PIC simulation of collective Thomson scattering in a non-equilibrium plasma

摘要

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 one-dimensional 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.

目录

Chapter1:background and purpose

1.1 Background

1.2 High power laser experiment of collisionless shock

1.3 Thomson scattering measurement[1]

1.4 Collective and non-collective Thomson scatterings

1.5 Plasma waves and collective Thomson scattering[2]

1.6 Collective Thomson scattering in non-equilibrium plasma

Chapter2:One dimensional Particle in cell (PIC) simulation

2.1 Basic equations in PIC simulation

2.2 Flow chart of PIC simulation

2.3 Simulation settings

2.3 Simulation parameters

3. Result of PIC simulation:Beam instability

3.1 Time evolution of energy and electron phase space

3.2 Wave characteristics

Chapter4:Result of PIC simulation:Virtual Thomson scattering

4.1 Run 3:Without beam

4.2 Run4:with beam

4.3 Dependence on intensity of probe light, EI

4.4 Dependence on beam velocity, ub

Chapter5. Summary and future issues

5.1 Summary

5.2 Future issues

参考文献