Investigations of Growing Waves Excited in a Plasma by an Electron Stream

摘要

An experiment was constructed for the study of waves excited in a plasma by an electron stream. A PIG source generates a hydrogen plasma of density up to 10 to the 13th power/cc and 30 eV electron temperature, confined by a 500 gauss field. A 40-milliampere, 1000-volt electron beam is pulsed into the plasma. Coherent, growing waves are excited at frequencies typically near 500 mc when the plasma frequency is 1800 mc and the cyclotron frequency 900 mc. The wave grows in both space and time until reaching a limiting amplitude, after which it decays; this entire process repeats at about a 40 mc repetition rate at a power level of several watts. Diagnostic equipment includes a 3000 mc oscilloscope, a spectrum analyzer, and various probes. If the dispersion equation governing the waves is solved for the finite geometry of the experiment, it becomes apparent that the growth occurs because of the interaction between the slow plasma wave on the electron beam and the electron cyclotron wave in the plasma. (Author)