Observation of Multiple Broadband Alfvénic Chirping Modes in HL-2A NBI PlasmasSupported by the National Key R&D Program of China (Grant Nos. 2018YFE0304102, 2019YFE03020000 and 2017YFE0301202), the National Natural Science Foundation of China (Grant Nos. 11875024, 11875021, 11835010 and 12005054), the Sichuan Provincial Science and Technology Project (Grant Nos. 2020YFSY0047 and 2020JDJQ0070).

Abstract

Multiple broadband Alfvénic chirping modes (CMs), with frequencies in the wide range of f ∼ 35–150 kHz and chirping down rapidly, are found in HL-2A neutral beam injection plasmas, and the CMs can even coexist. The frequency chirping down process can be completed within ∼1 ms, and the frequency shift can reach 30–50 kHz. The CMs propagate in ion diamagnetic drift directions poloidally. The toroidal mode number is confirmed to be n = 1, 2, 3 and 4 for the f ∼ 35–65, 55–90, 70–120 and 100–150 kHz CMs, respectively. The CMs are more like to be energetic-particle continuum modes (EPMs), since the modes almost locate on the Alfvén continuum.