Speaker
Description
Due to their relatively higher Vbeam/VAlvén ratio, spherical tokamaks like MAST-U are ideal to investigate high-frequency beam-ion driven modes such as Compressional Alfvén Eigenmodes (CAEs) and Global Alfvén Eigenmodes (GAEs) [1, 2]. Besides, the scintillator-based Fast-Ion Loss Detector (FILD) [3] in MAST-U, provides enough sampling frequency to detect fast-ion losses induced by such instabilities. Fourier analyses of the MAST-U FILD revealed coherent fast-ion losses in the range of 1 – 2 MHz, which is 0.3 – 0.45 times the cyclotron frequency of deuterium at the magnetic axis. The modes are identified as Global Alfvén Eigenmodes (GAEs) formed above the maxima of the Alfvén continuum [4]. To date, this is the most direct measurement of fast-ion losses induced by GAEs, showing for the first time that instabilities in the ion cyclotron range can trigger fast ion losses. Since the Neutral Beam Injectors in ITER will provide such a super-Alfvénic fast-ion distribution, they may be susceptible to drive GAEs unstable. Thus, understanding these losses becomes of paramount importance for ITER, as they can affect the heating and current drive capabilities to achieve burning plasmas.
[1] L. C. Appel et al., Plasma Phys. Control. Fusion 50, 115011 (2008) [2] S. E. Sharapov et al., Plys Plasmas 21, 082501 (2014) [3] J. F. Rivero-Rodriguez et al., Rev. Sci. Instrum. 89, 10I112 (2018) [4] M. Dreval et al., Nucl. Fusion 50, 115011 (2024) * See author list of J. Harrison, et al. 2024 Nucl. Fusion 64 112017
