無碰撞激震波在天文物理、太空、甚至是實驗室電漿的各種現象中是無處不在的。目前普遍 相信宇宙中的高能粒子或是宇宙射線是由無碰撞激震波所加速。在粒子加速的初始階段，或 稱無碰撞激震波的注入過程，粒子必須回到激震波的上游，也因此粒子在激震波表面的反射 於注入過程是不可或缺的。雖然有些解析與數值的研究說明了激震波表面的微擾與粒子的加 速和反射有關，這些反射粒子可能引起若干激震波的不穩定與重新排列，並致使激震波表面 產生微擾，然而在太空與宇宙中觀測這些現象是非常困難的。在此計畫中，我們在實驗上用 雷射產生電漿，並藉由觀測反射或回流的粒子來研究激震波表面的微擾。我們著重在激震波 馬赫數與磁場對於激震波表面的指向，其可由雷射能量與透過靶材和永久磁鐵的配置來控制。 我們藉由光學診斷以及湯姆生散射觀測到激震波的影像與局域電漿的分量，並且利用電離子 光譜儀來測量反射粒子的能量分布函數。我們闡明了激震波表面的微擾於激震波馬赫數與磁 場之指向的相依性，以及激震波表面的微擾與粒子加速之關係。 ;Collisionless shocks are ubiquitous in various phenomena in astrophysical, space and even laboratory plasmas. It is widely believed that energetic particles in the universe or cosmic rays are accelerated at collisionless shocks. At the very initial stage of the particle acceleration or the so-called injection process at collisionless shocks, some particles have to come back to the shock upstream, and thus, the particle reflection at the shock surface is essential in the injection process. The reflected particles can cause a number of instabilities and reformation of shock, resulting in shock surface perturbations. Although a number of analytic and numerical studies show the shock surface perturbations and relevant particle acceleration and reflections, it is hard to observe this in space and astrophysical plasmas. In this project we experimentally investigate the shock surface perturbations in laser-produced plasmas and observe the reflected or back streaming particles. We focus on the shock Mach number and the magnetic field orientation to the shock surface, which can be controlled with the laser energy and target configurations with permanent magnets. We observe the shock images with optical diagnostics and local plasma quantities with Thomson scattering. The energy distribution functions of the reflected particles are measured with electron-ion spectrometers. We clarify the dependence of the shock surface perturbations on the shock Mach number and the field orientation, and the relation between the shock surface perturbations and the particle acceleration.
