TRISONIC FLOWS IN THE PLASMA ACCELERATOR CHANNELS
The Keldysh Institute for Applied Mathematics, RAS, Moscow, Russia
Plasma dynamics is one of the promising branch in plasma physics. The achievements in this direction are connected with the new scientific and technical elaboration’s, in particular, with the creation and application of plasma accelerators. The existing estimations, experimental data, theoretical and numerical investigations show a real opportunity to get flows of a relatively dense plasma
n ³ 1014 ñì -3
with velocity
V » 107 + 108 ñì / ñ
in
the high-current plasma accelerators. Such opportunities allow to use
plasma accelerators in space as the electric jets and in various
applications including thermonuclear installations as well.
Schematically, the plasma accelerator [1] consists of two coaxial electrodes connected with the electric circuit. A neutral gas is introduced between the electrodes. Then the neutral gas breaks down and an ionization front is formed. Behind the front the ionized plasma is sharply accelerated along the channel axis owing to the azimuthal magnetic field Hj and the current j flowing between the electrodes due to the Ampere force
F = 1/c [j H] .
The process of plasma ionization and preliminary acceleration occurs, in particular, in the first stage of the coaxial heavy-current quasistationary plasma accelerator (QSPA) [2]. In the second stage the final acceleration is realized. In QSPA designing the numerical simulation and calculation of the channel flows play an important role [3].
The
theoretical and numerical investigation of the ionizing gas and plasma
flows was begun in [4,5] and continued in a series of other publications (
see, for example, [6,7] ). In addition to the accelerator channel the
electric circuit was incorporated in the mathematical model and an
unsteady case, in which the current in the channel varies in accordance
with the process of discharge of a storage battery in an electric power
circuit, was investigated. Moreover, the flows taking into account a
thermal conductivity and radiation have been under consideration. The
results of numerically modeling ionizing gas flows in the local
thermodynamic equilibrium approximation were given. In [8], in addition to
the MHD-equations, the physical model is based
on the equation of ionization and recombination kinetics. At the
ionization front it is possible to observe a clearly expressed deviation
from equilibrium. This refines the investigations carried out earlier.
The plasma accelerator is a magneto plasma dynamic analog of the Laval nozzle. The trisonic flow is realized in the plasma accelerator channel. The plasma is sharply accelerated, the velocity passing through the magnetogasdynamic sonic velocity
Ñs = ( g P / r + H2j / 4 p r )1/2 .
Thus,
at the channel inlet
we have a subsonic supply of matter and at the accelerator outlet we have
a supersonic plasma flow.
The
new direction of plasma dynamics is associated with the plasma flow
investigations in presence of the longitudinal magnetic field. The
following plasma rotation can essentially depress the Hall effect
influence [9]. For example, in figure the ion trajectories are depicted in
the channel with the trisonic flow in presence of the longitudinal
magnetic field
Hz
¹
0
for regime
with ion current. The ion
line of flux (curve A ), running out of anode at
z
= 0
, is the boundary of the plasma-core
flow and the anodic sub-flow. The curve
r
= r0
represents the
electron line of flux (equipotential electrode) at the beginning in the
same point. Due to the Hall effect the divergence of electron and ion
trajectories determines the region of anodic sub-flow. At condition
Hz
¹
0
this
region is essentially smaller than in case
Hz
=
0
(dotted
line in figure).
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