Design and construction of a computer-controlled data acquisition system for use on a Langmuir probe

Abstract

The Plasma Physics Laboratory (PPL) of the National Institute of Physics makes use of an ion beam source for studying TiN-film formation via a plasma-sputter type ion source. One of the diagnostic tools incorporated into its main chamber is a Langmuir probe. The probe is used to make localized measurements of the plasma characteristics which includes the electron density and the electron and ion temperature. The bias of the probe during experiments is with respect to ground. The system for automating data gathering with the Langmuir probe is described here. Signals are digitized by the analog-to-digital converter and is stored into the computer for processing. The entire system is controlled and calibrated by a program written in C. The program also includes data processing functions for calculation of the plasma parameters from the stored data. The system is tested on a glow discharge produced inside the ion source chamber. The data processing technique presented in this study would serve as a valuable aid in facilitating the procurement and interpretation of experimental data. By means of the method presented here, the plasma parameters can be independently measured at the same time as other experiments on the plasma are conducted.