Study On Ablation Characteristics And Propulsion Performance Of Nano-Modified Working Mediums In Laser-Electromagnetic Thruster

Laser-electromagnetic thruster has the characteristics of light weight,small volume,high specific impulse,high control accuracy and long service life.It can significantly increase the payload of space vehicle,shorten the flight time and extend the service life.It is suitable for deep space exploration,manned lunar landing,Mars development and other space missions.The performance of the laser-electromagnetic thruster can be further improved by modifying the working mediums.Therefore,in view of the demand of the laser electromagnetic thruster for high-performance working medium,based on the current commonly used solid polymer working medium,the development of the modified solid polymer working medium with better performance has become the focus of current research.In this paper,the nano-modified working mediums in laser-electromagnetic thruster are taken as the research objects.From the perspective of improving the absorption rate,ionization rate and thermal conductivity of the working mediums to laser,the ablation characteristics and propulsion performance of the nano-modified working mediums in laser-electromagnetic thruster are studied by the numbers through the method of comprehensive application of theoretical analysis and experimental research,mainly including:using optimized process to prepare the modified working mediums,building the ablation characteristics（the ablative mass,the ablative pit morphology,the ablative plume）andpropulsion performance（the impulse bit）platform.Under condition of different laser energy,different kinds of dopants and different ranges of doping ratios,the ablation mass and impulse bit of the laser ablative modified working mediums were measured,the micro morphology of the ablation pit was observed,and the kinetic process of the ablation plume was dynamically displayed.According to the experimental results,the influence rules of the type,proportion of the modified working mediums and the laser energy on the ablation characteristics and propulsion performancewere obtained,and the influence mechanism was explored.The results show that the ablation characteristics of the laser-electromagnetic thruster can be significantly improved by the modified working medium doped with dark nanoparticles of high thermal conductivity,and the improvement of the propulsion performance of the laser-electromagnetic thruster is better by the modified working medium doped with nanoparticles of low ionization energy.The main conclusions are as follows:（1）With the increasing of pulse width,the laser energy increases,the ablation mass of modified working mediums increases.The ablation mass can be improved obviously by the modification of working mediums,and in the range of doping ratio which is large enough,the ablation masstrend of the modified working mediums doped with different kinds of dopants is“increase-stability-decrease”with the change of doping ratio.The specific change is related to the physical properties of the dopants.（2）The ablation area and depth of the modified working mediums increase with the increasing of pulse width.The change of ablation area and depth with the change of pulse width and doping ratio can explain the change of ablation quality.Experiment finds that some of the modified working mediums have condensation ring around the ablation pit under certain laser energy and doping ratio,which will significantly reduce the utilization of laser energy of the modified working mediums.（3）For modified working mediumsof which the ablative plume is obvious,with the increase of pulse width,more energy will deposite in the modified working mediums in unit time,the time that the working mediums producing ablation plume will be earlier,the density of the generated ablation plume will be greater,the velocity of ablation plume will be faster,the arrival location of the front position will be farther in the same moment and the pulme influence area will be larger.With the increase of dopant ratio,the brightness of ablation plume of the modified working mediums is higher,which means higher plasma density and ionization degree.The larger the doping ratio is,the farther the ablation plume front position is in the same moment,which means higher ablation plume velocity.However,the modified working medium doped with Ti O₂ or KCl failed to produce obvious ablation plume due to its low ablation quality.（4）For different kinds of modified working mediums,the impulse bit increases with the increase of laser pulse width,however,the ablation quality increases faster,so the specific impulse under the pulse width of 1ms is the highest.Due to the limitation of thruster power,the ablation products of the modified working mediums are not fully ionized and accelerated,so the specific impulse of most modified working mediums is small.Among them,the modified working medium doped with KCl has the largest specific impulse because of its low ablation mass and high ionization rate.