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Running fermi with one-stage compressor: advantages, layout,performance

Description: CBP-Tech Note-345 (July 2005), devoted to a study of microbunching instability in FERMI@ELETTRA linac quotes '...the above analysis shows that the most of the gain in microbunching instability occurs after BC2, i.e. after transformation of the energy modulation to the spatial modulation that takes place in BC2. It is possible to avoid that if we use only BC1 for all our needs for bunch compression. There are also additional advantages for a mitigation of the microbunching instability related to that. First, we would need to increase R56 in BC1 (for given energy chirp in the electron beam). Second, a relative energy spread is significantly larger at BC1 than at BC2. Both these factors would contribute to instability suppression due to increased Landau damping effect.' One additional argument was however missed in that report. Instability smearing due to finite emittance is stronger in BC1 simply because the geometrical emittance is larger than in BC2. In spite of the considerations in favor of a lattice with one-stage compressor, it was thought at the time that the two bunch compressors configuration was still preferable as it appeared difficult to obtain a flat-flat distribution at the end of the linac with only one bunch compressor. A flat-flat distribution has constant medium energy and a constant peak current along the electron bunch. Now, two years later and more studies behind, this problem is solvable. It has been demonstrated1 that shaping the intensity of the electron bunch at the injector using intensity modulation of the photocathode laser allows to use the linac structural wake fields to advantage to obtain a flat-flat distribution at the end of the linac in a two-stage compressor. This report shows that, using the back-tracking technique, it is possible to obtain a flat-flat distribution also in a single-stage compressor. Preliminary results of ...
Date: May 25, 2007
Creator: Cornacchia, M.; Craievich, P.; Di Mitri, S.; Penco, G.; Venturini, M. & Zholents, A.
Partner: UNT Libraries Government Documents Department

E-Cloud Effects on Singe-Bunch Dynamics in the Proposed PS2

Description: One of the options considered for future upgrades of the LHC injector complex entails the replacement of the PSwith the PS2, a longer circumference and higher energy synchrotron. Electron cloud effects represent an importantpotential limitation to the achievement of the upgrade goals. We report the results of numerical studies aimingat estimating the e-cloud density thresholds for the occurrence of single bunch instabilities.
Date: October 8, 2010
Creator: Venturini, M.; Furman, M. & Vay, J.-L.
Partner: UNT Libraries Government Documents Department

Direct Numerical Modeling of E-Cloud Driven Instability of a Bunch Train in the CERN SPS

Description: The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the buildup and interaction of electron clouds with a proton bunch train in the CERN SPS accelerator. Results suggest that a positive feedback mechanism exists between the electron buildup and the e-cloud driven transverse instability, leading to a net increase in predicted electron density. Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS and other accelerators. So far, simulations of electron cloud buildup and their effects on beam dynamics have been performed separately. This is a consequence of the large computational cost of the combined calculation due to large space and time scale disparities between the two processes. We have presented the latest improvements of the simulation package WARP-POSINST for the simulation of self-consistent ecloud effects, including mesh refinement, and generation of electrons from gas ionization and impact at the pipe walls. We also presented simulations of two consecutive bunches interacting with electrons clouds in the SPS, which included generation of secondary electrons. The distribution of electrons in front of the first beam was initialized from a dump taken from a preceding buildup calculation using the POSINST code. In this paper, we present an extension of this work where one full batch of 72 bunches is simulated in the SPS, including the entire buildup calculation and the self-consistent interaction between the bunches and the electrons.
Date: March 1, 2011
Creator: Vay, J-L.; Furman, M.A. & Venturini, M.
Partner: UNT Libraries Government Documents Department

Development of a 2D Vlasov Solver for Longitudinal BeamDynamics in Single-Pass Systems

Description: Direct numerical methods for solving the Vlasov equation offer some advantages over macroparticle simulations, as they do not suffer from the numerical noise inherent in using a number of macroparticles smaller than the bunch population. Unfortunately these methods are more time-consuming and generally considered impractical in a full 6D phase space. However, in a lower-dimension phase space they may become attractive if the beam dynamics is sensitive to the presence of small charge-density fluctuations and a high resolution is needed. In this paper we present a 2D Vlasov solver for studying the longitudinal beam dynamics in single-pass systems of interest for X-FEL's, where characterization of the microbunching instability is of particular relevance. The solver includes a model to account for the smearing effect of a finite horizontal emittance on microbunching. We explore the effect of space charge and coherent synchrotron radiation (CSR). The numerical solutions are compared with results from linear theory and good agreement is found in the regime where linear theory applies.
Date: December 12, 2006
Creator: Venturini, M.; Warnock, R.; Zholents, A. & /SLAC
Partner: UNT Libraries Government Documents Department

A Vlasov solver for collective effects in particle accerators

Description: Integration techniques based on Lie algebraic methods have been successfully used in beam transport codes for particle accelerators. Generally these methods have been applied to problems of single-particle beam dynamics. Here we present an application of Lie algebraic techniques to the development of a Vlasov solver suitable for problems of beam transport in the presence of non-negligible particle self-fields. The solver we discuss is suitable for modelling a variety of collective effects that may arise at high current. In particular, we consider the case of coherent synchrotron radiation effects in magnetic bunch compressors which can cause instabilities limiting performance of high current accelerators.
Date: February 1, 2009
Creator: Migliorati, M.; Schiavi, A.; Dattoli, G. & Venturini, M.
Partner: UNT Libraries Government Documents Department

Microbunching studies for SPARX photoinjector

Description: The SPARX X-FEL accelerator will be the first FEL facility to operate with a hybrid (RF plus magnetic chicane) compression scheme. Numerical studies of propagation of beam density modulations stemming from photogun laser, through the photoinjector operating under velocity bunching conditions have been carried out. A semi-analytical model for the linear gain in a RF compressor is also being developed and some preliminary results are presented.
Date: May 1, 2009
Creator: Ronsivalle, C.; Ferrario, M.; Migliorati, M. & Venturini, M.
Partner: UNT Libraries Government Documents Department

Linear Gain for the Microbunching Instability in an RF Compressor

Description: Velocity (or rf) compression has been suggested as a technique for bunch compression complementary to the more established technique involving magnetic chicanes and represents an important research item being investigated at the SPARC test facility. One of the aspects of this technique still not sufficiently understood is its possible impact on the microbunching instability. The purpose of this report is to present the analytical framework for investigating this instability in rf compressors. We use methods similar to those successfully applied to magnetic compressors and derive some integral equations yielding the gain for the instability in linear approximation. The focus here is on the derivation of the relevant equations. Although examples of solutions to these equations are provided we defer a more comprehensive discussion of their implication to a future report. The present study is part of a larger effort for a more comprehensive investigation that eventually will include macroparticle simulations and experiments.
Date: May 1, 2009
Creator: Venturini, M.; Migliorati, M.; Ronsivalle, C. & Vaccarezza, C.
Partner: UNT Libraries Government Documents Department

High Resolution Simulation of Beam Dynamics in Electron Linacs for Free Electron Lasers

Description: In this paper we report on large scale multi-physics simulation of beam dynamics in electron linacs for next generation free electron lasers (FELs). We describe key features of a parallel macroparticle simulation code including three-dimensional (3D) space-charge effects, short-range structure wake fields, longitudinal coherent synchrotron radiation (CSR) wake fields, and treatment of radiofrequency (RF) accelerating cavities using maps obtained from axial field profiles. A macroparticle up-sampling scheme is described that reduces the shot noise from an initial distribution with a smaller number of macroparticles while maintaining the global properties of the original distribution. We present a study of the microbunching instability which is a critical issue for future FELs due to its impact on beam quality at the end of the linac. Using parameters of a planned FEL linac at Lawrence Berkeley National Laboratory (LBNL), we show that a large number of macroparticles (beyond 100 million) is needed to control numerical shot noise that drives the microbunching instability. We also explore the effect of the longitudinal grid on simulation results. We show that acceptable results are obtained with around 2048 longitudinal grid points, and we discuss this in view of the spectral growth rate predicted from linear theory. As an application, we present results from simulations using one billion macroparticles of the FEL linac under design at LBNL. We show that the final uncorrelated energy spread of the beam depends not only on the initial uncorrelated energy spread but also depends strongly on the shape of the initial current profile. By using a parabolic initial current profile, 5 keV initial uncorrelated energy spread at 40 MeV injection energy, and improved linac design, those simulations demonstrate that a reasonable beam quality can be achieved at the end of the linac, with the final distribution having about 100 keV energy spread, 2.4 ...
Date: January 5, 2009
Creator: Ryne, R.D.; Venturini, M.; Zholents, A.A. & Qiang, J.
Partner: UNT Libraries Government Documents Department

Billion particle linac simulations for future light sources

Description: In this paper we report on multi-physics, multi-billion macroparticle simulation of beam transport in a free electron laser (FEL) linac for future light source applications. The simulation includes a self-consistent calculation of 3D space-charge effects, short-range geometry wakefields, longitudinal coherent synchrotron radiation (CSR) wakefields, and detailed modeling of RF acceleration and focusing. We discuss the need for and the challenges associated with such large-scale simulation. Applications to the study of the microbunching instability in an FEL linac are also presented.
Date: September 25, 2008
Creator: Ryne, R. D.; Venturini, M.; Zholents, A. A. & Qiang, J.
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

Recent Developments in Impact and Application to Future Light Sources

Description: This paper discusses two recently added capabilities of the IMPACT suite that are relevant to modeling electron linacs, namely the new 1D coherent synchrotron radiation (CSR) modeling capability and the integrated Green's function (IFG) algorithm for modeling high aspect ratio beams. In addition, we present initial results of application of the enhanced version of IMPACT-Z to high-fidelity modeling of the microbunching instability in a realistic light source lattice.
Date: February 13, 2008
Creator: Pogorelov, I.; Qiang, J.; Ryne, R.; Venturini, M.; Zholents, A.; /LBL, Berkeley et al.
Partner: UNT Libraries Government Documents Department

Microbunching and RF Compression

Description: Velocity bunching (or RF compression) represents a promising technique complementary to magnetic compression to achieve the high peak current required in the linac drivers for FELs. Here we report on recent progress aimed at characterizing the RF compression from the point of view of the microbunching instability. We emphasize the development of a linear theory for the gain function of the instability and its validation against macroparticle simulations that represents a useful tool in the evaluation of the compression schemes for FEL sources.
Date: May 23, 2010
Creator: Venturini, M.; Migliorati, M.; Ronsivalle, C.; Ferrario, M. & Vaccarezza, C.
Partner: UNT Libraries Government Documents Department

Dynamics of Longitudinal Phase-Space Modulations in an rf Compressor for Electron Beams

Description: Free Electron Lasers (FELs) operating in the UV or x-ray radiation spectrum require peak beam currents that are generally higher than those obtainable by present electron sources, thus making bunch compression necessary. Compression, however, may heighten the effects of collective forces and degrade the beam quality. In this paper they provide a framework for investigating some of these effects in rf compressors by focusing on the longitudinal dynamics of small-amplitude density perturbations, which have the potential to cause the disruptive appearance of the so-called microbunching instability. They develop a linear theory valid for low-to-moderate compression factors under the assumption of a 1D impedance model of longitudinal space charge and provide validation against macroparticle simulations.
Date: May 21, 2010
Creator: Venturini, M.; Migliorati, M.; Ronsivalle, C.; Ferrario, M. & Vaccarezza, C.
Partner: UNT Libraries Government Documents Department

3D-Simulation Studies of SNS Ring Doublet Magnets

Description: The accumulator ring of the Spallation Neutron Source (SNS) at ORNL employs in its straight sections closely packed quadrupole doublemagnets with large aperture of R=15.1 cm an relatively short iron-to-iron distance of 51.4 cm. These quads have much extended fringe field, and magnetic interferences among them in the doublet assemblies is not avoidable. Though each magnet in the assemblies has been individually mapped to high accuracy of lower than 0.01 percent level, the experimental data including the magnetic interference effect will not be available. We have performed 3D computing simulations on a quadrupole doublet model in order to assess the degree of the interference and to obtain relevant data for the SNS commissioning and operation.
Date: May 5, 2005
Creator: Wang, J.G.; N., Tsoupas & Venturini, M.
Partner: UNT Libraries Government Documents Department

LINAC DESIGN FOR AN ARRAY OF SOFT X-RAY FREE ELECTRON LASERS

Description: The design of the linac delivering electron bunches into ten independent soft x-ray free electron lasers (FELs) producing light at 1 nm and longer wavelengths is presented. The bunch repetition rate in the linac is 1 MHz and 100 kHz in each of ten FEL beam lines. Various issues regarding machine layout and lattice, bunch compression, collimation, and the beam switch yard are discussed. Particular attention is given to collective effects. A demanding goal is to preserve both a low beam slice emittance and low slice energy spread during acceleration, bunch compression and distribution of the electron bunches into the array of FEL beamlines. Detailed studies of the effect of the electron beam microbunching caused by longitudinal space-charge forces and coherent synchrotron radiation (CSR) have been carried out and their results are presented.
Date: September 22, 2008
Creator: Zholents, Alexander A.; Kur, E.; Penn, G.; Qiang, Ji; Venturini, M. & Wells, R. P.
Partner: UNT Libraries Government Documents Department

Design and Commissioning Plan for a Laser Heater for FERMI@elettra

Description: The purpose of a laser heater is to increase the electron beam uncorrelated energy spread as a way to control and ideally suppress the microbunching instability in the linac drive for x-rays FELs. We review the motivations for equipping FERMI with a laser heater and provide a specification for the basics parameters as well as a description of a practical layout including desired diagnostics provisions for both the electron and laser beams. We also outline some useful operational guidelines for commissioning.
Date: October 25, 2008
Creator: Zholents, Alexander A.; Qiang, J.; Venturini, M.; Wells,, R.; Wilcox, R.; Di Mitri, S. et al.
Partner: UNT Libraries Government Documents Department

Self-Consistant Numerical Modeling of E-Cloud Driven Instability of a Bunch Train in the CERN SPS

Description: The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the growth rate and frequency patterns in space-time of the electron cloud driven transverse instability for a proton bunch train in the CERN SPS accelerator. Results suggest that a positive feedback mechanism exists between the electron buildup and the e-cloud driven transverse instability, leading to a net increase in predicted electron density. Comparisons to selected experimental data are also given. Electron clouds have been shown to trigger fast growing instabilities on proton beams circulating in the SPS and other accelerators. So far, simulations of electron cloud buildup and their effects on beam dynamics have been performed separately. This is a consequence of the large computational cost of the combined calculation due to large space and time scale disparities between the two processes. We have presented the latest improvements of the simulation package WARP-POSINST for the simulation of self-consistent ecloud effects, including mesh refinement, and generation of electrons from gas ionization and impact at the pipe walls. We also presented simulations of two consecutive bunches interacting with electrons clouds in the SPS, which included generation of secondary electrons. The distribution of electrons in front of the first beam was initialized from a dump taken from a preceding buildup calculation using the POSINST code. In this paper, we present an extension of this work where one full batch of 72 bunches is simulated in the SPS, including the entire buildup calculation and the self-consistent interaction between the bunches and the electrons. Comparisons to experimental data are also given.
Date: September 1, 2010
Creator: Vay, J-L.; Furman, M.A.; Secondo, R.; Venturini, M.; Fox, J.D. & Rivetta, C.H,
Partner: UNT Libraries Government Documents Department

Simulation of the Microbunching Instability in Beam Delivery Systems for Free Electron Lasers

Description: In this paper, we examine the growth of the microbunching instability in the electron beam delivery system of a free electron laser (FEL). We present the results of two sets of simulations, one conducted using a direct Vlasov solver, the other using a particle-in-cell code Impact-Z with the number of simulation macroparticles ranging up to 100 million. Discussion is focused on the details of longitudinal dynamics and on numerical values of uncorrelated (slice) energy spread at different points in the lattice. In particular, we assess the efficacy of laser heater in suppression of the instability, and look at the interplay between physical and numerical noise in particle-based simulations.
Date: November 2, 2007
Creator: Pogorelov, I.; U., /Northern Illinois; Qiang, J.; Ryne, R.; Venturini, M.; Zholents, A. et al.
Partner: UNT Libraries Government Documents Department

Self-Consistent Computation of Electromagnetic Fields and Phase Space Densities for Particles on Curved Planar Orbits

Description: We discuss our progress on the self-consistent calculation of the 4D phase space density (PSD) and electromagnetic fields in a Vlasov-Maxwell formulation. We emphasize Coherent Synchrotron Radiation (CSR) from arbitrary curved planar orbits, with shielding from the vacuum chamber, but space charge forces are naturally included. Our focus on the Vlasov equation will provide simulations with lower numerical/statistical noise than standard PIC methods, and will allow the study of issues such as emittance degradation and microbunching due to space charge and CSR in bunch compressors. The fields excited by the bunch are computed in the lab frame from a new double integral formula. The field formula is derived from retarded potentials by changes of variables. It is singularity-free and requires no computation of retarded times. Ultimately, the Vlasov equation will be integrated in beam frame coordinates using our method of local characteristics. As an important intermediate step, we have developed a 'self consistent Monte Carlo algorithm', and a corresponding parallel code. This gives an accurate representation of the source and will help in understanding the PSD support. In addition we have (1) studied carefully a 2D phase space Vlasov analogue and (2) derived an improved expression of the field of a 1D charge/current distribution which accounts for the interference of different bends and other effects usually neglected. Bunch compressors will be emphasized.
Date: November 2, 2007
Creator: Ellison, J.A.; Bassi, G.; Heinemann, K.A.; U., /New Mexico; Venturini, M.; /LBL, Berkeley et al.
Partner: UNT Libraries Government Documents Department

FERMI&Elettra Accelerator Technical Optimization FinalReport

Description: This report describes the accelerator physics aspects, theengineering considerations and the choice of parameters that led to theaccelerator design of the FERMI Free-Electron-Laser. The accelerator(also called the "electron beam delivery system") covers the region fromthe exit of the injector to the entrance of the first FEL undulator. Theconsiderations that led to the proposed configuration were made on thebasis of a study that explored various options and performance limits.This work follows previous studies of x-ray FEL facilities (SLAC LCLS[1], DESY XFEL [2], PAL XFEL [3], MIT [4], BESSY FEL[5], LBNL LUX [6],Daresbury 4GLS [7]) and integrates many of the ideas that were developedthere. Several issues specific to harmonic cascade FELs, and that had notyet been comprehensively studied, were also encountered and tackled. Aparticularly difficult issue was the need to meet the requirement forhigh peak current and small slice energy spread, as the specification forthe ratio of these two parameters (that defines the peak brightness ofthe electron beam) is almost a factor of two higher than that of theLCLS's SASE FEL. Another challenging aspect was the demand to produce anelectron beam with as uniform as possible peak current and energydistributions along the bunch, a condition that was met by introducingnovel beam dynamics techniques. Part of the challenge was due to the factthat there were no readily available computational tools to carry outreliable calculations, and these had to be developed. Most of theinformation reported in this study is available in the form of scientificpublications, and is partly reproduced here for the convenience of thereader.
Date: July 1, 2006
Creator: Cornacchia, M.; Craievich, P.; Di Mitri, S.; Pogorelov, I.; Qiang, J.; Venturini, M. et al.
Partner: UNT Libraries Government Documents Department

E-Cloud Drivent Single-Bunch Instabilities in PS2

Description: One of the proposals under consideration for future upgrades of the LHC injector complex entails the replacement of the PS with the PS2, a longer circumference and higher energy synchrotron, with electron cloud effects representing a potentially serious limitation to the achievement of the upgrade goals. We report on ongoing numerical studies aiming at estimating the e-cloud density threshold for the occurrence of single bunch instabilities.
Date: May 23, 2010
Creator: Venturini, M.; Furman, M.; Penn, G.; Secondo, R.; Vay, J-L.; De Maria, R. et al.
Partner: UNT Libraries Government Documents Department

Toward fully self-consistent simulation of the interaction of E-Clouds and beams with WARP-POSINST

Description: To predict the evolution of electron clouds and their effect on the beam, the high energy physics community has relied so far on the complementary use of 'buildup' and 'single/multi-bunch instability' reduced descriptions. The former describes the evolution of electron clouds at a given location in the ring, or 'station', under the influence of prescribed beams and external fields [1], while the latter (sometimes also referred as the 'quasi-static' approximation [2]) follows the interaction between the beams and the electron clouds around the accelerator with prescribed initial distributions of electrons, assumed to be concentrated at a number of discrete 'stations' around the ring. Examples of single bunch instability codes include HEADTAIL [3], QuickPIC [4, 5], and PEHTS [6]. By contrast, a fully self-consistent approach, in which both the electron cloud and beam distributions evolve simultaneously under their mutual influence without any restriction on their relative motion, is required for modeling the interaction of high-intensity beams with electron clouds for heavy-ion beam-driven fusion and warm-dense matter science. This community has relied on the use of Particle-In-Cell (PIC) methods through the development and use of the WARP-POSINST code suite [1, 7, 8]. The development of novel numerical techniques (including adaptive mesh refinement, and a new 'drift-Lorentz' particle mover for tracking charged particles in magnetic fields using large time steps) has enabled the first application of WARP-POSINST to the fully self-consistent modeling of beams and electron clouds in high energy accelerators [9], albeit for only a few betatron oscillations. It was recently observed [10] that there exists a preferred frame of reference which minimizes the number of computer operations needed to simulate the interaction of relativistic objects. This opens the possibility of reducing the cost of fully self-consistent simulations for the interaction of ultrarelativistic beams with electron cloud by orders of magnitude. The ...
Date: April 9, 2012
Creator: LLNL; Furman, M.A.; Furman, M.A.; Celata, C.M.; Sonnad, K.; Venturini, M. et al.
Partner: UNT Libraries Government Documents Department

Selection Tests of MnZn and NiZn Ferrites for Mu2e 300 kHz and 5.1 MHz AC Dipoles

Description: Mu2e, a charged lepton flavor violation (CLFV) experiment is planned to start at Fermilab late in this decade. The proposed experiment will search for neutrinoless muon to electron conversions with unprecedented sensitivity, better than 6 x 10{sup -17 }at 90% CL. To achieve this sensitivity the incoming proton beam must be highly suppressed during the window for detecting the muon decays. The current proposal for beam extinction is based on a collimator design with two dipoles running at {approx}300 kHz and 5.1 MHz and synchronized to the proton bunch spacing. The appropriate choice of ferrite material for the magnet yoke is a critical step in the overall design of the dipoles and their reliable operation at such high frequencies over the life of the experiment. This choice, based on a series of the thermal and magnetic measurements of the ferrite samples, is discussed in the paper. Additionally, the first results from the testing at 300 kHz of a prototype AC dipole are presented.
Date: September 9, 2011
Creator: Bourkland, K.; Elementi, L.; Feher, S.; Harding, D.J.; Kashikhin, V.S.; Makarov, A. et al.
Partner: UNT Libraries Government Documents Department