The Advanced Test Accelerator (ATA) is a linear induction electron accelerator whose design parameters are 50 MeV, 10 kA and 70 ns pulse duration. The key physics issues affecting performance of the accelerator involve beam dynamics during transport through the accelerator structure. In this report, we present experimental results describing the initial operating phases of ATA. These results illustrate the complexity of the beam transport phenomena but also indicate the means to stabilize beam dynamics. Improvements in beam transport, which result from deploying various stabilization techniques, are also presented.

Experiments with the Astron beam (5 MeV, 0.4 kA) and an FX-25 beam (1.5 MeV, 15 kA) show that the transport of self-focused electron beams in neutral gases is limited by two Instabilities. At gas pressures from nearly zero to a few torr, the propagation is dominated by a form of two-stream instability. At higher pressures the resistive hose instability dominates. Between the two regimes, a pressure window exists in which the higher current diode beam propagates stably in both conducting and Insulating drift tubes.

Measurements of the radial expansion from gas scattering of a low ν/γ relativistic electron beam are presented. The measured current density profiles approach a Bennett shape, as predicted theoretically, and the rate of expansion of the beam radius with distance is in good agreement with the predictions of an envelope equation. locus has been determined. It terminates at zero temperature at

in this region has never been demonstrated and constitutes the major uncertainty of the proposal and determines the critical path for project completion. This study produces a better understanding of the physics involved in chopping an H-beam in a dilute plasma background, and in transporting a chopped H-beam through a neutralized or partially neutralized plasma channel, as well as an estimate for the optimum neutralization strategy for the beam chopping and transport between the ion source and the RFQ.

This report describes important experimental results obtained in the last two years of the Astron Program, an LLL controlled nuclear fusion program which terminated in 1973. Little theoretical work is included, but an extensive bibliography is given. (auth)

A 150-A, 4-MeV electron accelerator has been designed and constructed for use in the ``Astron'' experiment. Design requirements include a beam quality less than 10−2 rad·cm and an energy spread of ±0.5%; the pulse length is 0.25 μsec and the repetition rate is variable to a maximum of 60/sec. The accelerating principle used is magnetic induction. Design features and the results of preliminary operation are discussed.