Abstract Density profiles in the pedestal region (H-mode) are measured in HL-2A and the characteristics of the density pedestal are described. Cold particle deposition by supersonic molecular beam injection (SMBI) within the pedestal is verified. Edge-localized mode (ELM) mitigation by SMBI into the H-mode pedestal is demonstrated and the relevant physics is elucidated. The sensitivity of the effect to SMBI pressure and duration is studied. Following SMBI, the ELM frequency increases and the ELM amplitude decreases for a finite duration. Increases in ELM frequency of are achieved. This experiment argues that the ELM mitigation results from an increase in higher frequency fluctuations and transport events in the pedestal, which are caused by SMBI. These inhibit the occurrence of large transport events which span the entire pedestal width. The observed change in the density pedestal profiles and edge particle flux spectrum with and without SMBI supports this interpretation. An analysis of the experiment and a model shows that ELMs can be mitigated by SMBI with shallow particle penetration into the pedestal.

For the first time supersonic molecular beam injection (SMBI) and cluster jet injection (CJI) were applied to mitigate edge-localized modes (ELMs) in HL-2A successfully. The ELM frequency increased by a factor of 2-3 and the heat flux on the divertor target plates decreased by 50% on average after SMBI or CJI. Energetic particle induced modes were observed in different frequency ranges with high-power electron cyclotron resonance heating (ECRH). The high frequency (200-350 kHz) of the modes with a relatively small amplitude was close to the gap frequency of the toroidicity-induced Alfvén eigenmode. The coexistent multi-mode magnetic structures in the high-temperature and low-collision plasma could affect the plasma transport dramatically. Long-lived saturated ideal magnetohydrodynamic instabilities during strong neutral beam injection heating could be suppressed by high-power ECRH. The absolute rate of nonlinear energy transfer between turbulence and zonal flows was measured and the secondary mode competition between low-frequency (LF) zonal flows (ZFs) and geodesic acoustic modes (GAMs) was identified, which demonstrated that ZFs played an important role in the L-H transition. The spontaneously generated E × B shear flow was identified to be responsible for the generation of a large-scale coherent structure (LSCS), which provided unambiguous experimental evidence for the LSCS generation mechanism. New meso-scale electric potential fluctuations (MSEFs) at frequency f ∼ 10.5 kHz with two components of n = 0 and m/n = 6/2 were also identified in the edge plasmas for the first time. The MSEFs coexisted and interacted with magnetic islands of m/n = 6/2, turbulence and LF ZFs. © 2013 IAEA, Vienna.