Based on first-principles calculations, this work investigates the co-adsorption properties of cesium (Cs) and hydrogen (H) on the LaB6 (100) surface and their influence on the surface work function. It is found that adsorption of Cs on the clean surface results in a work function of 2.0 eV, whereas on surfaces with pre-adsorbed H, the work function is reduced to 1.86 eV. In addition, the absolute value of the Cs adsorption energy Ead increases, with an improvement of 0.16-0.53 eV, which corresponds to an enhancement of Cs adsorption stability. Further analysis reveals that the reduction in work function primarily originates from Cs-induced electronic redistribution, which leads to a change in the surface dipole density. Meanwhile, H pre-adsorption promotes positive charge accumulation in the Cs layer and enhances the dipole moment pointing toward the substrate, thereby further lowering the work function.

Error fields resulting from deformations of coils are inevitable during fabrication, assembly and operation in all nuclear fusion devices. The magnetic topologies of stellarators are primarily produced by external coils, which are quite sensitive to these error fields, especially the magnetic island configurations. In future experiments, two types of magnetic island configurations with rotational transform ι = 2/5 and 2/6 will be achieved in the Chinese First Quasi-axisymmetric Stellarator (CFQS). Hence, it is essential to evaluate these two resonant error fields resulting from coil deviations. To identify the major coil deformations that have significant effects, each modular coil is examined individually in the standard 2/5 and 2/6 island chains in the CFQS, respectively. The stochastic perturbations are modeled with Gaussian processes and applied to describe irregular deformations in the coils. Several important results are achieved: (i) as the coil perturbations do not satisfy the stellarator (up–down) symmetry, the stellarator-asymmetry error fields appear, which are one order of magnitude lower than the stellarator-symmetry error fields. (ii) The sensitivity of resonant error fields to the same deformations of each coil is different. The deviations of some coils may lead to weak influences on the magnetic island topologies, in some cases being capable of compensating the resonant error fields. (iii) Certain stochastic coil perturbations have the potential to generate more optimal coils since the error fields are not proportional to the amplitude of coil deformations. These findings suggest that relaxing specific coil tolerances is expected to reduce engineering constraints on coil design and fabrication. Furthermore, this work will also help develop a computational model for the mapping experiments to precisely estimate errors in the CFQS magnetic field.

Fast particle confinement in the Chinese First Quasi-axisymmetric Stellarator (CFQS) is investigated using the MEGA code, comparing the standard quasi-axisymmetric (QA) configuration with a finite-beta (< β >=0.74%) equilibrium featuring magnetic islands. In the standard QA configuration, the drift associated with the vertical magnetic curvature term, ( ∇ × b ) z , is identified as the dominant loss mechanism, especially for co-passing particles. In the finite-beta configuration, magnetic islands trap low-energy particles. The ( ∇ × b ) z drift modulates this trapping, promoting escape for co-passing particles while reinforcing trapping for counter-passing particles, and remains a significant contributor to overall losses. These findings underscore the critical role of the ( ∇ × b ) z drift and the added complexities of magnetic islands for energetic particle confinement in finite-beta stellarator plasmas.

This study adopts first-principles computational approaches to explore the structural, electronic, mechanical, surface work function and thermodynamic behaviors of Ce1−xMxB6 (M = Ba, Sr, Ca) composites with doping ratios x ranging from 0 to 1 (0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1). Core properties including lattice constants, elastic constants, bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, surface work function, Debye temperature, and melting point are comprehensively examined. The findings reveal that doping typically results in a decline in the surface work function, with Ce0.375Ba0.625B6 attaining the lowest value of 1.47 eV. All Ce1−xMxB6 composites satisfy the mechanical stability criteria and exhibit brittle features (B/G < 1.75), with Ba doping enhancing shear resistance and Ca doping slightly improving ductility. Thermodynamic analysis demonstrates that the melting points of all composites exceed 2000 K, confirming their excellent thermal stability. These results offer valuable theoretical references for the development of cesium-free electrode materials suitable for plasma-facing applications in neutral beam injection (NBI) systems.

This study employs first-principles density functional theory (DFT) to systematically investigate the work function, mechanical properties, and thermodynamic performance of (La1-x-yPrxBay)B6 alloys. The calculations reveal that the work function exhibits strong composition dependence and pronounced non-monotonic behavior. Ba substitution effectively reduces the work function, yielding values as low as 1.79 eV (La0.125Ba0.625Pr0.25B6), whereas Pr mainly introduces local fluctuations through electronic effects. Mechanical analysis indicates that Ba doping significantly reduces elastic moduli, leading to lattice softening, while Pr tends to enhance ductility as reflected by increasing ratio B/G and Cauchy pressure. However, all compositions remain brittle according to the ratio B/G and Poisson's ratio. The negative Cauchy pressure suggests a strong directional bonding contribution, while the PDOS and Bader charge analyses further reveal mixed ionic-covalent-metallic bonding characteristics. Thermodynamic properties show that the Debye temperature and melting point slightly decrease with increasing Ba content, indicating reduced thermal stability. These findings suggest that (La1-x-yPrxBay)B6 alloys are promising candidates for Cs-free PG materials.

The effects of multi-scale interactions among the edge turbulence, geodesic acoustic mode (GAM) and tearing mode (TM) on the plasma confinement and transport under the positive bias (+300 V) are investigated in the edge plasma of J-TEXT tokamak. The experimental results show that with the positive bias, the central line-averaged density increases and H alpha emission decreases, which indicates the improvement of global particle confinement. Simultaneously, in the edge plasma, the low-frequency turbulence, TM and turbulent particle transport flux are found to be suppressed by a strong mean flow shear induced by the bias. Besides, the high-frequency turbulence (50-400 kHz) is modulated by both the TM and GAM. The wavelet-bispectrum analysis demonstrates the existence of nonlinear three-wave interactions among the turbulence, GAM and TM. In addition, the transfer entropy analysis shows that although the potential turbulence can directly influence the GAM by driving the Reynolds stress, it primarily regulates the magnetic fluctuation thereby affecting the GAM. It is also found that both the TM and GAM can affect the density turbulence and particle transport. And th effect of TM on the particle transport is stronger than that of GAM. As expected, a strong direct influence of the density turbulence on the particle transport is verified, which indicates that the regulation of transport by the TM and GAM is primarily mediated by the density turbulence.These results contribute to a deeper understanding of the impact of electromagnetic multi-scale interactions on the plasma confinement and transport in fusion plasmas.

Presence of wedge surfaces and variable-section geometries in conventional combustion chambers can modify the structure and propagation characteristics of detonation waves, furtherly influences the operational stability and propulsion efficiency of detonation engines. In this study, trapezoidal obstacles were symmetrically arranged within a shock tube to create channels incorporating convergent wedge sections with different angles (30 degrees, 60 degrees) and subsequent narrow straight segments with various heights (5, 10, 20 mm). Experimental and numerical investigations were conducted to analyze the propagation characteristics of stoichiometric ethyleneoxygen detonation waves in the channel. The results indicate that the detonation wave reflected by the wedge surface enters the narrow segment is overdriven, with the overdriven degree gradually decreasing during its propagation. At the 30 degrees wedge, Mach reflection occurs, and the detonation wave becomes overdriven upon reaching the contracted throat with an overdriven degree exceeds 1.5; whereas, at the 60 degrees wedge, regular reflection occurs, and the detonation wave reaches the throat with a lower overdriven degree of 1.3. However, the overdriven degrees finally decay to 1.1 in both cases. The channel contraction effect attributes to the induction of overdriven initiation in the throat, though it operates via distinct mechanisms as the wedge angle varies. For the 30 degrees wedge, channel contraction shortens the travel distance of triple points on the wavefronts of the incident detonation wave and Mach reflection-induced detonation wave, increasing their collision frequency, leading to significant energy accumulation in the throat region. For the 60 degrees wedge, channel contraction prevents triple points from entering the following narrow segment along trajectories corresponding to their original cell widths, furtherly induces structural self-adjustment to sustain propagation. These findings enhance the understanding of detonation wave propagation under complex geometrical conditions and provide valuable insights for the optimal design of combustion chamber structures in detonation engines. Novelty and significance statement This study innovatively investigates the propagation process of detonation waves in a convergent channel that simultaneously incorporates a wedge surface and a variable-section structure, thereby being more relevant to practical engineering scenarios. Furthermore, it innovatively examines the coupled influence mechanism of wedge surface reflection and wall contraction effects on the propagation characteristics of detonation waves, filling the gap in related research. A detailed comparison and analysis of the propagation processes of detonation waves entering narrow straight segments after different reflections was conducted, revealing the overdriven propagation characteristics of detonation waves during this process and their induction mechanism (frequent collision of triple points). This study provides new insights and support for the propagation dynamics of detonation waves in complex channels.

This paper introduces the mid-plane fast reciprocating probe (FRP) system in the HL-3 tokamak. Unlike traditional pneumatic cylinder or servo motor drives, this system achieves fast movement through the operation of a linear motor and a counterweight cabinet. The counterweight cabinet is chosen to balance the atmospheric pressure for the first time, without requiring a large linear motor with high output torque. As a result, the system takes up less space and has high speed, high acceleration, long stroke length, and adjustable movement distance. The front of this system can accommodate various compound probes with a maximum pin number of 19. At present, this system has been put into operation in the HL-3 tokamak, and preliminary experimental results confirm the novel design.

Dynamic features across the transition from low (L) to steady-state high (H)-mode in Large Helical Device are investigated. We focus on several transition processes from the L-mode, developing high confinement-mode (H-mode) towards the stable H-mode. It appears that for the initial L–H transition, the mean E _r × B flow curvature and nonlinear energy cascading of ambient turbulence both play significant roles for entering the developing H-mode. From the developing to stable H-mode, experimental results reveal essential effects of nonlinear energy coupling between turbulence and large-scale MHD modes on sustaining the steady H-mode, for which the MHD bursts act as a predator whereas turbulence is a prey. These findings provide additional insight into the dynamic evolution from the L-mode to steady-state H-mode.

The influences of biasing on turbulence and turbulent transport dynamics in the edge plasma of J-TEXT tokamak are investigated. Results demonstrate that applying either negative (−300 V) or positive (+ 300 V) biasing reduces the turbulent particle transport, with positive biasing yielding superior plasma particle confinement compared to negative biasing. Analysis of edge radial electric field (Er) profiles and turbulence evolution reveals distinct suppression mechanisms in negative and positive biasing cases: in the negative biasing scenario, the turbulent transport is suppressed due to the de-correlation mechanism of strong Er × B shear. However, excessive shear leads to the formation of a steep density distribution, which in turn drives turbulence and ultimately results in moderate transport suppression; in the positive biasing scenario, the transport suppression is primarily achieved by mitigating turbulence driving. Examination of turbulence driving indicates while the density gradient is an essential factor for driving turbulence, the strength of such driving also depends on the turbulent particle transport flux.

Plasma turbulence is a key factor in determining plasma transport behavior. Based on HL-2A edge plasma turbulence experiments, this study investigates nonlinear energy transfers among multi-scale fluctuations by observing phenomena such as inverse energy cascade, energy cascade, and dual cascade within turbulent systems. This is a comprehensive picture of the nonlinear energy transfer in tokamak edge-plasma turbulence. The turbulence spectral data were measured experimentally using the two-point method, and bispectral analysis was applied for data analysis. In edge plasma, a typical case is that the energy cascades from small-scale (in the high-frequency region) to large-scale structures (in the low-frequency region). The so-called inverse energy transfer can trigger or strengthen large-scale fluctuations. In another case, a certain portion (approximately 25%) of the energy in low-frequency turbulence cascades to higher-frequency turbulence, indicating that broadband free energy is transmitted to smaller scales through the coupling of E & times;B nonlinearity and large-scale potential fluctuations, causing the vortices to decrease and transform into higher-frequency turbulence. In the third case, in the two frequency regions, the energy in the relatively low-frequency and relatively high-frequency turbulence cascades and inversely cascades to medium-frequency turbulence, respectively, promotes the development of the latter. A concentrated three-wave coupling region is observed and it is distributed diagonally around the f1-f2 plane, where f1 and f2 represent the mode frequencies. Finally, some brief discussions were held on the relevant results.

The supersonic molecular beam injection (SMBI) technique has attracted considerable interest in magnetic confinement fusion because it offers an efficient fueling capability with relatively simple and economical hardware. As the key component of SMBI, the Laval nozzle largely determines the jet velocity, collimation, and thus the fueling performance. In this paper, we present an initial design of a Laval nozzle for the SMBI system on the Chinese First Quasi-axisymmetric Stellarator (CFQS). A reference gas flow rate for CFQS is estimated by scaling from well-diagnosed SMBI data from the Large Helical Device (LHD); the resulting value (similar to 12 Pam(3)/s) is used as an order-of-magnitude design input for nozzle sizing. To select a physically meaningful design Mach-number range, effective acceleration limits are discussed using a pressure-based criterion via the Knudsen number and a temperature-based criterion associated with hydrogen phase-change tendencies, and the clustering parameter Gamma(& lowast;) is evaluated to quantify condensation/cluster-formation range under typical operating conditions. Using Foelsch's method as an efficient analytical framework, the nozzle contour and key geometric parameters are obtained, and a baseline CFQS nozzle design is recommended (e.g., M-t equal 7, theta(1 )is 5(degrees), throat diameter 0.3 mm) considering both physical performance and engineering constraints, and an example engineering design diagram were presented. The present results provide a practical reference for the implementation and future optimization of the CFQS SMBI system.

The CFQS is a quasi-axisymmetric stellarator of which the concept combines the advantage of good confinement of a tokamak and the steady-state operation capability of a stellarator. The CFQS has 16 modular coils (MCs), which consist of four independent shapes. Accurate positioning of MCs is one of the most important requirements, in particular, in stellarator since coil misalignment may have a significant effect on the quality of magnetic flux surfaces. Assuming some cases of displacement of MCs, we have investigated the effect on rotational transform profile and magnetic flux surfaces in the vacuum field. According to the results, it was found that MC misalignment has no significant effect on the CFQS plasma if the displacement is within a range expected in the actual MC installation.

This study employed first-principles density functional theory using CP2K and VASP software to investigate the effects of hydrogen atoms adsorption on the work function of the LaB6 (001) surface. These results indicate that the most favorable adsorption site for hydrogen atoms is located on the top of the boron atoms in the center of the cell. As the hydrogen atom coverage density increases, the absolute value of the average adsorption energy decreases, while the surface work function gradually increases. The analysis shows that changes in the work function are strongly correlated with variations in dipole moment density, exhibiting a linear relationship. Furthermore, charge transfer induced by LaB6 substrate deformation, the intrinsic charge carried by the hydrogen adsorbate, and the charge transfer resulting from the interaction between the hydrogen adsorbate and the LaB6 surface substrate determine the variations in dipole moment. When the hydrogen coverage density is below 8.54 x 10-2 atoms/A & ring;2, its effect on the material's work function is relatively small, with the work function increasing from 2.14 eV to 2.47 eV. It is expected that this study can serve as a reference and theoretical basis for preliminary explorations into the application of LaB6 in the NBI system.

For magnetic confined fusion devices, magnetic probe diagnostic is a basic but very important diagnostic tool for studying plasma magnetic fluctuations. The first experimental phase of the Chinese First Quasiaxisymmetric Stellarator (CFQS), which is also called CFQS-T, needs magnetic probe diagnostics to provide plasma magnetic fluctuation measurements, especially the high-frequency ( 50 < f < 300 kHz) magnetic fluctuation measurements. In this paper, a newly developed high-frequency magnetic probe array (HFMPA) diagnostic on the CFQS-T is reported. This array consists of 8 identical three-dimensional high-frequency magnetic probes, each of which can simultaneously measure magnetic fluctuations in the poloidal, radial and toroidal directions. The HFMPA magnetic probes are carefully mounted on the inner vacuum vessel wall of the CFQS-T, and their positions are precisely measured by the laser tracker system. The HFMPA can be used to study the poloidal and toroidal propagation characteristics of magnetic fluctuations due to the optimized spatial arrangement, and its maximum toroidal mode number resolution is improved to n = +/- 16 compared with n = +/- 6 of the low-frequency magnetic probe array (LFMPA, used for the f <= 50 kHz magnetic fluctuation measurements). The main subsystems of the HFMPA diagnostic, such as the mechanical system, signal transmission lines, acquisition and control systems, and the challenges overcome in the development of each subsystem, will be briefly introduced in this paper. The effective areas of the HFMPA magnetic probes are calibrated by the relative calibration method, which shows that their areas are all around 0.02 m2. The in-situ frequency response of the HFMPA magnetic probes is calibrated with an LCR digital bridge with a maximum working frequency of 10 MHz. The resonance frequency of the HFMPA magnetic probe in each measurement direction is greater than 400 kHz, which meets the design requirements for measuring 50-300 kHz high-frequency magnetic fluctuations in CFQS-T. Preliminary applications of the HFMPA diagnostic in studying the low-frequency (1.5-16.0 kHz) magnetic fluctuations and high-frequency (65-105 kHz) magnetic fluctuations in CFQS-T are briefly introduced, which shows that the HFMPA diagnostic works well for providing the spectrogram, poloidal, and toroidal propagation information of low-frequency and high-frequency magnetic fluctuations. It is worth noting that the measurement and analysis results of high-frequency (65-105 kHz) magnetic fluctuations in CFQS-T are reported for the first time in this paper. The successful development of the HFMPA diagnostic will help to carry out in-depth research on plasma magnetic fluctuations in CFQS-T stellarator.

This study systematically investigates the effects of the stability and work function of barium (Ba) atoms adsorption on the Mo (110) surface using first-principles density functional (DFT) theory calculations. The results demonstrate that the long-bridge site represents the most stable adsorption configuration for Ba atoms on Mo (110) surface. As the Ba coverage increases, the work function initially decreases sharply and then increases slowly, reaching a minimum value of 2.25 eV at a coverage of 4/16 theta (3.35 x 1014 cm- 2), which is markedly lower than the work function of 4.85 eV for the clean Mo (110) surface. This indicates that the adsorption of Ba atoms on the Mo (110) surface substantially reduces the work function. Theoretical analysis reveals a linear correlation between work function variations and dipole moment density changes, with charge redistribution induced by Ba adsorption dominating the total dipole moment modification. These results provide the reference for the research of the Cs-free alternative materials for neutral beam injection systems in fusion research.

The isotope effect on zonal flows(ZFs)and turbulence remains a key issue that is not completely solved in fusion plasmas.This paper presents the first experimental results of the ab initio prediction of causal relation between geodesic acoustic mode(GAM)and ambient turbulence at different isotope masses in the edge of HL-2A tokamak,where transfer entropy method based on information-theoretical approach is utilized as a quantified indicator of causality.Analysis shows that GAM is more pronounced in deuterium plasmas than in hydrogen,leading to a lower heat transport as well as more peaked profiles in the former situation.The causal impact of GAM on conductive heat flux component is stronger than on the convective component,which is resulted from a larger causal influence of zonal flow on temperature fluctuation.While a stronger GAM in deuterium plasmas has larger influence on all flux components,the relative change in temperature fluc-tuation and coefficient is more obvious when the ion mass varies.These findings not only offer an in-depth understanding of the real causality between zonal flow and turbulence in the present isotope experiments,but also provide useful ways for the physical understandings of transport and zonal flow dynamics in future deuterium-tritium fusion plasmas.