QUASI-INSTANTANEOUS LANGMUIR CHARACTERISTIC DISPLAY FOR STEADY-STATE PLASMA PERTURBED BY UHF REPETITIVE PULSE

A technique for fast characterization, through Langmuir probe diagnost ics, of a steady state plasma perturbed by a repetitive UHF wave train is presented. By opening an instantaneous narrow window at a given de lay synchronously with respect to the frequency of the periodic pulse modulation, an averaged sample of the probe current is memorized while the probe potential is slowly sweeped. A Langmuir characteristics is then integrated and displayed. The use of this technique for the displ ay of temporal and spatial profiles of the electron density and temper ature in a UHF pulsed, low-temperature plasma experiment is described. The Langmuir probe measurements were performed both inside the pulse duration time and in the interval between two successive pulses.