Enhanced particle transport events are discovered and analyzed as the density limit of the J-TEXT tokamak is approached. Edge shear layer collapse is observed and the ratio of Reynolds power to turbulence production decreases. Simultaneously, the divergence of turbulence internal energy flux (i.e. turbulence spreading) increases, indicating that shear layer collapse triggers an outward spreading event. Studies of correlations show that the enhanced particle transport events are quasi-coherent, and manifested primarily in density fluctuations which exhibit positive skewness. Electron adiabaticity emerges as the critical parameter which signals transport event onset. For α < 0.35 as density approaches the Greenwald density, both turbulence spreading and density fluctuations rise rapidly. Taken together, these results elucidate the connections between edge shear layer, density fluctuations, particle transport events, turbulence spreading and plasma edge cooling as the density limit is approached.

In this article, we present an analysis of the avalanche growth in electronegative gases, including detachment as well as ionization and attachment processes. The model is used to determine swarm parameters from a pulsed Townsend discharge. As an example, the swarm parameters for SF6-CO2 of electron ionization, attachment and detachment coefficients have been determined. The value of transport coefficient for SF6-CO2 has also been given.

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.

Acid phosphatases (APases) are attractive enzymes for catalyzing large-scale industrial phosphorylation reactions owing to their capacity of utilizing cheap phosphate donors as phosphate sources as well as their broad substrate spectrum. However, APases exhibit strong hydrolytic activity that usually overwhelms the needed phosphorylation reaction. In the present study, we have solved the crystal structure of APase from Pseudomonas aeruginosa (PaAPase) and unraveled the mechanism of PaAPase-catalyzed L-ascorbic acid phosphorylation using multiscale computational studies. In addition, we have engineered the charged residues near the active site to investigate the local electric field effects on modulating the competition between hydrolysis and phosphorylation in PaAPase. In the optimal variant of Q6 containing Asp135 → Arg135 mutation, the corresponding phosphorylation/hydrolysis ratios have increased by 2.9-fold compared with those in the wild-type enzyme. In particular, our simulations show that the local electric field of Q6 could remarkably inhibit the hydrolysis of the phospho-His171 intermediate while having relatively minor effects on the overall phosphorylation reactions. Such an introduced local electric field shifts the phosphorylation/hydrolysis balance in favor of phosphorylation reaction. Our combined experiments and theories demonstrate that protein engineering focusing on local electric field optimization is a practical strategy for modulating enzymatic reactivity.