The effect of collisions on near-steady rotation in a vacuum arc centrifuge

Abstract

A two-dimensional fluid simulation of the plasma column present in a vacuum arc centrifuge after the anode grid has been developed. The simulation accounts for the effect of collisions on the plasma column, which is assumed to consist of multiply charged ions and electrons. It is found that the radial outwards plasma drift associated with collisions produces a spreading of the column density profile. With the plasma assumed to be in electrical contact with the anode grid, this in turn leads to a flow of current directed radially inwards, which increases the angular velocity of the plasma.

Breakdown of the Brillouin limit and classical fluxes in rotating collisional plasmas

“…The first new result with respect to the collisionless case is the occurrence of a radial velocity v r in addition to the azimuthal one v h . Integrating the previous relations Equations (32) and (33) with respect to the radius gives the ions and electrons azimuthal v h and radial v r velocities: v he ¼ X e r; v hi ¼ X i r and v re ¼ X e r=a e , v ri ¼ X i r=a i . To express the angular velocities X i and X e as a function of the plasma parameters, we consider Eq.…”

“…where we have used the previous definition of the free energy parameter x Ã2 integrated with respect to the radius: ÀMx Ã2 r ¼ @[e/ þ k B Tlnðn=n 0 Þ]=@r. The relations equations (37) and (38) describe the impact of collisions on the azimuthal motion. The radial dynamics for collisional rigid body rotations can be described through the integration of relation equation (33) with respect to the radius. The radial flux of particles associated with collisional rigid body rotations for electrons C en and ions C in is C en ¼ n e X Àe a Àe r ¼ n e X Àe x e À 2X Àe e r;…”

“…[16][17][18][19] Besides these classical fields, the general problem of angular momentum conversion [20][21][22] between static magnetic field, wave helicity, and plasma vorticity has received considerable attention in other contexts such as (i) particle acceleration and magnetic field generation in plasma channel and plasma bubble, [23][24][25] (ii) resonant particle acceleration and isotope separation with magnetized cylindrical particles beams, 26,27 (iii) mass separation with rotating crossed fields configurations, [28][29][30] (iv) and plasma propulsion. 31,32 Within the framework of most of these various studies, the problem of angular momentum dynamics in cylindrical magnetized plasmas has been mainly considered in the collisionless regime where rigid body rotations provide a simple and universal model; [9][10][11][12] although, in the collisional regime, resistive magnetohydrodynamic and perturbative models have been used to address the issue of collisional dissipation, 33,34 the collisional extension of the universality of rigid body rotations has never been explored. Rigid body rotation has been predicted and observed in collisionless plasmas experiments dedicated to isotope separation in vacuumarc 35,36 and nonneutral plasmas studies.…”

Performance of a vacuum arc centrifuge with a nonuniform magnetic field

“…The Hall parameter, ␤ϭ/v ie , is of order 100 in a typical vacuum arc centrifuge, and for this reason electron-ion collisions have been neglected in earlier works. 10 Recently Yue and Simpson 13 have shown that electron-ion collisions do have a small cumulative effect over the length of the rotation region in a VAC. For typical conditions, they predicted theoretically that the resultant plasma column expansion would lead to a reduction in the central ion density of less than 10% over the length of the VAC.…”

“…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.…”