beam on the physical-mechanical material properties, such as C for collimators, and Cu elsewhere. The high energy stored in each bunch can produce a shock wave near the impacting proton beam in these materials. The theoretical model for the investigations of shock wave propagation in the collimator materials takes into account ionization, electronic excitation, and energy transfer from excited electronic subsystem in the materials to the ionic subsystem. The change of other physical properties of the material is also considered. The deposited energy is calculated with FLUKA [1]. The numerical results of the microstructure change in the material are presented for different numbers of bunches. The method allows investigating changes of density and internal pressure, the distributions of atomic and sound velocities, and the temperature profiles in electronic and ionic subsystems of materials near the front of shock wave. These results are very relevant for the understanding the behavior of collimator materials used in LHC under 7 TeV proton beam.
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[1] A. Fasso et al. The physics models of FLUKA: status and recent development, CHEP 2003, LA Jolla, California, 2003 |
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| WEBY01 | Commisioning of Electron Beam Cooling at S-LSR | ion, beam-losses, proton, feedback | 247 | ||
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S-LSR is a new compact ion cooler ring at Kyoto University. The circumference is 22.557 m. The commissioning of the electron cooling was started using the 7 MeV proton beam from November, 2005. The total length of the electron cooler is 1.63 m. In order to maximize the effective cooling length in the limited space, the magnetic field of the solenoid and the troid coils was calculated precisely by the 3D code. The electrostatic deflector for the electron and the steering magnet for the ion are placed in the troid. The performances of these devices are evaluated by the cooling measurements. Experiments using the electron cooling are also stared. One is an induction sweep cooling of the proton beam. It is an cooling with the assist of the induction acceleration and possible to reduce the cooling time of the hot ion beams like secondary particles. We also observe the behavior of the cooled ion beam in the small ion number case and the large ion number case. We discuss about the possibility of the phase transition of the proton in the former case and discuss about the coherent instability conditions in the latter case.
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| WEBZ02 | BEAM TRACKING FOR J-PARC 3 GEV RCS INJECTION | injection, septum, emittance, quadrupole | 253 | ||
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In the J-PARC 3 GeV RCS injection system, the orbit-bump magnets of large-bore are located close with each other, and the incoming beam passes through the non-linear field region of the ring quadrupole magnet. Beam behavior under these conditions is analysed by means of the Runge-Kutta method in the three dimensional magnetic field distribution. The charge exchange foil is inserted between the bump magnets. Orbit of the stripped electrons from the foil is also investigated.
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| THAW01 | New simulation capabilities of electron clouds in ion beams with large tune depression | simulation, ion, quadrupole, bunching | 279 | ||
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We 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 [M. Furman, this workshop], 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) [experimental results discussed by A. Molvik, this workshop]. We will describe the capabilities and 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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| THAW02 | New experimental measurements of electron clouds in ion beams with large tune depression* | quadrupole, ion, diagnostics, simulation | 288 | ||
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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 [M. Kireeff Covo, et al., to be submitted to Phys. Rev. Lett.]. This, together with measurements of electron sources, will enable the electron particle balance to be measured, and electron-trapping efficiencies determined. We measure and simulate ~10 MHz electron oscillations in the last quadrupole magnet when we flood the beam with electrons from an end wall. 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 the initial results using electrode sets (in the middle and at the ends of magnets) to either expel or to trap electrons within the magnets.
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| THAW03 | RF Barrier Cavity Option for the SNS Ring Beam Power Upgrade | space-charge, proton, injection, target | 298 | ||
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RF barrier cavities present an attractive option for facilitating the path to higher beam intensity in the SNS power upgrade. Barrier cavities lead to flat longitudinal current densities, thus minimizing bunch factor effects. In addition to allowing more beam to be injected in this fashion, flat current profiles may lead to increased e-p instability thresholds due to reduced multipacting during the trailing stage of the bunch. Finally, it is possible to inject self-consistent beam distributions into barrier buckets, thus providing the additional advantages of uniform transverse beam density (good for meeting target constraints) and little or no halo (good for low losses). Simulations addressing all these issues will be presented and discussed.
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| THAW04 | Experimental Characterization of the “1st Pulse” e-p Instability at the LANL PSR | accumulation, diagnostics, injection, controls | 311 | ||
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A puzzling aspect of the e-p instability at PSR is the so called “1st Pulse” instability phenomenon. It shows up on the first beam pulse after a period (10 to 30 minutes or more) of beam off time. This pulse has a significantly lower threshold than subsequent beam pulses that follow with the standard time separation. While the standard PSR operation for Lujan Center operation is unaffected by this phenomenon, it does interfere with some high intensity, single pulse experiments using PSR beam. We will summarize the present experimental data characterizing this phenomenon as compared with the typical e-p instability observed at higher repetition rates at PSR and discuss some possible explanations.
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| THAW07 | Transverse electron-antiproton instability in the Recycler Ring | coupling, ion, resonance, impedance | 334 | ||
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Lifetime degradation of electron-cooled ions was observed at several electron coolers. In the Recycler, both the lifetime drop and emittance growth of the e-cooled pbars are seen. A possible reason for that can be a coherent interaction between the electron and antiproton beams. A theoretical model of this instability is presented, and a practical recommendation for its suppression is explained and discussed.
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| THAY04 | Review of high-brightness proton and ion acceleration using pulsed lasers | proton, laser, target, ion | 319 | ||
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In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. These sources have exceptional properties, i.e. high brightness and high spectral cut-off, high directionality and laminarity, short burst duration. We have shown that for proton energies >10 MeV, the transverse and longitudinal emittance are respectively <0.004 mm-mrad and <10-4 eV-s, i.e. at least 100-fold and may be as much as 104-fold better than conventional accelerators beams. Thanks to these properties, these sources allow for example point-projection radiography with unprecedented resolution. They also open new opportunities for ion beam generation and control, and could stimulate development of compact ion accelerators for many applications. We have shown [*] that there is an optimum in the laser pulse duration of ~200 fs-1 ps, with a needed laser energy level of 30 to 100 J, in order to achieve e.g. 200 MeV energy protons. Also, as, for such applications beam control is an essential requirement, we have developed [**] an ultra-fast laser-triggered micro-lens that allows tuneable control of the beam divergence as well as energy selection.
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[*] J. Fuchs et al., Nature Physics 2, 48 (2006). |
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| THBW02 | Electron-Cloud Benchmarking & CARE-HHH Codes | simulation, emittance, vacuum, single-bunch | 350 | ||
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The state-of-the-art in code benchmarking for various types of electron-cloud simulations is reviewed. In particular, we recall possible meanings of benchmarking, summarize past and more recent code comparisons, present examples of code verifications against machine experiments, describe some remaining uncertainties, and formulate a few goals for the future. The code-benchmarking effort is supported by the CARE-HHH initiative on accelerator physics simulation codes, whose other objectives include a common web repository and the practical extension of simulation codes.
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| FRAP01 | SUMMARY OF WORKING GROUP A AND A+B+D JOINT SESSION | simulation, impedance, emittance, feedback | 358 | ||
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We summarize the presentations and discussions of the HB2006 Working Group A, devoted to beam instabilities, and of the joint session of Working Groups A, B (on space charge), and D (beam cooling and experiments). First we review the progress on conventional instabilities and impedances, and then the advances on electron cloud.
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| FRAP05 | Summary of Working Group D | ion, scattering, simulation, beam-cooling | 372 | ||
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| FRAP08 | Summary of General Working Group A+B+D with a Focus on Code Benchmarking | simulation, resonance, emittance, site | 379 | ||
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