EGAM induced by energetic electrons and nonlinear interactions among EGAM, BAEs and tearing modes in a toroidal plasma

Abstract

In this Letter, it is reported that the first experimental results are associated with the GAM induced by energetic electrons (EGAM) in HL-2A Ohmic plasma. The energetic electrons are jointly generated by Ohmic electric fields and parallel electric fields during magnetic reconnection associated with tearing mode (TM). The EGAM localizes in the core plasma, i.e. in the vicinity of q = 2 surface, and is very different from one excited by the drift-wave turbulence in the edge plasma. The analysis indicated that the EGAM is provided with the magnetic components, whose intensities depend on the poloidal angles, and its mode numbers are | m / n | = 2 / 0 . Further, there exist intense nonlinear interactions among EGAM, BAEs and strong tearing modes (TMs). These new findings shed light on the underlying physics mechanism for the excitation of the low frequency (LF) Alfvénic and acoustic fluctuations. ► The EGAM has been recently observed for the first time on HL-2A. ► The EGAM is most probably excited by energetic electrons via the three wave resonance and precessional resonance. ► There exist intense nonlinear interactions among EGAM, BAEs and strong TMs.