Analog Plasma Diagnostic System

Abstract

The simple electronic diagnostic system described provides a calibrated oscilloscope display of a Langmuir probeI‐Vcharacteristic, its first and second derivative curves, the electron energy distribution function, and the ``cumulative'' electron number density. The system also provides a simple method for determining plasma potential and—if it exists—the electron temperature. Data taken in a low temperaturemercury discharge are compared with data taken by means of the well known harmonic second derivative technique. An electron number density of 4.9×1016 m−3 and an electron temperature of 9.7×103 K found with the new system compare very favorably to values of 4.7×1016 m−3 and 9.9×103 K determined from the harmonic second derivative data. The system described features more rapid data reduction and lower cost than harmonic systems.