ISSN:
1089-7674
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Motivated by the recently revived interest in electric propulsion, the neutralization regime of an ion thruster is investigated by means of a three-dimensional particle-in-cell simulation. Electrons enter the simulation box with a half-Maxwellian velocity distribution, while the ions are injected with a uniform bulk velocity. Focus is put on the dynamics of the electrons, and the actual electron to ion mass ratio of 1:250 000 is used. The injection velocity ratio η:=ve0th/vi0 between electron thermal velocity and ion bulk velocity turned out to be a crucial parameter for the electron dynamics within the plasma beam: For η〈1.7 a moving electrostatic shock forms with a potential jump of a few kTe0/e. Downstream of the shock front, the electron plasma becomes fully Maxwellian and drifts with the ion bulk velocity. For η〉1.7, the electrons still obtain a drift velocity roughly equal to vi0 within a few electron inertia lengths behind the emitting plane. However, a shock front does not form, and the electron velocity distribution does not become Maxwellian. On the basis of a tentative model, in which the plasma beam is regarded as a self-similarly expanding electron diode, the shock front can be identified with a kind of virtual cathode and the dependence of the shock velocity on the beam cross section can be explained. © 2000 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1322060
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