Table of Content

15 December 2023, Volume 43 Issue 4

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Nuclear Fusion Engineering

Design analysis and optimization of 80kV/50A/20ms high voltage power supply for neutral beam ion source experimental platform

WAN Yin-xiang, WEI Hui-ling, GENG Shao-fei, YU Pei-xuan, ZHOU Bo-wen, LUO Huai-yu, YANG Xian-fu, LI Ming, ZHANG Jin-tao, ZHOU Hong-xia, CAO Jian-yong

2023, 43(4):  373-379.  DOI: 10.16568/j.0254-6086.202304001

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The high-voltage power supply is the key equipment for the ion source beam extraction for neutral beam heating. Its operation parameters and performance directly determine the energy of the extracted beam particles and the extraction efficiency of the ion source. In order to further improve the high-voltage operation parameters and performance of the neutral beam ion source experimental platform, all modules of the 80kV/50A high-voltage power supply were re-optimized and developed. This article first introduces the main circuit topology and power module of the 80kV/50A high-voltage module power supply. The main circuit of the high-voltage power supply is simulated using simulation software, and the simulation results meet the design requirements. Finally, through debugging experiments, it was found that the power module has insufficient space insulation, rectifier bridge breakdown, and trigger control unresponsiveness. The analysis and optimization were carried out. Finally, the upgrade and development of the 80kV/50A high-voltage module power supply was completed. 

Development of real-time ELM control system based on deep learning in HL-2A tokamak

LI Xuan-yi, XIA Fan, YANG Zong-yu, GONG Xin-wen, CHEN Cheng-yuan, XIAO Guo-liang, ZHU Xiao-bo

2023, 43(4):  380-385.  DOI: 10.16568/j.0254-6086.202304002

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A real-time ELM (edge localized mode) control and mitigation system was developed in HL-2A tokamak using the deep learning-based ELM identification algorithm and ELM mitigation equipment such as supersonic molecular beam injection (SMBI). The system collects relevant input data in real time, calculates and analyzes them with the neural network, and sends out trigger signals according to the output of neural network. When continuous occurrence of ELM is detected, the system will trigger SMBI to inject molecular beams to mitigate ELM. The real-time ELM control system was tested in the HL-2A tokamak experiment. It can accurately detect the ELMy H mode in the plasma discharge by analyzing the diagnostic signal within a control period of 1ms and sends control signals when ELM occurs to trigger the ELM mitigation system, and the identification effect is obvious. The system can be applied to the real-time ELM mitigation and control in HL-2A plasma. 

Thermal-hydraulic analysis of the first wall of the supercritical CO₂ cooled lithium lead blanket for CFETR 

YU Yi, , MA Xue-bin , JIANG Ke-cheng , WU Qiu-ran, , CHEN Lei , LIU Song-lin

2023, 43(4):  386-391.  DOI: 10.16568/j.0254-6086.202304003

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Based on the design of the supercritical CO2 cooled lithium lead blanket for CFETR, the thermal-hydraulic analysis of the first wall cooled by supercritical CO2 was carried out. In order to provide guidance for subsequent structural design, the effects of channel pitch, wall roughness, channel size and inner wall heat flux on evaluation parameters, including driving power, outlet temperature and inner wall temperature, were analyzed by limiting the maximum temperature of the first wall. Moreover, the cooling capacity was compared with helium. All studies were performed using computational fluid dynamics (CFD) approach. Results indicated that better cooling performance can be obtained by reducing the channel pitch and increasing the wall roughness. At the same time, increasing the polar and radial dimensions of the flow channel can effectively reduce the driving power and the inner wall temperature, respectively. Considering the heat exchange between the first wall and the breeding zone, the maximum temperature of the inner wall would increase greatly. In addition, the driving power required for supercritical CO₂ to cool the first wall was less than that of helium. 

Numerical simulation of subcooled flow boiling on micro-/nanostructured surfaces in water cooling systems of divertors 

LIU Jin , ZHOU Zhan-ru , HUANG Sheng-hong , YE Min-you

2023, 43(4):  392-401.  DOI: 10.16568/j.0254-6086.202304004

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In order to improve the capacity of heat transfer and the thermal load in the water cooling systems of divertors, it is necessary to develop micro-nano structured surface enhanced heat transfer methods. Based on the experimental microscopic observations on micro-/nanostructured surfaces, the models of the contact angle, the bubble departure diameter, the bubble departure frequency and the nucleation site density are modified to simulate the subcooled flow boiling heat transfer on micro-/nanostructured surfaces. The modified models are used in water cooling systems of divertors with the working condition of a pressure of 4MPa, a velocity of 10m·s^-1 and the inlet temperature of 423K. The contours of the temperature and the vapor volume fraction of the smooth surface channel and the micro-/nanostructured surface channel are compared, and the heat transfer coefficients of the micro-/nanostructured surfaced are approximately doubled, the steady heat flux of the micro-/nanostructured surface channel can reach up to 14MW·m^-2 with the allowable temperature of OFHC and CuCrZr. 

Spectrum design of lower hybrid wave antenna in HL-3 high field side

ZUO Lan, BAI Xing-yu, LU Bo, LIANG Jun

2023, 43(4):  402-406.  DOI: 10.16568/j.0254-6086.202304005

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A new lower hybrid antenna in HL-3 high field side (HFS) is designed to improve the accessibility of lower hybrid waves in high-performance plasma. The simulation of HFS lower hybrid antenna using ALOHA code is introduced. For PAM (passive active multifunction) antenna with one module, the number of waveguides and the active/passive waveguide’s height, width and thickness are simulated respectively, the optimized structure and dimension are obtained. The launching parameters of the finally optimized antenna are: the parallel refractive index of spectrum center N_|| is 2.25, the reflection coefficient is less than 2%, and the directivity is greater than 0.59. 

Design and experimental research of magnetic filter for large area negative ion beam source

XIE Ya-hong, , XIE Jun-wei, , WEI Jiang-long , GU Yu-ming , JIANG Cai-chao, , PAN Jun-jun, , XU Yong-jian, , XIE Yuan-lai, , HU Chun-dong

2023, 43(4):  407-411.  DOI: 10.16568/j.0254-6086.202304006

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Neutral beam injection is an important auxiliary heating tool for magnetic confinement nuclear fusion research. Large area negative ion source is the core component of the neutral beam injector. When the negative ion source works, the negative ions are easily destroyed by electrons with high energy due to the low electron binding energy of negative ions (0.75eV). Therefore, a magnetic filter field should be introduced to decrease the electron temperature. And then the loss of negative ions can be reduced, and the component of co-extraction electron can also be decreased. According to the mechanical structure of the large area negative ion beam source two kinds of magnetic filter structures are designed respectively. One is produced by permanent magnet, the other is produced by the current through the plasma grid (PG). Through the finite element algorithm, the magnetic filter field was analyzed, tested and optimized on the negative ion beam source prototype. The electron temperature was decreased from 5eV to 1eV in the extraction region. This result verifies initially the performance of magnetic filter field for large area negative ion beam source and could support the development of large area negative ion beam source. 

Study on magnetization loss of high temperature superconducting circular helical conductor

LUO Rong-hua , LIU Jian , YANG Xin-sheng , ZHAO Yong

2023, 43(4):  412-417.  DOI: 10.16568/j.0254-6086.202304007

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The characteristics of magnetization loss of circular helical conductor, the basic structure unit of high temperature superconducting (HTS) coil, are analyzed by simulation calculation. Firstly, the reliability of three-dimensional T-A method is verified by experiment and simulation. Then, the magnetization loss characteristics of HTS circular helical conductor under different central circle radius and tube radius are studied on this basis. The results show that the magnetization loss of the circular helical conductor increases with the increase of the radius of the central circle. With the increase of tube radius, the magnetization loss of circular helical conductor decreases gradually.  

High power plasma ignition power supply based on PWM rectifier 

HE Min, YU Zi-quan, JIA Zhong-qi, MENG Fan-xing, ZHU Chao

2023, 43(4):  418-423.  DOI: 10.16568/j.0254-6086.202304008

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Pulse width modulation (PWM) rectifier is used in the high-power plasma ignition power supply, and the main parameters are designed. The control loop was designed according to the characteristics of plasma load to improve the anti-load disturbance ability of PWM rectifier output voltage. Experiments verify the effectiveness of the proposed scheme. 

Rescue mechanism research of key rotary joint of remote handling multi-purpose heavy-duty mechanical arm of tokamak 

BAI Xiao-wei, , YAO Da-mao

2023, 43(4):  424-428.  DOI: 10.16568/j.0254-6086.202304009

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To eliminate the potential failure of the key rotary joint of the multi-purpose heavy-duty mechanical arm, the joint rescue mechanism is conducted. To address its shortcomings of the conceptual design of the joint rescue mechanism, a feasible rescue mechanism design scheme was proposed. Following the principles of concise and modular design, the requirements of rescue working conditions and the spatial layout inside the rotary joint, a joint rescue mechanism was designed with the rescue gearbox and the motor brake opening mechanism. At the same time, the rescue operation process of the joint was clarified. 

Plasma Physics

Linear instability analysis of energetic particle modes with locally reversed magnetic shear configuration 

LI Man , WANG Xian-qu , SU Xiang , XU Yu-hong , CHENG Jun , LIU Hai-feng , HUANG Jie , ZHANG Xin , LIU Hai , TANG Chang-jian

2023, 43(4):  429-435.  DOI: 10.16568/j.0254-6086.202304010

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Energetic particles (EPs) excited m/n=2/1 energetic particle modes (EPMs), which is in the existence of multiple rational surfaces with the same safety factor value, are investigated for locally reversed magnetic shear configurations with HL-2A plasma parameters. The eigenvalue equation of the m/n>1 mode with effects of energetic particles driving and the toroidal coupling is given. The radial mode structure is then studied by numerically solving the eigenvalue equation. The dependence of the EPM growth rate and frequency of modes on the EP beta (β_h) is simulated. Numerical results show that under the locally reversed magnetic shear configuration, the global EPM can be destabilized by trapped energetic particles with a similar characteristic as m/n=2/1 fishbone-like mode, which provides theoretical explanation for the relevant experiments. The effects of EP parameters on the mode are discussed in detail. It is found that the mode tends to be stable with the particle radial distribution flattening. And the growth rate of instability is decreased by strong Alfven continuum damping when the beam injection energy increases. 

Simulation of toroidal Alfvén eigenmode instability in the HL-2A tokamak 

GUAN Jing-yu , KE Rui , BAO Jian , CHEN Wei , YE Min-you

2023, 43(4):  436-443.  DOI: 10.16568/j.0254-6086.202304011

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The linear wave properties of toroidal Alfvén eigenmodes (TAEs) in HL-2A tokamak are investigated using the eigenvalue code GAM. The simulation results are consistent with the experimental observations. Moreover, the continuum spectra, mode structures and frequencies of TAEs with different safety factor profiles are also analyzed. For the normal magnetic shear, it is found that the radial mode structure of TAE in the core ( _{$\sqrt{{{\psi }_{\text{T}}}}$} < 0.3 ) consists of two main adjacent poloidal harmonics, while the radial mode structure of TAE in the outer region ( $\sqrt{{{\psi }_{\text{T}}}}$ = 0.3~0.9) consists of eight higher poloidal harmonics, indicating that the magnetic shear plays an important role in poloidal harmonics coupling. When the core-reversed magnetic shear exists in the safety factor profile, TAE disappears therein and the mode radial width of TAE in the outer region becomes narrow. In the end, the effect of electron density profile on TAE is also investigated, which shows that the profile mode frequency decreases with the increase of electron density, while the mode structure is not sensitive to the change of electron density

Optimal calculation of electron cyclotron current drive in HL-3 tokamak 

WANG Zhuo , SUN Ai-ping , WANG Yuan-zhen , LI Zheng-ji

2023, 43(4):  444-449.  DOI: 10.16568/j.0254-6086.202304012

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 The integrated simulation and experimental analysis platform OMFIT is used to research the driving efficiency of electron cyclotron current drive (ECCD) in HL-3 tokamak. The toroidal and poloidal angle of ECCD system antenna, electron density, electron temperature and the plasma magnetic field that affect the driving efficiency and current profile location are analyzed. The study found that when the toroidal angle is 185°~200° and poloidal angle is 85°~105°, the driving efficiency is relatively high, and driving current profile located in normalized radius 0.4~0.6. It is also found that electron temperature significantly affects the ECCD efficiency, and the drive current increases with increase of the electron temperature, at the weak magnetic field side, the normalized radius decreases and drive current increases with reduction of the magnetic field (1.9~2.2T).  

Edge detection of ELM filament structures by high-speed VUVI system on EAST

DENG Rong-jing , CHEN Lin-fei , MING Ting-feng , LONG Fei-fei , LI Bang , SHI Qi-qi , HOU Shan-wei , GAO Shan-lu , ZHUANG Qing , LIU Xiao-ju , GAO Xiang, ,

2023, 43(4):  450-456.  DOI: 10.16568/j.0254-6086.202304013

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 High-speed vacuum ultraviolet imaging (VUVI) system is an important diagnostic facility in the study of the two-dimensional filament structures of ELMs on EAST. Affected by the working environment and high-speed acquisition, the signal-noise ratio of the original image data of the filament structures from the VUVI system is relatively poor. In this paper, the original data are processed using block-matching and 3D filtering (BM3D) algorithm, background subtraction, and morphology processing. BM3D algorithm is used to remove the noise and increase the signal-noise ratio of the collected images. The filament structures are extracted by the background subtraction. The edge position and pitch angle of the filament structures are obtained through image processing by morphology. Simulation and experimental data analysis show that the proposed method can effectively extract the details of filament structures edge obtained by VUVI, obtain the information such as the pitch angle of filament structures, and improve the utilization rate of experimental data. 

Design of neutral beam diagnostic system based on secondary electron emission 

YU Zi-chen, , CHEN Yu-qing , XU Yong-jian, , CHEN Li-ping, , LIU Xiao-xue, , WU Zheng-wei , MAO Wen-zhe

2023, 43(4):  457-461.  DOI: 10.16568/j.0254-6086.202304014

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A beam diagnostic system based on secondary electron emission for neutral beam injector (NBI) is designed. The principle of secondary electron emission is described, and the influence of beam energy and calorimeter surface temperature on secondary electron emission coefficient is analyzed. Then actual target model is established for preliminary simulation verification through the finite element analysis. A processing method of beam power density profile based on secondary electron data inversion is proposed, and the components of the system and the overall operation mode of the system are analyzed. The design flow chart of the beam diagnosis system is given, and the design of the diagnostic probe based on the secondary electron emission beam profile is determined. 

Identification of X-point of divertor based on image technology for edge detection 

ZHAI Wen-yan, HUANG Yuan, GAO Jin-ming, FENG Zhen, GUO Wen-ping, LIU Liang, LIU Chun-hua, HOU Zhi-pei

2023, 43(4):  462-468.  DOI: 10.16568/j.0254-6086.202304015

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The identification of X-point in the HL-2A divertor discharge based on image technology was promoted. Firstly, according to the analysis requirements of HL-2A divertor discharge image, the Canny edge detection processing model is established based on the edge visible light radiation model under the single zero discharge configuration under the more intuitive plasma standard. The plasma edge in the image is mainly preprocessed. After extracting the image feature points with Harris corner detection algorithm, the coordinate value of feature points in the image is determined by polygon approximation. The plasma boundary curves and their asymptotes on the strong and weak field sides were fitted respectively. The intersection of the asymptotes is approximately X-point, and the region surrounded by the approximation of the boundary curve to the center can be approximately X-point region. Through the HL-2A 37638th divertor discharge diagram verification, after simplified conditions, the fitting X-point and EFIT inversion error range is within 3cm. 

Investigation of wavelength calibration method for laser induced fluorescence diagnostics

MA Ming-jian , YIP Chi-shung , JIANG Di , MAO Shi-feng , ZHANG Wei , JIN Chen-yao , YE Min-you

2023, 43(4):  469-476.  DOI: 10.16568/j.0254-6086.202304016

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Laser Induced Fluorescence is a non-invasive diagnostic technology that obtains the velocity and temperature through the particle velocity distribution function obtained by laser scanning. In order to obtain a particle velocity distribution function with a higher signal-to-noise ratio, data from multiple scans needs to be averaged. This requires calibration of the laser wavelength of each scan to ensure that the wavelength range of each set of data is basically the same. For this reason, a scheme for wavelength calibration using iodine spectrum is developed. The minimum mean square error method, the error gradient descent algorithm and the convolutional neural network are tested respectively on the simulated iodine spectrum dataset in order to probe into the effective spectrum alignment algorithm. The results show that, minimum mean squared error has good alignment accuracy, and the average error of alignment is less than two sampling intervals. The laser wavelength of laser induced fluorescence experiment of Ar⁺ was calibrated by aligning iodine spectrum using the minimum mean squared error method. Multiple sets of velocity distribution function of Ar⁺ were averaged. Compared with Fabry-Perot etalon trigger peak calibration and laser scan synchronization calibration, the ion temperature obtained by iodine spectrum calibration is more accurate.  

Effect of gas flow and external magnetic field on the characteristics of negative corona discharge 

ZHANG Ze-li, SUN Shu-wei, CHEN Jia-yao, ZHONG Fang-chuan

2023, 43(4):  477-481.  DOI: 10.16568/j.0254-6086.202304017

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The effect of gas flow and external magnetic field on negative corona discharge was studied through the wire-cylinder corona discharge device. When the voltage is fixed, the corona discharge current increases rapidly with the increase of the gas flow rate, then drops rapidly after reaching a high value, and the discharge current climbs slowly with the increase of gas flow rate further afterwards. The addition of an external magnetic field will enhance the corona discharge current. However, in high gas flow rate, the magnetic field will cause the corona discharge current to decrease. Simultaneously, the external magnetic field causes the increase of the ozone generation until the rise of temperature leads to the rapid degradation of ozone. 

Discharge characteristics of capacitively coupled Ar plasmas driven by different frequencies with pressure  

YUAN Qiang-hua, LIU Shan-shan, YIN Gui-qin, QIN Biao

2023, 43(4):  482-488.  DOI: 10.16568/j.0254-6086.202304018

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The discharge characteristics of capacitatively coupled Ar plasmas driven by 13.56, 40.68, 94.92 and 100MHz are discussed when radio frequency power is 40W and pressure change from 3.3Pa to 26.6Pa. The electron excitation temperature and electron density were diagnosed experimentally by spectroscopic relative intensity method. Particle simulation and Monte Carlo collision model (PIC/MCC) are used to simulate the electron density and electron energy probability distribution (EEPF) under the experimental conditions. The results show that the electron density increases with the increase of pressure at each driving frequency, while the electron temperature decreases with the increase of pressure. The electron density of 13.56 and 40.68MHz has almost the same trend with the increase of pressure, while the electron temperature of 94.92 and 100MHz has almost the same trend with the increase of pressure. By comparing the EEPF, the electron temperature decreased with the increase of pressure, which was basically consistent with the spectral diagnosis results.