Numerical Simulation Of Cross Beam Energy Transfer In Laser Plasma Interaction

The parametric instability in laser plasma interaction has an important influence on inertial confinement fusion.When the laser propagates in the plasma,it is possible to excite the ion sound wave through stimulated Brillouin scattering(SBS),which will strongly scatter the incident light and affect the absorption of laser energy.When two laser beams cross in the plasma,the excitation of ion acoustic wave will lead to energy transfer between the two beams,which will directly affect the uniformity of the radiation field and destroy the implosion symmetry.Aiming at the typical experimental parameters of indirect ignition driven by inertial confinement fusion,the physical mechanism of cross beam energy transfer(CBET)is simulated by using the method of fluid theory and hybrid simulation.The main research contents are as follows:Firstly,the SBS process in a uniform plasma is studied.Particle simulation code EPOCH and hybrid simulation program CBETor are used to simulate respectively,and the physical images excited by ion acoustic waves are obtained.The frequency and wave number of ion acoustic wave obtained by CBETor simulation are in good agreement with the results of fluid theoretical calculation and EPOCH simulation,which verifies the effectiveness and accuracy of CBETor in the simulation of ion acoustic problems.Secondly,the CBET process in uniform plasma is studied.The hybrid simulation program CBETor is used to simulate the cross propagation of two lasers in plasma.The evolution characteristics of CBET on tens of picosecond time scale are obtained,and typical kinetic characteristics such as ion capture are observed.It is found that the cross laser intensity has a great influence on the energy gain of seed laser.When the cross laser intensity is high,significant ion capture and pump depletion will occur in the process of reaching saturation.As the result,the energy gain of seed laser is higher.Thirdly,the effect of initial ion temperature on CBET effect was studied.When the thermal velocity of the initial ion is higher than the phase velocity of the cross laser driving wave,the threshold of ion capture effect will be reduced,which will lead to the suppression of CBET effect.This provides a possible idea for inhibiting CBET effect in the experiment.