High-power electron-beam transport in long gas cells from 10−3 to 103 Torr nitrogen

Measurements and analyses show that the 13 TW, pulsed Hermes-III [J. J. Ramirez, Proceedings of the 1989 Particle Accelerator Conference, Chicago, 1989 (IEEE, New York, 1989), p. 1446] electron beam, with current near the Alfvén limit, has two regimes of stable transport: a low-pressure window (between ∼1 and ∼100 mTorr) that is dominated by propagation in the semicollisionless 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). Below ∼1 mTorr, there is insufficient ionization to confine the beam; between the windows, the two-stream and hollowing instabilities disrupt propagation; and above ∼100 Torr, the resistive hose instability degrades propagation.