Unsolved problems in Collisionless Shock Physics

Collisionless Shocks (CS) are a fundamental plasma phenomena that abound in the Universe. They are formed around ordinary stars, in binary systems, supernova remnants, in the interaction between stellar winds and their orbiting planets, gamma ray bursts, and many other objects in the Universe. Understanding the physics of CSs is crucially important for many astrophysical problems. The radiation generated by particles energised at CSs often provides the only valuable observable information about the processes occurring in the vicinity of remote astrophysical objects.

The main process that takes place at a shock front is the redistribution of the kinetic energy of the upstream bulk plasma flow, resulting in the heating of the plasma and the acceleration of a fraction of particles to high energies. Although ions (protons, Helium, heavier ions) carry the lion's share of energy, an understanding the role of electrons in the heating process occurring at the shock front is important, not only for the fundamental physics of CS, but also for the analysis of the different types of radiation emitted by various distant astrophysical objects. For example the ability to estimate the downstream ratio of the electron to ion temperatures is essential for interpretation of emissions observed from supernova remnants. Such emissions are mainly generated by electrons energised at CSs formed in the vicinity of supernova remnants.

In spite of their plentifulness, currently only the natural CS observed within the heliosphere can be subjected to in-situ observations with the most detailed observation being made at the terrestrial bow shock. The proposed project aims to exploit data obtained by the multisatellite MMS and Cluster missions to provide to investigate and further our understanding of the process of electron heating at the CS front.

In a collisionless plasma, any evolution of the particle distributions, including such process as thermalisation and acceleration, is related to...