Collisionless shocks play a role as an energy converter in space. In the vicinity of a collisionless shock, extremely large amplitude waves as well as nonthermal particles are often observed. However, the mechanisms how they are generated are not well understood. Our aim is to understand the physical processes associated with collisionless shocks by using theory, numerical simulation, spacecraft data analysis, and high power laser experiment.  

Microinstabilities as Energy Dissipation Mechanisms of Supercritical Shocks

A variety of microinstabilities are observed near collisionless shocks in space. At a collisionless shock, upstream flow energy is converted not only to thermal energy but also to the energy of large amplitude electromagnetic waves and of nonthermal particles as well. However, details of the energy conversion mechanisms are unknown. For example, the figure shows the thermal energy of downstream plasma as a function of Mach number of the shock. It is thought that the rate of thermal energy increase changes at a certain Mach number due to the change of the type of microinstability. We aim to understand the law controlling the mechanism and the efficiency of energy conversion at a collisionless shock in the wide parameter range in space.

High Power Laser Experiment of Collisionless Shocks

High power laser experiment has been paid attention as a new tool for empirical research in space physics and astrophysics, since it has advantages such as controllability and reproducibility. We are working on establishing experimental method including development of formation and measurement methods of collisionless shocks by using a world-leading high power laser facility, Gekko XII at the Institute of Laser Engineering, Osaka University.