7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Experimental Observation of Low-frequency MHD Instabilities Driven byEnergetic Electrons in LHCD Plasmas
L.M. Yu1*, W. Chen1, Z.B. Shi1, X.Q. Ji1, R.R. Ma1, P.W. Shi1, X.Y. Bai1, J.X. Li1, Y.G. Li1, Z.C.
Yang1, X.M. Song1, B. Lu1, Yi Liu1, L.W. Yan1, X.T. Ding1,W.L. Zhong1 and M. Xu1
1Southwestern Institute of Physics, P.O. Box 432 Chengdu 610041, Chinae-mail: yulm@swip.ac.cn
The 3.5 MeV alphas, generated by deuterium-tritium(D-T) fusion reactions in the burning plasma, willtransfer their energy mostly to electrons firstly. The small
resonant particle orbit width of energetic electrons (EEs)of device can be utilized to simulate and analyse theanalogous effect of alphas characterized by small
dimensionless orbits similar to EEs in tokamak plasmas.
It is the energy but not the mass that plays an importantrole between reactions of macro-MHD waves andenergetic particles. Therefore, investigating theinteractions between EEs and plasma waves will provide
important experimental experiences for burning plasmas,
especially for ITER and DEMO.
Low-frequency MHD instabilities, e.g., core localized
fishbone modes (FBs) and beta induced Alfvén
eigenmodes (BAEs) localized in edge, driven by EEs arefound in the co- and counter-driving low hybrid current
drive (LHCD) plasmas on HL-2A, respectively. These
modes all propagate in electron diamagnetic drift
direction in poloidal, though in the different LHCD
driving direction conditions. The FBs or BAEs even canco-exist at the same time.
There are 4 FBs with various frequencies of 2-5, 5-7,
10-12 and 13-15 kHz are observed on the spectrogram ofthe core soft X-ray (SXR) signals (inside q=1 surface,with d=2.4, 7.0 and 10.0 cm). The frequencies jump
phenomena of 4 FBs and even co-existance of FBs arefound, and the fluctuations from different channel SXR
indicate low-(2-5, 5-7 kHz) and high-frequency (10-12,13-15 kHz) FBs locate near r~2.4 and 10.0 cm,respectively.
While, 2 BAEs are found on the spectrogram of Mrinov
coil signal when the LHCD driving current is incouter-direction with plasma current. The frequency ofm/n=3/1 BAE mode are in the range of 9-11 kHz whenLHCD power (PLHCD) is 0.44 MW. The strong
15-17~kHz m/n=5/2 mode appears when PLHCD is 0.52
MW, and the weak 7-9 kHz 3/1 mode can coexists at thesame time, as shown in Figure.1. The frequencies of thetwo modes are closes to continue accumulation point
frequency frequency of BAE. With the increase of PLHCD,

the value of safety factor decreases from 3.0 to 2.5 (nearr~ 29cm) in which the BAEs located. It's indicated thatthe variation of mode numbers are caused by thechanged q values near mode position.

Figure.2 BAEs found in the counter-driving LHCD
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