Nuclear Fusion and Plasma Physics

Research on stress mitigation for toroidal field coils of a high magnetic field tokamak

WANG Fu-jia, CHEN De-hong, XU Guo-sheng, WU Jia-rong, WAN Bao-nian

2024, 44(1): 1-6. DOI: 10.16568/j.0254-6086.202401001

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In response to the problem that a high magnetic field tokamak toroidal (TF) coils are too excessive stress to be sustained by the structural and conductor materials, according to the principle for forming hydrostatic stress, the effectiveness for reducing the stress of inner leg of TF coils of a high magnetic field tokamak has been carried out. The stress reduction of TF coil magnet with external supporting structure in a liquid nitrogen cooled high magnetic field copper conducting tokamak was studied by using COMSOL finite element software. The thickness and volume of external supporting structure required were compared for beryllium copper alloy and oxygen free copper as conductor materials.

Establishment of datum network and component positioning measurement of HL-3 tokamak

LAI Chun-lin, LIU Jian, CAI Li-jun, LIU Kuan-cheng, ZHANG Long, HL- Development Team

2024, 44(1): 7-12. DOI: 10.16568/j.0254-6086.202401002

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According to the installation accuracy requirements of HL-3 assembly design, it is necessary to establish a high-precision datum network and adopt advanced measuring equipment such as laser tracker to measure spatial position of the installed components. The established datum network realizes the maximum uncertainty of the spatial coordinates of the reference points in the network to be 0.133mm. Especially, during the installation of vacuum vessel, temporary first wall/limiter and other components, positioning measurement, data feedback, installation and adjustment are carried out to achieve installation coaxiality of vacuum vessel in Æ1.84mm, which meets the coaxiality within Æ3mm; elevation deviation is between –0.08 and +0.136mm, which meets the elevation deviation within ±1mm. The maximum deviation of temporary first wall/limiter installation is +1.9351mm and the minimum deviation is –1.8337mm, which meets the surface position error of each module in ±2mm. The establishment of datum network and high-precision positioning and measurement of components ensure high-quality construction of HL-3 tokamak.

Establishment of measuring datum for the EXL-50 spherical tokamak

YANG Yuan-ming, CHEN Bo, BAI Ren-hua, SONG Yun-yang, WANG Yu, JIA Peng-mei, ZANG Hong, BO Xiao-kun, YUAN Bao-shan

2024, 44(1): 13-18. DOI: 10.16568/j.0254-6086.202401003

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During the installation of the EXL-50 spherical tokamak, a measuring reference network was established by placing reference points in the hall of the tokamak, and a global coordinate system was built by using the solenoid axis of the vacuum vessel and the middle plane, and the tokamak reference network was constructed. By using this reference network, accurate and consistent positioning reference can be provided to complete the subsequent installation of vacuum vessel, toroidal field coil, poloidal field coil, limiter and divertor. The installation results meet the design requirements.

Research on high-precision assembly technology for the vacuum vessel sector of the future fusion reactor

JI Hai-biao, MA Jian-guo, LIU Zhi-hong, WU Jie-feng, WU Hua-peng, FAN Xiao-song, ZHONG Ya-qi, LIN Xiao-dong, GAO Xiang

2024, 44(1): 19-23. DOI: 10.16568/j.0254-6086.202401004

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In the high-precision assembly for the CRAFT 1/8 vacuum vessel sector, the splice plate was designed to compensate the assembly error between sectors, its manufacturing scheme was introduced, and the on-line milling system was developed to ensure high-precision assembly on site.

Development of a lanthanum hexaboride plasma source in EAST-CTI test platform

MENG Fan-wei, ZHANG Xiao-hui, HU Guang-hai, KONG De-feng, YE Yang, HUANG Yan-qing, QI Mei-bin, ZHAO Zhi-hao, LI Bo, DONG Qi-long

2024, 44(1): 24-29. DOI: 10.16568/j.0254-6086.202401005

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In order to facilitate and study in depth the evolution of the plasmoid generated by the compact torus injection (CTI) system in the plasma, a large-size, uniform lanthanum hexaboride plasma source was designed to generate magnetized high-density plasma. The cathode of the plasma source is indirectly heated by a tungsten filament to reach the operation temperature, and the cathode temperature can reach up to 1800°C. The anode is a high-temperature resistant, 50% transmittance molybdenum mesh with an axial spacing to the cathode of 1m. A bias voltage of 40~200V is applied between the cathode and the anode, and the electrons emitted from the cathode collide and ionize with a neutral gas to produce a steady-state magnetized plasma column with length of 1m and diameter of 100mm. Discharge performance of the source was tested and the related plasma parameters were given in laboratory experiments. The experimental results show that the measured argon plasma electron density can reach the order of 10¹⁸m^‒3with an electron temperature of about 8eV at a cathode emission current density of 1~2A·cm^‒2, and the cathode emission current density can reach a maximum of 8.5A·cm^‒2 by increasing the bias between the cathode and anode, and the plasma parameters are similar to those at the tokamak boundary. The lanthanum hexaboride plasma source meets the design specifications and can use in the EAST-CTI system.

Design of intelligent energy management system for negative ion source neutral beam injector

DING Jian, LI Yi-bin, JIANG Cai-chao, SONG Shi-hua, LIU Sheng, DUAN Lian, XU Kang-xing, LIU Zhi-ming, XIE Yuan-lai

2024, 44(1): 30-35. DOI: 10.16568/j.0254-6086.202401006

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A set of intelligent energy management system has been designed to ensure the stability and quality of power supplied to the negative ion source neutral beam injection (NNBI) system. This system utilizes a Siemens programmable logic controller (PLC) in combination with a distributed input/output (I/O) system that continuously monitors the operational status of the power supply system circuits. The Modbus communication protocol is implemented to interact with multifunctional energy meters for this purpose. Additionally, an intuitive human-machine interface design has been incorporated into the system to provide the experiment operators with a convenient tool to assess the system status directly. This intelligent energy management system has a certain degree of compatibility and scalability. The test results show that the system is stable and reliable, and effectively fulfills the requirements for the NNBI system.

Preliminary design and thermal analysis of CFETR expansion plate cryostat thermal shield

CHAI Yong-sheng, CUI Li-min, GE Jian, CHEN Zhao-bo, ZHANG Long, PANG Xue-wei

2024, 44(1): 36-42. DOI: 10.16568/j.0254-6086.202401007

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In order to further reduce the thermal load of the superconducting magnets in the tokamak, the expansion plate structure is applied to the Cryostat Thermal Shield (CTS), which replaces the traditional tube-sheet CTS structure. The expansion plate structure is a sandwich space structure that allows coolant to flow between the shielding plates. 304LN stainless steel is selected as the CTS material, molding-welding is selected as the CTS forming method, and helium gas is selected as the coolant. The optimal solder joint parameters and shielding board parameters are determined. Firstly, the heat flux density on the surface of the CTS is calculated according to the principle of radiant heat, and then the thermal analysis of the CTS is carried out by using the fluid simulation software CFX to obtain the temperature of the CTS plates and the pressure drop between the inlet and outlet. The analysis shows that the temperature distribution of the expansion plate CTS is uniform, the temperature is significantly lower than that of the tube-sheet CTS, and then the superiority of the expansion plate CTS structure is proved theoretically.

Numerical study on current carrying capacity and AC loss characteristics of the HTS 6-channel conductor

MU Yong-chun, ZHANG Li-li, LIU Ji-wei, YANG Xin-sheng, JIANG Jing

2024, 44(1): 43-50. DOI: 10.16568/j.0254-6086.202401008

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In order to satisfy the magnet system’s requirements of large-current, high-magnetic field and good mechanical characteristics in the future fusion device, a 6-channel TSTC-CICC HTS conductor is proposed in this paper. Based on the self-consistent model and T-A formulation, the current carrying capacity and AC loss characteristics of the HTS 6-channel conductors for three structures were numerically studied by 2-dimensional finite element method，the stacking direction of the tapes in structure 1 is perpendicular to the radial direction, the stacking direction of the tapes in structure 2 is parallel to the radial direction, and the stacking modes of the tapes in structure 3 are perpendicular to the radial direction and parallel to the radial direction. From the calculated results, it can be seen that the critical current of the conductor-1 is the maximum. The current of the conductor-2 is the minimum and the current of the conductor-3 is the medium. In the low field, the isotropy characteristics of the critical current of conductor-1 and conductor-3 are better than that of the conductor-2. The variations of the critical current of the three conductors with the angle and intensity of the external magnetic field are different. The transport AC loss of the conductor-1 is the minimum and that of the conductor-2 is the maximum. The transport AC loss of the conductor-3 is the medium. The AC loss characteristics of the three conductors are different in different angles of external magnetic field.

Analysis of capacitor voltage imbalance at DC side of cascade STATCOM

WANG Jian-sheng, WU Ya-nan, MAO Hua-feng, LI Jun, MAO Zhi-wei, LU Jing, XU Liu-wei

2024, 44(1): 51-57. DOI: 10.16568/j.0254-6086.202401009

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During the operation of tokamak magnet power supply system, it is found that there is a DC side voltage imbalance among the phase chain nodes of its corresponding reactive power compensation device cascade Static Synchronous Compensator (STATCOM), and this imbalance tends to increase with the increase of compensation current. This problem will affect the stable and reliable operation of the device and directly lead to the stop of the device in serious cases. In this paper, the circuit model of STATCOM is established, and the corresponding mathematical model is established combined with its circuit model. The effects of grid harmonics, capacitor capacity, loss and pulse trigger delay on capacitor voltage imbalance are studied. Through the verification of MATLAB/Simulink simulation software, it is indicated that the power grid harmonic, capacitance difference, switch trigger pulse delay difference, parallel loss difference and hybrid loss difference are the important reasons for the capacitor voltage imbalance on the DC side of STATCOM.

Study on recrystallization of tungsten under transient heat loads

QU Miao, YAN Sha

2024, 44(1): 58-64. DOI: 10.16568/j.0254-6086.202401010

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In order to study the recrystallization behavior of tungsten under transient heat loads and its dependence on pulse parameters, the recrystallization and grain growth of tungsten were experimentally observed under 1~100 pulses of pulse electron beam with the energy density of 3.82MJ×m^-2 at 5ms pulse duration and the energy density of 1.5MJ×m^-2 at 1ms pulse duration. According to the grain size expression of non-isothermal uniform heating annealing process, the expression of normal grain growth under transient heat loads was derived. Combined with the experimental data, the dependence of grain sizes of tungsten under transient heat loads with pulse width of ms on pulse parameters was derived. The calculated grain sizes of tungsten irradiated by electron beam with pulse width of 5ms and 1ms using this formula are consistent with the experimental results that only normal grain growth occurs.

Simulation of CFETR parallel heat flux and blanket power deposition under radial turbulent transport

GAO Ze-shi, , WANG Ya-lei, LI Yan-long, TIAN Wen-xi, CAI Lai-zhong, WU Xue-ke, LIAN Qiang, LI Xin-ze, WANG Zhan-hui

2024, 44(1): 65-71. DOI: 10.16568/j.0254-6086.202401011

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The power deposition on the first wall of the CFETR blanket is simulated with the PFCFlux program coupling the BOUT++ transport program. It is shown that when the radial turbulent transport coefficient is 50m²·s^‒1, the poloidal average parallel heat flux on the Last Closed Magnetic Surface is 14058.5MW·m^‒2, and the plasma power entering the scrape off layer is 197.4MW. The power deposition on the first wall of the CFETR blanket is mainly concentrated in the high field side region of the vacuum chamber wall close to the central solenoid, and the maximum heat flux occurs in the middle part of this region.

Experimental study of the interaction between edge turbulence and zonal flows in the HL-2A tokamak

FANG Qian, CHENG Jun, WANG Wei-che, YAN Long-wen, HUANG Zhi-hui, WU Na, XU Yu-hong, TANG Chang-jian, SHI Zhong-bin, ZHONG Wu-Lü, XU Min

2024, 44(1): 72-77. DOI: 10.16568/j.0254-6086.202401012

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The dynamic interaction between edge turbulence and zonal flows has been studied using the combined Langmuir probe arrays on HL-2A tokamak. The experimental results illustrate that both the amplitude level of zonal flows and turbulence eddies size increase, and the turbulent intensity reduces correspondently meanwhile the edge radial electric field profile gradually steepens in the plasma recovery phase after particle injection. The experimental studies present the direct experimental evidence of the interaction between edge turbulence and zonal flows, indicating that energy transfer is the main cause for the excitation of zonal flows.

Effects of rotating magnetic island on the transport of trapped fast ions

ZHAO Jian-hua, CAO Jin-jia, XIANG Dong, DAI Yong-zhi, YANG Jun-hui, ZHAO Jia-wei, YANG Wen-jun

2024, 44(1): 78-84. DOI: 10.16568/j.0254-6086.202401013

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The transport of fast ions caused by the resonance between the rotating magnetic island and the bounce and precession frequencies (including precessions in poloidal and helical directions) of trapped fast ions is studied within the drift kinetic framework. The fast ion distribution functions in resonant and non-resonant cases are obtained by solving the banana orbital gyrocenter equation of trapped ion. The fast ion transport fluxes generated by magnetic drift, electric drift, and magnetic island rotation are calculated. The transport generated by magnetic and electric drifts, which are related to motions in the poloidal direction, has strong flow shear near the boundary of magnetic island, and is transported inward in the right-hand side of magnetic island. The transport induced by magnetic island rotation is opposite to the transport caused by magnetic and electric drifts, and the transport is radially outward on the side of the magnetic island near the plasma boundary and plays a dominant role. When the magnetic island width is greater than a certain threshold, the transport of fast trapped ions increases slowly and tends to saturation.

Hybrid simulation of non-resonant fishbone instabilities with reversed shear profile

XU Jing-kun, REN Zheng-zheng, WANG Wei-hua

2024, 44(1): 85-91. DOI: 10.16568/j.0254-6086.202401014

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The linear simulation of non-resonant fishbone (NRF) instabilities with reversed shear profile has been investigated by M3D-K. Based on EAST-like parameters, the NRF instability can be driven by the trapped energetic ions as minimum safety factor is a little larger than unity. The effect of important parameters on the fishbone such as the fraction of energetic particle beta β_hot/β_total, central pitch angle Λ₀, injection energy E, the minimum safety factor q_min, and radial position of q_min have been analyzed in detail, while beta-induced Alfvén Eigenmode (BAE) is found in some simulation cases. In addition, the instability transfers from the fishbone to BAE when q_min is larger than 1.08. Judging from the results obtained by the Fourier analysis with Λ₀=0.7 and the specific heat coefficients scanned with Λ₀=0.8, it is revealed that NRF and BAE can coexist when the central pitch angle is 0.7~0.9. Finally, the relation between mode frequency and the radial position of q_min is consistent with theoretical analysis.

Study of the effect of lower hybrid wave heating on the coaxial-tangential neutral beam collisional torque in EAST tokamak

YANG Ming, ZHANG Xin-jun, LI Xin-xia, LÜ Bo, GU Jing-ren

2024, 44(1): 92-97. DOI: 10.16568/j.0254-6086.202401015

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In order to study the effect of lower hybrid wave (LHW) heating on the beam power deposition and the collisional torque of the coaxial-tangential neutral beam injection, TRANSP code was used for simulation analysis combined the LHW heating experimental data. The simulated results show that the beam power deposition decreases, and the charge-exchange loss of fast ions increases about 20% with LHW heating when the coaxial-tangential beam is injected with energy 50keV and injected power 1.3MW. The percentage of ion absorbed power to the total beam deposition power goes up from 45% to 51%. The ratio of collisional torque to beam deposition power goes up from 1.327Nm·MW^‒1 to 1.457Nm·MW^‒1. The higher the plasma electron temperature, the larger the charge exchange loss and the ratio of collisional torque to beam deposition power, while the beam collisional torque during LHW heating remains stable.

Design and implementation of plasma equilibrium reconstruction code based on Python

BAO Na-na, HUANG Yao, YAN Xing-ting, WEI Shi-wen, WANG Zi-hao

2024, 44(1): 98-104. DOI: 10.16568/j.0254-6086.202401016

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Plasma equilibrium reconstruction algorithm is designed and implemented based on Python environment (Py-EFIT). NumPy and SciPy libraries are used to solve the scientific computation problems of matrix in equilibrium reconstruction algorithm, Matplotlib library is applied to realize the visualization of results, and a graphical user interface of Py-EFIT is designed and implemented based on interactive visualized design package QT Designer and PyQt library. The test results of Py-EFIT show that the operation of plasma equilibrium reconstruction has become simpler and more intuitive, which provides an effective tool for tokamak experimental data analysis.

Design and frequency response characteristics of the magnetic probe for TT-1 tokamak

CHEN Li-xing, CHEN Da-long, SHEN Biao, QIAN Jin-ping, CHEN Ming

2024, 44(1): 105-110. DOI: 10.16568/j.0254-6086.202401017

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The circuit simulation model of the magnetic probe in NI Multisim is used to obtain the frequency response characteristics of the magnetic probe for Thailand Tokamak 1 (TT-1). It is found that the distributed capacitance mainly affects the resonant frequency of the magnetic probe, while the circuit inductance has some influence on the resonant frequency and resonant peak value of the magnetic probe. Based on the Helmholtz coils, the frequency response calibration experiment of the probe is carried out, and the results show that the frequency response of the small probe is in good agreement with the simulation result. Furthermore, the influence of the probe transmission cable on the frequency response is analyzed through experimental and numerical studies. Finally, the frequency response parameters of the TT-1 probe are determined, which provide an important reference for the design of the probe size and the selection of signal transmission cable.

Numerical simulation of gas pulse discharge characteristics at different temperatures based on COMSOL

SONG Xian-ping, XI Jian-fei, LU Yang, CAI Jie, GU Zhong-zhu

2024, 44(1): 111-118. DOI: 10.16568/j.0254-6086.202401018

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In order to investigate the discharge characteristics of a wire-duct electrostatic precipitator based on the pulse power supply, an air discharge model is established using the COMSOL software. The calculated results are in good agreement with the experimental data. The detailed numerical simulation study is carried out to explore the influence of peak voltage, electrode size and gas temperature on discharge characteristics. The results show that with the increase of peak voltage and temperature, the density of electron and ion in discharge space increases gradually, and the range of high density area increases gradually. The smaller the electrode radius, the better the discharge effect and the higher the electron and ion density in the discharge space is. It is found that thermionic emission has a significant enhancement effect on the discharge at higher temperatures, which greatly improves the electron and ion density in the discharge region.

Study on electric and thermal characteristics of CO₂ arc plasma heater

ZHU Xing-ying, OU Dong-bin, YANG Guo-ming, ZENG Hui, ZHANG Zhi, WEN Peng

2024, 44(1): 119-124. DOI: 10.16568/j.0254-6086.202401019

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The electric and thermal characteristics of the axial CO₂ arc plasma heater with tubular cathode are researched experimentally, and the effects of different parameters including the arc current, gas mass flow, excitation current and length-diameter ratio of the front electrode on volt-ampere characteristic and heat efficiency of the CO₂ arc plasma heater are obtained. Based on the experimental data, the regression analysis is carried out with the similarity theory model and approximate expressions are attained. The results show that both the volt-ampere characteristic and heat efficiency of the arc plasma heater are obviously affected by the arc current and mass flow of CO₂, while the length-diameter ratio of the front electrode and excitation current have only effects on the heat efficiency. Values calculated by the regression equation of volt-ampere characteristic and coefficient of heat losses are in good agreement with the experimental data, and regression errors of volt-ampere characteristic and coefficient of heat losses are less than10.0% and 18.2% respectively.

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