Long pulse electron beam propagation

Propagation of a 1 μs electron beam over a distance of 90 m has been investigated in the EPOCH Laboratory at Sandia National Laboratories. The mode of propagation is Ion Focused Regime (IFR) transport. The plasma channel, which is required for IFR transport, is obtained by photoionization of trimethylamine gas with a krypton-fluoride laser. Beam voltage is 2.5 MV, and beam current is 1.1 kA. Propagation efficiencies better than 90% have been recorded. The ion hose instability is a key issue concerning long-pulse beam propagation. In previous work, growth of transverse beam oscillations (due to the ion hose instability) and moderate damping (due to phase-mixing) were measured in the first 6 m of beam propagation. Detailed displacement measurements in this region were used to determine the ion hose growth rate. [1,2] Damping of beam oscillations is accompanied by an increase in beam radius as measured from head-to-tail. This report describes extension of the previous work on ion hose in two areas: beam radius and beam displacement. A method which successfully reduced ion hose growth is also presented.