MHD stability of a hot-ion-mode plasma in the GAMMA 10 tandem mirror

Magnetohydrodynamic (MHD) stability of the GAMMA 10 tandem mirror is extensively studied in ICRF-heated, hot ion plasmas. Stability boundary for a flute interchange mode is predicted to depend on a pressure-weighted curvature integrated along the magnetic field line. It is found that the upper limit of the central-cell beta {beta}{sub C} increases linearly with the anchor-cell beta {beta}{sub A}. The critical beta ratio {beta}{sub C}/{beta}{sub A} above which the plasma cannot be sustained strongly depends on the pressure anisotropy P{sub PRP}/P{sub PLL} of hot ions. Stronger anisotropy greatly expands the stable region up to a higher critical beta ratio, owing to the reduction of the pressure weighting in the bad curvature region of the central cell. On both sides of the quadrupole anchor cells, there are flux-tube-recircularizing transition regions where the normal curvature is highly bad. Then the density and ion temperature of the cold plasma in the transition region are measured. Theoretical prediction on the flute stability boundary calculated by using the measured axial pressure profile of the hot-ion and the cold-plasma pressure can explain well the experimental results. 16 refs., 7 figs.