Recent Publications

Progress of understanding the effect of helium concentration on ion-electron collision and energy confinement on EAST

Qian Wang, Bin Zhang, Xianzu Gong, Jinping Qian, Xiaoming Zhong, Kedong Li, Wenbin Liu, Tianqi Jia, YuTong Guo, Wei Wang, et al.

Helium plasma experiments conducted on different tokamaks all demonstrate that the energy confinement are lower than those of deuterium plasmas under similar operation conditions. However, the origin of the difference in confinement between helium and hydrogen istopes remains unclear. To understand the influence of helium concentration, which leads to the variation of ion mass and charge number, on energy confinement, new helium experiments were conducted in the EAST tokamak with dominant electron heating and a tungsten divertor in 2025. A notable dependence on both ion mass and charge number is observed in the effective diffusion coefficient, as predicted by the gyro-bohm scaling χgB ∝ρi . The higher energy confinement time is observed with a lower ion mass. Conversely, when both the ion mass and charge number are increased, the energy confinement time is found to be similar. Power balance and transport analyses indicate that the ion-electron collision, significantly influenced by the variation of ion mass and charge number, appears to play a dominant role in regulating ion-scale turbulence in helium H-mode discharges. Furthermore, linear electromagnetic gyrokinetic simulation reveals that the Electron Temperature Gradient (ETG) turbulence was suppressed through the enhancement of ion-electron energy exchange in L-mode discharges. Consequently, it is crucial to take into account the role of electron-ion collision/energy exchange to understand the influence of ion mass and charge number on energy confinement. These results contribute to a better understanding of the transport characteristics in multi-ion-component plasma.

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.

Real-time multi-harmonic signal processing system based on FPGA+ARM architecture for MSE diagnostic on the EAST tokamak

Dongmei Liu, Biao Xiang, Jia Fu, Zhen Cheng, Ziyi Chang, Qian Liu

Hefei University of Technology, Institute of Plasma Physics, CAS

DKEKAN: A single-parameterized KAN surrogate for Drift Kinetic Equation Toward Fast Neoclassical Toroidal Viscosity Torque Modeling in Tokamaks

Jinpeng Huang, Xingting Yan, Mingyu Zhang, Nana Bao, Zixuan Song, Yuetao Meng, Weiyong Zhou, Youwen Sun

Anhui University, Hefei Institutes of Physical Science Chinese Academy of Sciences

The neoclassical toroidal viscosity (NTV) torque is a critical driver of toroidal rotation in tokamaks, profoundly influencing plasma stability and performance. Consequently, incorporating NTV effects is essential for modern integrated modeling frameworks that aim to self-consistently unify multiple physical processes. However, the high computational cost of NTV modeling precludes its self-consistent integration within such frameworks. This bottleneck arises because NTV calculation requires solving its governing equation--the drift kinetic equation (DKE)--in high-dimensional phase space. To address this issue, this study develops DKEKAN, a single-parameterized Kolmogorov-Arnold Network (SKAN) surrogate for solving DKE, to realize fast NTV modeling in tokamaks. The research process consists of the following steps: Firstly, a large dataset mapping DKE equation parameters to solutions is generated based on first-principle simulations under plasma parameters of the Experimental Advanced Superconducting Tokamak (EAST); Secondly, a surrogate model for solving DKE is developed based on the SKAN framework, which also incorporates a modular expert network design; Finally, the DKEKAN surrogate model is integrated with the NTV modeling framework to realize fast NTV calculation. With its physics-grouped expert layer and SKAN backbone, DKEKAN outperforms the tested MLP, KAN, and neural-operator baselines in overall prediction accuracy, while reducing the standalone DKE-solving time from 35.85s to 3.74s, corresponding to a speedup of approximately 9.6x, and reducing the total coupled NTVTOK runtime from 38.24s to 5.58s, corresponding to an overall speedup of approximately 6.9x. This work effectively overcomes the computational bottleneck in NTV simulations, thus supporting further integrated modeling that incorporates NTV effects.

Progress of LHCD experiment at 4.6 GHz towards long-pulse and high-power operation on EAST

Miaohui Li, Weiwei Zhang, Junlin Chen, Chenbin Wu, Bojiang Ding, Mao Wang, Liang Liu, Lianmin Zhao, Wendong Ma, Yong Yang, et al.

Chinese Academy of Sciences - Hefei Institutes of Physical Sciences, Institute of Plasma Physics Chinese Academy of Sciences, CEA

Recent achievements of lower hybrid current drive (LHCD) experiment at 4.6 GHz towards long-pulse and high-power operation on EAST tokamak are reported. The duration of long-pulse plasmas has been extended to 1056 s with 1.1 MW LH power in I-mode and 1066 s with 0.92 MW in H-mode. The operational domains in plasma current and line-averaged density for fully non-inductive discharges with LH alone and with the combined LH and electron cyclotron (EC) waves are presented. The dependence of LHCD efficiency on plasma density in both L- and H-mode discharges characterized by residual loop voltage Vloop = 0 is quantified. It is found that the LHCD efficiency is improved significantly by EC heating due to the increase of electron temperature. The dominant issues in long-pulse and high-power operation are summarized and discussed, including the power coupling imbalance, the hot spot and arc events in front of the antenna, and the deteriorated plasma heating effect with high LH power. Finally, prospects with a new 4 MW LHCD system at 4.6 GHz which is under development are given.

The role of data quality and alignment in cross-tokamak disruption prediction

Chengshuo Shen, Wei Zheng, Fengming Xue, Xinkun Ai, Bihao Guo, Dalong Chen, Zhongyong Chen, Yong Hua Ding

Huazhong University of Science and Technology, Institute of Plasma Physics, Chinese Academy of Sciences

Reliable disruption prediction across tokamaks is needed for next generation devices such as ITER, SPARC, and BEST, where disruptive target-machine data will be scarce by design. For a transferred predictor, target performance is limited by both the source-domain error and the mismatch between the source and target feature distributions. We use this distinction to revisit our previous J-TEXT to EAST study and to add three components for few-shot and zero-shot operation. An upgraded physics-guided feature extraction (PGFE-U) reduces geometry-dependent differences in Mirnov, soft x-ray and absolute extreme ultraviolet array features. A floating labelling strategy (FLS) replaces a fixed pre-disruption window with shot-dependent precursor onset labels. An estimation of the feature distribution (EFD) supplies target-machine z-score statistics from outside the classifier training set. With the supervised CORAL (S-CORAL) backbone, the area under the receiver operating characteristic curve (AUC) on the same EAST test set reaches 0.957 in a few-shot setting using only 10 disruptive EAST discharges, whereas the previous work required 110 EAST discharges to reach 0.890, and the partial AUC over false positive rates up to 10% (pAUC) rises from 0.428 to 0.858. The zero-shot AUC reaches 0.892 with no EAST discharge used for classifier training, against 0.592 for the same model normalised with J-TEXT statistics, and the zero-shot pAUC is 0.619 against 0.084. The EFD statistics are estimated from real EAST shots; a per-feature Monte-Carlo scan shows that the sensitivity is concentrated in a few global discharge parameters, the quantities most reliably estimated at the design stage. Shapley additive explanation (SHAP) based attribution shows that both transferred models preserve most of the qualitative feature-to-disruption trends of the abundant-data baseline. These results indicate that improving feature quality, labels and normalization statistics can recover a large fraction of abundant-data performance when target-machine shots are limited.

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

Effects of strike point location on divertor detachment in EAST predicted by machine learning

Bingqi Guo, Chen Zhang, Haopan Du, Yilin Wang, Xuele Zhao, Mingzhou Zhang, Dezhen Wang, Chaofeng Sang

Dalian University of Technology

Divertor detachment is critical for controlling particle and power exhaust in tokamaks, while the strike point (SP) location strongly influences divertor plasma and heat loads on the target. To overcome the high computational cost and limited scalability of conventional SOLPS-ITER parameter scan simulations, a machine-learning surrogate modeling framework is developed for studying detachment in the EAST divertor. Based on SOLPS-ITER simulations, a database is constructed spanning variations in input power, upstream density, and geometric parameters. Four surrogate models are developed: single-task fully connected neural network (NN-ST), multi-task fully connected neural network (NN-MT), single-task convolutional neural network (CNN-ST) and multi-task convolutional neural network (CNN-MT). These models enable rapid prediction of key edge-plasma parameters, including electron temperature, electron density, ion temperature, ion density, and heat flux density. Among them, the CNN-MT model exhibits the highest predictive accuracy, achieving R^2 > 0.8 and low normalized RMSE across all outputs. High-resolution parameter scans based on the optimal model indicate that the horizontal target near the corner obtains detachment at lowest density thresholds while satisfying the engineering heat flux limit (~10 MW m-2), therefore it constitutes a more optimal SP operating window. Furthermore, the Ordinary least-squares (OLS) method is employed to separately obtain scaling relationships for the detachment density threshold and SP location, as well as for neutral particle density and electron temperature. These results reveal the primary physical mechanisms by which geometry closure and neutral accumulation enhance volumetric losses facilitate detachment. This multi-task surrogate framework provides an efficient, physics-informed tool for high-fidelity divertor operation optimization, supporting the design and control of future high-power fusion devices.

Impacts of RMP toroidal phase on ELM mitigation and impurity control in EAST

Zihao Gao, Zhe Liang, Zixuan Wen, Jingtao Wang, Dezhen Wang, Shuyu Dai

Dalian University of Technology

An integrated modelling study, coupling the MARS-F code with the EMC3-EIRENE code, has been performed to examine the impacts of the toroidal phase (Δϕ) of resonant magnetic perturbation (RMP) on edge-localized mode (ELM) mitigation and impurity control in EAST. The modelling shows that the plasma response fundamentally reshapes the phase dependence of the edge resonant perturbations, with the maximum absolute response magnitude at Δϕ ≈ 90° and the minimum at Δϕ ≈ 270°. According to the edge resonant field criterion, amplification-dominated phases at Δϕ ≈ 90° are expected to be favorable for ELM mitigation, whereas screening-dominated phases at Δϕ ≈ 270° show weak performance. In the same phase scan, reduced tungsten (W) target erosion, enhanced edge screening, and decreased core accumulation are found to coincide with the same phase window for ELM mitigation. This finding indicates that appropriate RMP phasing could create a favorable regime for ELM mitigation and simultaneously reduced W accumulation, offering a practical guideline for toroidal phase optimization in RMP operation.

SafeDivertor: Faithful Divertor Heat Flux Reconstruction from Macroscopic Plasma State Signals via Time-Frequency Prior Exploitation

Hao Si, Zehua Chen, Qingquan Yang, Xiao Wang, Dengdi Sun, Wanli Lyu, Gaoting Chen, Guosheng Xu, Hang Su, Jin Tang, et al.

Divertor heat-flux analysis is essential for understanding plasma-wall interactions and protecting plasma-facing components in magnetic-confinement fusion devices, while conventional infrared-based inversion is usually performed after discharge and requires heat-conduction modeling with device-specific material properties, divertor geometry, and boundary conditions. Rather than accelerating this conventional infrared-based inversion paradigm, we introduce a new online-oriented signal-based reconstruction paradigm that directly reconstructs time-resolved radial heat-flux profiles from multi-source macroscopic plasma-state signals available during discharge. To enable systematic study of this task, we construct \textbf{DivMPS2HF}, a multi-source discharge dataset that provides the data foundation and benchmark for signal-based divertor heat-flux reconstruction. We further propose \textbf{SafeDivertor}, a task-driven framework designed to address the key challenges of signal-based heat-flux reconstruction. It employs physical prior-aware initialization to provide radial-distribution guidance for target channels, input perturbation to reduce over-reliance on specific heterogeneous signals, spectral-aware reconstruction optimization to exploit time-frequency priors and preserve transient dynamics, and progressive training to stabilize the optimization of these complementary objectives. Experiments on DivMPS2HF demonstrate that SafeDivertor achieves the best overall performance among the evaluated time-series baselines across all five metrics, establishing a new performance benchmark for signal-based divertor heat-flux reconstruction. The source code will be released on https://github.com/Event-AHU/OpenFusion

Multisampling Linear Active Disturbance Rejection Control with an Improved Extended-State Observer for the EAST Fast Control Power Supply

Haihong Huang, Jiacheng Wang, Haixin Wang

Hefei University of Technology

Effects of fusion-relevant gas atmospheres and pressures on hydrogen isotope characterization for fuel-retention diagnostics by LIBS

Hao Sun, Zhenhua Hu, Jian Wu, Ying Zhou, Xinyu Guo, Huace Wu, Fang Ding, Hai-Shan Zhou, Xingwen Li, Jiangang Li

Xi'an Jiaotong University, Institute of Plasma Physics,Chinese Academy of Sciences, Hefei Comprehensive National Science Center, Chinese Academy of Sciences Hefei Institutes of Physical Science

Fuel retention in plasma-facing components (PFCs) affects the operational efficiency and safety of fusion devices. However, detection of retained fuel by Laser-Induced Breakdown Spectroscopy (LIBS) remains challenging because the Hα and Dα Balmer lines commonly used for hydrogen-isotope identification are separated by only about 0.18 nm, making their discrimination highly sensitive to fusion-relevant ambient conditions. In this study, LIBS was employed to systematically investigate Hα/Dα discrimination on real EAST-exposed graphite tiles under various simulated ambient conditions. Depth-resolved measurements showed that the second laser pulse generally provided a more favorable Hα/Dα emission ratio and improved fitting quality, with the noise-normalized RMS residual decreasing from 3.6 to 1.26 compared with the first pulse. Meanwhile, time-resolved plume analysis helped explain the role of ambient environments in governing spectral broadening and isotope discrimination. At 100 Pa, the initial plume-height expansion rates within 200 ns were 15.6, 14.2, and 8.0 km/s in He, air, and Ar, respectively, revealing pronounced gas-dependent differences in plasma expansion. Combined spectral and plume analyses showed that vacuum provided high spectral resolution but suffered from a relatively short plasma lifetime. Within the investigated ambient parameters, a helium atmosphere at a moderate pressure of 100 Pa offered the most favorable balance between plasma lifetime and spectral resolution. In contrast, higher pressures or denser gases tended to enhance Stark broadening, leading to more severe peak overlap and a narrower effective discrimination window. The effective discrimination window was evaluated using the resolution factor Rs, with Rs ≈ 1.5 taken as a reference for baseline separation. These findings provide practical guidance for LIBS-based fuel retention diagnostics under EAST-relevant conditions.

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)

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

Institute of Plasma Physics, Chinese Academy of Science, University of Science and Technology of China, State Key Laboratory of Nuclear Physics and Technology

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.

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.

First Observation of Fishbone-Driven Zonal Flows with Fine Reversed Structure in Tokamak Plasmas

Liutian Gao, Yuehao Ma, Huishan Cai, Adi Liu, Bin Zhang, Ming Xu, Haiqing Liu, Liqing Xu, Chu Zhou, Feifei Long, et al.

We present the first direct experimental observation of fishbone-driven zonal flows in the core of the EAST tokamak. In contrast to the global pattern predicted by previous models and simulations based on the energetic-particle-expulsion mechanism, the observed flows exhibit a fine-scale, radially reversed structure inside the q = 1 rational surface. The flow rises faster and saturates earlier than the fishbone within a single burst, indicating that a beat-driven nonlinear process dominates the early stage rather than the energetic-particle-expulsion mechanism. Global nonlinear gyrokinetic simulations quantitatively reproduce the observed radial profile and reveal that this structure arises from the cancellation of comparable but opposite contributions from thermal ions and electrons. This cancellation mechanism is not captured in previous theoretical frameworks. These findings establish that the fishbone can generate sheared flows with a distinct radial topology, offering a promising pathway for regulating turbulence and improving core confinement.

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.

Investigation of Dynamic Radiation Belt Characteristics and Mechanisms in EAST Tokamak

Bingcheng Qi, Fang Ding, Qing Zhang, Tonghui Shi, Yue Yu, Jinju Yang, Jingsheng Yuan, Lin Yu, Lifeng Yang, Minrui Wang, et al.

Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, University of Science and Technology of China, Anhui University, Anhui University of Science and Technology

A dynamic radiation belt—exhibiting characteristics of intense radiation, high density, and low electron temperature, akin to multifaceted asymmetric radiation from the edge (MARFE)—was observed and investigated in the Experimental Advanced Superconducting Tokamak (EAST). This belt forms in the divertor region with impurity injection and subsequently migrates towards the X-point and the high-field side (HFS) of the plasma boundary after the transition from H mode to L mode (H-L transition) or confinement degradation. The belt traverses the inner mid-plane, reaches the opposite divertor, and subsequently retreats back to its initial divertor location. This migration is accompanied by a concurrent evolution of poloidal asymmetry in key plasma parameters, including electron density, radiation profiles, neutral pressure, and wall heat load distribution. The migration of the radiation belt is closely related to the evolution of the edge neutral pressure. Reversing the toroidal magnetic field (BT) direction inverts both the initial position of the radiation belt and its trajectory. The reversal of neutral pressure asymmetry between upper and lower divertors following BT direction change demonstrates the role of B-direction-dependent drift effects. Furthermore, the migration of the radiation belt is consistently accompanied by localized fluctuations with frequencies up to 10 kHz in both plasma radiation and density signals. During belt migration, the magnetic oscillations transition from a broadband spectrum to a coherent narrowband emission, identified as an m/n=2/1 magnetohydrodynamic (MHD) instability mode. The frequency of the mode is positively correlated with the distance of the radiation belt from its initial position. Excessive increases in the magnetic oscillation frequency typically precede plasma disruptions, which may suggest a critical link between oscillation spectral characteristics and disruption onset mechanisms.