simulation

Paper	Title	Other Keywords	Page
OPR00	Recent Studies of the Electron Cloud Induced Beam Instability at the Los Alamos PSR	accumulation, electron, linac, space-charge	1
	R. Macek, L. Rybarcyk, R. McCrady, T. Zaugg LANL J. Holmes ORNL
	Recent beam studies have focused on two aspects of the observed e-p instability at the Los Alamos Proton Storage Ring (PSR). 1) Most recently it has been observed that a stable beam with the standard production bunch width (290 ns injected beam bunch width) will become e-p unstable when the bunch width is shortened to 200 ns or less. This was not the case years earlier. Experimental characteristics and possible explanations of this recent “short pulse instability phenomenon” will be presented. 2) Other beam studies have focused on understanding the main sources and locations of electron clouds (EC), which drive the observed e-p instability. Significant EC signals are observed in drift spaces and quadrupole magnets at PSR which together cover ~65% of the ring circumference. Results making use of two longitudinal barriers to isolate the drift space electron diagnostic have provided definitive evidence that most of the drift space EC signal is “seeded” by electrons ejected longitudinally by ExB drifts from adjacent quadrupole magnets. This result can explain why weak solenoids and TiN coatings in several drifts spaces had no effect on the e-p instability threshold. Modeling of EC generation in 3D quadrupoles using a modified version of the POSINST code shows that a sizeable fraction of the electrons generated in the quadrupoles are ejected longitudinally into the adjacent drifts. The experimental findings and simulation results of this focus will be summarized.
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OPR03	Can Electron Multipacting Explain the Pressure Rise in the Cold Bore ANKA Superconducting Undulator?	electron, vacuum, undulator, photon	12
	S. Casalbuoni, S. Schleede, M. Hagelstein, D. Saez de Jauregui, P. Tavares Karlsruhe Institute of Technology
	Preliminary studies performed with the cold bore superconducting undulator installed in the ANKA (Angstrom source Karlsruhe) storage ring suggest that the beam heat load is mainly due to the electron wall bombardment. Electron bombardment can both heat the cold vacuum chamber and induce an increase in the pressure because of gas desorption. In this contribution we compare the measurements of the pressure in a cold bore performed in the electron storage ring ANKA with the predictions obtained using the equations of gas dynamic balance in a cold vacuum chamber exposed to synchrotron radiation and electron bombardment. The balance results from two competing effects: the photon and electron stimulated desorption of the gas contained in the surface layer of the chamber wall and of the gas cryosorbed, and the cryopumping by the cold surface. We show that photodesorption alone cannot explain the experimental results and that electron multipacting is needed to reproduce the observed pressure rise. Electron bombardment can at the same time explain the observed beam heat load.
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OPR05	Emittance Growth and Tune Spectra at PETRA III	emittance, electron, synchrotron, wiggler	21
	R. Wanzenberg DESY
	At DESY the PETRA ring has been converted into a synchrotron radiation facility, called PETRA III. 20 damping wigglers have been installed to achieve an emittance of 1 nm. The commissioning with beam started in April 2009 and user runs have been started in 2010. The design current is 100 mA and the bunch to bunch distance is 8 ns for one particular filling pattern with 960 bunches. At a current of about 50 mA a strong vertical emittance increase has been observed. During machine studies it was found that the emittance increase depends strongly on the bunch filling pattern. For the user operation a filling scheme has been found which mitigates the increase of the vertical emittance. In Aug. 2010 PETRA III has been operated without damping wigglers for one week. The vertical emittance growth was not significantly smaller without wigglers. Furthermore tune spectra at PETRA III show characteristic lines which have been observed at other storage rings in the connection with electron clouds. The measurements at PETRA III are presented for different bunch filling patterns and with and without wiggler magnets.
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DYN00	Feedback Control of SPS E-clouds / Transverse Mode Coupled Instabilities	feedback, controls, kicker, pick-up	50
	C. Rivetta, A. Bullitt, J. Fox, T. Mastorides, G. Ndabashimiye, M. Pivi, O. Turgut SLAC National Accelerator Laboratory R. Secondo, J. Vay LBNL W. Hofle, B. Salvant CERN
	Electron cloud driven instability can impose limitations on the maximum stored beam current in present and future accelerators. It drives inter-bunch and intra-bunch instabilities. Feedback control techniques have been proposed to mitigate transverse instabilities within a bunch as an extension of techniques used to control inter-bunch (coupled-bunch) instabilities. The US LHC Accelerator Research Program (LARP) has supported a collaboration between US labs and CERN to explore systems to mitigate E-cloud instabilities and transverse mode coupled instability (TMCI ) for the SPS and LHC machines. For intra-bunch (within a bunch) control of nanosecond scale bunch lengths the feedback channel has to be wide-band (GHz range) to be able to measure and control the vertical position of individual sections of a bunch. The design and implementation of the feedback control system involves the modeling and identification of the bunch dynamics, the design of a feedback control algorithm, and the selection of digital and analog hardware that operates in the GHz range. We present the goals of this collaboration and analyze the different research lines to implement and evaluate a full-function prototype feedback system for the SPS. We include details of the feedback system topology and technical limitations, modeling and identification of the bunch dynamics via simulators and machine measurements. We estimate the necessary control bandwidths, and complexity of the processing channel via design considerations for the control algorithm. Very initial efforts at modeling feedback control via reduced bunch models and semi-realistic feedback system specifications are presented.
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DYN02	Simulated Performance of an FIR-Based Feedback System to Control the Electron Cloud Single-Bunch Transverse Instabilities in the CERN SPS	kicker, feedback, controls, electron	56
	R. Secondo, J. Byrd, M. Furman, M. Venturini, J. Vay LBNL J. Fox, C. Rivetta SLAC National Accelerator Laboratory W. Hofle CERN
	The performance of High Energy proton machines like the SPS at CERN is affected by transverse single-bunch instabilities due to the Electron Cloud effect. In a first step to model a Feedback control system to stabilize the bunch dynamics, we use a Finite Impulse Response filter to represent the processing channel. The effect of this simplified processing channel in the bunch dynamics is analyzed using the simulation package WARP-POSINST. We report on simulation results, discuss the basic features of the feedback model and present our plans for further development of the numerical models used in the simulations.
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DYN05	Electron Cloud Instability in Low Emittance Rings	electron, emittance, positron, single-bunch	76
	K. Ohmi, H. Jin, Y. Susaki KEK
	We discuss single bunch instability in low emittance rings, especially focus side band appearance. Multi-bunch instability due to electron cloud in bending field is discussed.
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PST00	E-Cloud Effects on Single-Bunch Dynamics in the Proposed PS2	electron, emittance, extraction, injection	79
	M. Venturini, M. Furman, J. Vay LBNL
	One of the options considered for a future aupgrade of the LHC injection complex entails the replacement of PS with PS2, a larger circumference and higher-energy synchrotron. Electron cloud has been identified as a potential limitation to the machine performance. We review studies of e-cloud build-up and present recent results of simulations of short-term e-cloud effects on the single-bunch dynamics in the smooth-lattice, quasi-static approximation, as implemented in the code Warp.
PST03	Methods for Quantitative Interpretation of Retarding Field Analyzer Data	electron, photon, positron, pick-up	91
	J. Calvey, J. Crittenden, G. Dugan, M. Palmer Cornell University - CLASSE K. Harkay Argonne National Laboratory
	A great deal of Retarding Field Analyzer (RFA) data has been taken as part of the CesrTA program at Cornell. Obtaining a quantitative understanding of this data requires use of cloud simulation programs, as well as a detailed model of the RFA itself. In some cases the RFA can be modeled by postprocessing the output of a simulation codes, and one can obtain “best fit” values for important simulation parameters using a systematic method to improve agreement between data and simulation. In other cases, in particular in high magnetic field regions, the presence of the RFA can have an effect on the cloud, and one needs to include a model of the RFA in the simulation program itself.
PST05	Progress on Simulation of Beam Dynamics with Electron Cloud Effects: An update	electron, emittance, lattice, positron	100
	K. Sonnad Cornell University - CLASSE M. Pivi SLAC National Accelerator Laboratory J. Vay LBNL G. Rumolo, R. Tomas, F. Zimmermann CERN G. Franchetti GSI
	In this presentation, we will report the progress made in the past few years on simulations to study the electron cloud effects on the dynamics of beams in cicular accelerators. Results associated with various acclerators such as the Fermilab Main Injector, SPS, LHC, ILC damping rings will be shown. Comparisions between the results obtained from three codes, namely Warp, HeadTail and CMad will be discussed. More recent studies done on CesrTA will be discussed in greater detail.
PST06	Effects of Reflections on TE-Wave Measurements of Electron Cloud Density	electron, plasma, controls, background	103
	K. Sonnad, J. Sikora Cornell University - CLASSE K. Hammond Harvard University S. Veitzer Tech-X Corporation
	The simulation code VORPAL has been used as a tool to study charecteristics of TE wave transmission in the presence of electron clouds for CesrTA. We look at how the electron cloud induced phase shift is influenced by (1) reflections of the wave, caused by possible protrusions in the beam pipe and (2)effect of nonuniformities of the cloud density distribution in the transverse plane.
PST09	Electron Cloud Modeling Results for Time-Resolved Shielded Pickup Measurements at CesrTA	electron, pick-up, vacuum, positron	123
	J. Crittenden, Y. Li, X. Liu, M. Palmer, J. Sikora Cornell University - CLASSE S. Calatroni, G. Rumolo CERN N. Omcikus University of California at Los Angeles
	The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1-m-long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. They detect cloud electrons migrating through an 18-mm-diameter pattern of holes in the top of the chamber. A digitizing oscilloscope is used to record the signals, providing time-resolved information on cloud development. Carbon-coated, TiN-coated and uncoated aluminum chambers have been tested. Electron and positron beams of 2.1, 4.0 and 5.3 GeV with a variety of bunch populations and spacings in steps of 4 and 14 ns have been used. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron azimuthal and energy distributions at production, and the secondary yield parameters including the true secondary, rediffused, and elastic yield values. In particular, witness bunch studies exhibit high sensitivity to the elastic yield by providing information on cloud decay times.
PST10	Using Coherent Tune Shifts to Evaluate Electron Cloud Effects on Beam Dynamics at CesrTA	positron, electron, dipole, photon	130
	D. Kreinick, J. Crittenden, G. Dugan, Z. Leong, M. Palmer Cornell University - CLASSE R. Holtzapple, M. Randazzo California Polytechnic State University M. Furman, M. Venturini LBNL
	One technique used at CesrTA for studying the effects of electron clouds on beam dynamics is to measure electron and positron bunch tunes under a wide variety of beam energies, bunch charge, and bunch train configurations. Comparing the observed tunes with the predictions of various simulation programs allows the evaluation of important parameters in the cloud formation models. These simulations will be used to predict the behavior of the electron cloud in damping rings for future linear colliders.
MOD03	Accurate Simulation of the Electron Cloud in the Fermilab Main Injector with VORPAL	electron, proton, dipole, quadrupole	152
	P. Lebrun, P. Spentzouris Fermilab J. Cary University of Colorado Boulder S. Veitzer, P. Stoltz Tech-X Corporation
	We present results from a precision simulation of the electron cloud (EC) problem in the Fermilab Main Injector using the code VORPAL. Fully 3D and self consistent that include both distributions of electrons in 6D phase-space and E. M. field maps. Various configurations of the magnetic fields found around the machine have been studied. Plasma waves associated to the fluctuation density of the cloud have been analyzed. Our results are compaired with those obtained with the POSINST code. It is shown that the 3D effects are important. The response of a Retarding Field Analyzer (RFA) to the EC has been simulated, as well as the more challenging microwave absorption experiment. Definite predictions of their exact response are difficult to compute, mostly because of the uncertainties in the secondary emission yield and, in the case of the RFA, because of the sensitivity of the electron collection efficiency to unknown stray magnetic fields. Nonetheless, our simulations do provide guidance to the experimental program.
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MOD04	Modeling Electron Cloud Buildup and Microwave Diagnostics using VORPAL	electron, plasma, diagnostics, higher-order-mode	162
	S. Veitzer, P. Stoltz Tech-X Corporation K. Sonnad Cornell University - CLASSE P. Lebrun Fermilab
	We present an overview of recent electron cloud modeling results using the multi-dimensional, parallel, plasma simulation code VORPAL. We have used VORPAL to model cloud buildup in dipole, quadrupole, and field-free magnetic field configurations, in both circular and elliptical cross section pipes relevant to microwave diagnostics at the PEP-II experiment at SLAC, and ongoing experiments in the Main Injector at Fermilab. In addition, we present preliminary results for modeling electron orbits in the CesrTA wiggler, which is the beginning of a more detailed modeling effort to understand electron cloud effects in electron/positron accelerators, as well as connecting microwave side-band measurements to cloud densities. We also report on recent 3-Dimensional microwave transmission simulations through uniform and non-uniform clouds, and with higher order TE and TM waves using VORPAL.
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MOD05	Trapping of Electron Cloud in ILC / CesrTA Quadrupole and Sextupole Magnets	electron, quadrupole, sextupole, damping	167
	M. Pivi, L. Wang SLAC National Accelerator Laboratory
	This talk will discuss the electron trapping mechanism in quadrupole and sextupole magnets. We will present the results in CESRTA and ILC quadrupole and sextupole magnets.
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DIA02	The Ecloud Measurement Setup in the Main Injector	electron, proton, vacuum, antiproton	177
	C. Tan, R. Zwaska, M. Backfish Fermilab
	An ecloud measurement setup was installed in a straight section of the Main Injector in 2009. The goal of the setup was to compare the characteristics of different beam pipe coatings when subjected to proton beam. The setup consists of one coated and one uncoated beam pipe with the same physical dimensions installed at the same location. Four RFAs (retarding field analysers) and two BPMs (used for RF measurements) have been used to measure the ecloud densities. The RFAs have performed very well and have collected both the time evolution and energy distribution of the ecloud for bare and two types of beam pipe coatings.
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DIA03	Analysis of the Electron Cloud Density Measurement With RFA in a Positron Ring	electron, quadrupole, positron, synchrotron	184
	K. Kanazawa, H. Fukuma KEK P. Jain The Graduate University for Advanced Studies
	In a positron ring such as KEKB LER, clouding electrons receive an almost instantaneous kick from circulating bunches. Therefore, high energy electrons in the cloud are produced just after the interaction with the bunch locally around the beam. The authors gave an estimation of their density using a high energy electron current measured with RFA and a calculated volume neglecting their initial velocity before the interaction with the bunch. To evaluate the accuracy of this estimation, the process of the measurement is analyzed using the phase space density for the motion of electrons in the transverse plane of the beam. The expressions that can evaluate the accuracy of the estimation with the help of simulation are obtained. One of the authors has shown that the accuracy for a drift space is within ±5% error. For other cases such as in a solenoid field, in a quadruple field, the evaluation is not yet given. In addition to this discussion, some examples of the estimation with RFA are shown.
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FTR00	ILC Damping Rings: Benefit of the Antechamber or: Antechamber vs. SEY	electron, positron, dipole, photon	194
	M. Furman LBNL
	We review the simulation results for the electron cloud build-up for the ILC Damping Rings, for both lattice options considered (6 km and 3 km), in a field-free region and in a bending dipole magnet. While the 6 km lattice is slightly more forgiving than the 3-km lattice vis-a-vis the electron cloud effects, we conclude that, in general, the existence of an antechamber helps to dramatically reduce the electron-cloud density (factor ~50) only if the peak secondary yield of the chamber surface is below a certain critical value. This critical value is in the range ~1.1~1.3, depending on various details.
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FTR02	Simulation of Electron Cloud Induced Instabilities and Emittance Growth for CesrTA	emittance, electron, betatron, synchrotron	203
	M. Pivi SLAC National Accelerator Laboratory G. Dugan, M. Palmer, K. Sonnad Cornell University - CLASSE
	As part of the international Linear Collider (ILC) collaboration, we have compared the electron cloud (EC) effect for different Damping Ring (DR) designs respectively with 6.4 km and 3.2 km circumference and investigated the feasibility of the shorter damping ring with respect to the electron cloud build-up and related beam instabilities. The studies for a 3.2 km ring were carried out with beam parameters of the ILC Low Power option. A reduced damping ring circumference has been proposed for the new ILC baseline design and would allow considerable reduction of the number of components, wiggler magnets and costs. We also present the results for the luminosity upgrade option with shorter 3ns bunch spacing. In particular we will go through the evaluation of mitigation techniques for the ILC DR and discuss the integration of the CesrTA results into the Damping Ring design. Furthermore (with Kiran Sonnad, Cornell) we have performed detailed simulations using the CMAD code for CesrTA single-bunch instability and linear emittance growth below threshold and preliminary comparisons with experimental data are discussed here in view of the validation of the simulation codes prediction for the ILC DR.
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