Acceleration mechanism in vacuum arc centrifuges

Abstract

The azimuthal component of the force, which establishes rotation in vacuum arc centrifuges, is investigated. It is found that the design of the anode grid is one important factor influencing rotation. A range of tungsten-wire grids have been studied experimentally in a vacuum centrifuge operating with a magnesium cathode, and angular velocities have been determined by cross correlation of voltage probe signals. It has been verified that angular velocity increases when grids with higher effective electrical resistivity are used, as predicted theoretically. Grid heating during the 14 ms operating pulse increases resistivity and should also increase angular velocity; this effect has been observed experimentally and agrees with predictions.

Performance of a vacuum arc centrifuge with a nonuniform magnetic field

“…As done in the past [1][2][3][4][5] we assume that the plasma in the VAC rotation region is quasineutral and isothermal. Measurements 14 made with a Fabry-Perot interferometer show that the ion temperature does not vary over the duration of the discharge, and is observed to be uniform with radius.…”

“…1͒. The azimuthal and axial velocity components, together with the radial profiles of density and potential, are defined by physical processes in the driving region 5 and are specified at zϭ0 by…”

“…The interaction of the radial component of current with the externally supplied axial magnetic field sets the plasma into rotation at frequencies typically between 3ϫ10 4 and 4 ϫ10 5 rad/s. [5][6][7] Except for some recent experiments where an initial gas filling was utilized, 8 the chamber is evacuated before the discharge and the plasma in the VAC consists of multiply charged metal ions and electrons, with almost no neutral particles. 3 The rotating plasma streams through the anode grid and is deposited on the far end plate.…”

“…This was followed with experiments using background gas 8 in the Brazilian National Space Research Institute VAC facility, 12 suggesting that the separative performance of the device increased with the presence of a filling gas. In 1995, Simpson et al 5 showed experimentally and theoretically that the electrical conductivity of the anode grid creates a radial potential gradient that is responsible for azimuthal acceleration in the vacuum arc centrifuge. In 1996, Yue and Simpson 13 studied the effect of collisions on near-steady rotation in a vacuum arc centrifuge, showing that the effect of collisions on the plasma column after the anode grid is to increase the angular velocity, and possibly the separative performance of the plasma.…”

Instability of a Vacuum Arc Centrifuge

“…The interaction of the current with the axial magnetic field sets the plasma in rotation in the region to the left of the anode grid in the figure. 2 The rotating metal vapor plasma streams supersonically through the anode mesh, passing through the rotation region and eventually impinging on the far endplate. Table 1 shows typical parameters of the VAC for the experiments with a magnesium cathode described here.…”