The paper presents an MHD stability analysis for low frequency modes observed in the Tandem Mirror Experiment-Upgrade (TMX-U). This MHD flute mode analysis emphasizes two key points concerning TMX-U: (1) the central cell × rotation, with appropriate radial boundary conditions, is a significant instability drive for the m = 1 mode, and (2) the anchor hot electrons decouple from the MHD dynamics. It is found that the stability predictions and the oscillation frequencies are consistent with the selected TMX-U mode of operation that has been analysed. The principal stabilizing effect of hot electrons is to introduce a negative charge uncovering and to increase the effective curvature of the anchor region so that the sloshing ions can have a stabilizing influence. Instability can occur when ion charge uncovering caused by the finite Larmor radius cancels the negative effects of the hot electron charge uncovering.
Advances in global MHD mode stabilization research on NSTX