Intense electron-beam transport in the ion-focused regime through the collision-dominated regime

This paper reviews the transport of the 19-MeV, 700-kA, 25-ns Hermes-III electron beam in long gas cells filled with N2 gas spanning six decades in pressure from 10⁻³ to ∼10³ Torr. We show through measurements and theoretical analyses that the beam has two windows of. stable transport: a low-pressure window (between ∼1 and ∼100 Torr) that is dominated by propagation in the semi-collisionless IFR (ion-focused regime), and a high-pressure window (between ∼1 and ∼100 Torr) that is dominated by propagation in the resistive CDR (collision-dominated regime). In the CDR, 79±1.5% of the beam energy is transported over 11 m at 20 Torr. In the IFR we show that intense radiation fields with controllable rise times and pulse widths can be generated on axis at a bremsstrahlung target. In summary, the measurements and analyses presented here provide a quantitative description of the Hermes-III beam transport over six decades in pressure.