Statistical Characterization of Boundary Fluctuations in the HT—7 Tokamak

The statistical properties of plasma fluctuations are characterized in the boundary region of HT-7 tokamak. A non-Gaussian feature is observed in fluctuations of ion saturation current and floating potential in most of the scrape-off layer regions. The statistical properties of fluctuations have a clear radial dependence, showing a near-Gaussian character in the proximity of the velocity shear layer location and another region where the poloidal velocity has a trend to zero. Fluctuations show a bursty character with pulses asymmetric in time and the time asymmetry reaches the minimum around the shear layer. From the results, we can see an obvious coupling of the pulses and the poloidal flow.     

Measurements of Boundary Plasma in Synergy Discharges of IBW and LHCD on the HT-7 Tokamak

By applying ion Bernstein wave (IBW) heating into the lower hybrid current drive (LHCD) plasma, improved confinements have been obtained in the HT-7 tokamak. The central electron temperature was doubled and the storage energy was increased significantly. The core electron density and temperature were broadened and ther profiles near the edge were steepened. A transport barrier has been formed in the vicinity of the limlter radial location. An enhanced shear in poloidal phase velocity was found in the same region with reduction of the fluctuation levels and the coherences between fluctuations. The results suggest that the improved confinement in the IBW and LHCD plasma is at least partially due to the modification of shear in poloidal velocity and then the suppression of fluctuations and fluctuation induced fluxes via de-correlation effect.     

Bootstrap Current Increment After Siliconization on the HT—7 Tokamak

We present some results for the estimation of the bootstrap current after sillconization on the HT-7 tokamak.After siliconization,the plasma pressure gradient and the electron temperature near the boundary are larger than before siliconization.These factors influence the ratio of the bootstrap current to the total plasma current which increases from several per cent to above 10%.The results are expected to explain the previous experimental phenomena that,after siliconization,the plasma current profile is broadened and the higher current can be obtained easily on the HT-7 tokamak experiment.     

HT—7托卡马克中等离子体平衡研究

本文解决了二维轴对称近似下带铁芯的托卡马克中等离子体平衡问题，计算了ＨＴ－７托卡马克中的等离子体平衡位形以及极向场系统的非线性电感和垂直场系数。最后应用Ｋｉｒｃｈｈｏｆｆ方程组和平衡垂直场公式得到了一组等离子体，加热场和垂地直场线圈的电流波形的自洽曲线。     

Observation of Radial Propagation of Electrostatic Fluctuations in Edge Plasma of the Sino United Spherical Tokamak

Radial propagation of electrostatic fluctuations in the edge plasma of Sino-United Spherical Tokamak (SUNIST) has been measured using Langmuir probes. The propagation characteristics of the floating potential fluctuations are analysed by the two-point correlation technique. The results show radially outward propagation of the turbulent fluctuations at all measured radial positions. The power-average wavenumber profile is approximately constant in plasma edge region and suddenly increases to the limiter. These results are in good agreement with the model predictions proposed by Mattor which suggests that the drift wave propagation may be a source of edge turbulence.     

High Bootstrap Current Fraction during the Synergy of LHCD and IBW on the HT-7 Tokamak

More than 70% of the total plasma current is sustained by the bootstrap current and current drive during the synergy of lower hybrid current driving (LHCD) and ion Berstein wave (IBW) heating on the HT-7 tokamak.The lower hybrid non-inductive current source is off-axis and well localized, and more than 35% bootstrap current plasma has been obtained. The IBW in controlling electron pressure profile can be integrated into the LHCD target plasma. The largest steep gradient of the electron pressure profile in the region ρ - 0.5-0.7 mostly comes from the electron temperature profile, which may induce the large fraction bootstrap current. The large off-axis bootstrap current can help to create negative magnetic shear, and the good plasma confinement is achieved.     

Snake Studies in the HL-1M Tokamak

Lower-hybrid current drive (LHCD) experiments were carried out the HL-1M hydrogen plasmas. The effect of LHCD on central MHD activities [sawtooth (m=0), m =1 mode] were studied with the fluctuations observation of the soft X-ray (SXR) emission.     

Plasma Boundary Identification by Using Filament-Current Method on HL-2A Tokamak

The establishment of a divertor configuration is a task for a divertor tokamak. To achieve this goal, we have to identify plasma boundary at first. So, it is important to find a quick approach to calculate plasma boundary and other global parameters. Various methods     

Preliminary Observation on Coordination of Pellet Injection and Ion Bernstein Wave on a HT—7 Tokamak

A pellet injection (PI) experiment was performed during the application of the ion Bernstein wave on a HT-7 tokamak.A preliminary coordination effect was observed.With a lower wave power,shortly after PI,the coupling of the wave was enhanced,and the particle confinement was improved.With higher power,off-axis heating for 15% at about a/3 in the low field side was observed.     

The Plasma Boundary in Low-Parameter Divertor Discharges on the HL-2A Tokamak

Because the last closed flux-surface （LCFS） finally determines the shape of plasma cross-section, and the shaping of plasma is a key issue directly related with lots of the hot subjects of an advanced tokamak（AT） and of a reactor, e. g., the control on the current density, equilibrium, scrapeoff layer（SOL）, aspects of edge particle and energy, high plasma kinetic energy, and of course, the MHD instability suppression, the further studies on the LCFS related subjects, e. g., its determination, flux loss, etc., are still tokamak research. It equilibrium, poloidal needed for present is also important to get precise LCFS-related equilibrium or configuration properties for the controls on an AT and for the understandings on the underlying basic physical issues in a discharge.     

The First Results of Supersonic Molecular Beam Injection in the HL-2A Tokamak

HL-2A tokamak, the first tokamak with divertor in China, has been constructed and put into operation in 2002. The main parameters are R=1.65 m, a=0.4 m, BT=2.8 T, Ip = 0. 48 MA. The divertor of HL-2A is unique, because it is characterized with a large closed divertor chamber. The device has double divertor chamber, but now it is operating with lower single null configuration to study the physics of divertor for the next step design of a divertor. Supersonic molecular beam injection （SMBI） system with LN2 cooling trap was first installed and demonstrated on the HL-2A tokamak in 2004. The first results of SMBI into HL-2A plasma are to demonstrate the function of the HL-2A divertor and to observe the cold pulse propagation during multi-pulse SMBI on HL-2A Tokamak.     

HT—7超导托卡马克最新实验进展

HT－7超导托卡马克在过去的一年中取得较大进展：高参数放电时间长度接近4s,总加热功率超过1MW,在低杂波全波驱动、电流爬升、离子回旋共振加热、双波协同效应,射频壁处理,低环电压启动等方面都取得可喜的结果。     

HT-7装置新低杂波相控波导阵天线及其微波特性测量

介绍了HT－7装置新低杂波天线的结构。根据天线波导的特殊结构，设计了一些必要的测量器件（过渡波导和测量多结波导阵的波导－同轴转换器），并提出了新天线的测量方案，给出了测量结果及其功率谱计算结果。     

HT-7U等离子体位形与电流控制的数值模拟

通过数值求解了等离子体磁流体方程组，模拟了HT－7U装置自由边界等离子体位形及控制系统随时间的演变过程。模拟的结果对HT－7U装置及等离子体控制系统的设计具有重要的意义。     

HL—1M装置边缘等离子体特性研究

边缘和芯部等离子体的同时控制对优化托卡马克等离子体性能是重要的。边缘等离子体密度、温度和空间电位等通常采用朗缪尔静电探针测量,而旋转速度可用马赫探针测量。好的加料技术对于获得高性能等离子 体也很重要。在HL－1M装置上已开展了8发弹丸注入和分子束注入（MBI）加料实验,它能使等离子体产生中空的温度和电流密度分布,并容易获得高密度和良好的约束。本文主要介绍在低杂波电流驱动（LHCD）、多发弹丸注入和MBI三种典型放电中边缘等离子体参数的测量结果。