Rf. Hubbard et al., SIMULATION OF ELECTRON-BEAM TRANSPORT IN LOW-PRESSURE GAS CONDITIONING CELLS, Journal of applied physics, 73(9), 1993, pp. 4181-4196
The resistive hose instability can disrupt propagation of self-pinched
beams in dense gas. To reduce growth of the instability, beams can be
conditioned prior to propagation. The objectives of beam conditioning
are to center the beam in order to reduce initial transverse perturba
tions which seed the hose instability, and to ''tailor'' the beam emit
tance in order to detune the head-to-tail coherence of the instability
. Emittance tailoring can be performed by transporting the beam throug
h a ''passive ion-focused regime'' (IFR) cell, a low-pressure gas cell
that induces a head-to-tail taper of the beam radius. The radius tape
r is then converted to an emittance taper by passing the beam through
a thick exit foil which scatters the beam. Beam centering can be accom
plished by transporting the beam through either: (i) a passive IFR cel
l that is narrow enough to provide wall guiding, or (ii) a laser-ioniz
ed ''active'' IFR cell, or (iii) a wire cell in which the centering is
provided by a current-carrying wire. Axisymmetric particle simulation
studies of IFR tailoring cells, alone and in tandem with each of thes
e types of centering cells, and also the effect of supplementary focus
ing lenses and conducting foils are reported. The parameter choices th
at are conducive to effective beam conditioning are discussed. The emp
hasis is on conditioning configurations and beam parameters that have
actually been tested in experiments with the Advanced Test Accelerator
and SuperIBEX accelerator.