Wall Temperature Measurements Within a High-Power Inductive Plasma Discharge

Abstract

Electromagnetic plasma generators (inductive and helicon) are commonly used for planetary entry simulation and increasingly for electric propulsion applications. However, one obstacle in increasing the power and efficiency of these systems is a lack of knowledge regarding the distribution of tube wall temperature. The tube wall temperature acts as a mechanical limit to the thruster/generator operating conditions and is directly related to the distribution of thermal energy within the discharge volume. This paper presents the results of an experimental investigation to determine spatially resolved wall temperatures in a 180 kW inductive plasma generator. This investigation showed that significant wall heating does not occur until the midpoint of the inductive coil, increasing rapidly to reach peak temperature over a distance 15% of the total tube. During this rapid heating phase, one-third of the total tube heat flux is produced, assisting in quantifying previously observed mechanical failures due to thermal stress. The peak temperature difference between inner and outer wall surfaces was recorded as 619.1 K, approximately twice that of the previously proposed limit which considered integral rather than spatially resolved values. Using the results of this investigation, a refined estimate of critical wall temperatures for various tube thicknesses has been developed, allowing more targeted cooling systems to be implemented in the future generator designs.