Plasma Motion in a Time Changing Toroidal Octupole Magnetic Field

A gun-injected hydrogen plasma was contained in a toroidal octupole magnetic field. The plasma motion due to the changing magnetic field was studied and compared to a model based on the flux invariance of the motion. For early injection (while the field was rising) there was a strong motion toward the multipole rods while for late injection the motion was toward the wall. Magnetohydrodynamic theory shows that the plasma becomes unstable near the separatrix due to this motion. Although fluctuations were observed in this region, the plasma was found to be distributed stably.