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Title: Halo Formation And Emittance Growth of Positron Beams in Plasmas

Abstract

An ultrarelativistic 28.5 GeV, 700-{micro}m-long positron bunch is focused near the entrance of a 1.4-m-long plasma with a density n{sub e} between {approx}10{sup 13} and {approx}5 x 10{sup 14} cm{sup -3}. Partial neutralization of the bunch space charge by the mobile plasma electrons results in a reduction in transverse size by a factor of {approx}3 in the high emittance plane of the beam {approx}1 m downstream from the plasma exit. As n{sub e} increases, the formation of a beam halo containing {approx}40% of the total charge is observed, indicating that the plasma focusing force is nonlinear. Numerical simulations confirm these observations. The bunch with an incoming transverse size ratio of {approx}3 and emittance ratio of {approx}5 suffers emittance growth and exits the plasma with approximately equal sizes and emittances.

Authors:
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Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1028122
Report Number(s):
SLAC-PUB-14657
Journal ID: ISSN 0031-9007; PRLTAO; TRN: US1105370
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys.Rev.Lett.101:055001,2008; Journal Volume: 101; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ELECTRONS; FOCUSING; PLASMA; POSITRON BEAMS; POSITRONS; SPACE CHARGE; Astrophysics,ASTRO

Citation Formats

Muggli, P., /Southern California U., Blue, B.E., Clayton, C.E., /UCLA, Decker, F.J., Hogan, M.J., /SLAC, Huang, C., Joshi, C., /UCLA, Katsouleas, Thomas C., /Southern California U., Lu, W., Mori, W.B., /UCLA, O'Connell, C.L., Siemann, R.H., Walz, D., /SLAC, Zhou, M., and /UCLA. Halo Formation And Emittance Growth of Positron Beams in Plasmas. United States: N. p., 2011. Web.
Muggli, P., /Southern California U., Blue, B.E., Clayton, C.E., /UCLA, Decker, F.J., Hogan, M.J., /SLAC, Huang, C., Joshi, C., /UCLA, Katsouleas, Thomas C., /Southern California U., Lu, W., Mori, W.B., /UCLA, O'Connell, C.L., Siemann, R.H., Walz, D., /SLAC, Zhou, M., & /UCLA. Halo Formation And Emittance Growth of Positron Beams in Plasmas. United States.
Muggli, P., /Southern California U., Blue, B.E., Clayton, C.E., /UCLA, Decker, F.J., Hogan, M.J., /SLAC, Huang, C., Joshi, C., /UCLA, Katsouleas, Thomas C., /Southern California U., Lu, W., Mori, W.B., /UCLA, O'Connell, C.L., Siemann, R.H., Walz, D., /SLAC, Zhou, M., and /UCLA. 2011. "Halo Formation And Emittance Growth of Positron Beams in Plasmas". United States. doi:. https://www.osti.gov/servlets/purl/1028122.
@article{osti_1028122,
title = {Halo Formation And Emittance Growth of Positron Beams in Plasmas},
author = {Muggli, P. and /Southern California U. and Blue, B.E. and Clayton, C.E. and /UCLA and Decker, F.J. and Hogan, M.J. and /SLAC and Huang, C. and Joshi, C. and /UCLA and Katsouleas, Thomas C. and /Southern California U. and Lu, W. and Mori, W.B. and /UCLA and O'Connell, C.L. and Siemann, R.H. and Walz, D. and /SLAC and Zhou, M. and /UCLA},
abstractNote = {An ultrarelativistic 28.5 GeV, 700-{micro}m-long positron bunch is focused near the entrance of a 1.4-m-long plasma with a density n{sub e} between {approx}10{sup 13} and {approx}5 x 10{sup 14} cm{sup -3}. Partial neutralization of the bunch space charge by the mobile plasma electrons results in a reduction in transverse size by a factor of {approx}3 in the high emittance plane of the beam {approx}1 m downstream from the plasma exit. As n{sub e} increases, the formation of a beam halo containing {approx}40% of the total charge is observed, indicating that the plasma focusing force is nonlinear. Numerical simulations confirm these observations. The bunch with an incoming transverse size ratio of {approx}3 and emittance ratio of {approx}5 suffers emittance growth and exits the plasma with approximately equal sizes and emittances.},
doi = {},
journal = {Phys.Rev.Lett.101:055001,2008},
number = 5,
volume = 101,
place = {United States},
year = 2011,
month =
}
  • The optimization of high-current high-energy linacs against the low beam loss requirement is not straightforward or well-codified. Outlying particle losses at the 10{sup -5} up to 10{sup -8} level might have only a small effect on the rms properties of the beam, and thus the total beam size must be constantly kept under observation. RMS-physics has gained wide-spread acceptance as a necessary design tool, but its sufficiency is an issue for ATW/ABC accelerators.
  • The effect of an initial envelope mismatch on the transport of bunched spherically symmetric beams is investigated. A particle-core model is used to estimate the maximum radius that halo particles can reach. The theory is used to obtain an empirical formula that provides the halo size as a function of system parameters. Taking into account, the incompressibility property of the Vlasov dynamics and the resulting Landau damping, an explicit form for the final stationary distribution attained by the beam is proposed. The distribution is fully self-consistent, presenting no free fitting parameters. The theory is used to predict the relevant beammore » transport properties, such as the final particle density distribution, the emittance growth, and the fraction of particles that will be expelled to form halo. The theoretical results are compared to the explicit N-particle dynamics simulations, showing a good agreement.« less
  • The Paul Trap Simulator Experiment (PTSX) is a compact laboratory experiment that places the physicist in the frame-of-reference of a long, charged-particle bunch coasting through a kilometers-long magnetic alternating-gradient (AG) transport system. The transverse dynamics of particles in both systems are described by the same set of equations, including nonlinear space-charge effects. The time-dependent voltages applied to the PTSX quadrupole electrodes in the laboratory frame are equivalent to the spatially periodic magnetic fields applied in the AG system. The transverse emittance of the charge bunch, which is a measure of the area in the transverse phase space that the beammore » distribution occupies, is an important metric of beam quality. Maintaining low emittance is an important goal when defining AG system tolerances and when designing AG systems to perform beam manipulations such as transverse beam compression. Results are reviewed from experiments in which white noise and colored noise of various amplitudes and durations have been applied to the PTSX electrodes. This noise is observed to drive continuous emittance growth and increase in root-mean-square beam radius over hundreds of lattice periods. Additional results are reviewed from experiments that determine the conditions necessary to adiabatically reduce the charge bunch's transverse size and simultaneously maintain high beam quality. During adiabatic transitions, there is no change in the transverse emittance. The transverse compression can be achieved either by a gradual change in the PTSX voltage waveform amplitude or frequency. Results are presented from experiments in which low emittance is achieved by using focusing-off-defocusing-off waveforms.« less
  • The optimization of high-current high-energy linacs against the low beam loss requirement is not straightforward or well-codified. Outlying particle losses at the 10{sup {minus}5} up to 10{sup {minus}8} level might have only a small effect on the rms properties of the beam, and thus the total beam size must be constantly kept under observation. RMS-physics has gained wide-spread acceptance as a necessary design tool, but its sufficiency is an issue for ATW/ABC accelerators.