A hard x-ray (HXR) spectrometer has been developed and implemented on the ENN Xuan-Long 50U (EXL-50U) spherical torus to study runaway electron (RE) dynamics. The diagnostic system features adjustable viewing geometries and optimized shielding designs, ensuring reliable operation under high-parameter plasma conditions. By utilizing LaBr3:Ce detectors with millisecond temporal resolution, both thin-target and thick-target bremsstrahlung spectra have been measured during plasma discharges. The system demonstrates the feasibility of investigating RE behavior through γ-ray spectroscopy in compact fusion devices, with potential applications in next-generation spherical torus.

In this work, a Lorentz collision operator is implemented in the NLT code. This module uses the 4th order accurate finite-difference scheme and a correction algorithm, which suppresses the spurious diffusion and ensures the numerical conservation properties, respectively. Neoclassical parallel electrical conductivity and neoclassical ion thermal conductivity cases are tested, and the simulation results agree well with the theory. Finally, the formation of the parallel return flow through the ambipolar radial electric field and the collisional relaxation to the rigid-body toroidal rotation are further investigated.

In the 2018 EAST (Experimental Advanced Superconducting Tokamak) experiments, type-I ELMs (edge localized modes) were mitigated and suppressed by Ne-SMBI (supersonic molecular beam injection) injection during H-mode discharges. No energy confinement degradation was observed during ELM suppression, whereas approximately 10% degradation was observed during ELM mitigation. The observation of broadband MHD (magnetohydrodynamic) turbulence during ELM suppression indicates it may be the primary particle transport channel. The electron density profile in the pedestal top increased and the edge radiation increased with Ne-SMBI injection, which could reduce heat fluxes reaching the divertor. Pedestal profile changes appear adequate to trigger small transport events and mitigate large ELMs. In the 2022 EAST experimental campaign, stable 2 s ELM suppression was achieved by adjusting the Ne-SMBI injection rate. High-frequency coherent modes around 250 kHz, possibly corresponding to micro-tearing modes (MTM), appeared during ELM suppression. In addition to impurity SMBI injection, fuel particle D2-SMBI injection was also applied for ELM mitigation. Experimental results show D2-SMBI has small impact on the edge, increasing ELM frequency without significant ELM mitigation compared to impurity SMBI.

An improved Boris algorithm for simulating the motion of charged particles in electromagnetic fields has been developed. This enhancement addresses the issue of inaccurate fast-scale cyclotron phase calculations present in the original Boris algorithm, while preserving its advantage in simulating slow-scale guiding center motion. As a result, it strikes a balance between low and high-frequency dynamics, overcoming the limitations of traditional second-order volume-preserving algorithms (VPAs) which are constrained to a single characteristic frequency. Test particle simulations indicate that, in most cases, the improved Boris algorithm achieves significantly higher accuracy than conventional VPAs when simulating cases involving various frequencies of electric field within a typical tokamak magnetic field, highlighting its superior efficacy in handling problems across a wide range of characteristic frequencies.

A conventional single-null divertor geometry has been proposed for the China Fusion Engineering Demo Reactor (CFEDR). The divertor performance of CFEDR under the conventional high confinement mode (H-mode) scenario with a fusion power of 1.5 GW has been evaluated using the SOLPS-ITER code package. A comparative simulation has been carried out with two different gas puffing settings. The results indicate that simultaneous seeding with both argon (Ar) and deuterium (D) presents a promising solution to divertor power exhaust by increasing radiation losses and thus reducing heat flux. It has been demonstrated that both the inner and outer divertor targets can reach nearly full detachment with total peak heat loads lower than 10 MW m−2 and without notable impurity contamination in the core plasma. The heat loads on both targets contributed by radiation and neutrals are notable for the pronounced divertor detachment scenario. The simulation indicates that, to achieve a similar divertor condition, increasing the D puffing rate can significantly reduce the required Ar puffing rate. This causes a clear reduction in both the average Ar concentration and the effective ion charge number. Additionally, it is found that Ar has a higher compression in the inner divertor region due to the enhanced source-driven flow of recycling main ions in proximity to the outer divertor target. Furthermore, the erosion rate of tungsten divertor targets has been estimated using the DIVIMP code based on the background plasmas provided by SOLPS-ITER. The results indicate that the W erosion rate is generally within the acceptable lifetime requirement for the CFEDR divertor.

This study proposed a double-pulse laser-induced breakdown spectroscopy (DP-LIBS) signal enhancement method based on the shaping of vortex beams, effectively addressing the low-energy utilization of the second pulse in collinear DP-LIBS systems and significantly improving the detection sensitivity of trace elements in aluminum (Al) alloys. This study built a conventional collinear DP- LIBS system, and the second pulse laser was shaped into a vortex beam using a vortex half-wave plate. This study confirms that vortex beam shaping can enhance the spectral signal intensity and improve the stability of the plasma. The effects of spectral acquisition delay and inter-pulse delay on the performance of the vortex beam shaping technique in DP-LIBS were systematically investigated through experimental studies. The results demonstrate that compared with the traditional Gaussian beam method, the vortex beam shaping technology on average increases the spectral line intensity of the characteristic elements in the Al alloy sample by an average factor of 2.22, and the signal-to-background ratio increases significantly to 1.58. Additionally, the average value of relative standard deviation of the characteristic spectral lines was reduced from 8.54% to 4.39%. Trace elements such as Pb and Ti were also detected. Further analysis of transient plasma images confirmed that the vortex beam shaping technique enhances LIBS signals by modulating the spatial energy distribution and helical phase fronts of the second pulse laser, thereby altering the plasma evolution dynamics.

Polypropylene (PP), as a green and environmentally friendly material, is a potential material for power cable insulation. To improve the dielectric properties of PP cable insulation, octavinyl- sesquisiloxane (OV-POSS) was modified with the silane coupling agent KH550 and dielectric barrier discharge plasma treatment. PP nanocomposites containing elastomer-hydrogenated styrene–butadiene block copolymers (SEBS) were prepared by a melt blending method to investigate the effect of plasma-modified OV-POSS on the physicochemical and dielectric properties of the materials. The results show that the addition of OV-POSS nanoparticles, particularly after plasma treatment, significantly enhances the melting point and crystallinity of the composites. At room temperature, the DC breakdown strength of PP/30% SEBS/POSS nanocomposites with 1% mass fraction of plasma-modified OV-POSS reached 330.77 kV mm−1, representing a 19.2% improvement over PP/30% SEBS. The DC conductivity was reduced by 7.3 times, 3.5 times and 3.14 times at electric field strengths of 10 kV mm−1, 20 kV mm−1 and30 kV mm−1. The average charge density growth rate reduced from 28% to 12.3% compared with PP/30% SEBS. Plasma treatment of OV-POSS at an optimal power of 94 W further improved the DC breakdown strength to 297.31 kV mm−1, a 3.6% increase over the untreated sample, while reducing the DC conductivity at 10 kV mm−1, 20 kV mm−1 and 30 kV mm−1 by 1.85, 1.71 and 1.4 times, respectively. The plasma-modified OV-POSS effectively inhibits the accumulation of space charge, with the average charge density growth rate being reduced from 25.3% to 5.7%. These findings provide a robust foundation for the development of advanced PP power cable insulation materials with enhanced dielectric properties.

Plasma aerodynamic actuation generates induced jets through gas ionization and directional movement of charged particles under an electric field. The angle between the jet and the wall critically determines its applicability. Based on multi-jet synthesis theory, this study designs sector-shaped dielectric barrier discharge (DBD) plasma actuators with varying induced jet angles. The relationships between the central angle, jet synthesis velocity, and energy efficiency are analyzed. The electrical, thermodynamic, and aerodynamic characteristics of actuators with different central angles are explored, and a comprehensive performance analysis is conducted. Results show that, compared to the annular DBD plasma actuator, the 240° sector-shaped DBD plasma actuator achieves an 84.1% increase in overall efficiency, with the synthesized jet angle closer to 37°. The 120° sector-shaped DBD plasma actuator achieves an 13.4% increase in overall efficiency, with the synthesized jet angle closer to 59°. This research offers new insights for optimizing the geometric configuration of plasma actuators.

CO2 hydrogenation in dielectric barrier discharge (DBD) coupled with catalytic materials based on structured metal foams is an appealing approach to promote its performance. Here, plasma-assisted CO2 hydrogenation has been carried out in the DBD reactor packing plasma activated Ni and Cu foams, respectively. Measurements of electrical characteristics and optical emission spectra are performed to determine the influence of metal foams on the discharge characteristics. The CO2 hydrogenation performance under different packing conditions is then evaluated at different applied voltage magnitudes. The results show that packing metal foams into DBD changes the filamentary microdischarges into the combination of surface discharge on the metal foam surface and the spatially limited and weak microdischarges in the pores of the metal foams, and the conductive metal foams promote the spread and expansion of surface discharge. The H2/CO2 DBD packing with metal foams exhibits higher discharge power and effective capacitance, as well as stronger capability of charge generation and transfer compared with the plasma-only process at low applied voltage magnitude levels, while the opposite phenomena are observed when the applied voltage magnitudes are 7.5 kV and 8 kV. However, the relatively higher intensities of typical reactive particles are detected when packing the metal foams (especially the Ni foam), which might be due to the catalytic activity of the metal foams. The highest conversions of CO2 (32.5%) and H2 (16.1%) are achieved when the Ni foam is packed in the plasma reaction region at the applied voltage magnitude of 8.0 kV. The corresponding selectivity of CO and CH4 is 88.5% and 8.9%, respectively. Higher energy efficiencies for both converting CO2 and H2 and producing CO and CH4 are obtained in the presence of the Ni foam. The highest values of these two energy efficiencies are 0.17 mmol/kJ and 0.06 mmol/kJ when the applied voltage magnitude is 7.0 kV.

Tungsten erosion and re-deposition have been simulated by the Monte Carlo code ERO for the EAST upper outer divertor, with a comparative study specifically addressing the effects of carbon and lithium impurities on tungsten target erosion under helium versus deuterium plasma discharge conditions. The simulations indicate that tungsten erosion in helium discharges is significantly higher than in deuterium discharges due to a higher sputtering yield by helium ions. In deuterium discharges, the tungsten gross erosion rate initially rises with increasing carbon concentration in background plasma due to enhanced tungsten sputtering by carbon, and then decreases due to the protective effects of carbon deposition on the tungsten surface. In contrast, in helium discharges, an increase in background carbon concentration leads directly to a lower tungsten gross erosion rate, as helium sputtering dominates the tungsten erosion process. Lithium impurities play a notable protective role against tungsten erosion in both helium and deuterium discharges. Assuming suitable lithium and carbon concentrations, the modelling results align well with experimental data. The simulations offer key insights into tungsten erosion processes in deuterium and helium discharges.