Table of Content

15 March 2005, Volume 25 Issue 1

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Contents

Study of the HL-2A plasma boundary identification

YUAN Bao-shan, LIU Li, YOU Tian-xue, LI Fang-zhu,YANG Qing-wei, YAN Long-wen, HONG Wen-yu

2005, 25(1):  1-6. 

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To reconstruct the HL-2A plasma boundary, current filaments (CF) codewith the filament current model is written.Computed results based on the external magnetic measurements show that the CF code can accurately identify the limiter plasma,and the diverted plasma with its X point position. The time ofthe appearance and disappearance ofthe strike point at the target is in agreement with the signals measured by the static electric probes. Using an ordinary PC (Pentium 2.4GHz, 800MHz data bus), the calculation time of the plasma parameters is less than 1ms.

Determination of MHD mode with spatial Fourier analysis

FENG Bei-bin,YANG Qing-wei

2005, 25(1):  7-14. 

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The determination of MHD mode with spatial Fourier analysis is presented.In accordance with the situation of tokamak experiment,we run the simulation code under condition including the noise,the asymmetry of amplitude and the phase of Mirnov perturbation signals,etc.The systematic error of the method has been analyzed emphatically.A comparison between simulation results and the experimental data from the HL-1M tokamak are given as well.The simulation results indicate that the spatial Fourier analysis is a better method to determine the MHD perturbation mode in tokamak.

The mitigation effect of sheared axial flow on the Rayleigh-Taylor instability in Z-pinch plasma

ZHANG Yang1,DINGNing2

2005, 25(1):  15-21. 

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A magnetohydrodynamic formulation is derived to investigate the mitigation effects of the sheared axial flow on the Rayleigh-Taylor (RT) instability in Z-pinch plasma.The dispersion relation of the compressible model is given. The mitigation effects of sheared axial flow on the Rayleigh-Taylor instability of Z-pinch plasma in the compressible and incompressible models are compared respectively,and the effect of compressible on the instability of system with sheared axial flow is discussed.It is found that,compressibility effects can stabilize the Rayleigh-TaylorPKelvin-Helmholtz (RTP KH) instability,and this allows the sheared axial flowmitigate the RT instability far more effectively.We also find that, at the early stage of the implosion,if the temperature of the plasma is not very high,the compressible model is much more suitable to describing the state of system than the incompressible one.

Study of current profile control and improved confinement with lower hybrid current drive in the HT-7 tokamak

SHEN Wei-ci, KUANG Guang-li, SHAN Jia-fang, DING Bo-jiang

2005, 25(1):  22-28. 

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The effectiveness of the plasma current profile control and confinement improvement with lower hybrid current drive (LHCD) in the HT-7 superconducting tokamak has been observed successfully. Numerical simulations and hard X-ray evolution spectra indicate that the power spectrum of lower hybrid wave, toroidal magnetic field and plasma density are the key factors for changing the plasma current profile. In the optimal LHCD condition, profiles of plasma density and temperatures have been changed as expected. And the internal transportbarriers have appeared in the profiles of both electron and ion temperatures. Both the energy confinement time and the particle confinement time have been improved.

Electron cyclotron current drive in tokamak plasmas

PENG Xiao-wei, GONG Xue-yu, LIU Wen-yan

2005, 25(1):  29-36. 

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Electron cyclotron current drive is investigated with the relativistic Fokker-Planck equation incorporated into a raytracing code in the condition that the O-mode fundamental electron cyclotron (EC) waves are launched fromthe medium plane at the low field side in the paper. Numerical results show that, with increase of plasma temperature and density, both power deposition and current profile move towards the edge of plasma and the total driven current declines. The change in toroidal and poloidal injecting angles of EC waves can dramatically affect the power deposition, current profile and the total current.

Measurement and numerical calculation of the spectrum of LHCD antenna in the HL-2A tokamak

ZENG Jian-er, LU Zhi-hong, YUAN Yong, RAO Jun, LIU Yong

2005, 25(1):  37-41. 

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The LHCD antenna in the HL-2A tokamak is a modified version of the one used in the HL-1M tokamak formerly. The reflection of the mainwave-guide and the phase shift between the adjacentsub-wave guides have been measured. The measured results and spectrum calculation based on the measured parameters are described.The results show that the antennas will be useful for LHCD experiments in the HL-2A tokamak.

Studies of internal magnetic fluctuation in the HL-1M tokamak

ZHENG Yong-zhen, DING Xuan-tong, LI Wen-zhong

2005, 25(1):  42-48. 

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The transport of runaway electrons in a hot plasma can be comparatively easily measured in

steady state or perturbation experiments, which provide run away electron diffusivity Dr. The

diffusivity can be interpreted in terms of the magnetic fluctuation level. The runaway electron

diffusion coefficient is determined by internal magnetic fluctuations. The internal magnetic

fluctuations level (b_r/B_T) is estimated to be about (2~4)×10^-4 in the HL-1M plasma. The results

demonstrate the effectiveness of using runaway transport techniques for determining internal

magnetic fluctuations. A profile of the magnetic fluctuation level in the HL- 1M tokamak can be

estimated from D_r.

Isotope corrections of ablation rates in fusion plasma for different solid hydrogen molecule pellets

Deng Bai-quan,Peng Li-ling,Yan Jian-cheng,Wang Xiao-yu

2005, 25(1):  49-54. 

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The isotope corrections of ablation rates in fusion plasma forfive combinations of solid isotopic hydrogenic pellets, H₂, HD, D₂, DT, T₂ have been studied. The results show that modifications caused by the isotope effect for pellet erosion speeds range form 1 for hydrogen pellet down to 0.487 for tritium pellet and are not negligible in ablation rate calculations. These effects lead to deeper pellet substance deposition and improve the core fueling efficiency. The ITER core fueling difficulty will be moderately alleviated by taking into account of the isotope effects. For instance, our other numerical calculation results show that, with DT pellet of radius r_p0= 0.5cm injected from lower field side to get the penetration length L= 200cm in the ITER plasma, the required pellet speed will be reduced to 16.2km•s^-1 from 24.27km•s^-1 based on Kuteev 2D lentil model, and to 5.4km•s^-1 from 8.07km•s^-1 based on the Parks model. Our other work also shows if a DT pellet with size r_p0=0.5cm is injected from mid-plane high field side of ITER, the ablated substance of pellet can be deposited to the core plasma even if the velocity is as lowas 173m•s^-1 by considering the isotope effects and the drift in major radius direction caused by the vertical polarization current due to the difference of specific pressures between the inner and outer cloudlet.

Electron acceleration by Compton scattering in cone-shaped laser-plasma

HAO Dong-shan,HUANG Xiao-dong

2005, 25(1):  55-58. 

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Considering the characteristics and the electrostatic field energy in a cone-shaped femtosecond high power laser-plasma,the acceleration of the electrons of incident on a laser-plasma by the multiphoton nonlinear Compton scattering in this field isgiven byusingthe inelastic collisionmodel of relativistic electron and photon and relativistic electricity theory. We find that a vibration of electron acceleration energy takes place by the laser field in the laser plasma,and the electron acceleration effect is lowered by the electrostatic field. The conclusion on an electron acceleration energy rise is worked out using the two-photons nonlinear Compton scattering of the high-energy electron with photons in the cone- shaped femtosecond high power laser-plasma.

Vacuum system of the HL-2A tokamak

CAO Zeng, CUI Zheng-he, XU Yun-xian, FU Wei-dong,XUZheng-hua,LIU De-quan, CAI Xiao, GAO Xiao-yan

2005, 25(1):  59-64. 

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The basic design of a reliable vacuum system for the HL-2A tokamak is presented. It consists of the main pumping system, pumping divertor and glow discharge cleaning (GDC) system. The main pumping system provides the pumping capability for the high vacuum of chamber,out gassing by baking and GDC.The pumping divertor initially realizes the pumping and control of edge particles in tokamak discharge.The GDC system ensures the good wall condition of the device.The preliminary operation and the data obtained with these systems are also presented. The base pressure is 4.6 ×10^-6Pa,in the preliminary physical experiment operation of the HL-2A tokamak,and the total leak and outgassing rates of vacumm chamber is below 1.8×10^-5Pa•m³•s^-1 in 12 hours.

Development of a fast ionization gauge in the HL-2A tokamak

WANG Ming-xu,LI Bo,YANG Zhi-gang,YAN Long-wen,ZHANG Nian-man,LIAO Zhi-qing,YAN Dong-hai,GUO Jian-jun

2005, 25(1):  65-68. 

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A fast ionization gauge in a strong magnetic field and noisy environment is developed for

measuring the pressure in the divertor chamber of the HL-2A tokamak. The configuration, the

principles, the design outlines of the fast gauge and the results obtained on the HL-2A tokamak

are described. Without a magnetic field, the N₂ pressure region of the fast gauge is from

6.4×10^-6 to 0.6 Pa,and the ratio of ion current to electron current increases linearly with the

pressure. The highest pressure measured by the fast ionization gauge is 1.5 Pa for H₂ and 4

Pa for He. With magnetic field of 0.6T,the sensitivityof the fastgauge increases by a factorof 3.

The fastgauge has a fasttime response less than 4 ms and has high noise rejection.

Measuring the HL-2A divertor plasma with probes

HONG Wen-yu, YAN Long-wen, QIAN Jun, PAN Yu-dong,LUO Cui-wen, XU Zheng-yu, PAN Li,YUAN Bao-shan

2005, 25(1):  69-74. 

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In the HL-2A divertor experiments, the profiles of the electron temperature, density and floating potential on divertor plates are measured with the flush probe arrays fixed on the four divertor neutralization plates at the same toroidal cross-section in the HL-2A tokamak. The edge electron temperature during divertor configuration is higher than that during limiter one. Temperature asymmetry between the outer target plate and the inner one is compared. The result of magnetic surface reconstructed from signals of the 18 Mirnov coils is presented. Neutral gas pressure in the divertor chamber measured with fast ionization gauge during divertor discharge is given. The divertor experiment results indicate that the recycle of edge particles is reduced and the level of impurity flux is decreased in the main vacuum chamber.

Metal ion implantation source with a permanent magnetic field

MU Zong-xin1, LONG Zhen-hu1, LI Guo-qing1, GUAN Bing-yu2

2005, 25(1):  74-77. 

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The metal ion implanter has a maximum uniform beam current of 30mA with a pulse duration of 1ms at an accelerating voltage of 30kV and the frequency of 50Hz. The array of permanent magnets distributes around the ion chamber, confines the plasma and improves the uniformity of the radial ion density. The result indicates that the extractive characteristic of the implantor is improved.

Plasma diagnostic method using the transmission attenuation of microwaves at double frequencies

YUAN Zhong-cai, SHI Jia-ming

2005, 25(1):  78-80. 

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The plasma frequency and the electron collision frequency can be deduced with the plasma diagnostic method that utilizing the transmission attenuation of microwaves at two neighboring (double) frequencies in a non-magnetized plasma. The process of attenuation measurement is presented,which utilizes a systemconsisted of a sweep oscillator, a pair of broad-banded horns, and a scalar network analyzer, etc. Errors of the diagnostic results are discussed. This method is suitable for the elementary diagnostics of a atmospheric-pressure plasma.