Research On The Propulsion Perfermance Of Laser Induced Discharge Plasma

The laser-assisted pulsed plasma thruster(LAPPT)combines the advantages of Laser propulsion and electromagnetic propulsion to achieve a wide range of impulse control while providing low cost and high specific impulse characteristics.In this thesis,a LAPPT suitable for multiple propellants was designed,and the working characteristics and propulsion performance have been studied systematically.The laser-plasma characteristics are firstly studied experimentally.By using an intensified charge-coupled device,the laser-plasma plume was imaged and the speed of plasma wavefront was measured.It is demonstrated that the plasma velocity of polytetrafluoroethylene(PTFE),alumina,and aluminum are degressive.A Langmuir single probe was designed to diagnose the evolution of electron temperature and electron density of the alumina plasma produced by laser.During 1~6 ?s,the plasma potential is about 8 e V,and there are two peaks on the electron temperature curve,about 23.3 e V and 3 e V.Meanwhile,the electron density is between 1010~1011 cm-3.In addition,the measurements of laser propulsion performance show that the impulse of aluminum plasma is 1.65 ?Ns and that of alumina plasma is 0.46 ?Ns.Secondly,the researches on the characteristics of laser induced discharge indicate that the propellants of LAPPT have little effect on the resistance and inductance of the discharge circuit,but only cause different discharge delays.The evolutions of plasma plume during the discharge processes were also studied,drawing the following conclusions: In terms of light intensity,the plasma emission intensity varied periodically,out of synchronization with the current;In the aspect of plasma formation,plasma can be regarded as a whole under the condition of low current,and it will disperse into flocculent in the high current circumstance;In respect of the ablation of propellants,PTFE is badly ablated with low ionization degree in the discharge process,so it is not suitable to be used as the propellant of LAPPT.Thirdly,a theoretical model combining the laser-plasma characteristics calculated via MULTI program with the Slug model was proposed to simulate of the propulsion performance of the LAPPP loaded aluminum propellant.The results show that the impulse bit and the impulse coupling coefficient from the numerical simulation are in good agreement with those from the experiment,and the trend of the thrust efficiency with the discharge voltage is consistent with the experimental result.Finally,in order to investigate the influence of the electrode size on the LAPPT's propulsion performance,the time-of-flight spectra of LAPPT with different geometrical dimension were measured by using a Faraday cup.It was found that the thrust generated in the discharge process is attributed to the secondary ionization of neutral particle.Moreover,the propulsion performances of LAPPP were estimated.When the plate width was 5 mm and the discharge voltage reached 450 V,the impulse bit of the LAPPP that uses alumina as the propellant attained maximum,about7.9 ?Ns,while the specific impulse about 6650±350s,the impulse coupling coefficient about 38.6 ?Ns /J,the thrust efficiency of 10.4% were achieved.