Nonlinear circuit analysis of intermodulation currents in a floating Langmuir probe with a capacitive load

Abstract

When dual frequency ω α, ω β voltages with small amplitudes are biased toward a floating Langmuir probe, intermodulation currents of i ω β ± ω α, i ω β ± 2 ω α are generated due to the nonlinearity of the sheath near the probe tip. Electron temperatures and plasma densities can be obtained from the intermodulation currents using the sideband method. If the probe has a capacitive load such as a contaminated probe tip, harmonic and intermodulation voltages of the probe bias can be applied to the sheath. The sideband method can be modified using a harmonic balance technique that analyzes the nonlinear circuit. The intermodulation currents from the modified sideband were compared with the measured intermodulation currents. The electron temperatures and plasma densities obtained from the intermodulation currents are in close agreement with those of the electron energy probability functions in argon inductively coupled plasmas.