Extraction of large-area low-energy electron beams from a multi-dipolar plasma

Production of large-area low-energy electron beams extracted from low-pressure plasmas is investigated. In order to extract electron beams of given energy from a plasma, the plasma potential, as referred to the wall potential, must be stationary and independent of the extraction potential. Macroscopic neutrality of the plasma therefore requires that reactor walls are metallic and that the ratio of extraction area to reactor wall area is less than the square root of the ratio of electron to ion mass. These conditions are fulfilled in the source presented in this study where electrons are extracted from a multi-dipolar plasma sustained by microwaves at electron cyclotron resonance. Variations in plasma and beam potentials are measured by Langmuir probes as a function of the applied extraction voltage (0-200 V), showing that the electron energy varies according to the extraction potential. Electron source behavior and experimental results appear in good agreement with those expected from discharge balance calculations.