Behavior of relativistic electron beam in a gas-filled drift tube as a function of gas pressure

Several issues pertaining to electron-beam propagation and techniques for risetime enhancement of the Aurora electron beam and bremsstrahlung pulses are examined. Time-varying models for the double-humped current waveforms produced by propagating relativistic electron beams through gas cells of various pressures and gas species are developed and compared with experimental results. There is a pressure region in which the electron beam propagates until a virtual cathode is formed. At later times the virtual cathode is neutralized by the formation of positive ions by collisions between gas molecules and relativistic electrons. The beam can then propagate. The passage of the electron-beam through a gas cell can be used to control the risetime, pulse width, and general pulse shape of the final bremsstrahlung temporal pulse shape. At higher pressures (200 mtorr-He) nose erosion sharpens the 70-ns Aurora pulse risetime to approximately 20 ns. There is, however, a double-humped phenomenon at lower pressures