Overview of recent HL-2A experiments. (5th October 2015)

• Record Type: Journal Article
• Authors: Xu, M.; Duan, X.R.; Dong, J.Q.; Ding, X.T.; Yan, L.W.; Liu, Yi; Song, X.M.; Huang, Y.; Zou, X.L.; Yang, Q.W.; Liu, D.Q.; Rao, J.; Xuan, W.M.; Chen, L.Y.; Mao, W.C.; Wang, Q.M.; Li, Q.; Cao, Z.; Cao, J.Y.; Lei, G.J.; Zhang, J.H.; Li, X.D.; Xu, Y.; Ji, X.Q.; Cheng, J.; Chen, W.; Yu, L.M.; Zhong, W.L.; Yu, D.L.; Zhang, Y.P.; Shi, Z.B.; Chen, C.Y.; Isobe, M.; Morita, S.; Cui, Z.Y.; Dong, Y.B.; Feng, B.B.; Cui, C.H.; Huang, M.; Li, G.S.; Li, H.J.; Li, Qing; Peng, J.F.; Wang, Y.Q.; Li, B.; Yao, L.H.; Yao, L.Y.; Yuan, B.S.; Zhou, J.; Zhou, Y.; Itoh, K.; Liu, Yong;
• Other Names: collab.
• Is Part Of: Nuclear fusion. Volume 55:Number 10(2015:Oct.)
• Publication Date: 2015-10-05
• Subjects: fusion energy -- tokamak -- plasma physics -- HL-2A; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/55/10/104022
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: Since the last Fusion Energy Conference, the HL-2A experiment has made significant progress in the following areas: (i) physics on low-intermediate-high (L-I-H) transition and pedestal dynamics; (ii) magnetohydrodynamic (MHD) and energetic-particle (EP) physics; (iii) interaction between neoclassical tearing modes (NTMs) and non-local transport; (iv) and edge localized mode (ELM) mitigation by supersonic molecular beam injection (SMBI). Two types of limit-cycle-oscillations (LCOs) were observed in the intermediate phase (I-phase), which indicated a second type of predator-prey process between turbulence and pressure gradient in addition to the conventional predator–prey involving zonal flows and turbulence. It was found that a kink-type MHD mode often crashed prior to the I-H transition, which played a crucial role in triggering H-mode by increasing the edge pressure gradient and E × B flow shear and consequently suppressing turbulent transport. It was also found that impurity concentration played an important role in the multi-transitions between ELM-free H-mode and I-phase. Besides, a quasi-coherent mode around 50–100 kHz was found to be associated with pedestal density gradient saturation in ELM-free H-mode. For the first time, two types of magnetic activities with n = 0 were observed in the presence of strong tearing modes. Fourier bicoherence analysis suggested that these modes were generated by the nonlinear coupling between Alfvén eigenmodes (AEs) and low-frequency MHD modes. Up- and down-sweeping reverse shear Alfvén eigenmodes (RSAEs) were identified experimentally. The transitions between fishbone and long-lived mode (LLM) were also investigated. The results showed that fishbone could transit from/to LLM and even trigger tearing modes (TMs). For non-local transport, key characteristics of enhanced avalanches in the theory of self-organized criticality (SOC) were identified, including high Hurst exponents and large-scale radial propagation. Experimental results revealed a close correlation between NTMs and non-local transport. In addition, studies on ELM mitigation by SMBI have also progressed substantially.