Description
Neoclassical tearing modes (NTM) are a major threat for future tokamaks operation like ITER due to their significant impact on radial energy transport and ability to trigger major disruptions. Active mitigation methods are installed on tokamaks to either prevent their onset or control the magnetic island size.
This work, conducted with the AMON reduced MHD code [1], enables a coherent comparison between preventive (applied before seeding) and control (applied after) NTM mitigation methods via external current drive [2,3] to evaluate their respective efficiencies. To allow this coherent comparison a new seeding process is used. To replicate a sudden MHD event triggering a non-linear NTM growth of a linearly stable tearing mode: we inject a burst of localized and resonating current on the resonant surface. This method allows us to quantify the impact of the characteristic response time of detection and control actuators on magnetic island mitigation. As expected, prevention displays a higher efficiency as compared to control although reduced for a large seeding burst. An efficiency similar to the prevention method is also found for the control method if applied early enough after the seeding. This coherent comparison is also replicated for turbulence-driven magnetic island (TDMI) with a self-consistent interchange turbulent seeding highlighting how the presence of turbulence impacts the prevention and control of NTM [4].
Bibliography
[1] Muraglia M. et al, JPP (2024) ; Multi-scale physics of magnetic reconnection in hot magnetized
[2] Widmer F. et al, Nucl. Fusion (2019) ; Non-linear simulations of neoclassical tearing mode control by externally driven RF current and heating, with application to ITER
[3] Wang X. et al, Nucl. Fusion (2018) ; Numerical modelling on stabilizing large magnetic island by RF current for disruption avoidance
[4] Muraglia M. et al, Nucl. Fusion (2017) ; Amplification of a turbulence driven seed magnetic island by bootstrap current