Recent Publications

Soft H-L back transitions induced by RMP coils in high q95 plasmas on EAST

Linming Shao, Hui-Hui Wang, Shouxin Wang, Zichao Lin, R Chen, Shuai Gu, Wenbo Hua, Pan Li, Yichao Li, zhiguo li, et al.

Soft H-mode to L-mode (H-L) back transitions, combined with simultaneous particle and heat pumping via n=2 resonant magnetic perturbations (RMPs), have been achieved in EAST plasmas at low safety factor (q95=3.5-4.0) without reducing auxiliary heating power [Shao L M, et al., 2024 PPCF 66 035018]. For the termination control of ITER, which is also equipped with RMP coils, this process inevitably drives the plasma toward a high q95,where the established n =2 RMP is unlikely to produce a soft H-L back transition, because the edge-resonant surface at such high q95 requires a high poloidal mode number m, and the n=2 RMP field is strongly attenuated at such high m and couples only weakly to the edge. However, an n =1 RMP can restore edge coupling, enabling reliable particle and heat pump-out without radiative collapse or current-profile MHD risks on EAST. Within an operating window constrained by impurity and NBI conditions, both the n=1 and n=2 RMPs exhibit a reproducible energy confinement time threshold at the H-L transition τ^{H-L}_{e}∼ 49 ms, which can serve as a control trigger.

Design and reliability assessment of a support structure for high heat flux testing

Zhen Wang, Yinfeng Zhu, Xuebing Peng, Wei Song

Calculation of the electromagnetic radiation emitted from the D-T fusion process in tokamak reactors

Deng Zhou, Jinfang Wang

In the deuterium tritium fusion reaction an alpha particle is released with the kinetic energy ~3.5 MeV. Since the fusion reaction is governed by the strong interaction, the alpha particle is almost instantaneously accelerated to the final state with its kinetic energy ~3.5 MeV. According to the classical electrodynamics, electromagnetic radiation should be emitted in such an acceleration process. In this work, we calculate the electromagnetic radiation in the D-T fusion process using both the classical electrodynamics and the quantum mechanical models. The radiation is compared with the radiation from the core plasma bremsstrahlung for pure deuterium tritium plasmas in large tokamaks. The ratio between the radiation from the D-T fusion reaction and bremsstrahlung depends only on the plasma temperature. The radiation from the D-T fusion reaction is stronger than that from bremsstrahlung if the frequency is higher than a critical value. Although the predicted radiation is much weaker than its high frequency counterpart, it is still possible to be detected in the high fusion gain reactors under some circumstances. Its effect should also be taken into account if one uses the gamma-ray emission spectrum to diagnostic for plasma profiles.

Real-Time Hydrogen-Deuterium Fraction Feedback Control on EAST

Li Guo, Juan Huang, Kai Wu, Q. P. Yuan, Kedong Li, Wei Gao, Chengrui Wu, Junjie Huang, Chenyu Pan, Zixin Zhang

A simulink-to-FunctionBlock transformation framework for rapid integration of plasma control algorithms

J.Q. Zhu, Zherui Cai, Q P Yuan, Zhongmin Huang, Ruirui Zhang, Junjie Huang, Heru Guo, Gen Xu, Bingjia Xiao

To support high-performance long-pulse plasma discharges, the Lingshu Plasma Control System (PCS) has been successfully developed and deployed, shifting the focus of current research toward the development and iterative refinement of advanced control algorithms. Simulink is a widely used and powerful tool for control algorithm development. However, integrating Simulink models into the FunctionBlock-based architecture of Lingshu PCS still requires substantial manual adaptation, resulting in low integration efficiency and prolonged deployment cycles. To address this issue, this paper proposes a Simulink-to-FunctionBlock transformation framework for the Lingshu PCS. The framework establishes an automated workflow from model development to system deployment, enabling the direct conversion of Simulink models into deployable FunctionBlocks. By bridging the semantic gaps between Simulink models and the FunctionBlock architecture, the proposed approach significantly reduces manual integration effort and accelerates algorithm deployment. The proposed framework is validated using a plasma control algorithm from the EAST tokamak. Experimental results demonstrate that Simulink models can be successfully transformed into FunctionBlocks and deployed on the Lingshu PCS while preserving the original algorithm behavior and satisfying real-time control requirements, thereby validating the effectiveness of the proposed framework.IntroductionMagnetic confinement tokamaks offer a promising pathway toward the realization of clean fusion energy. In recent years, next-generation fusion facilities in China, including the China Fusion Engineering Test Reactor (CFETR)[1] and the Comprehensive Research Facility for Fusion Technology (CRAFFT/BEST), have entered an accelerated construction phase. These devices are designed to operate under more demanding conditions, featuring higher performance parameters and requiring steady-state plasma discharges with pulse durations extending to thousands of seconds or longer. To meet these stringent control requirements, a new plasma control system(PCS), named Lingshu, has been independently developed.Similar to existing fusion control frameworks such as MARTe[2], DCS[3][4], and RTF[5][6], Lingshu adopts a component-based architecture characterized by autonomous operation, low coupling, and high performance. Within the framework, control functionalities are encapsulated as Function Blocks (FBs) and deployed inside software components to implement signal acquisition, state diagnosis, plasma control, and command output. A set of supporting services, including workflow scheduling, parameter management, and data archiving, provides the underlying infrastructure for system-wide coordination and reliable operation.The system has been successfully applied to more than 9,000 discharges on the EAST tokamak. Its control components can operate with execution periods as short as 50 s, and simulation results indicate that the framework is capable of supporting steady-state long-pulse operation exceeding 25

Landau Damping Beyond Smooth Velocity Distributions: A Dispersion-Free Lagrangian Time-Domain Framework

Huasheng Xie, Jinsong Zhao

The classic theory of Landau damping requires the velocity distribution function (VDF) to be analytically continued into the complex plane, implicitly requiring analyticity, which imposes constraints far more severe than infinite smoothness. Yet physical plasmas---encountered in discrete simulations, noisy spacecraft measurements, or truncated fusion distributions---are inherently non-analytic. This discrepancy poses a foundational ``smoothness paradox'': why does Landau damping robustly persist in systems where the mathematical prerequisite of analyticity is profoundly violated? Here we resolve this paradox by demonstrating that wave-particle interaction is governed by a time-dependent resonance width $Δv_\mathrm{res}\sim 1/kt$. Using a dispersion-free Lagrangian time-domain solver, we show that this finite width kinematically coarse-grains microscopic VDF defects at early times, acting as a natural low-pass filter that validates smooth analytical proxies---explaining the observed robustness. However, as $t\to\infty$ the resonance width narrows, inevitably forcing the wave to resolve exact topological non-smoothness. This late-time resolution triggers three distinct breakdowns: VDF truncation arrests the resonant phase transition to yield undamped discrete Van Kampen modes; observational noise induces transient algebraic spikes via linear phase-space aliasing; and step-like gradients drive anomalously violent reactive instability growth. We establish the breakdown timescale $t_b\sim 1/kδv$, where $δv$ is the characteristic scale of the non-smooth defect, providing a quantitative criterion that redefines the validity boundaries of analytic continuation in kinetic theory.

Towards mitigating helium damage in nano-crystal iron and tungsten: A strategy based on the dual trap-channel functionality of grain boundaries tuned by their crystallographic character

Fangqing Qian, Xiaolin Li, He Tong, Binbin Fan, Xinru Wang, Yange Zhang, Yichun Xu, Rui Liu, X. P. Wang, X B Wu, et al.

Nuclear fusion structural materials in critical components like blanket and first-wall are subjected to intense helium (He) generation, causing severe microstructural degradation that limits operational lifetime. Nanocrystalline microstructures have emerged as a promising route toward healing displacement damage. However, the theoretical feasibility of such systems to effectively capture and subsequently expel He through the grain boundary (GB) network remains uncertain, given the intrinsic diversity of GB structures and characteristics. In this work, by combining molecular statics/dynamics simulations with object kinetic Monte Carlo and rate theory, we explore the differentiated behaviors of He at GBs via screening a wide spectrum of 〈1 0 0〉 and 〈1 1 0〉 symmetric tilt GBs with different characteristics in α iron (Fe) and tungsten (W). By quantifying three critical energy parameters, including He−GB binding energy, intra-GB migration energy barrier, and He−He binding energy, we demonstrate that GBs exhibit dual functional modes with respect to He accumulation: (i) fast-diffusion channels enabling rapid anisotropic pipe diffusion along specific crystallographic axes and (ii) strong-trapping sinks, characterized by low Frenkel pair formation energy and deep binding sites that immobilize He. A quantitative relationship between GB structural descriptors (notably local free volume) and key He energetics and kinetics is also established, revealing that atomic/free volume mediates He transport along GBs, thereby clarifying the structural origin of differential He transport/retention across GB types. Furthermore, we systematically discuss the influences of irradiation/thermal defects, as well as alloying elements such as chromium, on He-related functional behaviors of GBs. Based on three governing properties: capture strength, internal diffusivity, and binding stability, this work ultimately provides theoretical foundations for designing GB character-informed He management framework. Within this framework, GB networks can be rationally tailored to simultaneously capture He and facilitate its boundary-mediated expulsion, offering a viable pathway for enhancing the radiation resistance of materials.

Plasma-Chemical Degradation of Molybdenum and Tantalum as First Mirror Materials for the EAST Tokamak

Viktor Afanasyev, Lidiia Lobanova, Maxim Semenov-Shefov, Shouxin Wang, Ling Zhang, Haiqing Liu

A composite impurity-pressure index for assessing startup readiness during plasma recovery on EAST

Shuqi Yang, Yaowei Yu, Tao Zhang, Xiang Zhu, G Z Zuo, Xiang Gao

Reliable restart after vessel venting is controlled by the burn-through power balance: the plasma must ionize the residual neutrals, dissociate molecules and raise the electron temperature before ionization, charge-exchange and impurity-radiation losses exhaust the available ohmic or auxiliary power. In practice, however, operators usually do not know whether the wall has recovered until a shot has already been attempted. Six EAST plasma-recovery campaigns from 2023 to 2025 are analysed, and a pre-shot impurity-pressure index is introduced to combine the neutral pressure measured 2–3 s before breakdown with a weighted residual-gas-analyser proxy for nitrogen- and oxygen-bearing species. In this dataset, the index organises discharge duration, stable-shot probability and the loop voltage during the first 50–200 ms more clearly than either pressure or composition alone. Under the standard EAST startup condition used here, stable discharges become much more likely when the index falls to around 1 × 10-7 Pa. In the second 2025 campaign, the shot-by-shot evolution also shows threshold-like burn-through behaviour: the maximum line-averaged electron density in 0–0.2 s stays low at large index values, overshoots in a transition interval, and then settles to a more stable level as the wall recovers. Across campaigns, post-recovery values cluster much more tightly than the recovery paths themselves, indicating that the index characterizes the startup-ready wall state rather than a particular conditioning route. The metric therefore provides a practical pre-shot indicator of whether EAST has recovered sufficiently for reproducible stable startup.

Magnetic island structures in relativistic laser-driven plasma channels

Dongchi Cai, Zheng Gong, Guanqi Qiu, Deji Liu, Yinren Shou, Xueqing Yan

We develop a theoretical model for self-generated magnetic islands in relativistic laser-driven channels in near-critical-density plasmas. The islands arise from the nonlinear superposition of the quasi-static magnetic fields generated by the longitudinal channel current $j_x$ and the laser-front driven transverse current $j_y$. By deriving the critical conditions among laser depletion, transversely symmetric channel formation, and magnetic-island formation, we identify the laser-plasma parameter window in which the magnetic island structures can exist. Within this window, the balance between the laser ponderomotive force and the charge-separation force, expressed through an effec tive electron density $n_\mathrm{eff}$, determines the transverse island width $H$, whereas the mismatch between the laser group and phase velocities determines the longitudinal period $L$. Large-scale particle-in-cell simulations over a broad range of laser intensities and plasma densities validate the resulting scaling laws. The model turns the island geometry from a qualitative feature of the channel field into a predictable quantity, providing a basis for tailoring electron transport, particle acceleration, high-energy radiation, and novel fusion ignition schemes in relativistic laser-plasma interactions.

Per-tube parameter characterization and dual-gyrotron operation validation of the CRAFT 170 GHz ECRH test stand

Yu Wang, Zege Wu, Huaichuan Hu, Jingping She, Haoming Chang, Haibiao Zhang, Xiaojie Wang

Impact of ion-beam stopping power on proton-boron fusion yield in the pitcher-catcher scheme driven by ultra-intense laser

J. Y. Hua, X. F. Li, J. X. Wang, Y. X. Leng, Y. Tian, R. X. Li

The effect of stopping power on proton-boron fusion is investigated for a proton beam propagating through boron plasma. Due to the stopping power, the electron temperature of the boron target rises as the proton beam deposits energy. Consequently, a feedback mechanism becomes significant when the trailing part of the beam propagates into the preheated plasma. By coupling this phenomenon with the proton-boron fusion process, fusion yields are systematically investigated by varying the central energy of the proton beam, as well as the thickness and density of the boron target. It is found that, under the influence of stopping power, the optimal central energy for fusion deviates from the intrinsic 672 keV resonance and shifts to approximately 900 keV. Moreover, the present results are substantiated by particle-in-cell simulations, which provides a valuable reference for subsequent high-yield hydrogen-boron fusion.

Numerical studies of mode coupling induced by neoclassical toroidal viscous torque in error field penetration on EAST

Cheng Ye, Youwen Sun, Hui-Hui Wang, Yueqiang Liu, Pengcheng Xie, Jian Xu, Hui Sheng, Xin-Jian Wang, T Y Xia

Mode coupling induced by neoclassical toroidal viscous (NTV) torque governs error field penetration in toroidal plasmas , causing the $2/1$ penetration threshold to deviate from linear response prediction with respect to the RMP upper-lower coil phasing ($\Delta\phi_{UL}$). This behavior originates from nonlinear modulation of toroidal momentum transport by non-resonant three-dimensional magnetic field components. In this work, the characteristics of such mode coupling is systematically investigated using the MARS-Q code. Two aspects are examined. First, the dependence of mode coupling strength on key plasma parameters is analyzed. A larger momentum diffusivity ($\chi_M$) is found to strongly enhance mode coupling and invalidate linear response criteria, whereas at low $\chi_M$ linear prediction remains applicable. A NTV torque weighting factor based on linear response is identified as a qualitative indicator of mode coupling in the nonlinear field penetration. In addition, reduced resistivity ($\eta$), higher normalized beta ($\beta_N$), and larger inverse aspect ratio ($\epsilon$) all strengthen mode coupling. Second, a critical momentum diffusivity, $\chi_{M,crit}$, is introduced to characterize the impact of boundary-induced mode coupling on the $2/1$ penetration spectrum, with smaller value indicating stronger impact. The results show that $\chi_{M,crit}$ increases with initial plasma rotation, but decreases for rotation profile with reduced flow shear. Moreover, increasing $\eta$, as well as higher $\beta_N$ and $\epsilon$ also reduce $\chi_{M,crit}$, albeit through different physical mechanisms. Across broad range of numerical scenarios, these results highlight the essential role of mode coupling in error field control for future fusion devices.

Deuterium retention and surface modification of tungsten under exposure to deuterium-neon mixed plasmas and combined with transient heat loads

Yue Yuan, Ying Qin, Arkadi Kreter, A Terra, Sören Möller, Long Cheng, Di Hu, yuhao Li, Sijie Hao, Peng Zhang, et al.

Neon (Ne) seeding is essential in ITER to mitigate divertor heat loads, but it significantly influences plasma-surface interactions and fuel retention in tungsten (W). Moreover, transient heat loads from edge-localized modes (ELMs) further alter surface morphology and fuel retention behavior. This work investigates the combined effects of Ne seeding and ELM-like transient heat loads on surface modification and deuterium (D) retention in rolled W. Experiments were carried out in the linear plasma device PSI-2 using pure D plasma and D+10% Ne plasma at 500 K, with an ion energy of 40 eV, and a fluence of 1 × 1026 D m-2. Transient loads were applied using a pulsed laser (1 ms, 0.76 GW m-2, 1000 cycles), either successively or simultaneously with plasma exposure. For plasma-only exposures, Ne seeding caused pronounced erosion and fine cracks on blister caps, resulting in approximately 32% lower total D retention compared with pure D plasma. Transient heat loads generated temperature and stress fields, thereby causing surface roughening and dynamic recrystallization, as well as increasing D retention in both the near-surface (< 4 µm) and deeper regions. When combined with Ne seeding, the effects depended on the loading sequence. With sequential transient heat loads followed by plasma exposure, D retention decreased by about 44% in the near-surface and by 27% in total retention. In contrast, under simultaneous THL + plasma exposure, Ne seeding increased near-surface and total D retention by approximately 62% and 16%, respectively, and produced an additional broad D release peak at around 1200 K. This peak could be attributed to the formation of high-binding-energy Ne-vacancy complexes (Nei-V complexes) induced by the synergistic interaction of D-Ne and transient heat loading. These results demonstrate that both impurity seeding and transient heat loads critically determine D retention behavior, emphasizing the importance of accounting for their synergistic effects when predicting fuel retention and optimizing operation scenarios in future fusion devices.

Effects of parallel electric field, ion finite Larmor radius and plasma diamagnetic drifts on Alfvén continuum

Wenjie Sun, Jian Bao, Wenlu Zhang, Chao Dong, Jintao Cao, Pengfei Liu, Zhihong Lin, Ding Li

Based on the drift MHD model, we investigate kinetic effects on the Alfvén continuum, including the finite parallel perturbed electric field ($\delta E_\parallel$), ion finite Larmor radius (FLR), and plasma diamagnetic drifts. The $\delta E_\parallel$ arises from electron diamagnetic drift and electron Landau damping. It is shown that electron Landau damping couples the kinetic Alfvén wave (KAW) and the electron drift wave (EDW). The electron diamagnetic drift has a much weaker effect compared to the ion diamagnetic drift, as the latter can enhance the frequency of the ion mode. We find that ion FLR increases the continuum frequency in the core region, whereas its influence weakens towards the edge. These kinetic effects are also studied for the toroidal Alfvén eigenmode (TAE) within the self-consistent model. While $\delta E_\parallel$ has negligible impact on the mode structure and real frequency of TAE, it introduces radiative damping through electron Landau damping. These findings emphasize the importance of including kinetic effects in the analysis of Alfvén continuum.

Dimensionless analysis of H-mode plasmas for energy confinement and transport on EAST tokamak

Can Su, Shouxin Wang, Haiqing Liu, Xiao Lan Zou, Shiying Su, Zhuoyang Chen, Zheng Sun, Chen Cheng, Zichao Lin, Guangle Lin, et al.

This work presents an investigation of dimensionless parameter scaling laws for H-mode energy confinement and transport on EAST tokamak, through dedicated experiments designed to isolate the individual effects of normalized plasma pressure ( β ) and collisionality ( ν * ). The β scaling experiment revealed a weak dependence of energy confinement time on β, resulting in a scaling exponent of α β ≈ 0.24±0.20. This weak positive dependence, consistent with experiment observations and linear simulations, reflects an electrostatic turbulence dominated confinement regime in EAST H-mode plasmas. In contrast, a strong, negative dependence of confinement time on ν * was obtained, following the scaling B τ E ∝ ν * -0.71±0.32, indicating confinement improvement with decreasing ν * . Local transport analysis indicates that this strong ν* dependence is primarily associated with electron heat transport, while ion heat transport exhibits a comparatively weak sensitivity. While the linear instability spectrum is dominated by ion temperature gradient (ITG) modes across the explored parameter range, ν * strongly regulates turbulence characteristics relevant to electron heat transport, leading to a pronounced ν* dependence of global confinement. These distinct behaviors of electron and ion heat transport are associated with different physical mechanisms governing the confinement scaling with dimensionless parameters.The present results suggest that the confinement scaling exponents observed on EAST are closely tied to the turbulence regimes accessed in the dedicated β and ν* scans, providing physical insight into the differences with respect to global multi-machine scaling trends.

Understanding the toughness mechanism of high-boron stainless steel: impact of boron content

Xiang Geng, Qiang Qi, Sigui Qin, Yujia Jin, Zidan Zou, Linfang Cui, Xiaodong Tang

Experimental observation of neoclassical tearing mode stabilization by ICRF drive in EAST

Hua Yang, Wei Zhang, Lunan Liu, Pengjun Sun, tao JIN, Hui-Hui Wang, Liqing Xu, Zhengshuyan Wang, Tonghui Shi, Hailin Zhao, et al.

Neoclassical tearing modes (NTMs) in high-beta plasmas can degrade confinement and trigger disruptions. Experiments were conducted on EAST to investigate the effects of ion cyclotron range of frequency (ICRF) heating on NTMs through controlled variation of the power deposition location and fast-ion distribution. Using hydrogen minority heating, on-axis and off-axis ICRF heating scenarios were achieved by varying the toroidal magnetic field, together with additional ICRF power modulation. The results show that on-axis ICRF heating effectively suppresses the m/n = 3/2 tearing mode, while off-axis heating tends to enhance the m/n = 4/3 mode. On-axis heating also improves plasma confinement and increases the neutron yield. TROIC-TRANSP simulations confirm the distinct power deposition locations, while ASCOT calculations indicate that the fast-ion energy reaches up to 800 keV during on-axis heating, which is substantially higher than that in the off-axis cases. A modified Rutherford equation incorporating fast-ion effects suggests that the fast-ion-driven uncompensated cross-field current term is responsible for the observed NTM behaviors. These results demonstrate that controlling the ICRF resonance position is a feasible approach for NTM suppression and improved plasma performance.

Anisotropic Maxwell neural operator for rapid parametric full-wave modelling of ion cyclotron resonance heating

Heng Zhang, Xu Wang, Jiayi Li, Miao Zhang, Jiahui Zhang, Kaihao Wang, Yangdi Yi, Qin Hang, Xinjun Zhang

Full-wave calculations of ion cyclotron resonance heating (ICRH) under different plasma dielectric conditions require repeated assembly and solution of large-scale discretised systems, limiting parameter sweeps and multi-case response analysis. We therefore propose an anisotropic Maxwell neural operator (AMNO) for rapid parametric modelling of ICRH full-wave responses for the Experimental Advanced Superconducting Tokamak (EAST), which learns, within the one-parameter dielectric-field family generated by varying the hydrogen minority fraction X_H over 0.01-0.05 under otherwise fixed settings, a shared solution operator from the spatially varying complex anisotropic dielectric-tensor field to the three-component complex electric field under frequency-domain Maxwell constraints. It represents global spatial coupling through spectral operator layers and local fine-scale responses, and combines sparse reference-field supervision with the frequency-domain Maxwell-equation residual. Comparisons with COMSOL reference solutions for the same EAST frequency-domain Maxwell-dielectric model show that AMNO reconstructs the principal spatial and spectral features and maintains stable accuracy for unseen interpolation test cases. With reference-field points reduced to 7.5% of the dense full-wave set, AMNO reduces the relative L_2 error by 66.1%-89.9% compared with a sparsely supervised Fourier neural operator (FNO-Sparse) under the same supervision and requires about 0.25 s for single-case inference. AMNO thus reduces dependence on dense reference-field supervision while enabling subsecond parametric complex-field inference, providing a physics-constrained and data-efficient surrogate for rapid in-range X_H sweeps and cross-case response analysis within the modelled EAST configuration.

Radial phase variation and energy flow of Alfvén gap modes

Xinran Xu, Jian Bao, Wenlu Zhang, Chao Dong, Jintao Cao, Ding Li

Radially curved mode structures of Alfvén eigenmodes are commonly observed in fusion experiments associated with energy transport, which indicate the radial phase variation arising from non-ideal magnetohydrodynamics (MHD) and global effects. In this work, based on MAS global eigenvalue simulations with Landau-fluid bulk plasmas and non-perturbative gyrokinetic energetic ions, we investigate the physical mechanisms responsible for the curved poloidal mode structure tail of RSAE and the rapid phase change of radially coupled RSAE and TAE in DIII-D plasmas. The former one is due to kinetic interaction between RSAE and Alfvén continuum with enhanced mode conversion to kinetic Alfvén waves, and the latter one can be explained by global effects of higher-order radial eigenstate or RSAE-TAE hybrid modes with multiple poloidal harmonics. An improved energy transport model based on global mode structures is formulated and implemented in the MAS framework, which clearly demonstrates the radial phase variation and EI non-perturbative effects on the radial Poynting vector.