Editing Plasma stability (section)

=== Resistive Wall Modes ===
Resistive wall modes (RWM) develop in plasmas that require the presence of a perfectly conducting wall for stability. RWM stability is a key issue for many magnetic configurations. Moderate beta values are possible without a nearby wall in the [[tokamak]], [[stellarator]], and other configurations, but a nearby conducting wall can significantly improve ideal kink mode stability in most configurations, including the tokamak, [[Spherical tokamak|ST]], [[reversed field pinch]] (RFP), [[spheromak]], and possibly the FRC. In the advanced tokamak and ST, wall stabilization is critical for operation with a large [[bootstrap fraction]]. The spheromak requires wall stabilization to avoid the low-m, n tilt and shift modes, and possibly bending modes. However, in the presence of a non-ideal wall, the slowly growing RWM is unstable. The resistive wall mode has been a long-standing issue for the RFP, and has more recently been observed in tokamak experiments. Progress in understanding the physics of the RWM and developing the means to stabilize it could be directly applicable to all magnetic configurations. A closely related issue is to understand plasma rotation, its sources and sinks, and its role in stabilizing the RWM.