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The active control of internal transport barriers (ITBs) is an important issue to achieve high performance plasma in a fusion reactor. A critical challenge of ITB control is to increase the ITB position. The ITBs with internal kink modes (IKMs), such as fishbone (FB) instability and long-live mode (LLM) with mode number of m / n = 1/1 are frequently observed on HL-2A tokamak in neutral beam heated discharges. The correlation of FB instability/LLM with ITBs is analyzed in order to extend the ITB radius. It has been revealed that FB instability and LLM are often excited after the ITB formation. Therefore, FB instability and LLM play no role in triggering ITBs on HL-2A tokamak. On the other hand, they may slow down the outward radial expansion and then shrink the foot position of ITB, and damp the gradient growth of ion temperature and rotation velocity. Since the perturbation of LLM is weaker than that of FB instability, the shrinking effect of ITB foot and braking effect on gradient growth are slighter than those of FB instability. Compared with the LLM, FB instability routinely appears in plasmas with lower density, higher heating power and lower plasma current. In addition, large ITBs without IKMs are also discussed on HL-2A tokamak. The large ITB is the largest one, the FB ITB is the strongest one and the LLM ITB is the widest one in three ITBs, where the ‘large’, ‘strong’ and ‘wide’ qualifications correspond to ITB position ρ ITB, the normalized temperature gradient R /LT, and its width W / a. Therefore, the large ITB position may be obtained if the IKMs are effectively controlled in a tokamak. [ABSTRACT FROM AUTHOR]

The effects of a coherent mode (CM) at a frequency of f = 13–16 kHz on the redistribution of divertor particle flux have been studied in HL-2A H-mode plasmas using multiple diagnostics. The experimental results demonstrate that a CM localized at the middle of the pedestal results in outward particle transport, limiting the growth of the pedestal density gradient in the recovery phase of the pedestal, leading to a substantial increase in the localized particle flux striking the outer divertor target, which clearly deviates from the primary peak at the strike point. These observations indicate that the CM might play a crucial role in redistributing the divertor particle flux, which is important for understanding and controlling the divertor heat flux in future fusion-relevant devices. [ABSTRACT FROM AUTHOR]

Edge localized mode (ELM)-filament statistical characteristics and intermittent convective transport are studied during ELM mitigation (10–30�ms) induced by supersonic molecular beam injection (SMBI) on the HL-2A tokamak. Langmuir probe data show that the burst rate of large amplitude filaments (δne�>�4σ) decreases by 30–50% and their radial velocity decreases by 40–60%, which is an indication of an amplitude reduction. A decrease of long-range correlation along the magnetic flux surface is observed after SMBI, indicating a role of electron–ion collisionality on the filament parallel current in the ELM mitigation time. The transient particle and heat fluxes decrease about 40–50% and 50–60%, respectively. These observations indicate that SMBI might be an effective method to suppress the intermittent convective transport. [ABSTRACT FROM AUTHOR]