The ISSI Team “Unveiling Energy Conversion and Dissipation in Non-Equilibrium Space Plasmas” aims to investigate how space plasmas convert and dissipate energy, focusing on systems that are not in local thermodynamic equilibrium (LTE).

In collisional fluids and plasmas, such processes are well-understood: large-scale energy in the form of kinetic and/or magnetic energy is transferred to small scales, where viscosity and/or resistivity cause the irreversible conversion of energy into internal (thermal) energy. Collisions in such systems restrict the fluid or plasma to remain close to LTE. However, collisional processes in numerous space plasmas are weak, so the intuitive understanding derived from neutral fluids does not work in such systems. Weakly collisional and collisionless plasmas stray far from LTE, and the conversion and dissipation of energy are completely different than in LTE. In particular, degrees of freedom unavailable to collisional plasmas arise in non-LTE systems, and there is a growing appreciation that these degrees of freedom play a crucial role in energy conversion and dissipation in non-LTE systems.

Two complementary theoretical approaches to describe energy conversion in weakly collisional or collisionless plasmas have been developed – the so-called velocity-space cascade approach and an approach associated with entropy. These two approaches must be fundamentally interrelated. We propose to convene a team with a diverse and unique set of theoretical, numerical, and observational strengths to make a quantum leap in progress on this immensely challenging, yet increasingly important, problem. The implications of understanding these processes are broad, with applications to nearly all the Space Sciences research areas promoted by ISSI: Astrophysics, Fundamental Physics in Space, Magnetospheric and Space Plasma Physics, Planetary Sciences, Solar and Heliospheric Physics, and Solar-Terrestrial Sciences.