Electrostatic and Magnetic Pinch Effects in Beam-Generated Plasmas

Abstract

A kilovolt electron beam of a few mm diameter passing through a gas at pressures of 10⁻² Torr or lower is not significantly scattered by collisions with neutrals in distances of many beam diameters. The beam will ionize the gas and generate a plasma that has a potential distribution that will cause the beam to be pinched toward its axis. This electrostatic pinch effect is compared with the magnetic pinch and the electrostatic pinch is found to be the dominant effect at low voltages and currents. Experimental results confirming the results of early experiments at a few hundred volts demonstrate that the electrostatic pinch exists at higher voltages and can be more important than the magnetic pinch at voltages up to the order of 100 kV for typical plasma electron temperatures and beam currents. Computer studies of beam trajectories in a simulated beam‐generated plasma provide an explanation for the detailed structure of the beam profiles that have been observed.