In our previous letter, the geodesic acoustic mode (GAM) induced by energetic particles (EGAMs) was reported in low density ohmic plasma on HL-2A (Chen et al 2013 Phys. Lett. A 377 387). We extend the experimental results of the EGAM mode in this paper. During strong tearing modes (TMs), the beta-induced Alfvén eigenmodes (BAEs) and EGAM-induced density fluctuations are firstly measured by microwave Doppler reflectometers with different work frequencies. As predicted by theory, the measurements of magnetic probes and Doppler reflectometers suggest the EGAM magnetic oscillations have poloidal/toroidal mode numbers of m/n = 2/0, and are localized in the core with a broad radial structure. The mode frequency is less than that of the conventional GAM (i.e. fEGAM/fGAM < 1), and is constant in the radial direction. Our experimental results suggest that a density limit exists for the excitation of the EGAM in the ohmic plasma, and the density limit is improved with electron cyclotron resonance heating + neutral beam injection heating on HL-2A. The auto and cross squared bicoherences of magnetic and density fluctuations indicate that intense nonlinear interactions exist among EGAM, BAEs and strong TMs. These new observations will help us to understand the underlying physics mechanism for the excitation of fluctuations in the sub-Alfvén frequency range.
前文（Chen et al 2013 Phys. Lett. A 377 387）中，我们报道了HL-2A装置上低密度欧姆等离子体中由高能粒子驱动的测地声模（EGAM）。本文进一步扩展了EGAM模的实验结果。在强撕裂模（TM）期间，利用不同工作频率的微波多普勒反射计，首次测量到了β诱导的阿尔芬本征模（BAE）以及EGAM引起的密度涨落。与理论预测一致，磁探针和多普勒反射计的测量结果表明，EGAM磁振荡的极向/环向模数为m/n = 2/0，并且定域在芯部，具有宽的径向结构。其模频率低于常规GAM的频率（即f_EGAM/f_GAM < 1），且在径向上保持恒定。我们的实验结果表明，欧姆等离子体中EGAM的激发存在密度极限，而通过电子回旋共振加热加中性束注入加热，该密度极限在HL-2A装置上得到了改善。磁涨落和密度涨落的自双相干谱及互双相干谱分析表明，EGAM、BAE和强TM之间存在强烈的非线性相互作用。这些新的观测结果将有助于我们理解亚阿尔芬频率范围内涨落激发的潜在物理机制。