  The quantum kinetic equation for charged particles in strong electric fields
is derived and analyzed with respect to the particle flux. It is found that the
applied electric field is screened nonlinearly. The relaxation field is
calculated completely quantum mechanically and up to any order in the applied
field. The classical limit is given in analytical form. In the range of weak
fields the deformation of the screening cloud is responsible for the
Debye-Onsager relaxation effect. The result beyond linear response presented
here allows to investigate a field regime where no screening cloud is present.
The descreening field is determined as a function of thermal energy density of
the plasma. For stronger fields the moving charge is accelerated by accumulated
opposite charges in front of the particle. This can be understood in analogue
to the accoustic Doppler effect. A critical field strength is presented up to
which value a thermalized plasma is possible. The range of applicability of the
treatment is discussed with respect to applied field strength and space
gradients.
