Astrophysical reconnection and collisionless dissipation

Abstract

Magnetic reconnection and collisionless dissipation are common phenomena of astrophysical and fusion plasmas. While reconnection is responsible for disruptions of a fusion confinement, it causes flare explosions at the Sun and stars, in galaxies, planetary magnetospheres, and it causes aurorae and structure formation in the Universe as well as penetration through magnetic boundaries. Due to the weak coupling in astrophysical and fusion plasmas, dissipation is due to collective phenomena such as plasma waves and micro-turbulence rather than direct particle–particle collisions. Since astrophysical plasmas usually are not directly observable, laboratory investigations may help to verify theoretical plasma astrophysical predictions but for the transfer of knowledge one has to take into account some specifics of astroplasmas, their density, temperature, currents and magnetic field strengths, geometry and even topology. As an example we discuss magnetic reconnection in the solar corona which requires collisionless dissipation. Both are highly nonlinear processes that occur at totally different scales. Hence, we refer to numerical simulations. Finally, we list the most urgent open questions in plasma astrophysics which should be addressed in the near future.