Physical Review Special Topics. Accelerators and Beams (Jun 2005)

Stable two-plane focusing for emittance-dominated sheet-beam transport

  • B. E. Carlsten,
  • L. M. Earley,
  • F. L. Krawczyk,
  • S. J. Russell,
  • J. M. Potter,
  • P. Ferguson,
  • S. Humphries, Jr.

DOI
https://doi.org/10.1103/PhysRevSTAB.8.062002
Journal volume & issue
Vol. 8, no. 6
p. 062002

Abstract

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Two-plane focusing of sheet electron beams will be an essential technology for an emerging class of high-power, 100 to 300 GHz rf sources [Carlsten et al., IEEE Trans. Plasma Sci. 33, 85 (2005)ITPSBD0093-381310.1109/TPS.2004.841172]. In these devices, the beam has a unique asymmetry in which the transport is emittance dominated in the sheet’s thin dimension and space-charge dominated in the sheet’s wide dimension. Previous work has studied the stability of the transport of beams in the emittance-dominated regime for both wiggler and periodic permanent magnet (PPM) configurations with single-plane focusing, and has found that bigger envelope scalloping occurs for equilibrium transport, as compared to space-charge dominated beams [Carlsten et al., this issue, Phys. Rev. ST Accel. Beams 8, 062001 (2005)PRABFM1098-4402]. In this paper, we describe the differences in transport stability when two-plane focusing is included. Two-plane wiggler focusing degrades the transport stability slightly, whereas two-plane PPM focusing greatly compromises the transport. On the other hand, single-plane PPM focusing can be augmented with external quadrupole fields to provide weak focusing in the sheet’s wide dimension, which has stability comparable to two-plane wiggler transport.