Recent Publications

Cleaning rate and uniformity of simultaneous cleaning of two face-to-face mirrors using RF plasma

Yuxian Wen, Rong Yan, Chuannan Xuan, Lei Mu, Yuming Liu, Yuhao Pan, Zhaohui Wang, Baoguo Wang, Shuyue Sun, Rui Ding, et al.

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.

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 data-driven model for stable long-horizon autoregressive prediction of plasma current and control-oriented boundary evolution in EAST

Minglong Wang, Chenguang Wan, Yuehang Wang, Jia Huang, Zhi Yu, Jingjing Lu, Xiaojuan Liu, Zhisong Qu, Weidong Chen, Teng Wang, et al.

Accurate long-horizon prediction of tokamak plasma current, position, and boundary evolution is essential for magnetic control, rapid controller development, and reinforcement-learning-based optimization. However, high-fidelity physics-based simulators are often computationally prohibitive when large numbers of simulations are required for controller tuning and large-scale optimization. In this work, we develop a fast, data-driven model for the Experimental Advanced Superconducting Tokamak (EAST) to predict plasma current, position, and shape evolution over horizons of up to 1 s, with an inference time of 0.1 s on a single NVIDIA H800 GPU. Evaluated on a temporally separated test set comprising 5907 discharges, the model demonstrates strong generalization to evolving operating conditions and maintains stable agreement with experimental measurements during long-horizon autoregressive rollouts. The mean geometric error of the plasma centroid and the control-oriented boundary representation is 2.4 cm, indicating reliable centimeter-level accuracy for control-oriented prediction of plasma position and shape evolution. The proposed framework provides a practical, high-throughput alternative to first-principles simulators, enabling efficient control algorithm prototyping, large-scale scenario exploration, and future data-driven optimization for tokamak plasma control. This study focuses on the post-shaping phase of EAST discharges, where sustained plasma current and control-oriented boundary regulation are most critical.

Parametric effects and rate-limiting mechanism analysis of tritium extraction process in permeator against vacuum

Zuocong Liu, Qingjun Zhu, Qiankun Shao, Songlin Liu

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

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.

Molecular dynamics simulation of migration and mechanism transition of 1/2 <111> dislocation loops in tungsten

Zhaofan Wang, Chao Yin, Qi Xiong, Zhe Liu, Ze Chen, Shifeng Mao, Minyou Ye

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.

Investigation of high-Qfus L-mode plasma operation sustained by elevated pellet fuelling in ITER

Jie Zhang, Florian Koechl, Alexei R Polevoi, Clarisse Bourdelle, Sunhee Kim, Alberto Loarte, Simon D Pinches, Ge Zhuang

The enhanced confinement of tokamak plasmas (H-mode) makes it a preferred regime for achieving fusion power production goals in future devices such as ITER. Nevertheless, low confinement mode (L-mode) remains worthy to investigate in reactor relevant conditions, primarily due to no/reduced requirements for ELM and divertor heat load control. In this regard, this study aims at exploring a new potential approach to maximise the achievable fusion gain Qfus. This approach attempts to increase the core density with enhanced pellet fuelling and then investigates the feasibility of high Qfus L-mode operation in ITER. The JINTRAC integrated modelling suite has been employed for core-edge transport and source modelling, using the HPI2 module for pellet fuelling. In some of the scenarios considered, the core density reaches up to ∼185% of the Greenwald density, nGW, with edge densities approaching nGW, motivated by recent re-evaluations of the density limit that suggest a power-dependent threshold. We compare core transport modelling results obtained by applying the semi-empirical Bohm-gyro-Bohm (BgB) or the quasi-linear gyrokinetic TGLF-SAT2 anomalous transport models, with interpretive vs. predictive impurity transport modelling, and pellet fuelling describing continuous vs. discrete particle sources. The core plasma confinement of high-density L-mode operation in ITER predicted by the TGLF-SAT2 model is significantly better than that predicted by the BgB model, resulting in a significantly improved Qfus. Fusion performance metrics, including Pfus and Qfus, exhibit only minor changes when switching from the interpretive impurity model to the predictive SANCO model, and/or from the continuous ad-hoc pellet model to the discrete HPI2 pellet model. The highest Qfus value predicted in the ITER high-density L-mode simulations is ~ 4, with indications that further improvement may be limited by increased transport associated with electro-magnetic turbulence at elevated plasma beta. This integrated modelling prediction demonstrates the potential of improved Qfus L-mode operation in ITER and future fusion devices, while exploring its boundary.

Investigation on fast ion losses induced by neoclassical tearing mode in HL-3 high- β plasmas

Zhiyi Yin, Min Jiang, Baolong Hao, Ruirui Ma, Yuxiao Han, Yi Liu, Linge Zang, Sen Xu, Shuosu Yang, Deliang Yu, et al.

The fast ion losses (FIL) induced by m = 2 , n = 1 neoclassical tearing mode (NTM) are investigated dedicatedly in HL-3 high- β N plasmas, where m ( n ) is the poloidal (toroidal) mode number. The spectrogram of FIL fluctuation measured by FIL detector (FILD) shows a dominant characteristic frequency of the NTM rotation frequency, indicating that the NTM rotation modulates the fast ion (FI) loss. The lost FI population peaks at pitch-angle of 112 ∘ − 118 ∘ and energy ranges of 40 − 60 keV , consistent with the full energy of neutral beam. The intensity of the FILD signal is proportional to the square of island width, implying dominantly convective FIL. In addition, the NTM island structure passes through the lost orbit of the trapped FI, which is calculated backward in time from the FILD measurement, suggesting there exists an interaction between FI orbit and the NTM island. The calculation using ORBIT code reveals the wave-particle resonant condition is fulfilled between the NTM and the trapped FIs, further confirming the convective loss mechanism. The interaction primarily affects the toroidal canonical momentum rather than the energy of FIs due to the relatively low NTM frequency. These results enhance our understanding of NTM induced FI transport in high- β plasmas, providing valuable insight for optimizing the high-performance operation scenario for future fusion reactors.

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.

Revisit two-mode couplings of the ablative Rayleigh-Taylor instability in inertial confinement fusion

Xian Jiang, Shenming Xu, Dehua Zhang, Tao Tao, Jingfei Xin, Rui Yan, Hang Ding, Jian Zheng

Two-dimensional two-mode couplings of the ablative Rayleigh-Taylor instability (ARTI) under inertial-confinement-fusion (ICF) relevant parameters are revisited via numerical simulations, with a focus on the regimes where the wavenumbers of the initial modes are close to the cutoff wavenumber. In the quasi-linear stage in which the generated modes approximately grow exponentially with time, both the self-growth of the generated mode (as if in the single-mode regime) and the driven-growth due to mode couplings are found to be important. A series of linearly unstable modes are found to be generated by coupling of two linearly stable initial modes, and then compete for the dominant mode according to a proposed criterion. A model including the contribution of both the self-growth and the driven-growth with an empirically modified coupling coefficient is proposed and shown to accurately predict the growth of the generated mode. The findings have implications for assessing the impact of ARTI in ICF designs.

Two-fluid effects on the nonlinear dynamics of RFP relaxation

Wentan Yan, Ping Zhu, Hong Li, Wandong Liu, Bing Luo

This study investigates the role of two-fluid effects during magnetic relaxation in reversed-field pinch (RFP) plasmas. Within the multiple-helicity (MH) regime, two-fluid simulations produce distinct sawtooth oscillations, in contrast to the sawtooth-free state obtained in single-fluid simulations. Analysis of the magnetic field aligned projection of Faraday's law reveals that, tearing modes collectively generate a dynamo electric field that sustains the magnetic relaxation, a process analogous to the flux-pumping in tokamaks. Despite the reduced linear tearing-mode growth rates, stronger two-fluid effects produce more pronounced sawtooth activity over the parameter range considered. Modal energy analysis shows that Hall-mediated nonlinear energy redistribution disrupts the coherent tearing-mode dynamics required to sustain steady flux-pumping, thereby facilitating intermittent reconnection. This transition is interpreted as a Hall-mediated dynamical bifurcation between steady flux-pumping and quasi-periodic sawtooth relaxation.

Nonlinear correlation analysis of edge coherent mode on the EAST tokamak

Jun Jiang, Ran Chen, Chijin Xiao, Weixing Ding, Guanghai Hu, Minyou Ye

We report the first application of a nonlinear correlation algorithm based on phase-space reconstruction to investigate the nonlinear dynamics of the edge coherent mode (ECM) on the EAST tokamak. By adopting a unified reconstructed phase-space scale for parameter selection, we perform quantitative comparison and analysis of ECM nonlinear dynamical characteristics across different physical regimes. Key findings include: (1) distinct evolution of nonlinear directionality during the ECM establishment following the L-H transition as compared to that during the inter-ELM recovery phase; (2) the nonlinear correlation coefficient decreases before the ECM amplitude does, acting as a “precursor” to the ECM decay, while the linear correlation coefficient remains nearly constant; (3) higher-frequency, narrower-band ECMs exhibit stronger nonlinear correlation and a more pronounced directionality bias, whereas lower-frequency, broader-band ECMs show weaker coupling and balanced directionality. These findings provide a new nonlinear physical perspective for understanding the saturation mechanism of the ECM.

Magnetic equilibrium of the CN-H1 heliac: A comparative study of design,as-built, and historically built configurations

Zhengkun Gao, Axel Koenies, Jinjia Cao, Hengqian Liu, Guodong Yu, Dong Xiang, Caoxiang Zhu, Yong-Zhi Dai, Haipeng Wu, Michael Drevlak, et al.

The relocation of the Australian H-1 National Facility (H-1 NF) to China and its reconstruction into the CN-H1 device necessitated a rigorous reassessment of its magnetic configuration to address systematic deviations introduced dur ing the engineering process.This paper presents a comprehensive comparative study of the magnetic equilibrium across three distinct definitions of the de vice: the idealized H-1 Design, the historically built as-built H-1 NF, and the newly reconstructed CN-H1. High-precision laser tracker metrology was em ployed to generate a high-fidelity coil model for CN-H1, incorporating the re manufactured poloidal and helical windings. Calculations of the vacuum mag netic field reveal that, compared to the H-1 NF, the CN-H1 exhibits a systematic inward radial shift of the magnetic axis, a slight increase in the rotational trans form, while maintaining a comparable level of stellarator symmetry breaking. Three-dimensional MHD equilibria were reconstructed using the VMEC code and validated against field-line tracing. Comparative analysis across represen tative configurations demonstrates that the defining characteristics of the flexi ble heliac—including high rotational transform, shear tunability, and magnetic well depth—are preserved in CN-H1. Magnetic spectra in Boozer coordinates of CN-H1 are nearly indistinguishable from the H-1 NF historically built baseline, despite coil positioning errors in the millimeter range. These results validate the engineering fidelity of the CN-H1 reconstruction and establish a precise equilib rium basis for future finite-beta plasma experiments.

Sub-Second Collisionless Gyrokinetic Eigenvalue Solutions via Orbit-Invariant Decomposition

Anrui Luo, Jingyi Yu, Huasheng Xie, Jian Bao

Fast analysis of microscopic drift-wave instabilities based on linear gyrokinetic simulation is desirable for modeling anomalous transport in fusion device. In this work, we present an orbit-invariant decomposition method for solving collisionless gyrokinetic eigenvalue problems. By discretizing velocity space along orbit invariants using particle energy and magnetic moment, the full eigenvalue matrix is separated into independent orbit blocks that couple with each other through the field equation, greatly reducing both matrix dimension and computational cost without sacrificing physics. Based on this method, we extend the MGK code [Phys.\ Plasmas 24, 072106 (2017)] with both CPU and GPU implementations, supporting collisionless electrostatic linear simulations in $s$--$α$ and Miller equilibrium model with kinetic. For kinetic ion temperature gradient (ITG) and trapped electron mode (TEM) eigenvalue problems, the solver reduces single-solution times to the 0.01--0.1s range---more than three orders of magnitude faster than CGYRO on the same hardware---enabling efficient large-scale parameter scans. The eigenfrequencies and mode structures are verified by comparing with CGYRO results. The method is generally adapt to to all collisionless gyrokinetic eigenvalue formulations and can be extended to fully electromagnetic simulations.

A theoretical model for quantifying the imprinting sensitivity of direct-drive inertial confinement fusion implosions

Dongxue Liu, Jiaqin Dong, Yunxing Liu, Zhiyu HE He, Wei Wang, Yuqiu Gu, Xiuguang Huang, Jian Zheng

To quantify the sensitivity of diverse implosion designs to laser imprinting, we developed an equivalent perturbation model that maps laser imprinting as the initial target surface perturbation. By incorporating imperfections in target fabrication and thermal smoothing in the plasma, the model shows a reduced implosion sensitivity to laser imprinting, extending the analysis beyond geometric irradiation. The imprinting sensitivity threshold is defined as δh_{proxy}/δh{tar}(0)= 0.1, where δh_{proxy} is the imprinting amplitude and δh{tar}(0) is the initial target perturbation amplitude. Radiation-hydrodynamics simulations confirm that whenδh_{proxy}/δh{tar}(0)< 0.1, variations in nonlinear onset time and adiabat remain within 12\% of that with δh{tar}(0) alone. Moreover, the imprinting sensitivity is supported by OMEGA experiments. Overall, for linear perturbations of medium-to-high modes in direct-drive, the model enhances our physical understanding of how laser and target perturbations evolve and serves as a simplified tool to optimize implosion performance.

Hybrid simulation of transition from Beta induced Alfv'en Eigenmode to Reverse Shear Alfv'en Eigenmode on EAST

Andong Xu, Yiqi Liu, Wei Shen, Ming Xu, Baonian Wan

Kinetic-magnetohydrodynamic (MHD) hybrid simulations have been carried out to investigation the transition of different types of Alfv'en eigenmode based on Experimental Advanced Superconducting Tokamak(EAST). Two evolution processes of q profile starting with a reverse shear q profile with minimum $q_{min} < 2$ have been analyzed: ascending one based on magnetic diffusion effect and descending one inferred from coexistence of double tearing mode. The experimental phenomenon that type of Alfv'en eigenmode transit from Beta induced Alfv'en Eigenmode (BAE) to Reverse Shear Alfv'en Eigenmode (RSAE) and up-sweeping of RSAE frequency with multiple toroidal number n is reproduced in both processes. In the ascending process, transition from BAE to RSAE happens at $q_{min} = 2$ when rational surface of $q = 2$ vanishes. In the descending process, transition happens at $q_{min} = 1.92$ without vanishing of $q = 2$ rational surface and is accompanied by a sudden shift in mode location. Comparing frequency and growth rate pattern with experimental observation during mode transition, the descending process satisfies experiment better. In addition, different physical factors to affect the mode transition have been investigated including q profile shape and energetic particle pressure. It is found that smaller magnetic shear at rational surface is in favor of excitation of BAE, and RSAE frequency is influenced by second order derivative of q profile at its minimum. Moreover, the excitation of BAE is not sensitive to the peak location of energetic particle pressure gradient, but radial phase variance of mode structure is positively linked to distance between energetic particle drive location and mode location, which is also influenced by local magnetic shear. These systematical study on the effect of different physical factors on Alfv'en eigenmodes can provide guidance for controlling Alfv'en instabilities in future.

The Verification, Validation, and Uncertainty Quantification Framework of the EAST Tokamak Diagnostic System

Shuzhi Yuan, Haiqing Liu, Kazuaki Hanada, Mitsutaka Isobe, Yang Zhang, Ting Lan, Xiang Liu, Hui Lian, YuQi Chu, Shouxin Wang, et al.

The diagnostic system in a tokamak serves as the foundation for research in plasma physics, plasma operation control, and device protection. The accuracy and reliability of diagnostic data have long been critical considerations in tokamak data analysis and processing. To achieve systematic error assessment, optimized design, and coupling with other systems or simulation modules, the development of a digital diagnostic system module, digital twin, can significantly reduce labor and time costs. Based on a digital diagnostic model, uncertainty quantification and sensitivity analysis are conducted for the diagnostic system, providing a basis for its upgrade. Meanwhile, the engineering design, system hardware, and data processing system of the actual diagnostic system are hierarchically validated to identify uncertainty sources, which are then compared with those of the digital system. This enables complementary validation between the real system and its digital twin. By analyzing uncertainty sources and conducting sensitivity analysis, high-impact uncertainty sources are prioritized for optimization, thereby enhancing the accuracy and reliability of the diagnostic system. This paper quantifies uncertainties and sensitivities of the POINT system and its digital module. The VVUQ analysis yields a total uncertainty of 6.17% and a high confidence coefficient of 0.995. The agreement between experiment and digital module exceeds 97.5% except in the boundary region (≈82.5% due to missing chords). Sensitivity analysis shows that laser frequency stability (≈30%), core channel position (≈23%), and ion mass (≈11%) are the dominant factors. Future devices should improve frequency stabilization, core chord coverage, and fuel calibration to reduce density inversion uncertainty.