O. Ya. Savchenko

Diagnostics of a plasma jet with grid electrodes

We describe the diagnostics of a plasma jet ejected from the anode hole of a pulsed arc hydrogen plasma source [1-3]. The front part of this source and the grid electrodes are shown in Fig. i. Grid 1 is at the potential of the plasma, and grid 2 is grounded. Therefore, for a positive plasma potential such a grid diode forms a proton beam [4]. If the diameter of the grids is much larger than the distance between them, the effect of space charge between the grids on the divergence of the beam can be neglected. In a number of cases the effect of the space charge field after the grids can also be neglected if a charge-exchange cell (CC), into which gas is admitted to neutralize the space charge of the beam, is located right after the grids [2, 5]. Therefore, such parallel wire grid electrodes, when combined with a charge-exchange cell, form a beam whose divergence along the wires is determined mainly by the velocity distribution of the protons in the plasma jet [i, 2]. From the phase characteristic of this proton beam it is possible to recover the velocity distribution of protons in the plasma in the direction of the grid wires. It is particularly simple to recover this distribution by analyzing the fast hydrogen atoms formed from these protons in the charge-exchange cell rather than the protons. In this case the particle motion can be considered as free streaming, since the effect of space charge has been eliminated over the whole beam path.

Surface currents of a superconducting axisymmetric body that screen an external coaxial magnetic field

A time-saving method to find currents on the surface of a superconducting axisymmetric body is suggested for the case when the axis of the body and the symmetry axis of an external magnetic field coincide. The method is based on solving a one-dimensional integral equation. Analytical solutions are derived for the superconductor in the form of an ellipsoid of revolution that is placed in a uniform magnetic field and in the form of a sphere placed in a magnetic field varying as a polynominal at the symmetry axis. To find the current density on the surface of an arbitrarily shaped axisymmetric body placed in an arbitrarily varying magnetic field, a method of numerically solving the integral equation is proposed. It is a combination of the iterative regularization method and the projective method with a projector in the form of B splines. The results of numerical reconstruction of the sought functions by the latter method for a number of particular cases are presented.

Calculating the electric charges that shield from an external coaxial electric field on the surface of a conducting axially symmetric body

A method of solving a one-dimensional integral equation for finding charges on the surface of a conducting axially symmetric body is given. For the case of an ellipsoid of rotation in an electric field with polynomial values on the axis of symmetry, an exact solution is obtained. The axis of symmetry of the body and the axis of the external field coincide. A numerical algorithm based on a combination of a projective method and a method of iterative regularization for solving a Fredholm equation of the first kind is proposed. The projectors are chosen as B-splines. The charges calculated for an ellipsoid of rotation are close to the analytical ones.

Conducting axisymmetric body in a coaxial varying magnetic field

We calculate the vector potential and magnetic field strength in an axisymmetric conductor introduced into a preset coaxial external magnetic field varying harmonically with time. The proposed method involves the representation of the vector potential as the sum of a converging series each term of which is a solution to the Helmholtz equation with constant coefficient at infinity. The next terms of each series are determined from the preceding terms using the known Green function. The adequacy of the numerical results is confirmed by their comparison with the exact values for a sphere in a uniform magnetic field and by comparison of the numerical results obtained using two different series for an ellipsoid in a nonuniform magnetic field.

Time-of-flight probing of a plasma jet in a magnetic field

An arc proton source [i-3], used as a unit in a plasma diagnostics system [4] or as a unit in high-voltage injectors of precision proton beams [5, 6], is affected by external magnetic fields. Moreover, a magnetic field can be used to control the plasma flow [5, 7, 8]. In view of this, the effect of a longitudinal magnetic field was studied in [8, 9] in the range from 1 to i00 G on a plasma jet. In [8] we determined that the fourfold increase in current under the effect of a 40-G; magnetic field is due mainly to the focusing of the plasma jet; the reported data indicate that the focusing action is localized in a region 1 cm from the plasma generator anode. We also found that the focusing is associated with the existence of an electron current in the jet. In our study we generated a pulsed electron current, whose duration was much shorter than the time of flight of protons in the action region of the magnetic field; this enabled us to use the time-of-flight method to determine the distinctive features of the effect of the magnetic field on different parts of the jet.

Conducting object in the presence of a variable magnetic field

A numerical method is proposed to determine vector potential and gradient of scalar potential inside a conductor in the presence of a magnetic field that exhibits harmonic variations with time. The problem is reduced to the solution of the Helmholtz equation in a conducting object under the condition that the normal component of the right-hand side of equation on the conducting surface is zero. An iterative procedure is proposed for the solution of the original problem. First, the surface charge distribution that satisfies the boundary condition for the vector potential on the conducting surface is found, and, then, the next approximation for the vector potential is obtained with the aid of the Poisson equation. The method is illustrated using numerical experiments.

Flow around an ellipsoid of revolution in a harmonic coaxial vector field

We give an integral equation defining a coaxial magnetic field near the surface of a superconductive axisymmetric body and the velocity of the liquid near the surface of an axisymmetric body situated coaxially to the flow of an ideal liquid. Using this equation in the case when the axisymmetric magnetic field before the placement of an ellipsoid of revolution coaxially to the field changed along the axis by a polynomial law, we analytically define the densities of the surface current and the force with which the magnetic field acts on the ellipsoid. Also the velocity of the liquid is determined near the surface of the ellipsoid of revolution and the force acting on the ellipsoid placed coaxially in the flow of an ideal liquid when the velocity of the liquid before the placement of the ellipsoid changed along the axis of symmetry by a polynomial law.

Electromagnetic field of a dipole in an anisotropic medium

The harmonically varying field of point electric and magnetic dipoles in an anisotropic medium with an anisotropic axis is found for the first time.

Grid electrode in a plasma jet

Scattering of plasma-jet protons by a strip formed by long parallel metal filaments was investigated. The strip is located perpendicularly to the jet at a distance of70 mm from an ion extractor. Results of the experiment are adequately described by a model of a beam of noninteracting particles.

Plasma jet deviation in a transverse magnetic field

This paper presents a new method of determining the longitudinal energy from the rotation of a plasma jet in a transverse magnetic field. The authors consider the motion of a plasma jet with total current and ion current in a transverse magnetic field. The mass per unit length is related to the ion current and the longitudinal proton velocity by the expression M approx. = m /sub p/ I /sub p/ /eV. The paper shows two profiles of a jet with proton current of 0.6 A and total current of -1A, deviated by magnetic fields of +38 and -38 G.