Thermal velocity effects in magnetically confined beams

The spreading of magnetically confined electron beams caused by thermal velocities has been investigated theoretically and experimentally. An analysis of the spreading of confined beams of various geometries (strip, rectangular, and cylindrical) is presented. The thermal spreading of a confined cylindrical beam was measured at the anode of a parallel-flow Pierce gun. A transparent fluorescent screen was used for the anode. The spot size at the anode was measured as a function of magnetic field and an attempt made to relate the results to the theory.