Visualization of Spokes Mode in a Hall Effect Thruster

Abstract

The present work investigates the dynamics of rotating spokes modes in a Hall Effect Thruster (HET) also known as a Stationary Plasma Thruster (SPT). Understanding these modes is important to investigate electron transport phenomena which constitute power losses for the thruster. Furthermore, the results may be inputs to future simulation studies. In this paper, post processing technique of raw images to visualize the spoke modes is presented. Images of an 85 mm mean diameter SPT anode channel, operated at 783 W at a pressure of 3.2 𝑥 10 𝑚𝑏𝑎𝑟 were acquired via a High-Speed Camera. The images so obtained were extremely saturated with the cathode intensity while the anode channel intensity was dominated by its DC component. Automated image processing techniques were then applied. In this process, the images were normalized with respect to the camera specifications and the cathode and anode were segmented from the anode channel image frames using Otsu's thresholding. The normalized and extracted regions are subjected to a string of post-processing involving normalization by mean image and removal of noise and the DC component. This resulted in an improved contrast as well as removal of saturation in the images due to the cathode, enabling one to focus exclusively on spokes modes.