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Phys. Rev. Lett. 101, 055001 (2008) [4 pages]

Halo Formation and Emittance Growth of Positron Beams in Plasmas

P. Muggli,1 B. E. Blue,2 C. E. Clayton,2 F. J. Decker,3 M. J. Hogan,3 C. Huang,2 C. Joshi,2 T. C. Katsouleas,1 W. Lu,2 W. B. Mori,2 C. L. O'Connell,3 R. H. Siemann,3 D. Walz,3 and M. Zhou2
1University of Southern California, Los Angeles, California 90089, USA
2University of California, Los Angeles, California 90095, USA
3Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309, USA

Received 26 December 2007; published 29 July 2008

An ultrarelativistic 28.5 GeV, 700-µm-long positron bunch is focused near the entrance of a 1.4-m-long plasma with a density ne between [approximate]1013 and [approximate]5×1014 cm-3. Partial neutralization of the bunch space charge by the mobile plasma electrons results in a reduction in transverse size by a factor of [approximate]3 in the high emittance plane of the beam [approximate]1 m downstream from the plasma exit. As ne increases, the formation of a beam halo containing [approximate]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 [approximate]3 and emittance ratio of [approximate]5 suffers emittance growth and exits the plasma with approximately equal sizes and emittances.

©2008 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevLett.101.055001
DOI: 10.1103/PhysRevLett.101.055001
PACS: 52.40.Mj; 29.27.-a; 41.75.Ht; 52.59.Wd
  • 52.40.Mj
    Particle beam interactions in plasmas
  • 29.27.-a
    Beams in particle accelerators
  • 41.75.Ht
    Relativistic electron and positron beams
  • 52.59.Wd
    Emittance-dominated particle beams in plasmas
  • YEAR: 2008

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