General Cause of Sheath Instability Identified for Low Collisionality Plasma in Devices with Secondary Electron Emission
Authors: M.C. Campanell, A. Khrabrov and I Kaganovich
Abstract:
A condition for sheath instability due to secondary electron emission (SEE) is derived for low collisionality
plasmas. When the SEE coefficient of the electrons bordering the depleted loss cone in energy space exceeds
unity, the sheath potential is unstable to a negative perturbation. This result explains three different instability
phenomena observed in Hall thruster simulations including a newly found state with spontaneous ~20MHz
oscillations. When instabilities occur, the SEE propagating between the walls becomes the dominant
contribution to the particle flux, energy loss and axial transport.
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Submitted to: Physical Review Letters, APS (May 2012)
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