Table of Content

15 December 2025, Volume 45 Issue 4

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Nuclear Fusion Engineering

Studies on structural parameters influencing the heat transfer performance of HL-3 first wall by orthogonal experimental technique

LU Yong, CAI Li-jun, LIU Jian, XU Jie, LI Zai-xin, LIU Xiao-long, ZHAO Zhou, HL- First Wall Team

2025, 45(4):  373-380.  DOI: 10.16568/j.0254-6086.202504001

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Following the plasma parameters of the HL-3 tokamak gradually improving, the thermal loads that the first wall needs to withstand also gradually increase, especially the residual power of the first wall at the neutral beam shine-through area would be more than 1.0 MW·m^-2 and duration 5 s. Based on the thermal conduction and the convective heat transfer equations, numerical simulation and parameters optimization were conducted on key first wall structural design variables influencing the heat transfer performance, such as the graphite thickness, heat sink plate thickness, flow channel diameter and thermal contact conductance between combined surfaces in the high flux zones, using the orthogonal experimental technique. The results indicate that the above four factors are reversely correlated with the surface temperature of first wall for HL-3 tokamak pulsed plasma operation. Besides, the graphite thickness is the greatest impact on the heat transfer performance of the carbon-based first wall, followed by the thermal contact conductance between the graphite and the heat sink plate,while the thickness of the heat sink plate 316L and the cooling pipe diameter are relatively low impact on that.


Development of neutron flux measurement electronic system for fusion reactors

WEI Ling-feng, ZHAO Li, YUAN Guo-liang, YANG Qing-wei, LIU Zi-hao, ZHU Ren-jie, WEN Xin-cheng

2025, 45(4):  381-387.  DOI: 10.16568/j.0254-6086.202504002

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A neutron flux monitor (NFM) system is developed for fusion reactors with the operation parameters of International Thermonuclear Experimental Reactor (ITER), which can adapt to a wide range of neutron yields and has a certain radiation resistance capability. This system utilizes fission chambers to detect fusion neutrons and the back-end electronics are mainly composed of pre-amplifiers, signal processing units, high stability program-controlled power supplies, and temperature monitoring units. At present, the prototype of NFM system electronics has been developed, realizing the entire process of signal conditioning, discrimination,sampling, and processing. Partial testing work has been carried out on the HL-2A tokamak, and its result meets the design requirements.


Development of diamond disks for megawatt level gyrotron

LI Yi-feng, JIANG Long, AN Xiao-ming, GE Xin-gang, ZHANG Ya-lin, Tong Ting-ting, ZHANG Ping-wei, LIU Xiao-chen, Tang Wei-zhong, GUO Hui, SUN Zhen-lu

2025, 45(4):  388-395.  DOI: 10.16568/j.0254-6086.202504003

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The diamond disks for megawatt level gyrotron have been developed by microwave plasma chemical vapor deposition. Key parameters that affect the performance of diamond windows, such as compressive strength, thermal conductivity, coefficient of thermal expansion and dielectric loss tangent were characterized. The diamond disk with a diameter of 92 mm and a thickness of 1 mm can withstand a pressure of about 0.47 MPa. The thermal conductivity of diamond disk at room temperature reaches 20.1 W·cm⁻¹·℃⁻¹. The tanδ of 0.95 mm thick diamond disk is as low as 2.7×10⁻⁶. Finally, a low-microwave-loss diamond disk with a thickness of 1.8 mm was synthesized under optimized parameters and applied to a 140/105 GHz dual frequency gyrotron. A stable power output of 850 kW was achieved at 140 GHz with a window loss of approximately 0.11% and 760 kW was achieved at 105 GHz with loss of approximately 0.15%. The calculation results indicate that this 1.8mm diamond disk with tanδ=3.8×10⁻⁵ can be used for 1.5 MW long pulse gyrotron.


Study of resonant frequency feedback control system for EAST fishtail divertor magnet coil power supply

ZHOU Yu, SUN Hao-zhang, GUO Fei, HUANG Yi-yun

2025, 45(4):  396-403.  DOI: 10.16568/j.0254-6086.202504004

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The power supply of fishtail divertor magnet in EAST is multi frequency LC resonant power. In the experiment, the change of magnetic field will cause the current skin effect of the load magnet of the divertor,leading to the shift of resonant frequency and the attenuation of current. Therefore, the feedback control strategy based on the resonant frequency identification is adopted to ensure the output amplitude of the resonant current.As the resonant quality factors Q of the high frequency working point is larger than the low one, the current amplitude attenuation caused by the shift of resonant frequency at the high frequency point is much greater than the low point. The resonant current error will increase greatly when the frequency of working point increases due to the resonant frequency identification control with fixed scanning space and number. Therefore, a frequency scanning strategy based on multi-spaces is proposed to improve the output current feedback control accuracy. The effect of this frequency feedback optimal control strategy is verified by modeling and simulation.


The vacuum vessel electromagnetic load of high magnetic field compact tokamak during plasma vertical displacement event

CHEN Kai-jie, YANG Jin-hong, XI Xu-yao, WANG Wei-hua

2025, 45(4):  404-410.  DOI: 10.16568/j.0254-6086.202504005

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The high magnetic field compact tokamak (HFCT) has the advantages of small size, strong magnetic field, and high fusion gain. However, due to the strong current of plasma and external field coil in HFCT,the plasma current reduces rapidly during discharge disruption, resulting in the increase of electromagnetic load of vacuum vessel. This paper refers to SPARC Tokamak physics and engineering design, uses the TSC (Tokamak Simulation Code) program to simulate the discharge in the vertical displacement event (VDE) of HFCT, and the external coil current and plasma current simulated by TSC were imported into the three-dimensional ANSYS model of HFCT, and then electromagnetic load was analyzed based on the finite element model. The maximum magnetic field of HFCT vacuum vessel is 20.5 T, the maximum eddy current of the vacuum vessel module is 349MA·m⁻², the maximum electromagnetic force of the node is 54.231 kN, and the maximum first stress is 673 MPa,which is less than the allowable stress (800 MPa) of Inconel718 material. The engineering design meets the physical requirements. The analysis results can provide reference for the physical and engineering design of high magnetic field compact tokamak.


Numerical simulation of flat-type divertor module under high heat flux of 20 MW·m⁻²

MOU Nan-yu, FENG Ming-chi, LIN Qian-qian, , ZHENG Tai-xiong, YAO Da-mao

2025, 45(4):  411-417.  DOI: 10.16568/j.0254-6086.202504006

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As one of the key components of magnetic confinement fusion reactors, the divertor components must withstand highly cyclic heat, mechanical loads, and neutron irradiation, which will have a significant impact on the divertor lifetime and thus affect the actual operational safety of the fusion reactor. In this paper, structural,heat transfer and thermal fatigue analyses are carried out using the flat-type KW/ODS-Cu/RAFM divertor module,which is more suitable for the fusion reactor environment under the high heat flux of 20 MW·m⁻². The temperature and stress-strain distributions of the divertor module are obtained, and based on Manson-Coffin formula, the thermal fatigue lifetime of the divertor module is calculated. The simulation results indicate that under high heat flux of 20 MW·m⁻² and corresponding cooling conditions, the structure, heat transfer performance,and thermal fatigue resistance of the flat-type divertor meet the design requirements, which can provide data reference and engineering experience for the subsequent research of fusion reactors.


Research on the geometry algorithm of Monte Carlo particle transport based on direct CAD technology

LIU Ze-kang, YOU Peng-fei, CUI Wei-jie, LI Zai-xin

2025, 45(4):  418-424.  DOI: 10.16568/j.0254-6086.202504007

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Many traditional Monte Carlo transport programs use the Constructed Solid Geometry (CSG)method for modeling, which is time-consuming and labor-intensive for complex geometries. Therefore, it is necessary to find a method that can simplify the neutron modeling process. This paper explores the key technologies for Monte Carlo transport directly on the CAD model, such as geometric data structure, particle-solid collision algorithms, and the search for the next entity algorithm. Based on these technologies, a preliminary usable direct-method transport program was developed. Moreover, the bounding box acceleration algorithm was introduced to speed up the computation process. The geometric algorithm was validated by a simple model and compared with cosRMC. The results show that the direct method program agrees well with the cosRMC results,which confirms the correctness of the geometric algorithm. The direct method also demonstrates its advantages of high accuracy, intuitive display, and wide applicability by calculating the neutron flux on the surface of the human body model.


Manufacturing technology for HL-3 vacuum vessel support welding block assembly

WU Xiao-qiang, RAN Hong, ZHANG Dang-shen, RONG Hua

2025, 45(4):  425-429.  DOI: 10.16568/j.0254-6086.202504008

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The support welding block assembly is the key force component in the HL-3 vacuum chamber to connect adjacent sector segments and bear the support. According to the unique structure of hyperboloid and square window assembly, the key points of welding quality and deformation control, machining of hyperboloid and ultra-high vacuum step sealing surface, and welding of supporting welding block assembly with vacuum chamber are analyzed. By designing and manufacturing process equipment, processing three-dimensional curved groove of support block, taking post-welding processing, monitoring deformation during processing and timely adjusting the inner and outer processing processes and other construction process methods and process parameters,the problems of large-thickness welding technology and welding deformation control of the support welding block assembly, the machining technology of the support welding block assembly and the high quality requirement of the ultra-high vacuum step sealing surface, and the technical problems of the support welding block assembly and the vacuum chamber are overcome. Now the HL-3 plasma discharges have been successfully realized, and the related machining and welding technology has been verified.


Plasma Physics

Statistical studies of density operating space for ohmic discharges on HL-2A tokamak

LIU Yan-min, LONG Ting, TIAN Wen-jing, ZHAO Ju, LI Yong-gao, LI Bo, WANG Zhan-hui, CHEN Wei, XU Min

2025, 45(4):  430-436.  DOI: 10.16568/j.0254-6086.202504009

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Based on the ohmic discharge experimental database of the HL-2A tokamak since 2017, the density operating space of ohmic discharge is statistically analyzed and experimentally studied. The results show that the Greenwald density fractio f_GW≡n₀/n_G of the operating space is between 0.11 and 1.40. The siliconization wall conditioning is beneficial to improve the maximum density before the density limit. The highest density(~6.9×10¹⁹ m⁻³, ~1.40nG) of the operating space is achieved by gas puff fueling. The degree of density peaking under different fueling methods is analyzed. It is found that there is no significant difference in the density peaking factor under the four fueling conditions (no fueling, gas puffing, supersonic molecular beam injection, gas puffing + supersonic molecular beam injection), all of which are about 2.0. The relationship between the plasma confinement time and the density under different currents is studied. The phenomenon of transition from linear ohmic confinement (LOC) to saturated ohmic confinement (SOC) and the increase of density peaking during the transition are observed.


Experimental observation and investigation of fluctuation-induced inward transport in HL-2A NBI heated L-mode plasma

WANG Tian-xiong, WU Jie, LAN Tao, DING Wei-xing, WU Jia-ren, XU Min, NIE Lin, LIU A-di, XIE Jin-lin, LIU Wan-dong, ZHONG Wu-lü, ZHUANG Ge

2025, 45(4):  437-445.  DOI: 10.16568/j.0254-6086.202504010

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By employing Langmuir probe arrays at the boundary of L-mode plasma in the HL-2A device, the key parameters such as plasma density, temperature and electric potential were precisely measured. Subsequently,the characteristics of boundary fluctuation-induced particle transport were calculated, and their spectral features and the reversal law of fluctuation-induced transport direction were thoroughly analyzed using frequency-domain decomposition techniques. The research reveals that local poloidal flow shear exhibits a weak correlation with inward fluctuation transport, whereas broad-spectrum low-frequency fluctuations below 40 kHz dominate theinward particle transport. The reversal of transport direction is governed by an anti-correlation in the cross-phase between density fluctuations and velocity fluctuations. Based on the frequency-temporal evolution of fluctuation transport, the transport process can be divided into two stages: in the initial stage, the amplitude of outward fluctuation transport gradually decays, while fluctuations in certain frequency bands begin to transport inward.The interaction between these components suppresses the total transport flux. As the inward transport component accumulates and eventually surpasses the outward component, the total flux reverses to inward, leading to a significant improvement in particle confinement during this stage. Further analysis indicates that the fluctuation-induced heat conduction flux exhibits an inward trend during both the suppression and reversal phases of the fluctuation particle flux. Moreover, the onset of inward heat transport lags noticeably behind the reversal time of the fluctuation particle flux. This study presents the first observation of broad-spectrum low-frequency fluctuation-induced inward transport in a toroidal magnetic confinement device, unveils the physical mechanism behind the reversal of fluctuation transport direction, and provides critical experimental support and guidance for optimizing particle confinement performance in magnetically confined plasma devices.



Study of negative triangularity configuration on HL-3 tokamak

LI Ze-meng, SUN Ai-ping, WANG Yuan-zhen, LI Zheng-ji, WANG Zhuo, LIU Yi

2025, 45(4):  446-452.  DOI: 10.16568/j.0254-6086.202504011

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The equilibrium code EFIT is used to research the negative triangularity(NT) plasma configuration with different elongation (κ) and negative triangularity (δ) in the HL-3 tokamak, and GATO code is employed to perform ideal magneto hydrodynamic (MHD) stability analysis of these configurations as well as the influence of κ and δ on equilibrium stability. The EFIT research results show that the equilibrium configurations of 1 MA plasma current can be realized with elongation κ from 1.4 to 1.8 and negative triangularity δ from -0.4 to -0.7 under present magnetic field coil conditions in the HL-3 tokamak. GATO is used to analyze the n=1 kink mode, which has a decisive influence on MHD instability in tokamak plasma. The analysis results exhibit that the plasma elongation and the triangularity significantly affect the MHD instability, and the larger the plasma elongation, the more stable the plasma equilibrium configuration. In contrast, the plasma equilibrium become more instabilities with increase of the absolute value    |δ|.


Study of the influence of EAST high loop-voltage discharge on plasma MHD equilibrium energy

WU Xiao-dong, GAO Xiang, QIAN Jing-ping

2025, 45(4):  453-458.  DOI: 10.16568/j.0254-6086.202504012

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In EAST tokamak high loop-voltage discharges, some macro-parameters including plasma MHD equilibrium energy (W_mhd) are out of reasonable range, which are calculated through plasma equilibrium reconstruction. Induced vessel eddy can make W_mhd be unreasonable. To reduce eddy influence on magnetic signals and correct W_mhd, the eddy distribution model is constructed using poloidal coil current rate of change.Reconstructed eddy current distribution is verified by EAST test discharge data, after that, high loop-voltage plasma macro-parameters are calculated by using equilibrium reconstruction with eddy current. And the W_mhd is consistent with W_dia that is computed according to diamagnetic signal. The experimental results show that the influence of eddy current on W_mhd can be reduced by reconstructing the distribution of high induced current in the vacuum chamber.


The effect of dynamical lithium powder injection on fuel recycling in EAST

WANG Zhe, WU Kai, HUANG Yao, XU Wei, SUN Zhen, HUANG Ming, ZHOU Zhi-tai, GUAN Yan-hong, CHEN Yue, ZUO Gui-zhong, HU Jian-shen

2025, 45(4):  459-466.  DOI: 10.16568/j.0254-6086.202504013

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The control of fuel particle recycling during plasma discharges in magnetic confinement fusion devices is crucial for the steady operation of long-pulse. In order to explore the control effect of lithium powder injection at different flow rates on fuel recycling, the lithium powder control system was upgraded to allow for real-time, active adjustment of lithium powder flow rates during single plasma discharge. Tabletop test results showed a linear relationship between lithium powder flow rate and control voltage. Based on this, experiments were conducted at EAST to dynamically vary the lithium powder flow rate during a plasma discharge to control fuel recycling. The results demonstrated that the new lithium powder control system can dynamically adjust the lithium powder injection rate in real time during a plasma discharge. Moreover, increasing the lithium powder flow rate further reduced the neutral gas pressure and the D_α emission intensity in the divertor region. This confirmed that increasing the lithium powder injection rate can enhance the control of fuel recycling. This study provides support for future feedback control experiments on fuel recycling during long-pulse, high-performance plasma discharges at EAST.

Research on the mechanism of the electromagnetic emission bursts suppressed by lower hybrid wave in tokamak plasmas

WANG Liu-qing, HU Ye-min, BAI Shu-hang, LIU Yong

2025, 45(4):  467-474.  DOI: 10.16568/j.0254-6086.202504014

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Intense intermittent plasma frequency emission bursts near the electron plasma frequency (ω_pe) with high-energy narrowband features have been observed in many tokamak plasmas, related to the beam instability caused by a suprathermal tail. However, the ωpe emission bursts are not seen during lower-hybrid current drive (LHCD) experiment, despite the presence of a suprathermal electron tail, and tend to appear almost immediately after the LHCD is turned off. So far, there is no physical model to give reasonable explanation for this phenomenon. In this paper, a theoretical model based on four-wave interaction under the fluid approximation is proposed. In this model, the lower-hybrid wave as a pump wave, interacts with a beam-driven wave and itself sidebands, leading to parametric damping. The nonlinear dispersion relationship of the four-wave interaction is analytically derived. The spatial distribution of the beam-driven instability near the magnetic axis of tokamak plasma is given by solving the nonlinear dispersion relation numerically. The simulation results reveal that when the power of the pump wave is relatively low, the growth rates of the beam-driven instability decrease significantly with the increase of pump wave amplitude until it becomes negative, which indicates that lower-hybrid wave can effectively reduce the beam instability, and then suppress the occurrence of ω_pe emission bursts. The simulation results are consistent with the experimental ones.



Numerical simulation study on the impact of tokamak safety factor on sawtooth mode

XIAO Zheng, YANG Jin-hong, REN Zhen-zhen, CHU Jia-xuan, ZHANG Pei-jie, KUANG Jun, WANG Wei-hua

2025, 45(4):  475-482.  DOI: 10.16568/j.0254-6086.202504015

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This paper utilizes the kinetic-magnetohydrodynamic (MHD) hybrid model program M3D-K to numerically simulate and study the effects of safety factor and resistivity on sawtooth instability. The simulation results show that: (1) The linear growth rate decreases with an increase in the q=1 surface position, but it increases with q=1 surface magnetic shear and resistivity. (2) The sawtooth period increases with q=1 surface position, but it decreases with q=1 surface magnetic shear and resistivity. (3) The sawtooth amplitude increases with q=1 surface position and resistivity. It initially increases then decreases with the q=1 surface magnetic shear. These results indicate that to control the characteristics of sawtooth oscillation with high frequency and small amplitude,measures such as reducing the q=1 surface position or increasing its magnetic shear can be taken, while considering the combined influence of resistivity.


Experimental investigation of cesium transport enhancement in radio-frequency driven negative ion source

XIE Wei-min, GENG Shao-fei, ZHOU Bo-wen, ZHANG Xian-ming, ZHANG Yu-xuan, ZOU Gui-qing, ZHANG Song, HUANG Li-ping, ZHAO Miao, LEI Guang-jiu

2025, 45(4):  483-488.  DOI: 10.16568/j.0254-6086.202504016

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In order to enhance the transport of cesium vapor from the cesium nozzle to the plasma electrode in a radio-frequency driven negative hydrogen ion source, the cesium feeding process on a radio-frequency driven negative hydrogen ion source was experimentally investigated. In the experiment, elemental cesium was applied as the source of cesium vapor, and cesium gun was fed into the negative hydrogen ion source. A spectrometer was used to monitor the intensity of the cesium emission spectrum (852 nm) near the plasma electrode to assess the cesium vapor content. In the experiment, the emission spectrum intensities of cesium near the plasma electrode are compared for the diffusion chamber of the negative ion source under good cooling and the active heating conditions. The results show that the active heating of the diffusion chamber of the negative ion source can greatly enhance the transport of cesium. By comparing the effect of two different types of cesium nozzles (straight and side nozzles), it is found that the straight nozzles are difficult to produce uniformly distributed cesium deposition on the plasma electrode, but the combination of the side nozzles and the active heating of the diffusion chamber can make the cesium deposition on the surface of the plasma electrode more uniform.