Study On Supersonic Gas Cluster Jet Under High Backing Pressure

In recent decades, the interaction of ultra-short intense laser pulse with matter has been an active area of research. As a special interaction target, the gas cluster jet possesses the advantage of both solid target and gas target(i.e., the high local atom density within cluster, and the macroscopically low atom density in gas jet). In the study of laser-cluster interaction, a clustered gas jet has severed as a good target sample in many areas of research interest, such as the high energy ion, high energy electron, pulsed x-ray, terahertz radiation, harmonic generation, and so on. After the table-top deuterium-deuterium nuclear fusion by the interaction of a fs laser pulse with the deuterium clusters was reported, many theoretical and experimental works have been done to characterize the gas cluster jet and to optimize the yield of fusion neutron. However, the detailed characterization of a gas cluster jet under high gas backing pressure is still lack, including the cluster size, the atom density, and its spatial distribution in cluster jet. In this thesis, aiming to further investigate the gas cluster jet under high gas backing pressure, we carry out the following research work:(1) Fluent software is used to successfully simulate the argon gas jet under high backing pressure, in which the gas jet is produced by the adiabatic expansion of argon gas under a high backing pressure through a conical nozzle into vacuum and the different conical nozzles are considered(including the different half opening angles and the different nozzle lengths). The atom density and its spatial distribution at different conditions are investigated and the simulation results are compared with the corresponding results expected by the idealized straight streamline model in Hagena scaling laws. It is found that the central atomic density in gas jet is lower than that of the idealized straight streamline model, which is in agreement with the experimental results reported in literatures. Then, the simulated atom density is used to investigate the equivalent diameter of conical nozzle( deq) and its dependence on the nozzle length, the half opening angle of conical nozzle, and the gas backing pressure. The results indicate that the deq is close to the idealized deq in Hagena scaling laws in the case with the large half opening angle and the long nozzle length.(2) The Boldarev model is employed to simulate the supersonic argon gas jet under high argon gas jet and investigate the evolution of the average cluster size at the center of a cluster jet from the nozzle throat along the gas flow. Based on the simulation results about the evolution of the cluster size and the atom density in a cluster jet, the optimization of a nozzle length has been discussed under a given condition. It is found that the central atom density gradually decreases while the average cluster size increases gradually until it is close to the maximum with the increase of the distance from the nozzle throat. A proper nozzle length is about 20 mm for a usual conical nozzle with an opening angle of about 8.5 degree and a throat diameter of about 0.5 mm.This thesis focuses on the laser-cluster interaction and the evolution of the atom density and the average cluster size in supersonic gas cluster jet, and the equivalent diameter of a conical nozzle under high backing pressure are investigated based on the simulations. It could be helpful for the preparation of gas cluster sources and the understanding of the mechanisms of the laser-cluster interaction or the laser-matter interaction.