Modulation of turbulent electron temperature fluctuations () and density fluctuations () by an m/n  =  1/1 tearing mode island was observed in the core plasma region of the HL-2A tokamak. High spatiotemporal resolution two-dimensional images of show the first evidence that the turbulence modulation occurs only when the island width exceeds a certain threshold value ( cm) and the modulation is localized merely in the inner area of the island due to significant alteration of local profiles and turbulence drives. Evidence also reveals that for large islands turbulence spreading takes place across the island region. The results are generally consistent with theories and simulations.

Interactions among pedestal shear flows, turbulence, and the formation of the edge transport barrier have been studied in H-mode plasmas of the HL-2A tokamak by multi-channel Doppler reflectometry with high spatiotemporal resolution. Geodesic acoustic mode (GAM) has been observed during the L-I-H transition. It has been observed that the plasma transits into the I-phase when the mean E×B shear flow reaches a critical value. The bi-spectrum analysis has shown that there is a strong interaction between GAM and limit cycle oscillation (LCO), and the energy transfer is from GAM to LCO, suggesting that GAM can assist the L-I transition. The regulation of the edge turbulence by LCOs helps to build the steep pedestal and initialize the confinement improvement of the plasma. It has been found that the mean E×B shear flow is further increased just before the I-H transition, accompanied by the turbulence suppression, leading to the edge transport reduction and the pedestal formation. It has been demonstrated that the increase of the mean E×B shear flow prior to the L-I and I-H transitions is due to the ion diamagnetic component of Er. These results corroborate that the mean E×B shear flow plays a key role in the L-I and I-H transitions.

The effect of resonant magnetic perturbations (RMPs) on particle confinement is studied in J-TEXT tokamak by using externally applied rotating RMPs. It is found that RMPs cause improved (degraded) particle confinement when its frequency is higher (lower) than the natural m/n = 2/1 tearing mode frequency, and the amount of change in electron density is proportional to the difference between these two frequencies, where m and n are the poloidal and toroidal mode number, respectively. These results reveal the important role of the relative rotation between RMPs and the electron fluid in affecting the particle confinement. The experimental results are compared to numerical ones based on nonlinear two-fluid equations, and quantitative agreement is found. Resonant magnetic perturbations (RMPs) often exist, e.g., in solar flares, magnetotail and fusion devices, due to intrinsic plasma instabilities and have attracted much research efforts, since they are associated with magnetic reconnection. In fusion devices RMPs can also be generated by external coil current, which have important applications in fusion plasmas. Static RMPs are able to suppress or mitigate edge localized modes (ELMs) [1-5] and to affect other instabilities [6-12]. In addition, rotating RMPs were used to study the field penetration [13], their effect on plasma rotation [14] and plasma response on TEXTOR [15]. On DIII-D, rotating RMPs are utilized to control NTMs rotation [16] and detect the intrinsic error field [17].

Investigations of beta-induced Alfvén eigenmodes (BAEs) destabilized by resonant magnetic perturbations (RMPs) have been conducted on the J-TEXT tokamak. In the Ohmic discharges, with RMPs having finite perturbed amplitudes, two different types of Alfvén eigenmodes have been observed and identified. One is considered as m-BAE, due to the strong correlation with magnetic island in some noticeable aspects, for example, frequency characteristic, mode number and driving mechanism. Specifically, the standing wave nodes of m-BAE are located at the O point and X point of the magnetic island. Another one is discerned as the magnetic island-induced AE (labeled as the MIAE-like mode in this work), which is consistent with the prediction of theory (Biancalani et al 2010 Phys. Rev. Lett. 105 095002). The frequency of MIAE-like mode is found to be approximately proportional to the square of magnetic island width.

In the recent two years, three major achievements have been made on J-TEXT in supporting for the expanded operation regions and diagnostic capabilities, e.g. the 105 GHz/500 kW/1 s ECRH system and the poloidal divertor configuration. Especially, the 400 kW ECW has also been successfully injected into the diverted plasma. The locked mode (LM), especially the 2/1 LM, is one of the biggest threats to the plasma operation. Both the thresholds of 2/1 and 3/1 LM are observed to vary non-monotonically on electron density. The electrode biasing (EB) was applied successfully to unlock the LM from either a rotating or static RMP field. In the presence of 2/1 LM, three kinds of standing wave (SW) structures have been observed to share a similar connection to the island structure, i.e. the nodes of the SWs locate around the O- or X- points of the 2/1 island. The control and mitigation of disruption is essential to the safe operation of ITER, and it has been systematically studied by applying RMP field, MGI and SPI on J-TEXT. When the RMP induced 2/1 LM is larger than a critical width, the MGI shutdown process can be significantly influenced. If the phase difference between the O-point of LM and the MGI valve is +90° (or -90°), the penetration depth and the assimilation of impurities can be enhanced (or suppressed) during the pre-TQ phase and result in a faster (or slower) thermal quench. A secondary MGI can also suppress the RE generation, if the additional high-Z impurity gas arrives at the plasma edge before TQ. When the secondary MGI has been applied after the formation of RE current plateau, the RE current can be dissipated, and the dissipation rate increases with the injected impurity quantity, and saturates with a maximum of 28 MA/s.