On the Electrodynamics of Nonequilibrium Plasmas
Authors: Wilhelmsson Hans 
Published: January 2007

The problems of basic plasma physics play a very important rôle in the development of modern physics. In particular the collective plasma phenomena which can not be explained in terms of any
linear theory but instead have to be described by means of largeamplitude and turbulence analysis are of outstanding interest.
The experimental situations in present day applications of plasma
physics are often such that studies of the electrodynamics of non-equilibrium plasma are necessary. In the attempts to describe the
new and exceedingly fascinating results in radioastrophysics, e.g.
the radiation from compact sources relativistic descriptions of
charged particles are furthermore essential.
It is a characteristic feature of many of the new effects related
to plasma phenomena that they occur under very extreme conditions. Let us here mention the very strong magnetic fields, of
the order of 1012 gauss, in the pulsars. For the radiation of
pulsars plasmas are most likely a very essential ingredient. However, the very composition and structure of the plasma of the
pulsar magnetosphere is not known and "so far nobody has
succeeded in producing a theory to account for the pulsar radioemission which has been universally-or even widely-accepted"
[Karpman, Norman, ter Haar, Tsytovich, June 1974].
An other example where again the experimental conditions are
characterized by very exceptional figures is in connection with
the attempts to achieve fusion power by laser implosion of solid
material. Under the influence of very strong pulses of laser
radiation (104 Joules) released under very short times (100 ps - 1 ns) a dense and expanding plasma is created around tiny pellets
(diameter of .l mm) of initially frozen tritium-deuterium targets
which will become compressed (104 times) and heated to fusion
temperatures as a consequence of shock wave effects driven by
the intense laser pulse. For efficient utilization of the laser power
the phenomena occuring in the "plasma corona" created around
the pellet, such as stimulated Brillouin scattering and stimulated
Raman scattering are of great importance. In fact, the future
feasibility of a fusion reactor based on the tritium-deuterium
pellet principle may depend on such processes, which are governed
entirely by nonlinear effects. Computer studies as well as the
construction of simple physical models which could be treated
by analytical methods [Anderson and Wilhelmsson 1974] are
then useful in order to settle the rôle of those processes and
possibly to avoid undesired effects caused by them, such as anomalous backscattering.
When a high concentration of power becomes localized in plasmas this may lead to a state of strong turbulence. The description
of such a state poses formidable difficulties from a theoretical
point of view. It seems necessary to attack these problems having
in mind intuitive models which should characterize, hopefully,
important features of the state. In this connection the concept of
soliton has been put forward. It is used to describe a certain kind
of excitation which may be thought of as a localized concentration
of longitudinal plasma waves. The solitons propagate with essentially constant shape and exhibit certain features of stability
against perturbations. As such it seems that they may prove useful
to describe situations which have as yet been outside the scope of
theoretical analysis but which are most likely prevalent in many
experiments. Extensions of the present state of nonlinear plasma
physics to include these new ideas is therefore at present a challenging program.
The international working group on the problem "Electrodynamics of Nonequilibrium Plasma" which gathered in Göteborg, Sweden in May-June 1974 at Aspenäsgården, Lerum and
at Chalmers University of Technology, Göteborg considered a
number of the above mentioned and related topics. The workshop was a result of the collaboration of scientists of the USSR
and of Sweden, initiated by the Academies of these countries.
We were very pleased on this occasion that the workshop which
lasted for one month and in which about twenty foreign scientists
participated had the opportunity of wellcoming beside four
scientists from the USSR also participants from England,
France, Germany, USA, Japan and from our neighbouring
Scandinavian countries.
It is a pleasure to express from all the participants their sincere
gratitude to the Royal Swedish Academy of Sciences, to the
Royal Swedish Academy of Engineering Sciences for generous
help in organizing the workshop and to the Swedish Atomic
Research Council and the Swedish Natural Science Research
Council for support.