Nuclear Fusion and Plasma Physics

The radial stochastic localization of geodesic acoustic mode

ZHANG Yang-zhong

2013, 33(2): 97-101.

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In the previous paper “The ‘tadpole’ localization in radial structure of geodesic acoustic mode” [Ref.1], it was shown that the radial structure of geodesic acoustic mode (GAM) near turning point appears to be a ‘tadpole’ structure based on the consistency of GAM ordering with the experimentally observed small density to potential ratio without invoking the specific physical mechanism. The mechanism, so-called stochastic localization, is analyzed in the present paper in the framework of parametric destabilization to GAM, the coherent length, which remains to be answered in [Ref.1], is calculated and some aspects related with experiments are discussed.

Effect of modes interaction on the resistive wall mode stability

CHEN Long-xi, WU Bin

2013, 33(2): 102-106.

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Effects of modes interaction on the resistive wall mode (RWM) stability are studied. When considering the modes interaction effects, the linear growth rate of the most unstable (3, 1) mode decreases. After linear evolution, the RWM saturates at the nonlinear phase. The saturation can be attributed to flux piling up on the resistive wall. When some modes exist, the (3, 1) mode saturates at lower level compared with single mode evolution. Meanwhile, the magnetic energy of the (5, 2) mode increases correspondently, but the magnetic energy saturation level of the (2, 1) mode changes weakly.

Innovative researches on some important problems in fusion reactor tritium system design (Ⅱ)

DENG Bai-quan

2013, 33(2): 107-112.

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In part one published in the last issue, the tritium retention and the total tritium inventory in PFC materials of FEB-E fusion reactor had been calculated. The tritium well depth, tritium well time during the FEB-E fusion reactor start-up and initial operation phase had been obtained. In this part, how to improve tritium recovery efficiency in the ITER TBM solid breeder blanket with using purge gas has been discussed. Some new innovative schemes for reducing tritium retention and improving tritium recovery efficiency are proposed. Such as, sponge mechanism based on deuterium saturated PFC materials; deuterium and beryllium co-deposition layer created on first wall surface; SPB scheme for enhancing tritium recovery efficiency of purge gas in ceramic breeder blanket based on the electrical polarization rotations catalyzing isotope exchange rate enhancement resulted from applied low frequency electric-field, of Li4SiO4 grain and purge gas molecular particles and so on, are explored.

Discrete Afvén eigenmodes excited by energetic particles in JT-60U and JT-60SA

KONG Ran, HU Shuang-hui, WANG Shuai, WANG Yi-ru, CHEN Shu-ping

2013, 33(2): 113-120.

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Resonant excitations of Afvén eigenmodes by energetic particles in JT-60U and JT-60SA are investigated employing a gyrokinetic-magnetohydrodynamic (MHD) hybrid simulation code. It is found that multiple branches of αTAEs can be kinetically destabilized by energetic particles. The dependences of stability properties on energetic-particle beam velocity via resonance conditions are examined. The discrete Afvén eigenmodes in high β_p grassy ELM H mode regime are easier to be excited by energetic particles than in high β_p gaint ELM H mode regime. The discrete Afvén eigenmodes excited by energetic particles are shown to exist in diffrent potential wells in reversed magnetic shear discharges with an L-mode edge. The kinetically excited αTAE instabilities are also found in high β_p full non-inductive operation in JT-60SA. The global αTAE features are demonstrated along the magnetic field line and the radial direction.

Influence of the emission spectrum n_|| of ICRH antenna on the fast wave minority ion heating efficiency

REN Yu-hu1, GONG Xue-yu1,2, DU Dan3, LI Sheng1, CHEN Shuang-liang1, REN Jing1

2013, 33(2): 121-126.

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The relation of the power reflection coefficient in tokamak plasma surface and absorption attenuation of the ion cyclotron wave to the emission spectrum n_|| of ICRH antenna is studied by using a stratified plasma slab and the WKB approximation. The effect of fast wave minority ion heating in different emission spectrum conditions of ICRH antenna is numerical calculated. The simulation results show that under the same conditions, the coupling efficiency of the antenna with the plasma and the effect of fast wave minority ions heating can be improved and enhanced by suitable spectrum n_|| of ICRH antenna.

Molecular dynamics simulation of interaction of ionized molecule CH⁺ with fusion materials-tungsten

TIAN Shu-ping,CAO Xiao-gang,XIAO Jia-hao,ZHANG Jun-yuan,ZHANG Jing-quan,PAN Yu-dong,GOU Fu-jun

2013, 33(2): 127-134.

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The molecular dynamics simulation of interaction between CH⁺ with various energy and fusion material tungsten is conducted. The simulated results show that in the incident process, the sputtering rates of C and H atoms change suddenly at the different exposure doses when the incident energy is 50, 100 and 150eV respectively, a few of W atoms are sputtered in the interaction process, but the sputtering rate is less than 0.24%. When the exposure dose is about 3.92×10¹⁶cm⁻², the incident energy is 50eV, a hydrocarbon firm without W atom is formed on the sample surface bombarded by the ions. A mixed film of W, C and H is formed at the other energy. The deposited rates of C and H atom first decrease then increase with the incident energy increament, the minimum deposited rats appear at 250 and 200eV respectively. The density profiles of C, H atoms, C−H, C−C, W−C bonds in the sample after bombardment move towards the inside of sample, and the C sp³ dominated the sample.

Interturn shear stress analysis for HL-2M toroidal field coils

CAI Li-jun,ZOU hui,LIU jian,QIU Yin,LIN Tao,LU Bo,LI Guang-sheng,LIU De-quan

2013, 33(2): 135-141.

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The structural design of HL-2M toroidal field coils and the electromagnetic loads on the coils was introduced in this paper. It was carried on that the analyses of the horizontal pre-loading system, pre-stressed epoxy-glass cylinder and the anti-torque structure which have big effects on the interturn shear stress. The results showed that the toroidal compression stress caused by the preloads and pre-stressed cylinder enhanced the anti-torque stiffness of the center-post, and the shear stress were reduced with the increase of lateral support stiffness. For normal operating scenarios, the maximum in-plane shear stress was less than 8MPa. If the major disruption occurs, a peak value of 12MPa in-plane shear stress may be induced, a limitation has to be made on the number of allowed disruption.

EPICS deployment on the PLC of control system for HL-2A

WANG Chuan,XIA Fan,PAN Li,PAN Wei,ZHAO Li,SONG Xiao,LI Xin-yi,CHEN Liao-yuan

2013, 33(2): 142-146.

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In order to improve the efficiency of HL-2A tokamak experimental data exchange, EPICS system has been deployed on the HL-2A and combined with the PLC of control system. A viable method for sharing HL-2A’s instructions and data is established. At the end the instance of the program is given.

Optimized calculation of antenna parameters of ECRH system on EAST tokamak

WEI Wei,DING Bo-jiang,ZHANG Xin-jun, WANG Xiao-jie,LI Miao-hui,XU Han-dong,TANG Yun-ying,LIU Fu-kun

2013, 33(2): 147-154.

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The basic parameters such as launch angle, position of the antenna are optimized according to the propagation trajectory, power deposition and current drive of the electron cyclotron wave by TORAY code. The effects of different launch angle on the power deposition and current drive are analyzed, and the best launch radial position and height of the antenna and the adjustment range of poloidal and toroidal angle of the antenna mirror are given.

Design and optimization of cooling structure on EAST 4.6GHz LHCD components

LI Bo, WU Jie-feng, ZHU Wen-hua, ZHAO Lian-min, LIU Liang

2013, 33(2): 155-160.

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The active cooling structures consisting of long straight waveguide, 2 kinds of waveguide elbows, antenna unit were designed. A general finite element simulation software ANSYS is employed to calculate the heat generation and convection cooling on these components. Temperature distribution contour and structural deformation on components are calculated and shown. Optimized cooling plate on straight waveguide is the double cooling. Numerical results show that cooling structure on H-bend waveguide is better than that on E-bend. Instead of the original cooling tunnel on antenna unit, the temperature on head is too high and the thermal stress is too large to apply this design, the temperature rise on front end and thermal deformation of the optimized antenna unit meet the demands of LHCD experiments.

Ablation protecting for water cooling tube around V region under divertor in EAST

XU Wei-wei, CAO Lei, SONG Yun-tao, ZHOU Zi-bo, JI Xiang

2013, 33(2): 161-165.

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The in-vessel components worked very well in the past experiment runs and the main goals were achieved. Nevertheless, some damage was found, such as the ablation happened on graphite tiles, and the penetration happened on the water tubes around V area by the energetic particle bombardment as the power flux deposition was elevated locally. To protect the cooling pipes from damage, the outer graphite plate is extended for 20mm longer than the original one and a special structure using a group of node jacket pipes of 5mm which are made of molybdenum (Mo) material are designed. According to the theoretical and numerical analysis, we find that the effect of extension of the outer target on flow conductance is acceptable and the Mo material is the much more appropriate material and the thickness of 5mm can effectively protect the pipe. The following experimental results show that these adopted protecting measures solve the problems well.

Optimization of coolant arrangement for fusion-fission hybrid reactor and analysis of ex-core nature circulation

YU Zhang-cheng, XIE Heng

2013, 33(2): 166-174.

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The simulation and numerical computation with FLUENT code are conducted for the fuel zone of fusion-fission hybrid reactor. Two coolant flowing arrangement schemes, uniform flow, and proportional flow based on the gross heat of each fuel cell, are compared for optimization. The results of the numerical computation show that the heat conduction between adjacent fuel cells is weak and the heat is carried away by the coolant in the duct, and it is almost completely equal to the heat produced by corresponding fuel cell except the fuel cell 1. Then the value of heat structure of the coolant duct is the gross heat of each fuel cell that means there is no need to remodel the fuel zone with system analysis program. The fuel zone has lower maximum temperature and more even temperature distribution in the case of proportional flow compared with uniform flow, but the effect of flattening temperature is not obvious. The capacity of heat transfer of ex-core nature circulation in the imaginary LOCA is also evaluated. The results show that the reactor core will be melted within 520s after shut-down without the nature circulation and the maximum temperature in the fuel region will be only elevated to 584.4°C within 1000s after shut-down if with the nature circulation.

Preliminary analysis of the thermal-hydraulic behavior induced by first wall coolant pipe leakage accidents for ITER

LI Ruo-qing, TONG Li-li, CAO Xue-wu

2013, 33(2): 175-180.

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Using an integral safety analysis code, an accident analysis model for the vacuum vessel (VV), first wall (FW)/blanket, its primary heat transfer system and the pressure suppression system of ITER is built. The loss of coolant accident induced by the in-vessel first wall pipe double-ended rupture is selected with two different cases of single pipe rupture and multiple pipe rupture as the initial scenarios to investigate the thermal-hydraulic responses for the systems. For the accidents of in-vessel FW coolant pipe double-ended rupture, the pressure in VV increases with the coolant releasing, and then decreases with the rupture disk opening, which shows that the pressure in VV remains in the design limitation.

Numerical analysis of velocity distribution in inductively coupled argon thermal plasma

ZHU Hai-long,TONG Hong-hui,YANG Fa-zhan,YE Gao-ying,CHENG Chang-ming, CHEN Lun-jiang

2013, 33(2): 181-186.

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The velocity distribution characteristic of inductively coupled argon thermal plasma and the effect of the operation parameters on velocity distribution are investigated in detail. The results show that, compared with direct current arc plasma, inductively coupled thermal plasma has the characteristics of lower velocity, arc flow centralization, peak velocity appeared in the downstream of plasma torch and the reflow phenomenon appeared in on the upstream of coil section. Moreover, it is found that plasma velocity distribution depends strongly on the operating parameters such as injection gas flow rate, induction current. The results would be theoretically helpful for plasma spheroidization of powder and other applications.

Numerical simulation of the impact gas injection on the lead-bismuth liquid flow and heat transfer parameters

ZOU Wen-zhong, ZHOU Tao, SU Zi-wei, LIU Meng-ying, LI Jing-jing

2013, 33(2): 187-192.

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Two-phase flow theory on heat transfer is used, and a two-dimensional model is created. The lead-bismuth liquid flow segment at stable entrance flow rate with gas injection was simulated with FLUENT code. The simulation studied the impact of the volume fraction or the relative velocity of the injected gas on the pressure and heat transfer between lead-bismuth and the injected gas, the temperature and pressure profiles under the different conditions were obtained. Analysis shows that with volume fraction decreases, the radial temperature profile is more uniform in the lead-bismuth fluid, at the center the fluid has a lower temperature, and the total pressure of lead-bismuth shows a tendency to decline. The results show that the velocity has a little effect on the heat transfer and the total pressure changes a little too，but the dynamic pressure increases a lot at the center.

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