Special Configuration Of The Target Characteristics Of Laser Proton Acceleration

The production of energetic protons and ions in ultra-intense (>1018 Wcm-2) laser interaction with solid target has been studied extensively both experimentally and theoretically in the past few years. These protons can be wildly used in an amount of recent and future significant applications for its high energy, short pulse duration, high current, low proton beam divergence, and good directionality. Such as high-brightness ion sources, the fast-ignition scheme in inertial fusion, radioisotope generation, worm dense matter generation, compact acceleration for high-energy charged particles and x Rays, cancer therapy in medicine and proton radiography etc.This thesis began with a brief introduction of the high field physics, and the development of the protons produced in the interaction of ultra-short laser pulse with solid target. Secondly, we expatiate in detail the theory of the laser proton acceleration mechanisms and its relative hot electron generation. Then we introduced the theory and the arithmetic of the PIC computer simulation which will be used to research the proton acceleration mechanism. At last and most importantly, we introduced the researches on the proton beam divergence control and the improvement of the conversion efficiency from laser to protons both in experiments and simulations.The experiments were performed at the ultra-short and ultra-intense laser facility-SILEX-I in the Laser Fusion Research Center (LFRC) of China Academy of Engineering Physics. The full emission angle of proton beam was obtained by measuring the proton track distribution on CR39. A maximum reduction about 2/3 in the proton beam divergence with cylinder targets comparing to ordinary plain targets was found in our experiments. Moreover, the emission characters of cylinder targets with length of 983μm,1983μm,2983μm have been compared each other, and the experimental results indicate that there is an optimum length for cylinder targets. The reduction in the proton beam divergence for cylinder targets agrees with the situation that observed in PIC simulations, which is due to the electric fields on the inner surface of cylinder targets set up by the hot electrons.The conversion efficiency from laser to protons was simulated by VORPAL code; ErH3 showed a 125% increase in the conversion efficiency to protons above 4 MeV relative to CH4 targets with the same geometry and laser parameters. Proton accelerating experiments with ErH3 plain targets have been conducted on SILEX-I facility and the results indicated that the ErH3 targets have higher yields of protons than the Cu foil targets in the same thickness, which is coincident with simulations.