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Trapping of Electron Cloud LLC/Cesrta Quadrupole and Sextupole Magnets

Description: The Cornell Electron Storage Ring (CESR) has been reconfigured as an ultra low emittance damping ring for use as a test accelerator (CesrTA) for International Linear Collider (ILC) damping ring R&D [1]. One of the primary goals of the CesrTA program is to investigate the interaction of the electron cloud with low emittance positron beam to explore methods to suppress the electron cloud, develop suitable advanced instrumentation required for these experimental studies and benchmark predictions by simulation codes. This paper reports the simulation of the electron-cloud formation in CESRTA and ILC quadrupole and sextupole magnets using the 3D code CLOUDLAND. We found that electrons can be trapped with a long lifetime in a quadrupole and sextupole magnet due to the mirror field trapping mechanism. We study the effects of magnet strength, bunch current, ante-chamber effect, bunch spacing effect and secondary emission yield (SEY) in great detail. The development of an electron cloud in magnets is the main concern where a weak solenoid field is not effective. Quadrupole and sextupole magnets have mirror field configurations which may trap electrons by the mirror field trapping mechanism [2]. Fig.1 shows the orbit of a trapped electron in a quadrupole magnet. The electron makes gyration motion (called transverse motion) and also moves along the field line (called longitudinal motion). At the mirror point (middle of the field line), there is a maximum longitudinal energy and minimum transverse energy. When the electron moves away from the mirror point, its longitudinal energy reduces and the transverse energy increases as the magnetic field increases. If the magnetic field is strong enough, the longitudinal energy becomes zero at one point and then the electron is turned back by the strong field. Note that the electrons are trapped in the region near the middle of the field lines. Although ...
Date: August 18, 2011
Creator: Wang, L. & Pivi, M.
Partner: UNT Libraries Government Documents Department

CMAD: A Self-consistent Parallel Code to Simulate the Electron Cloud Build-up and Instabilities

Description: We present the features of CMAD, a newly developed self-consistent code which simulates both the electron cloud build-up and related beam instabilities. By means of parallel (Message Passing Interface - MPI) computation, the code tracks the beam in an existing (MAD-type) lattice and continuously resolves the interaction between the beam and the cloud at each element location, with different cloud distributions at each magnet location. The goal of CMAD is to simulate single- and coupled-bunch instability, allowing tune shift, dynamic aperture and frequency map analysis and the determination of the secondary electron yield instability threshold. The code is in its phase of development and benchmarking with existing codes. Preliminary results on benchmarking are presented in this paper.
Date: November 7, 2007
Creator: Pivi, M. T. F.
Partner: UNT Libraries Government Documents Department

Mitigation of the electron-cloud effect in the PSR and SNS proton storage rings by tailoring the bunch profile

Description: For the storage ring of the Spallation Neutron Source(SNS) at Oak Ridge, and for the Proton Storage Ring (PSR) at Los Alamos, both with intense and very long bunches, the electroncloud develops primarily by the mechanism of trailing-edge multipacting. We show, by means of simulations for the PSR, how the resonant nature of this mechanism may be effectively broken by tailoring the longitudinal bunch profile at fixed bunch charge, resulting in a significant decrease in the electron-cloud effect. We briefly discuss the experimental difficulties expected in the implementation of this cure.
Date: May 20, 2003
Creator: Pivi, M. & Furman, M.A.
Partner: UNT Libraries Government Documents Department

A preliminary comparative study of the electron-cloud effect for the PSR, ISIS, and the ESS

Description: We present preliminary electron-cloud simulation results for the Proton Storage Ring (PSR) at LANL, ISIS at RAL, and the European Spallation Source (ESS). For each storage ring, we simulate the build-up and dissipation of the electron cloud (EC) in a representative field-free section of the vacuum chamber. For all three cases, we choose the same residual gas temperature, secondary emission yield (SEY), and secondary emission spectrum. Other variables such as proton loss rate, bunch profile, intensity and energy, residual gas pressure and chamber geometry, are set at the corresponding values for each machine. Under these assumptions, we conclude that, of the three machines, the PSR is the most severely affected by the electron cloud effect (ECE), followed by the ESS, with ISIS a distant third. We illustrate a strong sensitivity of the ECE to the longitudinal bunch profile by choosing two different shapes for the case of the PSR, and a weak sensitivity to residual gas pressure. This preliminary study does not address the ECE in other regions of the machine, nor the beam instability that might arise from the EC.
Date: June 20, 2003
Creator: Furman, M.A. & Pivi, M.T.F.
Partner: UNT Libraries Government Documents Department

Electron-cloud simulation results for the PSR and SNS

Description: 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.
Date: July 8, 2002
Creator: Pivi, M. & Furman, M.A.
Partner: UNT Libraries Government Documents Department

Electron-cloud updated simulation results for the PSR, and recent results for the SNS

Description: 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 are presented in this paper. A refined model for the secondary emission process including the so called true secondary, rediffused and backscattered electrons has recently been included in the electron-cloud code.
Date: May 29, 2002
Creator: Pivi, M. & Furman, M.A.
Partner: UNT Libraries Government Documents Department

Synchrotron radiation and beam tube vacuum in a Very Large Hadron Collider, Stage 1 and Stage 2 VLHC

Description: Synchrotron radiation induced photodesorption in particle accelerators may lead to pressure rise and to beam-gas scattering losses, finally affecting the beam lifetime [1]. We discuss the beam tube vacuum in the low field Stage 1 and Stage 2 Very Large Hadron Collider VLHC. Since VLHC Stage 1 has a room temperature beam tube, a non-evaporable getter (NEG St101 strip) pumping system located inside a pumping antechamber, supplemented by lumped ion pumps for pumping methane is considered. In Stage 2, the {approx}100 K beam screen, or liner, illuminated by the synchrotron radiation, is inserted into the magnet cold bore. Cryo-pumping is provided by the cold bore kept at 4.2 K, through slots covering the beam screen surface. Possible beam conditioning scenarios are presented for reaching design intensity, both for Stage 1 and 2. The most important results are summarized in this paper.
Date: June 30, 2001
Creator: Pivi, M.; Turner, W.C.; Bauer, P. & Limon, P.
Partner: UNT Libraries Government Documents Department

Simulations of electron cloud build-up and saturation in the APS.

Description: 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.
Date: June 13, 2002
Creator: Harkay, K.; Rosenberg, R.; Furman, M. & Pivi, M.
Partner: UNT Libraries Government Documents Department

Electron-cloud simulation results for the SPS and recent results for the LHC

Description: 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.
Date: June 19, 2002
Creator: Furman, M.A. & Pivi, M.T.F.
Partner: UNT Libraries Government Documents Department

Microscopic probabilistic model for the simulation of secondary electron emission

Description: 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.
Date: July 29, 2002
Creator: Furman, M.A. & Pivi, M.T.F.
Partner: UNT Libraries Government Documents Department

Beam tube vacuum in a Very Large Hadron Collider; Stage 1 VLHC

Description: Synchrotron radiation induced photodesorption in particle accelerators may lead to pressure rise and to beam-gas scattering losses, finally affecting the beam lifetime. We discuss the beam tube vacuum in the low field Stage 1 Very Large Hadron Collider VLHC. Since VLHC Stage 1 has a room temperature beam tube, a non-evaporable getter (NEG St101 strip) pumping system located inside a pumping antechamber, supplemented by lumped ion pumps for pumping methane is considered. A possible beam conditioning scenario is presented for reaching design intensity. The most important results are summarized in this paper. More detailed reports of the calculations will be presented at the PAC2001 Conference, Chicago, IL to be held in June 2001, and at the Snowmass Conference, CO, to be held on July 2001.
Date: April 20, 2001
Creator: Pivi, M. & Turner, W.C.
Partner: UNT Libraries Government Documents Department

Updated electron-cloud simulation results for the Large Hadron Collider (LHC)

Description: 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.
Date: June 26, 2001
Creator: Furman, M. A. & Pivi, M.
Partner: UNT Libraries Government Documents Department

Simulation results for the electron-cloud at the PSR

Description: We present a first set of computer simulations for the main features of the electron cloud at the Proton Storage Ring (PSR), particularly its energy spectrum. We compare our results with recent measurements, which have been obtained by means of dedicated probes.
Date: June 26, 2001
Creator: Furman, M.A. & Pivi, M.
Partner: UNT Libraries Government Documents Department

Electron-Cloud Effects in Transport Lines of a Normal Conducting Linear Collider

Description: In the transport lines of a normal conducting linear collider, the long positron bunch train can generate an electron cloud which can then amplify intra-train offsets. This is a transient effect which is similar to the electron-cloud driven coupled bunch instabilities in a positron storage ring. In this paper, we study this phenomenon analytically. Some criteria on the critical cloud density with respect to given collider parameters are discussed.
Date: June 15, 2005
Creator: Wu, Juhao; Raubenheimer, T.O.; Pivi, M.T.F.; Seryi, A. & /SLAC
Partner: UNT Libraries Government Documents Department

Build up of electron cloud with different bunch pattern in the presence of solenoidal field

Description: We have augmented the code POSINST to include solenoid fields, and used it to simulate the build up of electron cloud due to electron multipacting in the PEP-II positron ring. We find that the distribution of electrons is strongly affected by the resonances associated with the cyclotron period and bunch spacing. In addition, we discover a threshold beyond which the electron density grows exponentially until it reaches the space charge limit. The threshold does not depend on the bunch spacing but does depend on the positron bunch population.
Date: April 1, 2004
Creator: Cai, Y.; Furman, M.A. & Pivi, M.
Partner: UNT Libraries Government Documents Department

Electron cloud development in the Proton Storage Ring and in theSpallation Neutron Source

Description: We have applied our simulation code "POSINST" to evaluatethe contribution to the growth rate of the electron-cloud instability inproton storage rings. Recent simulation results for the main features ofthe 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 are presented in this paper. A key ingredient in our modelis a detailed description of the secondary emitted-electron energyspectrum. A refined model for the secondary emission process includingthe so-called true secondary, rediffused and backscattered electrons hasrecently been included in the electron-cloud code.
Date: October 8, 2002
Creator: Pivi, M.T.F. & Furman, M.A.
Partner: UNT Libraries Government Documents Department

Simulations of electron cloud build-up and saturation in the APS

Description: 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.
Date: June 19, 2002
Creator: Harkay, K.C.; Rosenberg, R.A.; Furman, M.A. & Pivi, M.
Partner: UNT Libraries Government Documents Department

The Effect of Gas Ion Bombardment on the Secondary Electron Yield of TiN, TiCN and TiZrV Coatings For Suppressing Collective Electron Effects in Storage Rings

Description: In many accelerator storage rings running positively charged beams, ionization of residual gas and secondary electron emission (SEE) in the beam pipe will give rise to an electron cloud which can cause beam blow-up or loss of the circulating beam. A preventative measure that suppresses electron cloud formation is to ensure that the vacuum wall has a low secondary emission yield (SEY). The SEY of thin films of TiN, sputter deposited Non-Evaporable Getters and a novel TiCN alloy were measured under a variety of conditions, including the effect of re-contamination from residual gas.
Date: January 25, 2006
Creator: Le Pimpec, F.; /PSI, Villigen; Kirby, R.E.; King, F.K.; Pivi, M. & /SLAC
Partner: UNT Libraries Government Documents Department

Suppressing Electron Cloud in Future Linear Colliders

Description: Any accelerator circulating positively charged beams can suffer from a build-up of an electron cloud (EC) in the beam pipe. The cloud develops through ionization of residual gases, synchrotron radiation and secondary electron emission and, when severe, can cause instability, emittance blow-up or loss of the circulating beam. The electron cloud is potentially a luminosity limiting effect for both the Large Hadron Collider (LHC) and the International Linear Collider (ILC). For the ILC positron damping ring, the development of the electron cloud must be suppressed. This paper discusses the state-of-the-art of the ongoing SLAC and international R&D program to study potential remedies.
Date: May 27, 2005
Creator: Pivi, M; Kirby, R.E.; Raubenheimer, T.O.; /SLAC; Le Pimpec, F. & /PSI, Villigen
Partner: UNT Libraries Government Documents Department

A Perfect Electrode to Suppress Secondary Electrons inside the Magnets

Description: An electron cloud due to multipacting in the positron ring of B-factories and the damping ring of the International Linear Collider (ILC) is one of the main concerns. The electron cloud in the drift region can be suppressed by a solenoid. However, the solenoid doesn't work inside a magnet. Numerical studies show that there is strong multipacting in a dipole magnet of a B-factory positron ring. Electrons also can be trapped inside quadrupole and sextupole magnets. The electron cloud from dipole magnets and wigglers in the positron damping ring of the ILC gives a critical limitation on the choice of a circumference of the damping ring, which directly results in a choice of two 6 km rings as the baseline for the positron damping ring. Various electrodes have been studied using the program CLOUDLAND. Our studies show that a wire type of the electrode with a few hundred voltages works perfectly to kill the secondary electrons inside various magnets.
Date: July 19, 2006
Creator: Wang, L.; /SLAC; Fukuma, H.; Kurokawa, S.; /KEK, Tsukuba; Pivi, M. et al.
Partner: UNT Libraries Government Documents Department

Modeling of E-Cloud Build-Up in Grooved Vacuum Chambers using POSINST

Description: Use of grooved vacuum chambers have been suggested as a way to limit electron cloud accumulation in the ILCDR. 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.
Date: January 23, 2008
Creator: Furman, Miguel A.; Vay, Jean-Luc; Venturini, M.; /LBL, Berkeley; Pivi, M.T.F. & /SLAC
Partner: UNT Libraries Government Documents Department

Experimental Studies on Grooved Surfaces to Suppress Secondary Electron Emission

Description: Grooved surfaces are effective to suppress the secondary electron emission, and can be a promising technique to mitigate the electron cloud effect in positron/proton storage rings. Aiming for the application in a dipole-type magnetic field, various shapes of triangular grooved surfaces have been studied at KEK. The grooves tested here have vertex angles of 20-30{sup o}, depths of 2.5-5.0 mm, and vertex roundness of 0.05-0.2 mm. In a laboratory, the secondary electron yields (SEY) of small test pieces were measured using an electron beam in a magnetic-free condition. The grooved surfaces clearly had low SEY compared to flat surfaces of the same materials. The grooves with sharper vertexes had smaller SEY. A test chamber installed in a wiggler magnet of the KEKB positron ring was used to investigate the efficacy of the grooved surface in a strong magnetic field. In the chamber, a remarkable reduction in the electron density around the beam orbit was observed compared to the case of a flat surface with TiN coating.
Date: June 15, 2010
Creator: Suetsugu, Y.; Fukuma, H.; Shibata, K.; /KEK, Tsukuba; Pivi, M.; Wang, L. et al.
Partner: UNT Libraries Government Documents Department