The Electron Thermal Transport In Spherical Geometry Simulated By Fokker-Planck

Shock Ignition has become apparent since it been proposed by Betti at2007. In the’shock ignition’ route to fusion, the target is compressed at a relatively low temperature and pressure state by a compression phase, then ignited using high intensity laser which drives a strong shock into the center of the fuel. The ignition laser pulse has to be properly timed and sufficiently intense to allow the achievement of the needed hot spot pressure. The high temperature or density gradient in shock ignition lead to the hydrodynamic or Vlasov descriptions break down, so we assess the physical phenomenon by using Fokker-Planck (FP) simulation. In this paper, the one-dimensional planar geometry Fokker-Planck code is extended to cylindrical and spherical geometries. Then simulated some typical processes such as plasma expansion and laser ablation with the FP and fluid codes.The one-dimensional Fokker-Planck code is revised to include cylindrical and spherical geometries, and is validated by comparing with fluid simulations in the fluid limit. The expansions of plasma at high temperature in different spatial geometries are simulated and analyzed with the FP and fluid codes. The Spizer-Harm model calculate thermal flow would be run out when the temperature gradient is large. The flux limit model substitute Spizer-Harm model to inhibit the electron thermal transport, and the flux limiter is time dependent. By comparing the spherical and planar geometry it is found that the geometrical curvature effect will decrease the nonlocality of transport, which lead to a smaller thermal transport inhibition and preheating in expanding plasmas as compared with the planar case.Then we analyze the shock ignition progress by MULTI code. Simulating the compressed core with or without a shock and the total energy is the same. The core with a shock has a larger pressure and density. It is important to observe that the ignitor shock collides with the return shock inside the shell. After the collision, two new shocks are generated:an inward and outward moving shock. The inward shock that impulsively accelerates the inner shell surface and enhancing the piston action and leading to ignition. Then we simulate the neutron yield with different shock time to conform the ignition window. The pressure and velocity caused by abortion would be different as regulating the flux limiter, this is another cause affect the neutron yield. The thermal transport inhibition and preheating in shock ignition are the main characters of nonlocal transport. Then we discuss the nonlocal electron transport in laser-plasma simulated by FP and fluid codes. The ratio of the thermal electron mean free paths to the characteristic temperature scalelength is large and the thermal transport inhibition are strong. The nonlocal effects become significant as the laser intensity is increased and generated suprathermal electron.