Numerical Simulation And Experimental Studies Of Pulsed Plasma Thruster Plume

As a competitive electric propulsion system, pulsed plasma thruster (PPT) has combined advantages of high specific impulse, low power, simple structure, light weight, high reliability and so on. It is considered as an attractive propulsion option for a variety of applications including altitude control, station-keeping, drag compensation and constellation control of formation flight. In recent years, PPT has become the recipient of much interest in the microsatellite community.Integration of PPT onboard spacecraft requires the mastery of plume's characteristics and distribution, the evaluation of potential plume/spacecraft interactions. In this thesis, a hybrid model is employed to simulate the unsteady plasma plume expansion processes of a NASA Glenn Research Center PPT. Neutral plume species are modeled with the Direct Simulation Monte-Carlo (DSMC) method. Ion plume species are modeled with the Particle-in-Cell (PIC) method.Electrons are modeled as a massless fluid. The effectiveness and validity of this model are demonstrated by comparison to previously published experimental data. Simulation results show the expansion of neutral species as a relatively compact puff of gas, the emergence of two high-concentration regions of ions with different velocities, the generation of slow ions and fast neutrals due to charge exchange collisions, and the generation of neutral and ion backflow. The simulation also reveals that, as a result of electric field effects, ions have greater velocities relative to neutrals in the backflow area, and the charged species are spread over a larger region than the neutrals.The basic principle of langmuir probe diagnostics is presented, and the specific methods of measuring the unsteady PPT plume using a single probe are discussed; furthermore, a trigger circuit is designed to carry out the diagnosis. The composition of the PPT plume is studied by means of mass spectrum analysis, identifying C, F, CF, CF2, CF3, CF4 and various sputtering materials. High speed photography is conducted inside the electrode channel to observe the discharge process. An analysis of these images shows that, propellant decomposes and ablates after discharge for a long time, thrust generated in the positive current phase is larger compared with the reverse current phase, the plume is drawn towards the cathode electrode, producing a thrust component towards the anode electrode.