Soft H-L Back Transitions Induced by RMP Coils in High q95 Plasmas on EAST

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Abstract

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The termination phase of ITER demands a simultaneous decay of plasma current, stored energy and particle density, while maintaining precise control over plasma position, shape, vertical stability, and radiation levels. In relation to ITER termination control, ‘soft’ H-mode to L-mode (H-L) back transitions, coupled with simultaneous particle and heat pumping via n=2 resonant magnetic perturbations (RMPs), have been achieved in EAST plasmas at low safety factor (q95 =3.5-4.0) [Shao L M, et al., 2024 PPCF 66 035018]. For high q95 (q95 > 5.0), high toroidal field (BT ≥ 2.4T) and high-performance EAST plasmas, such soft H-L transitions are not observed using n=2 RMPs, but can be accomplished by employing n =1 RMPs along with a concurrent ramp-down of plasma density and stored energy. In these high q95 discharges, no significant increases in plasma radiation or loop voltage were detected upon the application of n=1 RMPs. The core toroidal rotation was reduced by the neoclassical toroidal viscous torque induced by the n =1 RMP field, whereas no obvious decrease in core electron and ion temperatures was observed. The energy confinement time at the controlled soft H-L transition τeH-L is comparable between favourable (∼ 50 ms) and unfavourable (∼ 48 ms) configurations, and exhibits independence from core line-averaged electron density, q95 and upper/lower single-null divertor configurations.

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About the Speaker

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Linming Shao earned his Ph.D. in Plasma Physics from the University of Chinese Academy of Sciences in 2016, under the supervision of Prof. Guosheng Xu (EAST experimental team) and Prof. Elisabeth Wolfrum (ASDEX Upgrade device). From 2016 to 2022, he served as an associate researcher at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). Since 2022, he has continued his role as an associate researcher at ASIPP.

 

Linming Shao’s interests include turbulence, L-H/H-L confinement transition physics and power threshold and microwave diagnostics.