Time-dependent degradation of an ion-focused ATA beam

The authors have made detailed measurements of the time-dependent beam quality of an ATA pulse transported on a KrF laser-photoionized benzene channel. The authors have found that the tail portion (τ ≥ 20-30 ns) of the pulse becomes severely degraded both at high currents (I > 3kA) and at long transport distances. Non-axisymmetric channel ion motion is suspected as the predominant source of the problem. The authors discuss various experiments which varied laser properties (timing, fluence, profiles), background ion pressure, and electron beam current in order to study the physics behind this degradation. 4 refs., 2 figs