Simulation Study Of High Quality Positron Source Production From Laser Plasma Accelerated Electron Bombarding Target

Since the positron was predicted and found in the 20 th century 30 s, the positron has been widely applied in nuclear physics, atomic and molecular physics, solid-state physics, surface interface physics, materials science, high energy physics, medical imaging and many other research areas. Positron source has been a research subject of common concern in the related research. Currently, usually experiment research using positron source mainly comes from the radioactive isotopic β+ decay, like 22 Na and electron linear accelerator or the nuclear reactor, but they are cannot used for basic research and applied research, especially astrophysics research because of the longer pulse durations, lower energy or expensive cost. In recent years, with the development of laser techniques, relativistic positron beams created by ultra-intense lasers have attracted considerable attention owing to their outstanding properties, such as high yield, high density, high energy and short pulse.Considering the current research status of the laser-based positron source, we consider the positron beam generate on the laser indirect way, Use the international monte carlo simulation toolkit- Geant4, set up for producing relativistic positron beam from the interactions between laser-plasma-accelerated electrons and solid target, simulate the laser plasma acceleration experiment at the university of Michigan and the Chinese academy of sciences the laser plasma accelerated electrons as input. The main characteristics of positron beam such as the positron yield, spectral and angular distributions were investigated, and study the key parameters with the solid target material and geometry size of dependencies. These studies provide the optimal experimental conditions for ultrashort positron generated in the laboratory.Simulation results show that gold and tantalum targets could be regarded as a good electron-positron converter. For metal targets with constant areal density, the positron yield was proportional to the fourth power of the atomic number Z and varies inversely with the square of atomic mass A. For different target materials, the positron yield was proportional to the square of the target thinness d, but exists an optimized target thickness. The positron yield, which is optimized the target material and thinness could be 0.3 e+/e-. Usually, the optimized thinness of high Z material is thinner than the optimized thinness of low Z material. The positron beam spectrum is Maxwell distribution, the energy peak is near 5 Me V, and the highest energy can reach more than 140 Me V. Emergent positron is leaning forward, divergence Angle peak is at about 10 o, and the emergent positron energy is higher, the forward is more obvious. Behind the solid target, we add a magnetic field to separate electron, gamma photons and positron and optimize the size of the upper and lower two pieces of deflection magnetic field shielding, provides the parameters of the detectors size and position for the experiment.