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Beam Handling and Emittance Control

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Technical rept. 1 Sep 1986-28 Feb 1988

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This report reviews the results of calculations which concern techniques of beam handling and emittance control for high current beams in advanced accelerators. Beam quality requirements for acceptable performance of beam driven free electron laser devices for SDI missions are examined. The beam quality achievable in high current, space-charge-limited diodes is reviewed and found to be potentially high. Emittance growth during gas-focused transport due to streaming instabilities between beam electrons and gas ions is briefly examined, and estimated to be modest. The principal threat to beam quality degradation is estimated to occur during the lengthy process of acceleration and transport past protuberances, constrictions, or discontinuities in the waveguide wall, or during beam aperturing. A Hamiltonian-theoretic analysis of emittance growth during high current electron beam transport, coupled with an envelope equation analysis of the induced transverse beam oscillations, is applied to develop scaling laws for the emittance growth suffered during such events as beam acceleration, propagation past irises or constrictions in the waveguide wall, beam aperturing, and axial variation in the magnetic guide filed strength. Criteria area developed for preventing excessive emittance growth by avoiding abrupt axial variations and providing sufficiently strong focusing forces. Designed variations in the waveguide wall shape and and in the strength of the magnetic guide field may be introduced to greatly reduce emittance growth during such events as beam acceleration. Keywords Strategic defense initiative Beam brightness Emittance control Beam quality Beam transport Image charge fields.

Subject Categories:

  • Antimissile Defense Systems
  • Directed Energy Weapons

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