Abstract Corona discharge plasma is a promising technology for soil remediation, butt the underlying discharge mechanisms within complex piled soil media remain poorly understood. This study establishes a physical model for corona discharge in piled soil particles under negative DC voltage using a pin-plate electrode configuration. First, the charging behaviour of individual soil particles is analysed to reveal the local electric field distortion induced by mutual particle interactions. Subsequently, by integrating Townsend discharge theory with species transport equations, a theoretical criterion for corona inception and discharge range in inter-particle micro-gaps is derived. To validate the model, experiments were conducted to capture discharge images and measure key parameters across varying voltages and bulk densities. Results demonstrate that the model accurately predicts the discharge characteristics, with the calculated corona inception voltage aligning well with experimental observations. This work transitions soil remediation research from empirical optimization to mechanism-based design, providing a theoretical foundation for the engineering scale-up of plasma-based soil treatment systems.
Abstract Dielectric Barrier Discharge (DBD), capable of sustaining non-thermal plasmas at atmospheric pressure, shows great potential for many emerging applications. This paper presents a tutorial demonstration of fundamental plasma parameters in DBDs based on the one-dimensional fluid model with Local-Mean-Energy Approximation. The model incorporates the electron density and energy balance equations coupled with Poisson’s equation, and its accuracy has been verified by comparison with experimental results. The validated model was subsequently utilized to investigate detailed DBD characteristics, encompassing discharge current, gap voltage dynamics, charge accumulation on dielectric surfaces, Lissajous figures for power calculation, and discharge symmetry. The transition of the discharge from the symmetric single-period (SP1) to the asymmetric single-period (AP1) mode is analyzed, and the formulation for the gap voltage components is derived. This work is designed to serve as a practical guide for practitioners to computational plasma discharge simulations.
Abstract Plasma disruption poses a severe challenge to the safe operation of tokamak devices and future fusion reactors. Although deep learning has demonstrated outstanding accuracy in disruption prediction, its "black-box" decision-making nature and "blind confidence" when facing out-of-distribution (OOD) data raise serious concerns about whether such methods can be safely and reliably deployed in the control systems of future fusion reactors. To address these issues, this study proposes a highly trustworthy disruption prediction framework based on Temporal Convolutional Networks (TCN) for the HL-3 tokamak, constructing a dual safety barrier of "knowing boundaries and understanding mechanisms" by integrating OOD detection with real-time interpretability analysis. First, the framework introduces autoencoder-based manifold learning and data generation techniques to delineate the model's safe cognitive boundary. This mechanism can accurately identify unseen operating conditions or anomalous diagnostics that deviate from the training distribution, effectively intercepting random outputs and false alarms produced by the model in unknown domains. Second, under the premise that input data is legitimate and within the reliable boundary (in-distribution), for high-confidence disruption predictions, a Monte Carlo-accelerated SHAP (SHapley Additive exPlanations) method is employed for real-time feature attribution. This algorithm can quantify the contribution of each diagnostic channel to the prediction result within the time window required by the control system, revealing the key physical causes of instability onset (such as horizontal displacement, impurity accumulation, etc.) in real time. Validation on the HL-3 dataset demonstrates that the OOD detection module achieves an average area under the receiver operating characteristic curve (AUC) of 0.931 across seven anomaly modalities, effectively intercepting OOD inputs and reducing false alarms; the Monte Carlo SHAP method completes per-window feature attribution in 4.72 ms (T=100 samples) and 1.50 ms (T=10 samples), representing a 5.2x and 16.5x speedup over the exact SHAP computation (24.72 ms), while satisfying the real-time requirements of the HL-3 plasma control system. This trustworthy framework provides real-time decision support with clear physical significance for operational control, establishing an important paradigm for the safe and reliable application of deep learning in future large-scale fusion devices.
Abstract The effects of initial current-sheet structure on symmetric magnetic reconnection are investigated using 2.5D resistive two-fluid (electron–ion) simulations. With the background plasma parameters and the initial magnetic configuration held fixed, we systematically vary the plasma density and temperature within the initial current sheet to examine their impact on reconnection dynamics. High-density current sheets undergo prolonged thinning and energy accumulation followed by an abrupt transition to explosive reconnection with highly localized dissipation and enhanced peak reconnection rates. In contrast, low-density current sheets develop reconnection rapidly without pronounced compression, forming broad ion diffusion regions, strong macroscopic plasma outflows, and spatially distributed energy conversion. The results reveal that the internal current-sheet density acts as an effective organizing parameter that self-consistently affects the diffusion-region structure, plasma flow patterns, energy conversion pathways, and spatial distributions of temperature, electric fields, and density within the present model framework. By continuously varying the internal current-sheet density, the system exhibits a continuous transition between electron-dominated and ion-dominated evolution regimes. These results suggest a possible framework for interpreting the diversity of reconnection behaviors observed in space and laboratory plasmas.
Abstract In future fusion reactors such as ITER, erosion of first wall materials (FWMs) induced by neutral particles will increase rapidly with rising heating power and operating time. In tokamak devices, magnetic shadow areas (MSAs), such as the gaps between first wall modules, exhibit a reduced neutral particle flux due to their enclosed structure, which reduces erosion. To study the effect of gap size on neutral-induced FWMs erosion, a dedicated aluminum (Al)-coated sample exposure experiment was carried out on the Experimental Advanced Superconducting Tokamak (EAST). Two Al-coated samples were installed 50 mm behind the main limiter at a major radius of 2.4 m and shielded by molybdenum (Mo) sleeves with different heights. These sleeves mimic a gap-like region, restricting neutral particle incidence on the samples while protecting them from charged particle bombardment. These two samples were exposed to 485 discharges, and the neutral energy spectrum was measured using a Low Energy Neutral Particle Analyzer (LENPA). The thicknesses of Al coating on each sample were quantified by Rutherford Backscattering Spectrometry before and after exposure. For Sample 1, the Mo sleeve with a length-to-inner-diameter ratio of 0.5 yielded a smaller solid angle (1.84 sr), resulting in an Al erosion rate of 1.01×1013 atoms cm-2 s-1. For Sample 2, the Mo with a length-to-inner-diameter ratio of 0.4 sleeve provided a larger solid angle (2.36 sr), with an Al erosion rate of 1.50×1013 atoms cm-2 s-1. Using the neutral energy spectrum by LENPA as input, an estimate based on physical sputtering theory was used to compute the theoretical erosion rates of the samples. The computed Al erosion rates for the Sample 1 and 2 were 2.81×1013 atoms cm-2 s-1 and 3.61×1013 atoms cm-2 s-1, respectively. The calculated Al erosion rates are approximately 2.5 times those of the experimental results, this discrepancy may arise from impurity deposition on the samples’ surface, particularly during disruptions. Results indicate that increasing the solid angle from 1.84 sr to 2.36 sr enhances the experimental erosion rate by about 50%. This study experimentally demonstrated that the gap size can modulate the neutral-induced FWM erosion by altering the solid angle, providing a reference for future research on the erosion and deposition processes of the FWMs in the MSA of fusion reactors.
Abstract The efficient escape of energetic electrons from laser-irradiated near-critical-density (NCD) plasmas is crucial for applications such as radiotherapy. Electron escape dynamics in NCD plasmas play a key role in determining beam performance. Here, using particle-in-cell (PIC) simulations, we demonstrate an important confinement mechanism. Strong self-generated magnetic fields at the target rear, combined with intense lateral scattering and the longitudinal electric field, effectively trap electrons. This combined suppression limits the fraction of escaping electrons to approximately 2% of the total accelerated population. To overcome such strong confinement, our results indicate that increasing the laser pulse duration effectively reshapes the rear-side plasma profile and modifies the electromagnetic field configuration, which suppresses beam branching and enlarges the magnetic-null region. As a result, the escaping electron charge is enhanced by a factor of 30, offering an effective strategy for generating high-quality electron beams suited for applications including radiotherapy.
Core-localized electron cyclotron resonance heating(ECRH)often raises the electron temperature,whereas the ion temperature may remain unchanged or even decrease.We investigate this ion-channel response in deuterium L-mode plasmas on the HL-3 tokamak using kinetic profiles,interpretive power-balance analysis,and local turbulence modeling.Three states are compared:#11843 at 425 ms under neutral beam injection only(NBI-only,pre-ECRH),#11843 at 600 ms(NBI+ECRH),and#11844 at 600 ms(NBI-only reference).After ECRH is applied,the core electron temperature increases whereas the core ion temperature decreases.Source analysis identifies no significant reduction in net ion heating between the two#11843 states.The inferred increase in ion heat transport is dominated by the turbulent component after neoclassical subtraction.Local trapped gyro-Landau-fluid(TGLF)sensitivity scans indicate that this behavior is consistent with enhanced ion-scale turbulent transport driven by changes in local dimensionless parameters,rather than by a reduction in net ion heating.
Abstract Pulsed discharge in water can generate high-intensity shockwaves with complex propagation characteristics, and existing methods struggle to accurately analyze their dynamic evolution. The Smoothed Particle Hydrodynamics (SPH) method, owing to its high accuracy and strong robustness, has become an effective tool for investigating such problems. To address the insufficient accuracy of the explosive-equivalent approach in SPH-based numerical simulations of pulsed discharge in water, this paper proposes the Plasma Internal Energy Regulation Method (PIERM). This method neglects variations in plasma mass under different discharge conditions and instead precisely controls shockwave intensity by adjusting the specific internal energy of the plasma. An axisymmetric SPH model is developed to simulate shockwaves generated by the pulsed discharge in water, and the time-history pressure signals of the shockwave are analyzed in detail to investigate its propagation characteristics. The results show that the peak shockwave pressures predicted by the axisymmetric SPH-PIERM model agree closely with experimental measurements, with a mean relative error (MRE) of less than 2%. Moreover, the model successfully captures key physical features such as wall-reflected waves and rarefaction waves from the free liquid surface, demonstrating its capability to accurately represent shockwave propagation under complex boundary conditions. This advancement facilitates deeper exploration of the underlying propagation mechanisms of shockwaves generated by pulsed discharge in water.
This work systematically investigates the role of catalyst Oxygen Vacancies (OV) in plasma-catalyzed ammonia synthesis over MnO x /MgAl Layered Double Hydroxide (LDH). Experiments show that the MnO x /LDH-500 catalyst (where -500 indicates calcination at 500 degrees C) with the highest surface oxygen vacancy concentration achieves an ammonia concentration of 12056 parts per million (ppm), which is 1.54 times that obtained with the bare LDH support possessing the lowest vacancy content, 1.27 times that of MnO x /LDH-300 and 1.33 times that of MnO x /LDH-700. Meanwhile, the energy yield increased significantly with increase in oxygen vacancies. The MnO x /LDH-500 catalyst achieved an energy yield of 1.10 g & centerdot;kWh-1, which is 1.54 times that of the bare LDH support. In situ optical diagnostics reveal that the key intermediate, excited N2, is first generated in the gas phase and then adsorbed onto the catalyst surface to form NH x species for ammonia formation. The benefit of oxygen vacancies lies in providing surface sites for excited N2 adsorption. These findings offer scientific guidance and a practical strategy for designing efficient catalysts compatible with plasma processes.
Abstract An atmospheric-pressure plasma jet (APPJ) device was optimized by enlarging the plasma discharge region to enhance the production efficiency of plasma-activated water (PAW), particularly under air discharge conditions. The physicochemical properties of PAW were found to be strongly dependent on the working gas and treatment duration. Under the same discharge conditions, PAW prepared by air discharge contained higher concentrations of NO₃⁻ and NO₂⁻, whereas PAW prepared by Ar discharge was richer in O₃ and H₂O₂. Meanwhile, increasing the discharge time led to a continuous decrease in pH, accompanied by sustained increases in both conductivity and oxidation–reduction potential. In addition, the effects of PAW were further investigated under soilless conditions. The results indicated that PAW enhanced the water absorption capacity of seeds, while different PAW compositions induced varying degrees of modification to the seed coat. When the physicochemical properties of PAW were adjusted to the optimal range for maize seed growth, both germination rate and seedling growth were significantly promoted. These findings demonstrated the strong potential of PAW for agricultural applications.
Abstract Turbulent transport in tokamak plasmas is strongly affected by changes in magnetic topology associated with magnetic islands (MIs). To examine how dynamic MIs generated by intrinsic instabilities, such as the resistive tearing mode (RTM), influence transport, we perform simulations of the nonlinear interaction between trapped-electron-mode (TEM) turbulence and RTM fluctuations using a compact gyro-Landau fluid model. Our simulations reveal novel oscillatory transport dynamics in multi-mode, multi-scale turbulence. Under moderate TEM and RTM instability, turbulent particle and heat fluxes display oscillatory behavior. In particular, periodic bursts of electron heat flux are linked to the repeated formation and evolution of m / n = 2/1 MIs (where m and n denote the poloidal and toroidal mode numbers, respectively). At the same time, the ion heat flux alternates between inward (thermal pinch) and outward (thermal diffusion) transport. When the RTM becomes more unstable, the ion heat flux can shift to predominantly inward transport with periodic oscillations. The oscillation timescale is comparable to trapped-electron precession drift frequency, while its amplitude depends on the relative strength of TEM and RTM instabilities, which are governed by plasma parameters such as β , resistivity, and viscosity. Analysis of the transport response to dynamic MIs shows that the 2/1 mode is periodically excited through alternating phases of magnetic reconnection and island shrinkage, leading to cyclic transitions of the n = 1 RTM eigenmodes. Meanwhile, the 3/1 mode, associated with nearly stationary islands of finite width, modulates these cycles through toroidal coupling with the neighboring 2/1 mode. These results offer new insight into the intermittent or oscillatory transport observed in tokamak plasmas with dynamic MIs and provide connections to experimental observations.
Investigating impurity transport properties in tokamaks is crucial for understanding plasma behavior and improving confinement performance.Carbon,a common low-Z impurity in fusion devices,is particularly prevalent in those using plasma-facing materials containing graphite.Hence,precise measurement of its impurity concentration is highly necessary.A combined diagnostic method utilizing Charge eXchange Recombination Spectroscopy(CXRS)and Direct Current Beam Emission Spectroscopy(DC-BES)has been applied on Experimental Advanced Superconducting Tokamak(EAST)to derive absolute radial profiles of carbon impurity concentrations.This approach eliminates systematic uncertainties from line of sight differences between the two systems and the neutral beam attenuation calculations.Additionally,as the charge exchange and beam emission rates depend on the beam energy,a forward modeling technique was employed to extract the fraction of full (Eb),one-half(Eb/2),and one-third(Eb/3)beam energy components from the BES spectral intensities.The obtained carbon concentrations range from approximately 0.3％to 0.8％,indicating that the application of lithium wall conditioning effectively reduces the carbon impurity concentration in the plasma.
Abstract The Air-Breathing Electric Propulsion (ABEP) system, as a critical technology, provides a sustainable propulsion solution for ultra-low Earth orbit (ULEO) satellites by capturing sparse atmospheric molecules as propellant. The intake duct, as the core component of the ABEP system, plays a pivotal role in determining the overall effi0ciency of the system. In this study, the Direct Simulation Monte Carlo (DSMC) method is employed, and the wall accommodation coefficient (σ) is introduced to simulate the evolution of wall reflection modes. The variations in the intake performance of the D-MDAR and ESA intake ducts during the wall degradation process are investigated. The results reveal that as the wall reflection characteristics evolve from specular reflection (σ=0) to diffuse reflection (σ=1), both capture efficiency and compression ratio exhibit significant degradation. For example, in the D-MDAR intake, the capture efficiency drops from 66.28% to 37.87%, and the compression ratio increases from 9.8 to 30.3. Similarly, in the ESA intake, the capture efficiency decreases from 22.53% to 6.21%. To address this issue, two optimized designs, LD-MDAR and H-ESA, are proposed. The capture efficiency of LD-MDAR increases to 52.8%, and the compression ratio reaches 24.24, while H-ESA achieves a capture efficiency of 17.35% and a compression ratio of 24.61. The optimized designs significantly improve the performance of the intake ducts in actual orbital environments. This study provides theoretical support and practical guidance for the performance degradation assessment and long-term lifetime design of ABEP intake ducts.
This paper presents disruption simulations for the EXL-50U spherical tokamak in support of the 1 MA experimental campaign conducted in 2025. A two-stage approach, available through the PECAN framework, was employed to capture plasma dynamics and the resulting 3D electromagnetic (EM) loads. The assumed current quench (CQ) durations, bounded by limits derived from the ITPA disruption database, were later validated against the newly established EXL-50U disruption database, showing good agreement with experimental observations. The analysis revealed a distinct nonlinear behavior in the vertical displacement event (VDE) evolution, attributed to the combined effects of plasma shape variation and the stabilizing effect of the passive stabilizing plates (PSP). The simulations predict plasma-PSP contact consistent with observed PSP damage, emphasizing the need for enhanced vertical control. The computed EM loads highlight significant contributions from poloidal eddy currents interacting with the toroidal field, producing peak forces in the inboard vessel leg up to twice those from toroidal eddy currents-an interaction often overlooked in similar analyses in the field, yet one that should be carefully assessed in spherical tokamaks due to their inherently compact design. Overall, these results provide a detailed 3D EM load dataset for structural analysis and offer key feedback for disruption control and mechanical design for EXL-50U, while informing the development of ENN's next-generation EHL-2 spherical tokamak.
Abstract This review summarizes how three-dimensional particle-in-cell (PIC) simulations are used to investigate the electron drift instability (EDI) in Hall thrusters and its link to anomalous cross-field electron transport, with emphasis on transport closures and computational feasibility. EDI dynamics are intrinsically three-dimensional, owing to their strong coupling to axial ion acceleration and radial plasma wall/sheath interactions; consequently, reduced dimensionality (1D/2D) PIC models tend to bias the mode structure and the inferred transport, motivating fully 3D PIC simulations. The review traces the evolution of 3D PIC modeling from early cost-driven reduced or scaled studies to high-fidelity channel--plume simulations enabling quantitative characterization. Advances from our group are also summarized, spanning WarpX-based investigations and the in-house PMSL code, with a focus on convergence acceleration, realistic field configurations, and transport-resolving diagnostics. Finally, representative computational workloads and wall-clock costs are compiled, and practical strategies for reducing time-to-solution while strengthening verification and enhancing the credibility of 3D PIC predictions are outlined.
Abstract The energy level distribution and transition characteristics of highly charged calcium ions are key data for astrophysics, plasma radiation characteristic research, and EUV light sources. To deeply explore the extreme ultraviolet (EUV) spectral characteristics of highly charged calcium ions, this study employs Nd:YAG laser pulses with a wavelength of 1064 nm and a pulse width of 10 ns to ablate high-purity solid calcium targets to generate plasma. High-resolution EUV spectrometers are used to obtain spatially and temporally resolved spectra in the 8‒14.5 nm wavelength range. Theoretical calculations are conducted using the Cowan program based on relativistic Hartree‒Fock configuration interaction. Characteristic emission lines of highly charged calcium ions (Ca7+‒Ca10+) are identified. Combined with the collision radiation model and the normalized Boltzmann distribution hypothesis, precise simulation of experimental spectra is achieved. In particular, four isolated characteristic peaks that are very sensitive to plasma electron temperature are discovered, which are expected to become “probes” for real-time diagnosis of plasma states.
Abstract The Field-Reversed Configuration (FRC) is widely considered an ideal target plasma for magneto-inertial fusion owing to its high-beta properties. To study the magnetized target in plasma-jet-driven magneto-inertial fusion (PJMIF), we have developed LFX (Large-scale magnetized target Formation eXperiment), a specialized device for FRC formation and translation. It aims to produce a long-lifetime, large-relative-radius target FRC, and will subsequently be used to study target FRC transport as a function of relative radius. This paper reports the initial experimental results obtained with LFX: the FRC achieved a peak electron density of 6.88×1019 m−3, and an estimated temperature of 32 eV, and a reversed magnetic field of 40 G.
Abstract The transmitted current in vacuum thermionic energy converters (TECs) is often limited by space-charge effects. Existing one-dimensional (1D) models and numerical benchmarks provide valuable insights into this limitation. In practical devices, however, the emitter often has a finite area and may be spatially nonuniform; these features can reshape the self-consistent space-charge structure and electron backflow paths and thus degrade performance. We employ two-dimensional (2D) particle-in-cell simulations to compare electron transport and backflow in vacuum TECs with different emitting areas. We first assume a fixed initial velocity for the emitted electrons. The results show that decreasing the emitting area leads to the formation of backflow channels, causing the transmitted current density to fall systematically below the prediction of 1D space-charge-limited (SCL) theory. Replacing the fixed initial velocity with a velocity distribution, we find that the transmitted current increases only gradually with the emission current and the oscillations vanish; nevertheless, reducing the emitting area still induces backflow and decreases the transmitted current. These findings indicate that finite emitting area and emission nonuniformity can modify 1D predictions via geometry-induced backflow and should be accounted for as a key geometric parameter in vacuum TEC modeling and design assessment. They may also serve as a useful reference for the design and optimization of micro-patterned emitter arrays.
Abstract Radio-frequency (RF) ion thrusters, as electrodeless plasma sources, offer significant advantages such as simple structure and long operational lifetime. However, their discharge efficiency is often limited by wall losses and the skin effect. Among various optimization approaches, the application of additional magnetic fields has emerged as an effective method for improving discharge performance. In this study, a compact radio-frequency ion thruster (RIT) was equipped with additional magnetic fields of different configurations. Ion beam currents were systematically measured under various operating conditions. The results show that under a Type-I magnetic field with a strength of approximately 20 G, the ion beam current is significantly enhanced by up to 22.3% at low xenon mass flow rates. Furthermore, plasma parameters inside the discharge chamber, including ion density and electron temperature, were characterized using a double Langmuir probe. The results indicate that appropriately applied additional magnetic fields can reduce ion losses to the walls and partially compensate for the skin effect, thereby improving the beam-current-related discharge characteristics. However, if the magnetic field is too strong, it may overly restrict electron motion and suppress collisionless heating, which in turn negatively affects the discharge process.
Abstract With the increasing demand for high-performance electric propulsion in micro-nano satellites, the cathode of tungsten has become an ideal neutralizer solution. However, its neutralization characteristics and performance degradation mechanisms in a coupled environment remain unclear. In this study, a coupled cathode-thruster experimental system is constructed to systematically investigate the neutralization characteristics and performance degradation mechanisms. The results show that a “keeper critical voltage” related to the heating power exists; operation below this value triggers neutralization deterioration. This critical voltage exhibits a linear negative correlation with the tungsten filament temperature, validating the “thermionic-field complementary” emission mechanism of the cathode. Long-term experiments indicate that the performance of the cathode of tungsten continuously degrades over time during long-term coupling. Surface analysis confirms that carbon deposition is the primary form of contamination, while a positive feedback effect between coating loss and carbon contamination accelerates the performance degradation process. This study reveals the neutralization characteristics and degradation mechanisms of the cathode of tungsten in a coupled environment, providing theoretical basis and experimental support for the reliable design and lifetime assessment of micro electric propulsion systems.
