Radio-Frequency Probes in a Nonlinear Isotropic Plasma

Abstract

Nonlinear cold-plasma and scalar-pressure theories are derived and applied to a spherical RF probe in a plasma. With two specified RF potentials on the probe at different frequencies, calculations are presented for the second-order probe output responses. These include the second harmonic, the sum and difference frequencies, and the d.c. increment (resonance rectification). The nonlinear response as a function of frequency is shown to depend strongly on whether the input signals are maintained at a constant current or a constant voltage; for diagnostics, the constant-current technique permits identification of the plasma frequency, whereas the constant-voltage technique does not.