PIC Simulation Of Collective Thomson Scattering In A Non-equilibrium Plasma

Recently,a variety of high energy astrophysical phenomena have been successfully reproduced in laboratory experiments using high power laser facilities.We take part in the experiment of collisionless shocks in collaboration with a group at the Institute of Laser Engineering at Osaka University.The transition region of the collisionless shock is usually in a highly non-equilibrium state.In order to understand the mechanism of energy dissipation at the collisionless shocks,we need to clarify the relaxation processes occurring there.To diagnose such a local plasma,the Thomson scattering(TS)measurement has been widely used.Here,the TS is defined as an elastic scattering of a low frequency incident electromagnetic wave due to its interaction with free electrons in a plasma.Although the TS measurement has been used for a long time to measure the plasma not only in experimental devices but also in space(ionosphere),detailed theory of the TS in a non-equilibrium plasma has not been well established.In this thesis we investigate how a non-equilibrium plasma near the shock transition region is observed by the TS measurement.First,we assume that a plasma just upstream of a shock consists of background electrons,ions,and beam electrons.The beam instability generated in such an unstable local plasma is reproduced by using onedimensional full particle-in-cell(PIC)simulation.Then,a monochromatic electromagnetic wave,as a proxy of the probe light of the TS measurement,is incident upon the system to reproduce virtual collective TS.It is shown that the so-called electron feature of collective TS is strongly enhanced in the beam-plasma system.The characteristics of the enhanced electron feature is discussed in detail.