Dynamics of plasma injection along magnetic field lines in the PBFA II [Particle Beam Fusion Accelerator II] plasma opening switch

In the magnetically injected plasma (MIP) plasma opening switch (POS) presently under study for use on the Particle Beam Fusion Accelerator II (PBFA II), plasma is injected along an imposed poloidal field to control the position of the plasma. The magnetic field and the plasma density combine to make the Alfven velocity very high relative to the injection velocity of the plasma. In fact, the ration of these velocities, the Alfven-Mach number of the flow, ranges from 0.001 to 0.01. Explicit computation at these low Mach numbers is exceedingly tedious, and implicit computation without a very high convergence rate scheme is little better. However, the physical effect is clear: the field lines are effectively very stiff and not subject to displacement by the plasma. The plasma motion may thus be computed by simply restricting the velocity to lie along the field. Simulations in the true experimental geometry using this approach agree qualitatively with microwave interferometry measurements of the plasma density in the experimental test stand. The agreement is quantitative, subject only to the adjustment of the unknown plasma source mass flux rate. 2 refs., 17 figs