Numerical and experimental investigation of inductively coupled plasma cathode for electric propulsion applications

Abstract

Plasma cathodes are insert free devices that are developed to be employed as electron sources in electric propulsion applications as a practical alternative to more commonly used hollow cathodes. Inductively coupled plasma (ICP) cathode, or Radio Frequency (RF) plasma cathode, is introduced in recent years. Because of their compact geometry, and simple and e cient plasma generation, RF plasma cathodes have certain advantages over hollow cathodes. In this thesis, RF plasma cathodes have been investigated theoretically and experimentally. Extraction of electron from plasma cathode devices, and especially RF plasma cathode, strongly depends on the formation of a secondary plasma known as \anode spot." Previous Experimental studies show that the anode spot electron density and electron temperature is higher than the bulk plasma. Before the formation of the anode spot, the extracted electron current from the device is very low. By the formation of the anode spot, extracted current increases dramatically. In this thesis, it is demonstrated that the anode spot is a nonequilibrium steady state (NESS) plasma. The non-equilibrium nature of the anode spot is put forward as the reason for high electron generation and high electron density inside it. The jump in the extracted electron current is due to high electron generation inside the anode spot. Two di erent concepts of RF plasma cathode are designed and manufactured. Experimental measurements have been conducted to study the e ects of geometric and operational parameters. Experimental studies in this thesis show that operation of the RF plasma cathode device strongly depend on the geometric parameters such as ori ce diameter, chamber length, chamber diameter, antenna geometry, as well as the operational parameters such as RF power and gas mass ow rate.