Experimental And Theoretical Study On The Energy Distribution Mechanism In Pulsed Plasma Thrusters

Pulsed plasma thrusters(PPTs)are high specific impulse,reliable,relatively simple,inexpensive,and able to operate at less than 10 W,making them useful for applications such as altitude control for satellites and propulsion for microsatellites and nanosatellites.However,the thrust efficiencies of PPTs are very low(usually <10%)compared with most other electric thrusters,such as ion thrusters and Hall thrusters.In the past 50 years,many researches were carried out to improve the PPT thrust efficiency.However,less studies were about the PPT energy distribution mechanism which is very important for improving the thrust efficiencies in PPTs.Therefore,the PPT thrust efficiency is still low now.In this paper,the energy distribution mechanism of PPTs is studied to investigate the reasons of the low thrust efficiencies in PPTs and provide a reference for the design of high-performance PPTs.At first,the energy distribution mechanism in PPTs is analyzed.The results show that the PPT thrust efficiency(the ratio between the kinetic energy which is computed by the average velocity of fluid jets and the total energy)is lower than its efficiency(the ratio between the kinetic energy of fluid jets and the total energy)because the velocities of the fluid jets are different.The thrust efficiency is an important PPT performance parameter which is proportional to the product of the specific impulse and the thrust power ratio.The efficiency is just a factor which affects the value of the PPT thrust efficiency.No only the energy conversion but also the fluid jet velocity distribution would affect the value of PPT thrust efficiency.If the impulse provided by the neutral gas is ignored and the plasma velocities are assumed to be equal,the thrust efficiency is equal to the product of the efficiency and the propellant utilization(the ratio of the plasma mass and the total propellant ablated mass)of PPTs.The PPT discharge circuit and ideal PPT are analyzed,the results show that the energy distributions would affect the thrust performances of PPTs.To improve the thrust efficiency of PPTs,a new PPT named multi-pulse discharge PPT is proposed.The multi-pulse discharge PPT is a PPT which stores its energy to two or more capacitors and releases energy through the capacitor discharges at difference times and spaces to control the energy distribution in the PPT.Secondly,the energy distribution mechanism in PPTs is studied by simulation.An one-dimensional multi-sheets model which can simulate the gas ionizations and rarefied plasma flows between the electrodes of PPTs is established.Several PPTs which were studied in the past are simulated by new model.The results show that the new model can be used to simulate the ionization processes and rarefied plasma flow processes in PPTs simply.The gas ionization simulation results indicate that an PPT with a lower average propellant ablation rate and higher average electric field intensity between electrodes should have higher propellant utilization.The thrust performances of PPTs can be estimated using this model as well.The model provides a new tool with which to study the physical mechanisms of PPTs and a reference for the design of high-performance PPTs.The energy distribution mechanism in an classical single discharge PPT is studied in this paper.The discharge parameters and the propellant ablated mass are measured to estimate the thrust performance parameters of the PPT.The propellant utilization of the single discharge PPT is obtained by the multi-sheets model which is established in this paper.The energy distribution mechanism of the PPT is analyzed.The results show that the impulse bit,the thrust power ratio,and thrust efficiency of the PPT increase as the capacitor voltage increased,the specific impulse of the PPT decreases at first and rises latter with the increasing of the capacitor voltage.However,the simulation results show that the propellant utilization of the PPT decreases as the the capacitor voltage increased.The energy distribution analysis results show that the energy loss is higher when the PPT is working at a lower capacitor voltage which leads to a lower efficiency.An double electrodes PPT is designed in this paper.The energy of the double electrodes PPT is stored in two capacitors and discharges at difference space(electrodes).The discharge parameters of the PPT are measured to estimate the thrust performance parameters.The results show that the double discharge PPT has higher impulse bit,specific impulse,and thrust efficiency comparing with the single discharge PPT which has same discharge energy.The specific impulse and thrust efficiency of the double electrodes PPT increase as the secondary capacitor energy increased.The impulse bit of the double electrodes PPT decreases at first and rises latter with the increasing of the secondary capacitor energy.An double electrodes PPT which has longer insulation channel would has lower thrust performance.According the energy distribution analysis,the reason why the double electrodes PPT has a higher thrust efficiency is that more energy is distributed to the plasma kinetic energy which lead to a higher efficiency.The breakdown process of PPTs is investigated in this paper to provide references to the design of multi-pulse discharge PPTs.The results show that there is a time delay(~1–10?s)between spark plug ignition and capacitor discharge.The delay time decreased as the capacitor voltage increased,and in increased as the electrode gap widened and the number of APPT ignitions increased.The delay time can be ignored for the design of multi-pulse discharge PPTs.