Nuclear Fusion and Plasma Physics

Statistical analysis on the intermittency and turbulent particle transport on the HL-2A tokamak

WANG Lian, QIAN Wei, BAI Quan, WEI Ran, CHE Tong, LIU Xing, XU Li-sha, ZHENG Peng-fei

2020, 40(4): 289-293. DOI: 10.16568/j.0254-6086.202004001

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By the calculation of particle probability distribution function, it is found that the frequency of intermittency breakout increases at the edge of higher density plasmas. Positive and negative breakouts of intermittency are distinguished using a conditional average algorithm, indicating that positive and negative intermittency events have different space characteristics. It is also demonstrated that existence of intermittent events greatly enhances the turbulence particle transport by computing the turbulent particle transport at different gradients of fluctuating densities. At higher densities, the enhancement of intermittency roughly accounts for the increase of turbulent particle transport.

Toroidal rotation braking induced by n=4 RMP in EAST

LI Xin-yu1, 2, SUN You-wen1, ZANG Qing1, LI Ying-ying1

2020, 40(4): 294-299. DOI: 10.16568/j.0254-6086.202004002

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An obvious toroidal plasma rotation braking effect was observed during the application of n=4 resonant magnetic perturbation (RMP) in EAST, which shows a global profile and a peak located near the plasma center. Neoclassical toroidal viscosity (NTV) theory is one of an effective explanation in magnetic braking. The variation of toroidal angular velocity reproduced with neoclassical toroidal viscosity (NTV) torque shows good qualitative agreement with the measured rotation variation profile in most radial regions, and the difference is 1~2 times.

ELM real-time recognition research based on deep learning

HUANG Yao, XIA Fan, YANG Zong-yu, ZHONG Wu-lü, LIU Chun-hua

2020, 40(4): 300-308. DOI: 10.16568/j.0254-6086.202004003

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Based on the deep learning method, this paper introduced an ELM real-time recognition algorithm on HL-2A tokamak. The algorithm used data from 5200 shots (about 241,900 data slices) for learning and a 22-layer convolutional neural network was obtained. The algorithm has recognized all historical data of HL-2A since it achieved stable ELMy H-mode discharge in 2009. A total of 1665 shots of H-mode have been recognized, of which 35 shots were misidentified, with the false positive rate (FPR) of 2.10%. In the actual 1634 shots of H-mode, the system missed to recognize 4 of them, with the false negative rate (FNR) of 0.24%. The FPR and FNR fulfill the precision requirements of real-time ELM recognition. In the simulated real-time environment, the algorithm’s average calculation time of a single slice is 0.46 milliseconds, which satisfy the calculation speed requirements of the real-time ELM recognition.

Preliminary study of compressed plasma of EAST based on vertical magnetic field

HANG Qin1, 2, LI Ge1，ZHANG Heng1, 2

2020, 40(4): 309-314. DOI: 10.16568/j.0254-6086.202004004

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Based on the scaling laws that the plasma parameters change with the major radius and minor radius for compressed plasma by considering two-step magnetic compression, the vertical magnetic field and related plasma parameters are analyzed during flat-top phase of plasma current. Non-linear dimensionless magnetic field is utilized to analyze the effect of non-inductive current drive, including the effect of bootstrap current. Furthermore, the relationship of vertical magnetic field and line-averaged density is derived and validated during flat-top phase for given plasma current to further study the compressed plasma. Results based on EAST No.41195 discharge show that an increase in magnetic strength of vertical field will allow high T_e, high ne, high β_p and high bootstrap current fraction fBS to be reached, which provide a possibility reference for the high plasma parameters, especially high β_p.

Numerical investigation on exploding wires in vacuum

WANG Kun, JIANG Lin-cun, ZHANG Dong, ZHANG Yue, WANG Tian-hao

2020, 40(4): 315-320. DOI: 10.16568/j.0254-6086.202004005

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A computational model is established to describe the physical process of exploding wires in a vacuum. The computational model is coupled with equation of state and transport coefficient model that can describe the phase transition of the wire from the solid state to the plasma state. The characteristics of exploding aluminum wires of different diameters are studied and compared with relevant experimental data.

Numerical research on strengthening secondary flow of tokamak in-vessel coils’ water-cooling pipe joints

JIANG Jia-ming1, HUANG Shu-long1, WU Wen-jie1，ZHANG Guo-shu1, LIU Yi2, ZHANG Kai3

2020, 40(4): 321-328. DOI: 10.16568/j.0254-6086.202004006

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The tokamak in-vessel coil water-cooling pipe joints of different deflector curvature radius ratios are studied based on the computational fluid dynamics (CFD). The impact on the average Reynolds number distribution from the coils water-cooling pipe of different ratio of the coil pipe joint deflector curvature radius and related inlet velocity has been analyzed, using turbulence numerical simulation method. The results indicate that the average Reynolds number distribution curves of different deflector curvature radius ratio are similar, and the numbers increase with the increase of inlet velocity, while the outlet Reynolds numbers of the pipe joint decrease with the increase of the deflector curvature radius ratio. The deflector of the small curvature radius ratio is more suitable for the secondary flow enhancement of the coil water-cooling curved pipe. In addition, the relationship between the outlet Reynolds numbers of the coil joint and its inlet velocity is fitted for the pipe joint with deflector curvature radius ratio of 0.2, which provides a theoretical basis for further study of the secondary flow enhancement of the similar curved pipe joint with tokamak in-vessel coil pipe.

Simulation of PSM high voltage power module based on compensation network

XIA Yu-yang, LI Qing

2020, 40(4): 329-335. DOI: 10.16568/j.0254-6086.202004007

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The regulation module of the high-voltage power supply system for lower hybrid current drive of the China Engineering Test Fusion Reactor (CFETR) is simulated on MATLAB platform. Impact of power grid fluctuations, load changes and filter parameters on the output voltage is analyzed in the static state. The compensation network can greatly reduce the ripple of the output voltage and increase its stability. The stabilization time of the system is within a few milliseconds, and the ripple factor is <1%. The simulation results show that it is reasonable to adopt PID (proportional integral derivative) control and lead-lag compensation strategy for the high-voltage power system regulation module.

Simulation study of the radiative divertor under different gas puffing locations for CFETR

ZHOU Yi-fu1, MAO Shi-feng1, ZHAO Deng2, YE Min-you1, 3

2020, 40(4): 336-343. DOI: 10.16568/j.0254-6086.202004008

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The simulation study of the radiative divertor for China Fusion Engineering Test Reactor (CFETR) was performed with argon impurity puffing using the edge plasma numerical simulation code package SOLPS. The simulated Zeff at the core-edge boundary (ρ=0.9) of the outer mid-plane are 2.8, 3.1, 3.4 and 2.7, respectively, for four different gas puffing schemes (deuterium and argon mixed gas puffing from upstream; deuterium and argon mixed gas puffing from outer divertor; deuterium and argon mixed gas puffing from inner divertor; deuterium gas puffing from upstream and argon puffing from outer divertor) with fixed total radiated power (P_rad~170MW). The simulation results are similar to the experimental observation on DIII-D and C-MOD. Better impurity screening can be achieved with deuterium puffed from upstream due to the increased background plasma flow in the scrap-off layer, while the puffing location of argon has a minor influence on the simulation results since divertor target recycling is the major impurity source.

Preload structure optimization design and mechanical analysis of the CFETR central solenoid model coil

YIN Da-peng 1, 2, WU Yu 2, HAN Hou-xiang 1, 2, XU Ai-hua1

2020, 40(4): 344-349. DOI: 10.16568/j.0254-6086.202004009

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The central solenoid model coil (CSMC) on China Fusion Engineering Test Reactor (CFETR) is introduced. CSMC mainly includes Nb₃Sn coil, NbTi coil, preload structure, buffer zone, joint, joint support, cooling helium pipe and helium pipe support. The preload structure consists of 15 preload beams, 30 preload rods and supporting plates. A total of 75MN preload force will be applied to the preload structure at room temperature. Based on the electromagnetic analysis and optimization design module of ANSYS, the optimization design and mechanical analysis of the preload structure have been performed. The results of mechanical analysis show that the preload structure meets the operation requirements.

Preliminary design and development of ITER divertor Langmuir probe system

ZHAO Wei1, WANG Ya-li1, JIN Yu-zhong1, ZHAO Li1, ZHOU Hong-xia1, ZHONG Guang-wu1, NIE Lin1, LIU Chun-jia2

2020, 40(4): 350-356. DOI: 10.16568/j.0254-6086.202004010

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According to the measurement requirements of ITER Langmuir probe system, the preliminary design and partial development of the probe system are carried out. The measurement methods of different plasma parameters and the corresponding probe system operation modes are determined by the detailed physics analysis of the probe system measurement requirements. Temperature field and stress field under 10MW×m^-2 steady-state heat load of Langmuir probe are obtained by structural design, thermal and mechanical simulation. Meanwhile, based on ITER vacuum material handbook, the preliminary selection of probe and shield material is forged tungsten, and the machining processing technology and welding technology were studied. According to the measurement requirements of probe system and operation modes, the design and analysis of power supply, probe operation modes switching and signal conditioning unit are carried out for the electronics system, and the technical verification prototype of power supply is being developed. The preliminary design of the instrument and control system has been completed, of which the main functions include command dispatching, state monitoring, calibration, data acquisition, communication with ITER CODAC and real-time measurement of ion flux on divertor target.

Structural analysis and fatigue test of helium inlet for EAST PF8 coil

FANG You-wei1, 2, HU Xian-guo1, DU Shuang-song2, XI Wei-bin2, WEI Jing2, LU Kun2

2020, 40(4): 357-363. DOI: 10.16568/j.0254-6086.202004011

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In order to solve the leakage of the helium inlet of East PF8 coil, four kinds of working conditions are established by analyzing the boundary conditions of the current structure of helium inlet. The finite element model of PF8 helium inlet is established, and the static analysis under the four working conditions is carried out. The calculation results show that thermal load and enforced displacement from the fixed support plate G11 are the main reasons of weld failure. The fatigue test of a full-size PF8 helium inlet sample has been carried out at 4.5K and with more than 2×10⁵ cycles, which satisfies EAST requirement. Through detaching the PF8 helium pipe from the G11 plate, the additional loads are completely avoided, and the repaired PF8 helium inlet has good structural performance and meets the requirements of EAST.

Effects of synergistic implantation of helium and hydrogen ions on morphology and phase structure of zirconium film

FU Yu-xin, LI You, SU Chao, MA Shi-xin, JIANG Hong-wei, WEI Jia-jun, LIU Yang

2020, 40(4): 364-371. DOI: 10.16568/j.0254-6086.202004012

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Zr-Mo films were prepared by magnetron sputtering, then films were co-implanted with He⁺ and H⁺ ions at doses of 2.80×10¹⁷~1.12×10¹⁸ ions×cm^-2 in a low energy electrostatic accelerator. The synergistic injection effects of He⁺ and H⁺ ions on the microstructures of Zr-Mo films were studied by optical lenses, scanning electron microscopy, atomic force microscopy and X ray diffraction. Experimental results show that the surface grain of the original Zr-Mo film is clearly visible with a size of about 200nm, micro damage region on the surface of Zr-Mo film can be induced by radiation effect, and injection of H⁺ on the basis of He⁺ leads to more serious damage to the film. It is found that Zr-Mo film surface is gradually becoming smooth as a result of the gradually etched grain boundary by the ion beam sputtering effect. Co-implantation of He⁺ and H⁺ ions can distort the lattice of Zr-Mo films, but it is still not noticed a phase transformation of ZrH during the injection.

Study on the effect of atmospheric pressure on the discharge characteristics of capacitively coupled Ar/O2 plasma at low pressure

WU Liang-chao, YIN Gui-qin, MENG Xiang-guo, ZHOU You-you, WANG Jin-jing

2020, 40(4): 372-378. DOI: 10.16568/j.0254-6086.202004013

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Influence of gas pressure on electron temperature and electron density of argon-oxygen plasma induced by dual radio frequency (RF) source with a high-frequency of 94.92MHz and a low-frequency of 13.56MHz is studied. Under the condition that the low-frequency power and the high-frequency power are fixed at 60W and the argon-oxygen gas ratio is 1:9, the characteristic lines in the discharge spectrum of the argon-oxygen mixed plasma at different pressures is analyzed. The electron temperature and electron density is simulated with the one-dimensional PIC-MC (Particle-in-cell and Monte-Carlo) electrostatic model. The results show that the electron temperature decreases first and then rises with the increase of air pressure, consistent with the experimental result; the electron density first increases and then decreases with the increase of air pressure.

2020, 40(4): 379-384.

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