The disruptive instability in diverted tokamaks when q at the 95% poloidal flux surface, q95, is driven below 2.0 is shown to be a resistive kink. The mode is a resistive counterpart to the current driven ideal mode that traditionally explained the disruption in limited cross sections when qa, the safety factor at the outermost closed flux surface, lies just below a rational value. Diverted plasmas, in which qais formally infinite in the MHD model, have presented a longstanding difficulty since the theory would predict stability, yet, the disruptive limit occurs in practice when q95, reaches 2. Numerical calculations show the resistive kink mode is linearly destabilized by the rapidly increasing resistivity at the plasma edge when q95> 2. The resistive kink also occurs for limiter plasmas but quickly transforms to the ideal mode when the rational surface exits the plasma; this also explains an observed small discrepancy in onset conditions.
|Publication status||Published - 2016|
|Event||43rd European Physical Society Conference on Plasma Physics, EPS 2016 - Leuven, Belgium|
Duration: 1 Jan 2016 → …
|Conference||43rd European Physical Society Conference on Plasma Physics, EPS 2016|
|Period||1/1/16 → …|
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics
Turnbull, A. D., Hanson, J. M., Turco, F., Ferraro, N. M., Lanctot, M. J., Lao, L. L., ... Martin, P. (2016). The external kink mode and the role of q. Paper presented at 43rd European Physical Society Conference on Plasma Physics, EPS 2016, Leuven, Belgium.