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Title: Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques

Abstract

In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1048459
Report Number(s):
FERMILAB-CONF-12-381-APC
TRN: US1204228
DOE Contract Number:
AC02-07CH11359
Resource Type:
Conference
Resource Relation:
Journal Name: Conf.Proc.C1205201:3012-3014,2012; Conference: Presented at the 3rd International Particle Accelerator Conference (IPAC-2012), New Orleans, Louisiana, 20-25 May 2012
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCELERATION; ACCELERATORS; ELECTRON BEAMS; OPTIMIZATION; SHAPE; TRANSFORMERS; Accelerators

Citation Formats

Lemery, F., Mihalcea, D., Prokop, C.R., /Northern Illinois U., Piot, P., and /Northern Illinois U. /Fermilab. Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques. United States: N. p., 2012. Web.
Lemery, F., Mihalcea, D., Prokop, C.R., /Northern Illinois U., Piot, P., & /Northern Illinois U. /Fermilab. Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques. United States.
Lemery, F., Mihalcea, D., Prokop, C.R., /Northern Illinois U., Piot, P., and /Northern Illinois U. /Fermilab. 2012. "Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques". United States. doi:.
@article{osti_1048459,
title = {Optimization of Drive-Bunch Current Profile for Enhanced Transformer Ratio in Beam-Driven Acceleration Techniques},
author = {Lemery, F. and Mihalcea, D. and Prokop, C.R. and /Northern Illinois U. and Piot, P. and /Northern Illinois U. /Fermilab},
abstractNote = {In recent years, wakefield acceleration has gained attention due to its high acceleration gradients and cost effectiveness. In beam-driven wakefield acceleration, a critical parameter to optimize is the transformer ratio. It has been shown that current shaping of electron beams allows for enhanced (> 2) transformer ratios. In this paper we present the optimization of the pulse shape of the drive bunch for dielectric-wakefield acceleration.},
doi = {},
journal = {Conf.Proc.C1205201:3012-3014,2012},
number = ,
volume = ,
place = {United States},
year = 2012,
month = 7
}

Conference:
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  • The transformer ration of collinear beam-driven techniques can be significantly improved by shaping the current profile of the drive bunch. To date, several current shapes have been proposed to increase the transformer ratio and produce quasi-uniform energy loss within the drive bunch. Some of these tailoring techniques are possible as a results of recent beam-dynamics advances, e.g., transverse-to-longitudinal emittance exchanger. In ths paper, we propose an alternative class of longitudinal shapes that enable high transformer ratio and uniform energy loss across the drive bunch. We also suggest a simple method based on photocathode-laser shaping and passive shaping in wakefield structuremore » to realize shape close to the theoretically optimized current profiles.« less
  • Collinear high-gradient O(GV/m) beam-driven wakefield methods for charged-particle acceleration could be critical to the realization of compact, cost-efficient, accelerators, e.g., in support of TeV-scale lepton colliders or multiple-user free-electron laser facilities. To make these options viable, the high accelerating fields need to be complemented with large transformer ratios >2, a parameter characterizing the efficiency of the energy transfer between a wakefield-exciting “drive” bunch to an accelerated “witness” bunch. While several potential current distributions have been discussed, their practical realization appears challenging due to their often discontinuous nature. In this paper we propose several alternative continuously differentiable (smooth) current profiles whichmore » support enhanced transformer ratios. We especially demonstrate that one of the devised shapes can be implemented in a photo-emission electron source by properly shaping the photocathode-laser pulse. We finally discuss a possible superconducting linear-accelerator concept that could produce shaped drive bunches at high-repetition rates to drive a dielectric-wakefield accelerator with accelerating fields on the order of ~60 MV/m and a transformer ratio ~5 consistent with a recently proposed multiuser free-electron laser facility.« less
  • Collinear high-gradient O(GV/m) beam-driven wakefield methods for charged-particle acceleration could be critical to the realization of compact, cost-efficient, accelerators, e.g., in support of TeV-scale lepton colliders or multiple-user free-electron laser facilities. To make these options viable, the high accelerating fields need to be complemented with large transformer ratios >2, a parameter characterizing the efficiency of the energy transfer between a wakefield-exciting “drive” bunch to an accelerated “witness” bunch. While several potential current distributions have been discussed, their practical realization appears challenging due to their often discontinuous nature. In this paper we propose several alternative continuously differentiable (smooth) current profiles whichmore » support enhanced transformer ratios. We especially demonstrate that one of the devised shapes can be implemented in a photo-emission electron source by properly shaping the photocathode-laser pulse. We finally discuss a possible superconducting linear-accelerator concept that could produce shaped drive bunches at high-repetition rates to drive a dielectric-wakefield accelerator with accelerating fields on the order of ~60 MV/m and a transformer ratio ~5 consistent with a recently proposed multiuser free-electron laser facility.« less
  • The transformer ratio R is a parameter that characterizes the efficiency of the energy transferred from the drive beam to the trailing witness beam passing through a wakefield accelerating structure (all metal or dielectric based) or a plasma chamber. Using a ramped bunch train (RBT) rather than a single drive bunch, the enhanced transformer ratio (ETR) technique is able to increase the transformer ratio R above the ordinary limit of 2 for a single bunch in a collinear wakefield accelerator. The RBT is a train of electron bunches separated by half integer multiples wavelength of the wakefield. The charge ofmore » the leading bunch is lowest and subsequent bunch charges are increased in such a way as to maximize R. In this article, an experimental study of this scheme is presented in which an RBT of 2 bunches with charge ratio of 1:2.5 and bunch length {sigma}{sub z} = 2 mm were used to enhance the transformer ratio. Measurement results and data analysis show good agreement with theoretical predictions. The ETR technique demonstrated here can be used in any collinear wakefield accelerator configuration, either structure- or plasma-based.« less
  • The key to the theoretically predicted high performance of a low aspect ratio tokamak (LAT) is its ability to operate at very large plasma current*I{sub p}. The plasma current at low aspect ratios follows the approximate formula: I{sub p} {approximately} (5a{sup 2}B{sub t}/Rq{psi}) [(1 + {kappa}{sup 2})/2] [A/(A {minus} 1)] where A {quadruple_bond} R/a which was derived from equilibrium studies. For constant q{psi} and B{sub t}, I{sub p} can increase by an order of magnitude over the case of tokamaks with A {approx_gt} 2.5. The large current results in a significantly enhanced {beta}{sub t} ({quadruple_bond} {beta}{sub N}I{sub p}/aB{sub t}) possiblymore » of order unity. It also compensates for the reduction in A to maintain the same confinement performance assuming the confinement time {tau} follows the generic form {approximately} HI{sub p}P{sup {minus}1}/{sup 2}R{sup 3}/{sup 2}{kappa}{sup 1}/{sup 2}. The initiation and maintenance of such a large current is therefore a key issue for LATs.« less