Speaker
Dmitri D. Ryutov
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/I5.012.pdf
Collisional and collisionless shocks
D.D. Ryutov
Lawrence Livermore National Laboratory, Livermore CA 94550, USA
Shock waves are one of the most common plasma phenomena. They play a significant role in
astrophysical and magnetospheric environments, as well as in laboratory plasmas. The
classical collisional shocks usually connect two well-defined equilibrium states (those before
and after the shock transition). Each of these equilibrium states is characterized by the
thermodynamic parameters of density, temperature, and pressure, whose upstream and
downstream values are related by the continuity of mass, momentum, and energy flux. In the
collisionless plasmas, however, the initial state can be any of the much broader class of states
as long as constrained only by the requirement of being micro-stable. To find a final state
(which is micro-stable but, generally, non-Maxwellian) one now has to follow the evolution
of the system through the whole transition, and a lot of universality is lost. Despite this
important conceptual difference, there are also many similarities between the two types of
shocks: i) a formation mechanism by the hydrodynamic overtaking, ii) an important role of
the electron and ion mass disparity, iii) the presence of several sub-scales in the shock
transition, and iv) the composition variation within the shock transition. These general
features will be illustrated by examples from laboratory astrophysics, high-energy-density
fusion experiments, and edge plasmas of toroidal devices. A special class of shock-like
transitions in the form of double layers will also be discussed. Taken together, these
phenomena reveal a fascinating interplay of hydrodynamics, statistical mechanics, and
plasma physics. This work was performed under the auspices of the U.S. Department of
Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52-
07NA27344.
