Low-frequency MHDModes Driven by Energetic Electrons in HL-2A LHCD Plasmas

The energetic electrons (EEs) can be generated directly by radio frequency heating (electron cyclotron resonant heating/current drive (ECRH/ECCD), low hybrid current drive (LHCD)) and toroidal Ohmic electric field. Besides, energetic ions (EIs), produced by neutral beam injection (NBI) and ion cyclotron resonant heating (ICRH), and 3.5 MeV alpha ( α ) particles generated by D-T reaction in burning plasma will heat the background electrons firstly, when the energy of EIs and α is higher than critical energy [1]. Abundant EEs induced magnetohydrodynamic (MHD) instabilities and even their nonlinear interactions have been identified and studied [2-12]. The small resonant particle orbit width of EEs can be utilized to simulate and analyse the analogous effect of α characterized by small dimensionless orbits similar to EEs in tokamak plasmas [12, 13]. The LHCD system is designed and planned for off-axis current drive and assisted ramp-up in the second phase of International Thermonuclear Experimental Reactor (ITER) operation [14]. The MHD instabilities maybe excited by the EEs during high-power LHCD. Two kinds of basic EE induced low-frequency MHD instabilities [7], e.g., core localized electron fishbone (e-FB) mode and edge localized electron beta-induced Alfvén eigenmode (e-BAE), are found in coand counter-current drive LHCD plasmas on HL-2A, respectively. The e-BAEs in LHCD plasmas are found for the first time.