Collisionless Shocks in Active Galaxies and in a Laboratory Plasma

在许多天体物理系统中，热等离子体在与其环境的边界处形成无碰撞激波，在那里，湍流相互作用代替碰撞，使更快的等离子体减速。突出的例子是地球的弓形激波，很可能是活动星系核的喷流。然而，对于这两种情况，都需要严格的定量测试来证实关于这些冲击如何形成的广泛讨论但纯粹定性的理论。我将从数值和实验两个角度研究促进无碰撞激波两侧狭窄过渡的湍流。从我将在德国和美国的计算集群上运行的大型数值粒子在细胞中的模拟开始，我将以迄今为止无与伦比的精度计算带电粒子在无碰撞冲击中的散射率。这些速率决定了活动星系核喷流中的宇宙射线粒子所能达到的最高能量。w<s:1>茨堡大学已经开发了一种半解析模型，它将利用这些数据来预测活动星系核发出的辐射的可变性。因此，我们将能够从测量中推断出观测到的辐射有多少是由于强子的加速造成的。与此同时，在洛杉矶进行的高能激光实验将首次在实验室等离子体中产生平行无碰撞冲击。将收集的数据与混合模拟进行比较，我将解释观察结果并为优化实验做出贡献。我们将能够直接测量哪些不稳定性在形成激波时最重要。这一发现将帮助我们理解等离子体湍流在行星弓形激波形成过程中所起的作用。

In many astrophysical systems, a hot plasma forms a collisionless shock at the boundary with its environment, where, instead of collisions, turbulent interactions decelerate the faster plasma. Prominent examples are the bow shock of the Earth and most likely the jets of active galactic nuclei. For both cases, however, rigorous quantitative tests are needed to confirm widely discussed yet purely qualitative theories as to how these shocks may be formed. I will investigate the turbulence that facilitates the narrow transition between both sides of a collisionless shock from two perspectives, both numerically and experimentally.Starting with large numerical particle-in-cell simulations that I will run on computing clusters in Germany and the USA, I will calculate the scattering rates of charged particles in collisionless shocks with as yet unrivalled precision. These rates determine the highest energy that cosmic-ray particles in the jets of active galactic nuclei can achieve. A semianalytic model which has already been developed at the University of Würzburg will use these data to predict the variability of the radiation emitted by active galactic nuclei. Thus, we will be able to infer from measurements how much of the observed radiation is due to the acceleration of hadrons.Meanwhile, experiments with high-energy lasers in Los Angeles will produce the first parallel collisionless shocks in a laboratory plasma. Comparing the collected data with hybrid simulations, I will interpret the observations and contribute to optimising the experiment. We will be in a position to measure directly which instabilities are the most important in forming the shock. This insight will help us understand the role that plasma turbulence plays in the formation of planetary bow shocks.