Electron transport dynamics in a 10.8-m gas cell operating in the collisional regime on HERMES III

Summary form only given. The compound-lens diode is used to extract and inject the 19-MV, 700-kA, 25-ns electron beam from HERMES III into long, gas-filled metal drift cells for transport in the collisional regime to targets for bremsstrahlung production. Efficient and stable transport is required for optimal and repeatable bremsstrahlung production. The transport has been characterized as a function of injection parameters and gas pressure over the range 0.5 to 630 torr. It has been shown experimentally and theoretically that the region of optimal energy transport lies in a "propagation window" between two regions of instability caused by beam-plasma interactions. Below /spl sim/2 torr, as the ratio of the collision frequency to plasma-electron frequency decreases, the semi-collisionless two-stream instability disrupts the beam. Above /spl sim/80 torr, as the plasma-electron mean-free-path is reduced by dissociative recombination with gas neutrals, the resistive hose instability enhances transverse oscillations in the beam centroid.