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In magnetically confined fusion devices, energetic particles produced by external heating systems such as neutral beam injectors (NBI) or ion cyclotron resonance heating (ICRH) may excite MHD instabilities such as Alfven Eigenmodes (AEs) which can degrade confinement in tokamak plasmas and potentially damage the plasma facing components [1]. Externally applied 3D Magnetic Perturbations (MPs) have previously been proposed as an effective actuator for controlling NBI-driven AEs in several devices, including ASDEX Upgrade [1,2], KSTAR [3], EAST [4,5] and NSTX [6,7].
During the 2024-2025 and 2025-2026 ASDEX Upgrade experimental campaigns, a series of discharges with B0 = -2.5 T and Ip=500 kA incorporating minority-H ICRH heating and counter current ECCD were to investigate the effect of the n=2 and n=4 MPs on Toroidal Alfven Eigenmode (TAE) stability. The n=2 minority-H ICRH-driven TAE amplitude has been tracked along a varying differential phase for the MP and TAE mitigation was observed for an optimal value of the differential phase near 0°. The results also show that the modulation is independent of the absolute phasing of the MP coils for ICRH-driven TAE as opposed to NBI-driven TAE.
In this work, we present these experimental results supported by numerical modelling with MEGA [8] and ASCOT [9]. The simulations predict the appearance of unstable ICRH-driven TAEs across various possible values of energetic particle anisotropy and pressure. The TAE modulation found in experiments has been numerically investigated with a set of simulations incorporating MPs of differing differential phases and toroidal numbers. These simulations also incorporate ICRH energetic particles, which are modelled as a highly anisotropic hydrogen slowing down distribution function. This aims to provide a drive for the TAE while also being able to resonate with the MP fields.
[1] M.Garcia-Munoz et al., Plasma Phys. Control. Fusion 61 054007 (2019)
[2] J.Gonzalez-Martin et al., Phys. Rev. Lett. 130, 035101 (2023)
[3] K.Kim et al., Nucl. Fusion 60 126012 (2020)
[4] N.Chu et al., Nucl. Fusion 58 104004 (2018)
[5] J.Zhao et al., Plasma Sci. Technol. 095101 (2021)
[6] G.J.Kramer et al., Plasma Phys. Control. Fusion 58 085003 (2016)
[7] A.Bortolon et al., Phys. Rev. Lett. 110 265008 (2013)
[8] Y.Todo et al., Phys. Plasmas 5, 1321–1327 (1998)
[9] K. Särkimäki et al 2016 Plasma Phys. Control. Fusion 58 125017
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.