Design and Development of Automated Linear Feed-through Drive for Electric Probe Measurement in Plasma

Abstract

Plasma experiment requires point to point measurement of plasma accurately and precisely. The objective of this project is to develop motorized Linear Vacuum feed-through drive for an electric probe to acquired the data two dimensionally. A software in Labview has been developed for the analysis of various plasma parameters like Floating potential, Plasma potential, Electron temperature and Electron density using Tangent method, First derivative and Second derivative method. Usually electric probes are inserted inside vacuum chamber that typically withstand very low vacuum on the order of 10−4 Pa. The probes feed-through must withstand the differential pressure while the probes position is precisely maneuvered with linear displacement as small as 1 mm. In order to achieve this, stepper motor is used for driving the probe shaft. The probe drive is designed with two movable parts, a rotational axis for turning the probe while inside the plasma device and horizontal axis for moving probe in and out of the chamber. The horizontal axis consists of ball screw set upon base blocks at each end with a stepper motor attached in the back. The ball screw having pitch 5mm, thus it moves slider at 5mm per turn with motor turning at increments of 1.8 degree. Rotational motor mounted on the carriage provides the angular motion with an accuracy of 10 degree turn. Using Automated Linear feed-through drive, electric probe has been driven at various radial and linear locations. Electron temperature and electron density were measured at various distance. Using L-shape electric probe, data were obtained at various angles, and plasma potential were observed at various distance and angles.A software prepared in Labview along with an oscilloscope is used for data acquisition at precise intervals inside the vacuum chamber so that analysis of plasma parameters for all the possible profiles can be achieved.