Coherent Structures in Plasmas Relevant to Electric Propulsion

Abstract : Magnetized plasmas in E x B configurations exhibit complex behavior resulting in variety of turbulent and coherent fluctuations that can critically affect E x B plasma thruster devices and performance. Rotating structures have been observed in laboratory and technological plasma devices with magnetized electrons and non-magnetized ions. These oscillations have low mode number with a characteristic frequency that lies between the electron and ion gyro-frequencies. Experimental studies of Hall and Penning discharges demonstrated that low frequency (10s kHz) disturbances contribute to electron cross-field transport. Studies carried out in mesoscale magnetrons place these coherent fluctuations at much higher frequencies (100s of kHz) and also contribute substantially to the electron transport. For Hall thrusters, electron cross-field transport is of practical importance because it diminishes the thrust efficiency. Fluctuation-induced transport reduces the local electric field, potentially leading to increased plume divergence and thruster wall erosion. This program is to better understand the physics behind these fluctuations and their relevance to propulsion devices through experimental, theoretical, and numerical studies.