Multichannel rf-compensated Langmuir probe array driven by a single bias supply

Abstract

A multichannel Langmuir probe array driven by a single bias supply was constructed. For the probes to be used in harsh radio frequency (rf) environments, the individual probe has a rf-compensation circuit. For simultaneously obtaining I-V curves from the probe array, shunt resistors were placed between the probe tips and the active terminal of the bias supply. The pickup signal due to the stray capacitance of the signal lines and the shunt resistance is discussed. Modification of the probe bias circuit by utilizing lock-in amplifiers was attempted to obtain the electron energy distribution function. The multichannel probe array and the relevant circuit driven by a single bias supply were successfully tested to obtain plasma parameters from various plasma conditions not only in rf plasma but also in tokamak ohmic plasma. (C) 2002 American Institute of Physics.