The absolute rate of nonlinear energy transfer among broadband turbulence, low-frequency zonal flows (ZFs) and geodesic acoustic modes (GAMs) was measured for the first time in fusion-grade plasmas using two independent methods across a range of heating powers. The results show that turbulent kinetic energy from intermediate frequencies (20-80 kHz) was transferred into ZFs and GAMs, as well as into fluctuations at higher frequencies (>80  kHz). As the heating power was increased, the energy transfer from turbulence into GAMs and the GAM amplitudes increased, peaked and then decreased, while the energy transfer into the ZFs and the ZFs themselves increased monotonically with heating power. Thus there exists a competition between ZFs and GAMs for the transfer of turbulent energy, and the transfer into ZFs becomes dominant as the heating power is increased. The poloidal-radial Reynolds stress and the mean radial electric field profiles were also measured at different heating powers and found to be consistent with the energy transfer measurement. The results suggest that ZFs play an important role in the low-to-high (L-H) plasma confinement transition.

The HL-2A tokamak has a very closed divertor geometry, and a new infrared camera has been installed for high resolution studies of edge-localized mode (ELM) heat load onto the outer divertor targets. The characteristics of power deposition patterns on the lower outer divertor target plates during ELMs are systematically analysed with infrared thermography. The ELM energy loss is in the range of 3%–8% of the total plasma stored energy. The peak heat flux on the outer divertor targets during ELMs currently achieved in HL-2A is about 1.5–3.2 MW m−2, the wetted area is about 0.5–0.7 m2, and the corresponding integrated power decay length at the midplane is about 25–40 mm. The rise time of the ELM power deposition is in the range of about 100 μs to 400 μs, and the decay time is typically 1.5 to 4 times longer than the corresponding rise time. Convective transport along open field lines during the ELM rise phase from the midplane towards the divertor targets is implied due to the correlation of parallel transport time in the scrape-off layer (SOL) and ELM power rise time. The peak ELM energy fluence is compared with those predicted by models and with experimental data from JET, ASDEX Upgrade, MAST, and COMPASS. The results, as a whole, show a good agreement.

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The controllability of the heat load and impurity in the divertor is very important, which could be one of the critical problems to be solved in order to ensure the success for a steady state tokamak. HL-2M has the advantage of the poloidal field (PF) coils placed inside the demountable toroidal field (TF) coils and close to the main plasma. As a result, it is possible to make highly accurate configuration control of the advanced divertor for HL-2M. The divertor target geometry of HL-2M has been designed to be compatible with different divertor configurations to study the divertor physics and support the high performance plasma operations. In this paper, the heat loads and impurities with different divertor configurations, including the standard X-point divertor, the snowflake-minus divertor and two tripod divertor configurations for HL-2M, are investigated by numerical simulations with the SOLPS5.0 code under the current design of the HL-2M divertor geometry. The plasmas with different conditions, such as the low discharge parameters with I p   =  0.5 MA at the first stage of HL-2M and the high parameters with I p   =  2.0 MA during the normal operations, are simulated. The heat load profiles and the impurity distributions are obtained, and the control of the peak heat load and the effect of impurity on the core plasma are discussed. The compatibility of different divertor configurations for HL-2M is also evaluated. It is seen that the excellent compatibility of different divertor configurations with the current divertor geometry has been verified. The results show that the snowflake-minus divertor and the tripod divertor with d x = 30   cm present good performance in terms of the heat load profiles and the impurity distributions under different conditions, which may not have a big effect on the core plasma. In addition, it is possible to optimize the distance between the two X-points, d x , to achieve a better performance in terms of the parameters of discharges.

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