Electron series resonant discharges: Comparison between simulation and experiment

  • Qiu W
  • Bowers K
  • Birdsall C
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Abstract

Plasma discharges driven at the electron series resonance (ESR) frequency
have many desirable properties. The input resistance is small and
the drive voltage and current are in-phase. Also, the drive voltage
is small (similar toT(e)) and the average plasma potential is low
(similar to10T(e)). Particle-in-cell simulations with Monte Carlo
collisions (PIC-MCC) show that a strongly kinetic phase space bunching
process provides electrons of sufficient energy for ionization, allowing
discharge operation at low neutral pressures and low electron temperatures.
Simulations also show that, at these low pressures, the ion flux
to the wall has a narrow angular spread about the normal and the
ion bombarding energy distribution has a sharp peak at the plasma
potential. In this paper PIC-MCC simulations recreating the ESR discharge
experiment by Godyak are performed. The driven V-I characteristics
of a plasma diode (magnitude and phase angle) are measured in simulation
and found to compare well with experimental results. Steady state
characteristics and the response of an ESR discharge to slow changes
in RF drive amplitude and frequency are shown as well. The steady
state properties of an ESR sustained discharge are demonstrated in
simulations at different pressures. The applied RF voltage in these
discharges is comparable to the electron temperature and well below
the ion sheath potential. This is in stark contrast to capacitive
discharges where the ion sheath potential is comparable to similar
to0.8V(RF). Scaling laws at fixed pressure (n alpha omega(RF)(3),
s alpha omega(RF)(-1)) are shown to hold RF when RF is varied smoothly
('chirping'), demonstrating continuous density control. Hysteresis
is observed in the V-I characteristics. The behaviour about hysteresis
suggests resonant discharges should be initiated from a capacitive
state rather than from an inductive state.

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Authors

  • W. D. Qiu

  • K. J. Bowers

  • C. K. Birdsall

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