Measurements of Beam Relaxation Length in an Electron Beam Plasma Experiment

Abstract

£ nb/no 2 x 10-2, and beam energy Wb 200 eV in an unmagnetized plasma, using argon and helium gases. The measured relaxation lengths show a transition from quasi-linear to nonlinear regime, as predicted by Galeev et al., 1977. There is evidence that for some range of the beam plasma parameters the threshold for modulational instability is reached. In that case it is possible to observe that the beam propagates relatively unperturbed for larger distances than the ones predicted by quasi-linear theory.]]>

End-boundary sheath potential, electron and ion energy distribution in the low-pressure non-ambipolar electron plasma

“…The general shape of the V A 300 V EEDf s in figure 3(c) was also reported in electron-beam-excited plasma [2,5,7] and plasma that contains a mono-energetic electron beam [26,27]. Miyano et al found that beam-electron energy is nearly equal to the plasma potential when the beam is strong [2].…”

“…Pal et al found that the electron-beam energy is almost equal to the applied source biasing voltage and the beam energy spreads due to various types of instabilities [5]. Prado et al revealed that when the beam density is high enough, beam relaxation length showed a transition from a quasi-linear to a nonlinear regime [26]. As a result, the electron beam can propagate through the plasma relatively unperturbed while retaining most of its energy [26].…”

“…Prado et al revealed that when the beam density is high enough, beam relaxation length showed a transition from a quasi-linear to a nonlinear regime [26]. As a result, the electron beam can propagate through the plasma relatively unperturbed while retaining most of its energy [26]. These research results well support the EEDf results in figure 3(c): when the extracted electronbeam power exceeds a critical value, the excess beam electrons cannot dissipate their power sufficiently and will pass through the NEP plasma and reach the end-boundary floating surface with their maximum energies approximate to the accelerator voltage.…”