  Reduced magnetohydrodynamic (MHD) equations are used to study the nonlinear
dynamics of external kinks in a quasi-axisymmetric (QA) stellarator with
varying fractions of external rotational transform. The large bootstrap
currents associated with high beta plasmas may make QA configurations
susceptible to low n external modes, limiting their operational space. The
violence of the nonlinear dynamics, and, in particular, when these modes lead
to a disruption, is not yet understood. In this paper, the nonlinear phase of
external kinks in an unstable QA configuration with an edge safety factor below
two is simulated. An axisymmetric approximation of this stellarator is
constructed in the nonlinear MHD code, JOREK, capturing the influence of the
external rotational transform. The use of this approximation for the considered
stellarator is validated by comparing the linear dynamics against the linear
viscoresistive MHD code, CASTOR3D. The nonlinear dynamics of this stellarator
approximation are compared with an equivalent tokamak to understand the
influence of a relatively small external rotational transform. While the
external rotational transform does have a stabilising influence on the MHD
activity, it remains violent. To explore the first order influence of a larger
external rotational transform, this equilibrium parameter is artificially
increased for the considered stellarator, reducing the effective plasma
current. The violence of the kink instability is quantified, and shown to
reduce with the increasing external rotational transform. At the same time, the
external kink triggers internal modes that exacerbate the loss in confinement
during the nonlinear phase, such that it remains large over much of the
parameter space. It is only with a significant fraction of external rotational
transform that these subsequent modes are stabilised.
