Experimental Research On The Interaction Of Ultrashort Ultra-intens Laser Pulse With Gas Cluster

In recent decades, theoretic and experimental research on the interaction of ultra-short-pulse laser with cluster is a very hot topic, and has drawn worldwide attention. With high bulk density, high laser deposition rate and no debris, cluster target displays many advantages in the interaction with laser, which is able to produce high-energy ion (MeV magnitude), high-yield neutron and strong X-ray radiation. So the detailed studies of the interaction would contribute to the research about laser fusion and X-ray laser greatly.In the thesis, it was firstly illustrated that progress of laser technology and the research of interaction of ultra-short-pulse laser with material. Particularly, the interaction of laser with cluster, the development of the cluster fabrication and diagnosis were emphasized. Secondly, introduced the concept of cluster, and simulated the cluster resource characterization. Thirdly, described and compared the experimental methods for investigating the behavior of cluster resource. Fourthly, introduced in detail the arrangement of the fabrication and diagnosis system in our lab, and made discussion on our experiment results. Finally, it introduced the interaction of ultrashort ultra-intense laser with deuterium cluster experiment carried out in our lab.The paper has developed the work in a relative systemic way, it's mainly consist of four parts: simulating and calculating of the cluster growing process, setting up the cluster fabrication system, setting up the cluster diagnosis system, operating the interaction experiment of ultra-short-pulse laser with deuterium cluster.The entropy and the T-S curve from 20K to 38K were obtained by employing the Clapeyron differential equation, the vapor-liquid equilibrium equation and the heat of gasification. Further, according hydrodynamics, we simulated and calculated the gas density, pressure and temperature distributions along the axis of nozzle, and found that the three physics parameters decreased quantitatively with the distance away the nozzle throat. Also analyzed the factors (back pressure, initial temperature, nozzle geometry size) working on the density distribution, and obtained several important results: gas density; the nozzle with large throat diameter and small angle was to produce high-density gas flow; the density of double-atom gas (such as deuterium) was 1.2 times larger than that of single-atom gas (such as argon, krypton). At last, combined the forenamed two steps and made certain the position for cluster beginning to grow which depended on the initial condition of gas (back pressure, initial temperature) and nozzle geometry size. All the theoretic simulation and calculation was expected to provide valuable guidance for the design of cluster fabrication system.Set up two fabrication systems which were capable of producing two kinds of cluster stably and repeatedly with high pressure(70atm),room temperature and high pressure(70atm),extremely low temperature (-170℃) , respectively. The size and the density of argon, krypton cluster produced by our fabrication system with room temperature, were 1200atoms/cluster, 2500atoms/cluster, 3.0×10¹⁹/cm³m,2.8×10¹⁹/cm³. More importantly, we had adopted the fabrication system with extremely low temperature to produce high-quality deuterium cluster source with large size (23 60atoms/cluster) and high density (3.5×10¹⁹ atoms/cm³) by supersonic jet. The produced cluster resource would provide target which established the basis for the interaction experiment.Set up Rayleigh scattering experimental system for characterizing cluster size and M-Z inference experimental system for characterizing gas density, both of which could operate synchronously with the fabrication system. (1)The Rayleigh scattering experimental system was used to measure the relative size of argon cluster, krypton cluster and deuterium cluster with different experimental parameters. We discussed some factors vital to cluster formation, thus optimized the experimental parameters for large-size cluster. The main results were listed in the following: measured the deuterium cluster size in various back pressure, and fitted cluster size as a function of back pressure which was expressed as ; compared the deuterium cluster size at different temperatures by varying cooling time (liquid nitrogen was used), obtained that temperature played an very important role in cluster size, even vital to the formation of cryogenically cooled deuterium cluster; compared the size of krypton cluster and argon cluster in the same experiment condition, and found that the first were 3～4times larger than the latter. All the results were accordant with Hagena's empirical formula. (2) The M-Z inference experimental system was used to investigate spatial distributions along nozzle axis, temporal distribution of density, and the varying density when conditions changed, such as back pressure, initial temperature and nozzle size for the three clusters. The experiment data could support our foregoing simulation work. (3) The time between probe laser fired and valve pushing pulse sent, delay time namely. At a series of different delay times the cluster size and the gas density were investigated by Rayleigh scattering system and M-Z inference system respectively. In the temporal spectrums, both the size and the density kept max value from 3ms to 25ms, which may mean our system ran very stably during this period. We considered that these temporal spectrums didn't reveal growth process of a single cluster, but the formation of a cluster resource. Moreover, the temporal spectrums depended on the mechanical structure of valve mainly. The characterization of cluster resource was the important preparation for the interaction experiment. It made certain the best time and the best position for laser focusing on cluster resource.For the first time, completed interaction experiment of 20TW laser with deuterium cluster (back pressure 38atm, initial temperature 100K) in the laser fusion research center of CAEP in China, through which we have observed the deuterium ions energy from 1keV to 100keV, with the average energy about 20keV beyond the energy requirement for fusion. Furthermore, deuterium cluster fusion experiment was achieved on the 10TW laser installation in the Korean atomic energy research institution. The large deuterium cluster was produced through the low temperature cluster resource which set up by us in extremely low temperature (80K) and high back pressure (55atm). In this experiment, the laser absorption ratio reached 65%, and the neutron yield was about 10³/shot.