Recent Publications

Characteristics of core beta-induced Alfvén eigenmodes with shear flow in EAST NBI heating plasmas

Lizhe Guo, Jian Bao, Ming Xu, Hailin Zhao, Yingying Li, Chao Dong, Jintao Cao, Zhiyong Qiu, Wenlu Zhang, Zhihong Lin, et al.

Chinese Academy of Sciences Institute of Physics, Chinese Academy of Sciences - Hefei Institutes of Physical Sciences, Hebei Key Laboratory of Compact Fusion, University of California Irvine

The basic features and relationship with zonal flows of multiple branches of beta-induced Alfv'en eigenmodes (BAEs) are investigated in the EAST tokamak. Those branches of BAEs, excited by tangentially injected NBI, are located in the central region ($0.2 \leq \rho \leq 0.4$), with frequencies in the range of 50 $\leq f \leq$ 70~kHz and low toroidal mode numbers $1 \leq n \leq 5$. The excitation of BAEs is clearly characterized by three typical features: an increase in the $\omega_{EXB}$ shear locally, accompanied by simultaneous rises in both central rotation velocity and electron temperature. Radial profiles of the mode phase angle from electron cyclotron emission (ECE) diagnostics vary significantly with $n$. Global gyrokinetic simulations of core BAEs are performed in both linear and nonlinear regimes. In the linear regime, the unstable BAE branches are consistent with experiment on toroidal mode number, real frequency and the mode structure phase angle. The radial variation of BAE phase angle is primarily caused by bulk plasma kinetic effects rather than the energetic particle (EP) non-perturbative drive. In the nonlinear regime, single-$n$ BAE without zonal fields saturates at a large amplitude that triggers the non-adiabatic frequency chirping on a fast timescale of sub-millisecond, while the self-organized zonal flow beat-driven by BAE greatly reduces BAE saturation amplitude below the chirping threshold, which is in consistency with experimental observation. Moreover, it is confirmed that the criterion of zonal flow regulation on dissipative-type instability (such as AEs) becomes $\omega_{E\times B} > \omega_r$ rather than traditional $\omega_{E\times B} > \gamma_L$ for reactive-type instability. In general, the self-organized zonal flow can improve plasma confinement through regulating both BAEs and drift-wave turbulence.

Change of the Tungsten neoclassical particle transport characteristic due to the coexisting of the lower-Z impurity in the tokamak plasmas

Chengkang Pan

Chinese Academy of Sciences

The high-Z impurity Tungsten neoclassical particle transport in the tokamak plasmas with the coexisting of the lower-Z impurity is investigated. The lower-Z impurity could reduce or enhance the Tungsten neoclassical particle transport. The Tungsten neoclassical transport characteristic will be changed with the lower-Z impurity content large enough. The dependence of the Tungsten neoclassical transport on the bulk ion radial gradients predicted by the existing impurity neoclassical transport theory will be broken. The existing impurity transport theory will over-predict (under-predict) the Tungsten neoclassical particle transport for the bulk ion radial gradients less (larger) than the critical value. The effect of the lower-Z impurity on the high-Z impurity neoclassical transport is through the parallel friction force coupling and it should be included in the Tungsten neoclassical particle transport calculation.

Observation of fast ion acceleration under EGAM in EAST pure ECRH plasma with tearing mode

Chaowei Mai, liqing xu, Shiyao Lin, Tianfu Zhou, Tonghui Shi, Kangning Geng, Yifei Jin, Yanmin Duan, Kaiyun Chen, Yan Chao, et al.

Institute of Plasma Physics, Chinese Academy of Sciences, Chinese Academy of Sciences, Guangdong Ocean University, Chinese Academy of Sciences - Hefei Institutes of Physical Sciences

In magnetically confined fusion plasmas heated only by Electron Cyclotron Resonance Heating (ECRH), ion temperature typically saturates in the 1–3 keV range. The EAST tokamak, equipped with an ITER-like tungsten divertor, has operated deuterium H-mode discharges with high-power pure ECRH. In a specific discharge, a continuous ion acceleration process is observed, with ion energy ranging from an off-axis supra-thermal component above 6 keV to an isolated Gaussian peak reaching 1.8 MeV. The acceleration occurs at the location of a large 2/1 magnetic island, and an EGAM-like electrostatic mode at ∼ 23 kHz is detected by microwave diagnostics. The MeV-range cutoff energy, the mode power, and the island width exhibit pairwise strong linear correlations (R2 > 0.9), and the three are spatially coincident. Transfer entropy analysis and a 0D collisional-radiative model suggest a mechanism from island to mode to ion acceleration, excluding a purely electric-field-driven process. These observations provide experimental evidence of MeV-range ion acceleration accompanied by an EGAM-like mode in a pure ECRH plasma without auxiliary ion heating, offering a new data point for understanding ion acceleration under ECRH operation in tungsten-wall devices, particularly with degraded boron wall coating

Radial phase variation and energy flow of Alfvén gap modes

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

Chinese Academy of Sciences Institute of Physics

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.

WEST long-pulse achievements in support of next-step fusion devices

Remi Dumont, Theo Fonghetti, Patrick Maget, Pierre Manas, Jean-Francois Artaud, Tullio Barbui, Clarisse Bourdelle, Laurent Colas, Guido Ciraolo, Yann Corre, et al.

French Alternative Energies and Atomic Energy Commission, Chinese Academy of Sciences, Princeton University Plasma Physics Laboratory, IUSTI, Koninklijke Militaire School

The WEST tokamak is equipped with a superconducting toroidal magnetic field system, a multi-megawatt radiofrequency auxiliary power system, and an actively cooled ITER-grade tungsten divertor. As such, it is well adapted to explore experimental aspects related to the long pulse operation of next-step devices. Supported by predict-first integrated modeling, bespoke scenario development has allowed zero-loop voltage pulses to be achieved. The resulting discharges, with plasma currents in the range I p ∼0.22-0.28 MA exclusively sustained by the Lower Hybrid Current Drive (LHCD) system as an auxiliary power source, have achieved durations in excess of 22 min and injected/extracted energies up to 2.61 GJ. Plasma performance is characterized by ranges of poloidal beta β p ∼1.6-2.0, normalized toroidal β N ∼0.6-0.9 and confinement factor H 96L ∼1.0-1.3. Mild MHD activity, identified as resulting from the interaction of 3/1 and 4/1 tearing modes, is occasionally present, depending on the LHCD antenna combination used. This article describes the predict-first approach that has been employed in the context of this long-pulse scenario development endeavor. The main achievements and the physics analyses performed are reviewed, including post-experiment integrated modeling aspects. Prospects for further long-pulse developments are drawn.

Controllable Demagnetization Strategy for Magnet Power Supply Based on Linear-Region MOSFETs

Hao Yin, Yanan Wu, Jing Lu, Jun Li, Baocan He, Liuwei Xu, Yunxiang Tian, Pengfei Wang, Nan Liu, Xiao Ma, et al.

Chinese Academy of Sciences, Institute of Energy, Hefei Comprehensive National Science Center

Investigation of the corrosion behavior of 310S SS and Incoloy 800 alloys in static liquid PbLi at 700 °C

X.C. Meng, Z.P. Liu, D.H. Zhang, K.C. Jiang, X.Q. Liu, L.Z. Liang, G.Z. Zuo, J.S. Hu

Hefei Comprehensive National Science Center (Anhui Energy Laboratory), Chinese Academy of Sciences, Anhui University of Science and Technology

Activation analysis and radioactive waste assessment for COOL blanket in CFETR

Xiaokang Zhang, Qiuran Wu, Lin Kong, Xilong Tong, Shanliang Zheng

Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China

Wave Beating and Fast Frequency Chirping via Two-Dimensional Particle Dynamics Influenced by Density Inhomogeneity

Lipeng Wang

Chinese Academy of Sciences

Application of an improved YOLOv11-OBB algorithm based on multi-scale local feature enhancement and deformable convolution in EAST divertor target plate defect detection

Tao Zhang, Wei Wang, Haibiao Ji, Chunzhe Ye, Zelin Wu, Yongping Shi, Yuze Li

Hefei University of Technology, Chinese Academy of Sciences, Lappeenranta University of Technology (LUT)

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.

Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Kyushu University, Mahasakham University, National Institutes of Natural Sciences

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.

A TF based Intelligent Manufacturing System of First Wall Components for EAST Tokamak

Changle Liu, Jiahui Pan, Xiaoyun Ding, Lei Li, Lei Cao, Damao Yao

West Anhui University, Chinese Academy of Sciences

Hybrid simulations of fishbones with high order harmonics in EAST tokamak

Shengfa Wu, Wei Shen, Zhiyong Qiu, Liqing Xu

Chinese Academy of Science, University of Science and Technology of China

The linear stability and nonlinear dynamics of fishbones with high order harmonics have been investigated by the global kinetic-magnetohydrodynamic (MHD) code M3D-K in the Experimental Advanced Superconducting Tokamak (EAST). Based on EAST discharge parameters with Neutral Beam Injection (NBI) heating, linear simulations show that the modes with different toroidal mode numbers are primarily driven by trapped energetic particles through toroidal precession resonance. The n=1 mode is the typical fishbone, while there exists a transition for n=2 mode from fishbone-like mode to Energetic Particle Mode (EPM) when the energetic particle pressure exceeds a critical value. For the n=3 mode, the mode frequency remains almost unchanged with different energetic particle pressures. Nonlinear simulations show that with weak energetic particle drive, the m/n=2/2 mode is driven by the MHD nonlinear coupling of the fundamental m/n=1/1 mode. In this regime, the frequency of the m/n=2/2 harmonic is twice that of the m/n=1/1 mode, with both modes exhibiting downward frequency chirping. With strong energetic particle drive, beta-induced Alfvén eigenmodes (BAEs) with higher mode frequencies emerge for both m/n=1/1 and m/n=2/2 components, and the m/n=3/3 component is driven unstable with frequency chirping up. These simulation results highlight that nonlinear MHD coupling and fast ion redistribution are critical for understanding the dynamics of fishbones with high order harmonics.

Experimental study of the influence of boronized wall conditioning on tungsten sputtering in the EAST divertor

Qing Zhang, Fang Ding, Bingcheng Qi, Lin Yu, Y.H. Guan, Weixi Cao, Chen-Yuan Zhang, Yanze Peng, Zhe Wang, Zhenhua Hu, et al.

Chinese Academy of Sciences

Boronization, a critical wall conditioning technique in fusion devices, is employed to suppress light impurities like carbon (C) and oxygen (O) and mitigate material sputtering, with future applications planned for ITER. This study examines the effects of two boronization methods-glow discharge boronization (GDB) and real-time boron powder injection (BPI)-on tungsten (W) sputtering behavior in the EAST divertor, utilizing spectroscopic diagnostics to monitor both W atoms and tungsten deuteride (WD) molecules. Results demonstrate that GDB effectively reduces C/O impurities and suppresses physical W sputtering but unexpectedly enhances WD sputtering due to increased deuterium retention on the W surface, while BPI simultaneously suppresses both W and WD sputtering through radiative cooling and reduced impurity levels. These findings provide valuable insights for optimizing wall conditioning strategies in all-metal first-wall fusion devices, highlighting the importance of method selection for impurity and erosion control.

Mitigation of stimulated Brillouin scattering in two-color lasers via shared-trapping-induced frequency shift

D.J. Liu, Qing Wang, Q.S. Feng, S.T. Zhang, R.J. Cheng, X.X. Li, S.Y. Lv, Z.M. Huang, Z.J. Chen, Z.Y. Xu, et al.

Institute of Applied Physics and Computational Mathematics, State Key Laboratory of Nuclear Physics and Technology, Key Laboratory of HEDP of the Ministry of Education, Peking University, Beijing University of Posts and Telecommunications

A novel coupling mechanism for stimulated Brillouin scattering (SBS) in two-color laser systems with large frequency separation is proposed, using a representative combination of 527 nm and 351 nm beams. Owing to the near-linear dispersion of ion-acoustic waves (IAWs), both lasers excite IAWs with similar phase velocities. Consequently, the strong IAW driven by the high-intensity 351 nm laser induces pronounced particle trapping, which in turn generates a significant nonlinear frequency shift in the IAW driven by the 527 nm laser. The frequency shift from Vlasov simulation shows excellent quantitative agreement with our shared-trapping-induced nonlinear frequency-shift theoretical model. This newly identified mechanism suppresses the linear growth of SBS driven by the 527 nm laser, thereby providing a lower initial SBS level when the previously proposed two ion decay (TID) coupling mechanism (2024 Nucl. Fusion 64 126020) becomes active in the nonlinear stage, and enabling the total SBS reflectivity to be suppressed to an even lower level. The mechanism operates within a well-defined parameter window, where the SBS growth rate of the 527 nm laser lies between that of the TID instability and the higher growth rate driven by the 351 nm laser. For fixed total intensity, increasing the fraction of 527 nm light causes the total reflectivity to first decrease and then increase. When the SBS reflectivities driven by the two lasers become comparable, the shared-trapping-induced frequency-shift mechanism and the TID coupling act cooperatively, yielding the minimum total reflectivity. At the optimal intensity fraction, the simulation results show that the total SBS reflectivity is reduced by ∼ 40 % compared with a pure 351 nm laser at the same total intensity, with the instantaneous reflectivity remains no higher than that of the corresponding single-color cases throughout the simulation. These results demonstrate the potential of large-frequency-separation two-color lasers for improving laser–target coupling efficiency in future high-gain laser fusion schemes.

Impact of tungsten plasma facing components on H-mode operational space in EAST in support of ITER new baseline

Manni Jia, Alberto Loarte, Youwen Sun, Qingquan Yang, Hua Yang, Shuai Gu, Ling Zhang, Wenmin Zhang, Tianqi Jia, Hui Sheng, et al.

Chinese Academy of Sciences, ITER Organization

Recent experiments in EAST have demonstrated the compatibility of tungsten (W) as main wall plasma facing material with high confinement H-mode with low or no boron coverage. The experiments were conducted in plasmas with q 95 ≈ 6.0, which allowed access to both type-I and type-II ELMy H-modes in EAST with a W wall and low normalized input torque similar to ITER. Central electron cyclotron (EC), neutral beam injection (NBI) and lower hybrid waves (LHW) were applied as auxiliary heating in a range of total power injected into the plasma from 3 MW to 5 MW. Small amplitude high frequency type-II ELMs allow maintaining good H-mode energy confinement even when the distance between the separatrix and the main W limiter is as low as 4 cm. The normalized H-mode energy confinement can reach H 98 factors up to 1.1 for both EC+NBI and EC+LHW power combination in the type-II ELMy H-mode regime. In addition, for these type-II ELMy H-mode conditions, nitrogen puffing from divertor region has been used to achieve partial detachment without significant impact on H 98 nor on the core W concentration. On the contrary, EAST operation in the type-I ELMy H-mode is strongly affected by the main wall W source. The use of n = 2 resonant magnetic perturbations (RMPs) to achieve type-I ELM suppression in EAST reduces the core W level but at the cost of about 10% reduction on energy confinement. These results complement existing W-wall findings, providing a preliminary foundation from EAST for evaluating the impact of the W first wall in ITER, as proposed in the new ITER baseline, and highlight that the achievement of sufficient ELM control levels with low deterioration of energy confinement is key to minimize this impact.

Unveiling long-term defect evolution in fusion materials: a dynamic coupling of molecular dynamics with object kinetic Monte Carlo for iron and tungsten

Jintong Wu, Zhiwei Hu, Juan-Pablo Balbuena, Qigui Yang, Marie-France Barthe, Maria J. Caturla, Fredric Granberg

University of Helsinki, Helmholtz Center Dresden-Rossendorf, Universidad de Alcala, Chinese Academy of Sciences, CNRS

Exposure of materials to radiation in nuclear test reactors and power plants can strongly modify the microstructure and long-term performance of structural parts. Although the primary damage event develops within pico- to nanosecond time scales, its consequences can govern defect evolution over experimentally relevant irradiation periods. Classical molecular dynamics (MD) can resolve collision cascades with atomistic detail, but its accessible time scale leads to dose rates that are far above experimental conditions. Object kinetic Monte Carlo can reach much longer time scales, but it usually represents irradiation damage through simplified defect insertion rules and therefore neglect important information on cascade morphology and cascade interaction with existing defects. In this work, we present a method that embeds complete MD cascade simulations directly into object kinetic Monte Carlo (OKMC), allowing irradiation to be followed at realistic dose rates while retaining the atomistic character of cascade overlap. The approach is applied to tungsten and iron, two key materials for nuclear environments. We show that explicit cascade treatment changes both the total defect populations and the resulting cluster size distributions. In tungsten, cascades enhance vacancy clustering at low temperature, whereas at elevated temperature they can also destroy and divide pre-existing voids. In iron, cascades produce a clear reduction in the size of C15 Laves-phase clusters and lead to clustering behavior that is not captured by conventional OKMC, even at room temperature. These results demonstrate that cascade overlap can introduce mechanisms that are absent from standard long time scale models, and that such mechanisms should be included as they control the microstructure evolution during irradiation.

From cold start to sustainable operation: a strategy for disruption prediction across the tokamak lifecycle

Xinkun Ai, Zhong Yu, Wei Zheng, Ming Zhang, Yonghua Ding, Zhongyong Chen, Dalong Chen, Bihao Guo, Chengshuo Shen, Nengchao Wang, et al.

Huazhong University of Science and Technology, Chinese Academy of Sciences

Plasma disruption is a significant challenge in tokamak fusion, especially in large-size future devices like ITER, where it causes severe damage. Safeguarding future tokamaks throughout their entire lifecycle demands a disruption prediction strategy that addresses the sequential challenges from initial data scarcity to evolving discharge scenarios. This article combines three different disruption prediction methods with a strategy that maximizes the protection from the beginning of a new device to later high performance operation phase. First, for the early phase with no disruption data from the new device, we design anomaly detection-based disruption predictors that require only non-disruption samples for training, enabling protection from the first discharge. Second, to maintain the model’s performance as discharge scenarios evolve, we explore adaptive disruption prediction strategies that allow the model to continuously self-update and track evolving plasma operation scenarios. Finally, to quantify and manage the cumulative impact of disruptions on device integrity, we introduce the operation management based on disruption budget consumption (DBC) framework. The integration of DBC with adaptive prediction shifts the system’s objective from mere event forecasting to proactive risk-aware operation, by accumulating more data when the DBC of discharge is low and prediction is not accuracy enough, and utilizing the data to train better predictor adaptively for high DBC discharge. Together, these components form a comprehensive methodology, enabling resilient disruption prediction that is essential for the safe and sustainable operation of future tokamaks.

Effect of surface roughness on corrosion behavior of CLF-1 steel in magnetic field environments: increased surface roughness accelerates corrosion

Ye Li, Yi-Ming Lyu, Shufeng Zhang, Ning Liu, Jiejie Li, Yuxin Xiao, Guoping Yang, Shanliang Zheng

Hefei Comprehensive National Science Center (Anhui Energy Laboratory), Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Southwestern Institute of Physics

Tokamak discharge simulation for EAST by coupling METIS and free-boundary equilibrium code FBT

Wenyi Lu, Wenbin Liu, Jinping Qian, Miaohui Li, Ye Tao, Zhengping Luo, Dehong Chen, Rundu Hu, Feifei Long, Jian Liu, et al.

Chinese Academy of Sciences, University of Science and Technology of China, Dalian University of Technology, Shandong University

Fast and reliable discharge modeling is an essential tool for tokamak scenario development, as extensive simulations are required to explore the feasible operational space and translate physical targets into implementable actuator waveforms. In this work, a fast discharge simulator for Experimental Advanced Superconducting Tokamak (EAST) was developed by coupling the fast integrated tokamak modeling tool METIS with the free-boundary equilibrium code FBT from the MEQ (Matlab EQuilibrium) suite. METIS provides the evolution of the plasma profiles by self-consistently solving heat and particle transport with source profiles. The generated outputs are then used directly in FBT to computes the poloidal field (PF) coils currents needed in order to obtain a given plasma shape. The coupling strategy is based either on matching the free functions ( p ′ ( ψ ) and F F ′ ( ψ ) ) on the right-hand side of the Grad–Shafranov equation, or on matching global quantities such as the plasma current I p and stored energy W MHD . Both approaches are effective in ensuring consistency of the pressure and current-density profiles between the two codes. The last closed flux surface (LCFS) curve computed by FBT is fed back into METIS to update the LCFS, and METIS is then run again. The METIS – FBT iteration is repeated until convergence is reached. The results obtained with the equilibrium code FBT are first benchmarked against experimental data and reconstruction results available on EAST. The coupled METIS-FBT workflow is then assessed through a post-shot simulation of an radio-frequency heated EAST discharge, showing its ability to reproduce the main plasma evolution and generate inverse free-boundary PF-coil current trajectories consistent with experimental references. Its predictive scenario-design capability is further demonstrated through the design of a synthetic discharge scenario.