Observation of momentum confinement time scalings in a rotating plasma

The Maryland Centrifugal Experiment (MCX) is designed to explore the use of supersonic rotation and strong perpendicular velocity shear for plasma confinement [R. F. Ellis, A. B. Hassam, S. Messer, and B. R. Osborne, Phys. Plasmas 8, 2057 (2001)]. This paper reports MCX data showing scalings with the strength and geometry of the magnetic field and comparisons to some standard models of confinement, none of which fit the data over the whole range. For midplane fields less than 1200 G and mirror ratios between 3 and 17, the momentum confinement time suggests a combination of Bohm-like diffusion and mirror losses. At mirror ratio 9, τM increases with B, saturates for B≈1 kG, and then decreases. The measured confinement times peak in the range of 200 μs, which is much longer than a magnetohydrodynamic instability growth time. The data do not exclude the possibility that confinement is strongly affected by charge exchange collisions with neutrals.