Lithium–sulfur (Li–S) batteries are promising candidates for next‐generation energy storage devices owing to their advantages such as high theoretical specific capacity and energy density. However, the shuttle effect of polysulfide intermediates and the slow electrochemical kinetics have a severe passive effect on the cycling stability and rate performance. A Co3W3C@C composite was prepared through a simple one‐pot pyrolysis method and used as a modifying layer on a commercial separator. The obtained modified separator not only prevented the shuttle effect through both strong chemical interaction and a physical barrier toward polysulfides, but also acted as a catalytic membrane to catalyze the electrochemical redox of active sulfur species. By employing the coated separator, the cathode with 60 wt % sulfur delivered a high initial capacity of 1345 mAh g−1 at 0.1 A g−1, excellent rate performance with a high capacity of 670 mAh g−1 even at 7 A g−1, and outstanding cycle performance with a low decay rate of 0.06 % per cycle and an average Coulombic efficiency of 99.3 % within 500 cycles at 1 A g−1. Even at a sulfur loading of 3 mg cm−1, a high initial capacity of 869 mAh g−1 and 632 mAh g−1 after 200 cycles at 1 A g−1 were obtained. The results demonstrate the advantages of Co–W bimetallic carbide in preventing the shuttle effect and promoting the redox kinetics for high performance Li–S batteries.
A radiofrequency (RF) ion source with a megawatt power extraction, thunder I, has been developed for the neutral beam injector (NBI) on HL-2A tokamak. A full solid-state RF generator with output power of 80 kW and frequency of 2 MHz was built by an RF combiner using 8 modules of solid-state RF generator with power of P
RF = 10 kW. The line electric efficiency of whole RF generator reaches 92% and its voltage standing wave ratio (VSWR) is 1.01, thus no water-cooling system is supplied. A quartz vessel with the inner diameter of 250 mm is directly adopted for resisting atmospheric pressure, which can dramatically simplify source structure. Nowadays, the extracted beam parameters of RF hydrogen ion source are 32 kV/20 A/0.1 s on a test bed, while the design parameters are 50 kV/20 A/3 s. The beam density profile measured by the infrared imaging technique at 1.3 m downstream from the grounded grid obeys a Gaussian distribution, and the corresponding half width of 1/e power decay at the matched condition is about 80 mm. Plasma homogeneity is over 90% at low RF power. The beam divergence angle meets the requirement of NBI system on HL-2A tokamak. The extractable current density increases almost linearly with the RF power. It reaches 2400 A m−2 at P
RF = 32 kW. The ion density in front of plasma grid is about 1 × 1018 m−3, corresponding to an ionized fraction of about 1% at the gas pressure of 0.5 Pa. Single hydrogen ion fraction reaches 79% at the beam current of 12.4 A. Some improvements have been considered for optimizing ion source performance on next experimental campaign. One smaller auxiliary RF discharge chamber equipped with a gas feed path, driven by 13.56 MHz/3.5 kW generator, is connected to main discharge chamber driven by 2 MHz/40 kW generator. By this dual-driven configuration, the innovative RF plasma source with high-pressure density gradient solves the initial ignition problem of powerful RF ion source even if the gas pressure below 0.1 Pa. In addition, the RF negative hydrogen ion source of 200 kV/20 A/3600 s is also developed at SWIP for the China fusion engineering test reactor.
The current-carrying capacity is one of the key factors that restrict the safe operation of cables. Accurately grasping the current-carrying capacity of cables is an important means to improve the efficiency and economic benefits of cable operation. The calculation standard of IEC60287 not only ignores the differences between different types of cables but also makes it difficult to make timely calculations and corrections according to the changes in cables during operation. Therefore, taking the WDZ-YJY3×16 cable as an example, the electromagnetic–thermal coupling simulation model is established and the finite element simulation analysis is carried out. First, the distribution characteristics of the cable core current are analyzed by establishing a good model for simulation calculations. Then, based on this, the imbalance of the three-phase current and the relationship between the core radius and sheath loss are studied. Finally, combined with the cross-sectional area of the cable core, the influence of the loss factor on the current-carrying capacity of WDZ (low-smoke halogen-free cables) is analyzed. The results show that when the cross-sectional area of the cable reaches 700 mm2, the relative error of the current-carrying capacity of the cable reaches about 9.1%. The calculation results lay a foundation for reasonably determining the current-carrying capacity of WDZ.
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