Experimental Study On Start-up Transient Of Hall Thrusters

The Hall thruster is a typical plasma propulsion device with crossed electric field and magnetic field. Start-up of a Hall thruster is the first and also the most important step in its operation. The start-up process in a Hall thruster is a gas breakdown process with orthogonal electromagnetic field. An in-orbit thruster will be ignited for thousands times. The environmental differences and parameters changes will affect the reliability of ignition. Besides, the avalanche ionization of gas in the ignition process accompanied hundred amps of instantaneous current will impact the entire power supply system and affect the safe operation of the Hall thruster system. So it is necessary to study the reliability and surge current of Hall thrusters ignition process, and the subject exhibits important theoretical and applied significance.First of all, based on the gas discharge theory, the physical mechanism of start-up transient in a Hall thruster is studied. The dark current characteristics in channel of thruster are given through changing the discharge voltage and the voltage characteristic of dark currents is obtained. The results show that t he dark current voltage characteristic curve can be divided into linear segment and exponential increase segment, the slope of the linear segment and the increase rate of the exponential increase segment are all proportional to the flow rate of anode and inversely proportional to the magnetic field strength, which respectly related to electron conduction and successive collisions. Then, based on the dark current trends with ignition parameters, the experiments of boundary of Hall thrusters ignition by reducing coil current are carried out. The results draw conclusions of the relationship between ignition border and discharge parameters.Secondly, with the results of pressure measurement and ignition experiments under varying discharge parameters, the formation mechanism and characteristics of pulse current in the start-up transient are studied. It is indicated that the current peak of thruster is proportional to the mass flow rate and anode voltage, while the duration of pulse current is proportional to the mass flow rate and inversely proportional to anode voltage. At the same time, it shows that the magnetic field intensity do not affect the ignition surge current, but affecting the ignition border. It is also illustrated that integrated area of pulse curren t during ignition process is determined by the density of atoms in the discharge channel before ignition.Thirdly, the pulse current in the power supply side is one of the important factors that affect the safety of the power supply system. Based on the un derstanding of pulse current of thruster and the characteristics of the fiter unit in the discharge circuit, the formation mechanism and influcing factors of the pulse current of supply are given. Moreover, the theoretical prediction formula of pulse curre nt on the power supply side is deduced. The theoretical results have a good coincidence with the experimental results. Then reference to the above theoretical analysis and comparison of the power pulse current peak under the different inductor, the optimization direction of filter inductance is given.Finally, from a practical point of view, the influence of ignition parameters on the reliability and surge current of the Hall thruster ignition process are studied by the semi-quantitative analysis. Taking into accout the design contradiction between the ignition reliability and surge current during start-up transient, the concept of ignition margin is introduced. Then, based on multiple ignition experiments, the influence of ignition parameters, component parameters of ignition circuit, cathode characteristic and the vacuum degree of ignition margin are given. Further, according to the above results, it is indicated the optimization direction of ignition parameter and practical design methods.