Macroscopic Stability of a Supersonic Plasma Flow in a Divergent Magnetic Mirror

Macroscopic behavior of a high-beta and supersonic plasma flow is investigated in the HITOP device. It is found that a cylindrical plasma begins to rotate eccentrically around the center axis in a divergent magnetic mirror. The eccentric radius increases with the increase in the mirror ratio and the beta value of the plasma. The rotating frequency changes with the radial electric field in the plasma, which is controlled by end-plate biasing technique. The rotation direction and its velocity are consistent with E × B drift motion. This behavior seems to be a flute/ballooning mode driven by static and dynamic pressure gradient in a bad curvature region of the divergent field line.