Resonant Mode Transition in the RF-Controlled Hollow Cathode


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Resonant Mode Transition in the RF-Controlled Hollow Cathode


Abstract

The mechanism behind a sharp transition from low- to high-plasma-density modes that was recently discovered through numerical simulations of a promising hollow cathode concept is investigated using numerical modeling. The RF-Controlled Hollow Cathode concept adds radio-frequency power to a large-diameter cathode for high-power, long-lifetime electric thruster applications. By exploring the basic parameters and behavior of a simplified two-dimensional model where an RF plasma is introduced into a thermionic cathode, it was found that a nonlinear transition was caused by both a jump in the electric field amplitude due to a resonant cavity condition and an increase in the reduced electric field E/n0 from neutral depletion. This transition results in an increase of the maximum plasma density by an order of magnitude, which benefits the cathode’s operational lifetime and discharge current capability. Surface waves were ruled out as a transition contributor as the model does not account for them, though they may be present in future experimental studies. Evidence for a beneficial hysteresis in the operational parameters of the cathode is also presented.