Observation of Multiple Broadband Alfvénic Chirping Modes in HL-2A NBI Plasmas

Multiple broadband Alfvénic chirping modes (CMs), with frequencies in the wide range of f\sim35–150 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 \sim1 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\sim35–65, 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.