Experimental investigation of PDI bifurcation of lower hybrid waves during electron density ramp-up in EAST

作者：G.H. Yan, B. Ding, Cong-Feng Wu, Miaohui Li, S. G. Baek, F. Napoli, Taotao Zhou, Kangning Geng, N. Yan, M. Wang, Xinnan Zhang, H. Xu, J. Yang, Weiqian Ma · 发表于：Nuclear Fusion · 年份：2024 · DOI：10.1088/1741-4326/ad4fa0 · 被引用次数：6 · 研究领域：Magnetic confinement fusion research、Ionosphere and magnetosphere dynamics、Particle accelerators and beam dynamics

Abstract The effect of parametric decay instability (PDI) on the current drive efficiency of 4.6 GHz lower hybrid (LH) waves in EAST is investigated experimentally, showing the PDI channel bifurcation of LH waves for the first time in EAST. First, experiments with three platforms of LH power were performed, achieving the LH power required for the PDI occurrence. Second, PDI bifurcation experiments were further carried out by ramping up the plasma electron density. The loop voltage increases with an increase in density, implying a decrease in the current driven by the LH wave. PDI bifurcation during electron density ramp-up was studied by analyzing the parallel refractive index ( n ∥ ) and the frequency spectrum broadening, which is measured with a radio frequency magnetic probe array recently installed close to the LH antenna. It is observed for the first time that they both first increase with density, then there is not much variation and a clear sideband in the frequency spectrum is also observed when the density is up to 4 × 10 19 m − 3 , suggesting a change in the PDI channel. Calculation of the mode growth rate driven by PDI shows that when the edge electron density is up to 1.9 × 10 18 m − 3 , the growth rate of the ion cyclotron quasi-mode (ICQM) will exceed that of the ion sound quasi-mode (ISQM), quantitively explaining that with a...