Description
Tokamak plasmas are subject to disruptive events. While such events are expected to be rare in future large devices, they are problematic since, in addition to other off-normal loads, part of the electrons can be accelerated to relativistic velocities and can damage the device [1]. Currently, one of the promising approaches for RE mitigation is ‘benign termination’ via low-Z injection and excitation of an MHD instability to expel the electrons without their regeneration [2]. The key to success lies in converting magnetic energy into thermal energy and spreading it over a larger area. MHD instabilities are a crucial component of this conversion and spreading process. It is believed that broad stochasticity initiated by large MHD perturbations can distribute the heat load evenly across the device. Unlike other tokamaks, these MHD modes are not always locked in the ASDEX Upgrade. This paper investigates the development and behaviour of these MHD instabilities, as well as the dependence of their amplitudes and growth rates on different parameters (pressure, total radiation, etc). These results will help us understand the physics of benign termination, providing a basis for comparison with nonlinear MHD simulations and enabling us to predict applicability of the ‘benign termination’ to ITER.
References
[1] B. N. Breizman et.al., Nucl. Fusion 59 (2019) 083001
[2] U. Sheikh et. al., Plasma Phys. Control. Fusion 66 (2024) 035003