A. I. Morozov

The conceptual development of stationary plasma thrusters

The history of the development of the concept of the stationary plasma thruster is described. The data obtained indicate the possibility of creating extended (over a distance substantially longer than the Debye radius) electric fields in a fully ionized plasma with a relatively high electron temperature (Te>10 eV) and a conductivity close to the classical one. Based on these results, a number of fundamentally new plasma-dynamic systems were proposed; in particular, the principles of plasma optics were formulated and verified experimentally. In the course of these investigations, new physical processes, such as the formation of the distribution function of the electrons in their collisions with the wall and the effect of the near-wall conductivity, were discovered. The structure of the Debye layer for the case in which the coefficient of the secondary electron emission of a dielectric wall is larger than unity was investigated.

Theory of the near-wall conductivity

A model describing the phenomenon of the electron current in a plane plasma slab bounded by parallel dielectric walls in the presence of a homogeneous magnetic field perpendicular to the walls and an electric field oriented along the walls is presented. The current flows along the electric field because of the electron collisions with diffusely scattering walls. The model takes into account the presence of Debye layers and the non-Maxwellian character of the electron distribution function. Collisions in the plasma volume are ignored.

Sructure of steady-state Debye layers in a low-density plasma near a dielectric surface

Exact steady-state analytic solutions describing kinetic processes in a low-density plasma layer near a dielectric surface are found in a time-dependent one-dimensional model with allowance for secondary electron emission. It is shown that, at low electron temperatures, both the electric potential and electron density monotonically decrease toward the dielectric surface (Debye layer). As the electron temperature increases, an anti-Debye layer first forms, in which the potential monotonically increases toward the wall, and regimes with a nonmonotonic potential profile then arise.

One-dimensional hydrodynamic model of the atom and ion dynamics in a stationary plasma thruster

A one-dimensional hydrodynamic model of the atom, ion, and electron dynamics in the channel of a stationary plasma thruster is developed. The relevant set of integrodifferential equations is derived and investigated both analytically (steady-state solutions) and numerically (dynamic regimes). It is shown that adjusting only one parameter (the channel resistivity) makes it possible to achieve a good agreement between the calculated global parameters and experimental data. The general features of oscillations revealed with the help of the model are also found to agree fairly well with the experiment.

One-dimensional model of the Debye layer near a dielectric surface

A study is made of the processes occurring in a low-density plasma near a dielectric wall. A one-dimensional non-steady-state model of the electron dynamics is constructed that takes into account secondary electron emission. The Vlasov-Poisson equations are solved numerically. According to the results obtained, the steady-state potential distribution that forms at a low temperature of the incident electrons gives rise to a wall layer whose characteristic thickness is about several Debye lengths and in which the electrons are decelerated. In this case, the electron density is lowest near the wall. The situation in which the temperature of the incident electrons is high is far more complicated: the solution is quasi-periodic in character and the electron density near the wall is the highest.

Global characteristics of an ATON stationary plasma thruster operating with krypton and xenon

The global characteristics of an ATON stationary plasma thruster operating on xenon and krypton are investigated. It is shown that, with krypton, the thrust at the same mass flow rate of the working gas is greater and the efficiency is somewhat lower than those with xenon. An efficiency of ∼60% was achieved with krypton for the specific impulse attaining 3000 s. The jet divergence is ∼±22° for krypton and ∼±11° for xenon.

Kinetics of a low-density plasma near a dielectric surface with account for secondary electron emission

Exact steady solutions in a one-dimensional kinetic model of the processes in a low-density plasma layer near a dielectric surface are constructed analytically with allowance for secondary electron emission. It is shown that, for low electron temperatures, the solutions describe a regime in which the electric potential and electron density decrease monotonically toward the dielectric wall (a classical Debye layer). For higher electron temperatures, there are solutions describing regimes such that the electric potential and electron density increase monotonically toward the wall (an inverse Debye layer).

One-Dimensional hybrid model of a stationary plasma thruster

A one-dimensional hybrid model of the dynamics of atoms, ions, and electrons in the channel of a stationary plasma thruster is developed. The relevant set of integrodifferential equations is studied numerically. The results obtained are compared with the results of previous calculations based on a hydrodynamic model. It is shown that, with the use of one fitting parameter (the channel resistance), the calculated integral characteris-tics agree well with the experimental ones. The current-voltage characteristic is obtained. The general features of low-frequency oscillations that have been revealed in numerical simulations using the model proposed are also in fairly good agreement with experimental results. The value of the electron thermal conductivity is estimated.

Axisymmetric Plasma-Optic Mass Separators

A systematic description is given of the principles of operation of axisymmetric plasma-optic mass separators with azimuthators that are compatible with stationary plasma thrusters with closed electron drift. Two schemes of plasma-optic separators (with electrostatic and with magnetic ion focusing) are considered. Results are presented from calculations of the parameters of model devices for separating ions whose masses are on the order of those of xenon ions.

Injection of plasma into the Trimyx Galathea

The Galathea-3 device, which consists of a coaxial plasma gun, a plasma guide, a lock chamber, and the Trimyx Galathea confinement system with three myxines, is briefly described. The plasma parameters at the outlet from the plasma gun, in the plasma guide, and in the confinement system are presented. It is shown that the plasma can be efficiently entrapped into the Galathea and spread out along it. The confined plasma is found to go beyond the Ohkawa surfaces. Estimates show that the particle losses from the system are on the order of the classical ones.