Stabilization of the resistive shell mode in tokamaks

Abstract

The stability of current-driven external-kink modes is investigated in a tokamak plasma surrounded by an external shell of finite electrical conductivity. According to conventional theory, the ideal mode can be stabilized by placing the shell sufficiently close to the plasma, but the non-rotating "resistive shell mode," which grows on the characteristic L/R time of the shell, always persists. It is demonstrated, using both analytic and numerical techniques, that a combination of strong edge plasma rotation and dissipation somewhere inside the plasma is capable of stabilizing the resistive shell mode. This stabilization mechanism does not necessarily depend on toroidicity or the presence of resonant surfaces inside the plasma. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or respnsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Physics of advanced tokamaks

“…It remains a key challenge for the advanced tokamak program to demonstrate resistive wall stabilization at beta values significantly beyond the no-wall value for long durations. Sustained plasma rotation and active non-axisymmetric feedback stabilization (Fitzpatrick 1996, Jensen 1997 are presently thought to be the means to meet this challenge.…”

Nonlinear three-dimensional simulations of resistive wall modes

“…In these experiments, there is a rapid toroidal rotation due to unbalanced neutral beam injection. Theoretically, it is shown that the combination of plasma rotation and some dissipation model can stabilize RWMs [4][5][6][7]. When the RWMs are destabilized, the RWM results in major collapse.…”

Response to “Comment on ‘The interaction of error fields and resistive wall modes’ ” [Phys. Plasmas 12, 084701 (2005)]

“…10,11 There is another possible mechanism for the stabilization of RWMs, described by Fitzpatrick and Aydemir. 12 This relies on the existence of a cool and viscous edge region at the plasma edge, which plays a similar role ͑i.e., providing dissipation and drag͒ to that of the internal resonant surfaces. In Ref.…”