  The Madison Symmetric Torus (MST) is a toroidal device that, when operated as
a tokamak, is resistant to disruptions. Unlike most tokamaks, the MST plasma is
surrounded by a close fitting highly conducting wall, with a resistive wall
penetration time two orders of magnitude longer than in JET or DIII-D, and
three times longer than in ITER. The MST can operate with edge q_a < 2, unlike
standard tokamaks. Simulations presented here indicate that the MST is unstable
to resistive wall tearing modes (RWTMs) and resistive wall modes (RWMs). They
could in principle cause disruptions, but the predicted thermal quench time is
much longer than the experimental pulse time. If the MST thermal quench time
were comparable to measurements in JET and DIII-D, theory and simulations
predict that disruptions would have been observed in MST. This is consistent
with the modeling herein, predicting that disruptions are caused by RWTMs and
RWMs. In the low q_a regime of MST, the RWTM asymptotically satisfies the RWM
dispersion relation. The transition from RWTM to RWM occurs smoothly at q_a =
m/n, where m,n are poloidal and toroidal mode numbers.
