Ions Measurement at the Edge of HT-7 Tokamak

A reliable method of measuring ions and ion temperature in tokamak plasma is necessary, for which an omegatron-like instrument has been developed on the HT-7 tokamak. The basic layout of the omegatron-like instrument is shown in this article. The measurement of working gas ion has been performed in the last experimental campaign on HT-7 tokamak. The relations among ion current, the electron repeller voltage and trap voltage have been investigated. This omegatron-like instrument has also provided the edge-plasma ion temperature.     

Methods of Power Balance Analysis and Estimation of Current Density Profile for LHCD and IBW Discharges in HT-7 Tokamak

In this paper a simple code has been developed to analyze power balance and qualitatively evaluate current profiles for discharges with lower hybrid current drive （LHCD） and ion Bernstein wave （IBW） heating in the HT-7 tokamak. Electron and ion thermal diffusivity, profiles of the bootstrap current density and total plasma current density can be estimated by this code using the experimental data. This code offers an easy and reasonable means to understand plasma transport in HT-7.     

Impact of Toroidal Effect on Lower Hybrid Current Drive in Tokamak

The main topics concerning lower hybrid wave heating （LHH） and lower hybrid current drive （LHCD） in tokamak systems are presented. The inherent properties of tokamak systems give the ‘gap＇ filling on Brambilla＇s spectrum, which are conducive to LHCD, but, on the other hand, induce a consumption of wave energy by the trapped electrons, which reduce the current drive efficiency. The methods for the enhancement of the current drive efficiency may be derived from detailed analyses by drawing upon the ray tracing technology on toroidal geometry and the Fokker-Planck theory on velocity space.     

磁调制DCCT调制噪声及测量方法研究

硬X射线自由电子激光装置要求电源输出电流分辨率优于2.5×10^-6,因此,直流电流互感器（DCCT）的分辨率也必须高于以上指标,而降低DCCT调制噪声是提高其分辨率的重要方法。为降低调制噪声,本文提出了一种调制噪声的数学模型,导出了磁调制噪声的近似表达式,分析了调制噪声与相关因素的关系。同时提出了一种调制噪声的评估方法,该方法利用Matlab的periodogram命令获得噪声功率谱。利用数学模型和评估方法分析了Sinap-DCCT产品的噪声特征,结果表明,调制噪声与相关因素的关系符合数学模型的推论。据此,给出了降低DCCT调制噪声的解决方向。     

Experimental Results of MHD Suppression with Modulated LHCD on the HT-7 Tokamak

Modulation of lower hybrid current drive was used successfully to suppress MHD activity. This was achieved in discharges with MHD m = 2 tearing modes during the discharge conditions Ip = 110 kA, Bt = 1.75 T, ne0 - 1.1 ×1013 cm-3. The delivering time of LHCD pulse is less then 30 μs. The amplitude, interval and the period of LHCD modulation pulse can be adjusted very conveniently. The modulation LHCD can be delivered very fast at any time during the discharge. The modulation LHCD period was always much shorter than the plasma resistive time (Tη≈100 ms). So the profile of plasma current is changed much faster than the plasma resistive time. The different forms of LHCD modulating can be proved.     

The Experiment of Modulated Toroidal Current on HT-7 and HT-6M Tokamak

The Experiments of Modulated Toroidal Current were done on the HT-6M tokamak and HT-7 superconducting tokamak. The toroidal current was modulated by programming the Ohmic heating field. Modulation of the plasma current has been used successfully to suppress MHD activity in discharges near the density limit where large MHD m = 2 tearing modes were suppressed by sufficiently large plasma current oscillations. The improved Ohmic confinement phase was observed during modulating toroidal current (MTC) on the Hefei Tokamak-6M (HT-6M) and Hefei superconducting Tokamak-7 (HT-7). A toroidal frequency-modulated current, induced by a modulated loop voltage, was added on the plasma equilibrium current. The ratio of A.C. amplitude of plasma current to the main plasma current △Ip/Ip is about 12% ～ 30%. The different formats of the frequency-modulated toroidal current were compared.     

HL-2A托卡马克上等离子体环电流、环电压测量系统研制

详细描述了HL-2A托卡马克装置上等离子体环电流、环电压诊断系统,其中包括测量原理、诊断安排、实验等方面的内容。对实验中出现的杂散场干扰问题,及补偿技术做了全面的研究和探讨。并结合HL-2A的实验数据对诊断系统进行了验证。     

Study of the DEF Feedback Control System in AC Operation of Superconducting Tokamak

AC operation with multiple full cycles has been successfully performed on the superconducting tokamak HT-7. In the experiment, it was discovered that the saturation of the transformer magnetic flux with DEF, a signal name, was one of key aspects that affected the AC operation. The conditions of DEF were examined through the DEF feedback control system. By controlling the working patterns of the subsystems, namely the poloidal field control system and density control system, it was guaranteed that DEF would remain in the non-saturated status.     

Measurement of Zonal Flows in a Tokamak Using Langmuir Probe Array

Zonal flows have been measured with several novel Langmuir probe array on the HT-7 tokamak since 2002. The forked probe and its improved generation, the farmer forked probe were designed based on the original idea of the Reynolds stress triple tips array. In order to measure the radial shearing rate of zonal flows, the pyramid probe was also designed. This paper addresses the technical aspects regarding this new application. Since the zonal flows dynamics is now widely believed crucial to plasma confinement physics, an important application field of Langmuir probe was opened up.     

Vacuum Poloidal Magnetic Field of Tokamak in Alternating-Current Operation

Vacuum poloidal magnetic field of tokamak in alternating-current (AC) operation is investigated. It is found that the vacuum magnetic field in AC operation is qualitatively different from that in direct-current (DC) operation. In the DC case, the vacuum magnetic field varies along the poloidal direction with one period, while in the AC case, the vacuum magnetic field varies along the poloidal direction with two periods. This implies that two sets of vertical field coil may be needed for the AC operation.     

Current drive operation in a tokamak

Three modes of current drive operation in a tokamak — continuous, cyclic, and rfinitiated-are studied for air core and iron core transformer. It is found that the air core transformer is in general more flexible than the iron core transformer for current drive operation. For continuous operation, the shutoff time of the Ohmic heating circuit of the air core transformer can be reduced to zero by using a bias current. On the other hand, the shutoff time of the iron core transformer remains finite even if the bias current is used, because of hysteresis. For cyclic operation, methods of shortening the recharging time are investigated for both types of transformer. The effects of the transformer on rf-initiated operation are investigated. A model design of a saturable iron core tokamak for current drive experiments is also presented.     

Design of Magnetic Measurement System on SUNIST Spherical Tokamak

A magnetic measurement system consisting of magnetic probes and flux loops for spherical tokamak SUNIST, is uniquely designed due to the strongly shaped plasma cross section and the narrow space near the central solenoid. Plasma equilibrium reconstruction with the current filament method is performed to determine the number and positions of the magnetic probes and flux loops, as well as their design precision required.     

Measurement of Magnetic Island Width by Multi-Channel ECE Radiometer on HT-7 Tokamak

A 16-channel electron cyclotron emission (ECE) radiometer has been employed to observe the (m; n) = (2; 1) magnetic island structure on HT-7 tokamak, where m and n represent the poloidal and toroidal mode number respectively. The results indicate that the island width is about 7 cm when the magnetic island is saturated during the m=n = 2=1 mode. The location of resonance surface can be determined by plotting the contour of ECE relative fluctuation.This method could be applied to the HT-7 and EAST campaigns in the future for the research of neoclassical tearing modes (NTMs).     

小球形托卡马克嬗变堆堆芯参数分析

本文探讨作为聚变能中间应用的一种可行性 :利用低环径比球状托卡马克堆的高能聚变中子嬗变核电站的核废物。计算了堆芯等离子体物理参数、中心柱增益并进行参数学分析、几种可能的电流驱动方案比较和中心柱冷却方案设计及其计算。为了减轻偏滤器和第一壁材料的要求 ,我们有意选择较低堆芯物理参数 ,较低的中子壁负载运行。结果表明中心柱增益较低。建议从理论上探索研究由球状托卡马克等离子体顺磁性 ,建立一个无力球马克极向电流壳为中心区提供大部分或全部Bt,旨在建立无中心柱的低径比球状托卡马堆。如果可行 ,它的性能将会大大改善     

Fuelling and Diagnostics with Pellet Injection in the HL-1M Tokamak

The pellet injection experiments for fuelling and diagnostics have been carried out on the HL-1M tokamak. The eight-pellet injector was installed on HL-1M. A reliable monitordetector and camera system was set up to take initial pellet photographs and measure the initial pellet speed and size. High fuelling efficiency of 60 % - 100 % and a density profile with a peaking factor of 1.8 - 2.0 were obtained. The maximum density close to 10^14/cm^3 in HL-1M was achieved with newly optimized combined fuelling techniques. Two typical models of pellet ablation have been utilized for simulative calculation of the ablation rates in HL-1M. In comparison with the distribution of the measured Hα emission intensity from the digital data of the CCD camera, the experimental result seems more optimistic for core fuelling than theoretical predictions by the two models. The safety factor profile q（r） has been extracted from the information provided by the CCD camera during the pellet injection. The reliability of the measured results depends mainly on the calibration of the imaging space position. Based on the calibration, the measured q-profile becomes more reasonable than those published previously for the same shot number and same photograph.     

A Consideration on Increasing Current Density in Normal Conducting Toroidal Field Coil for Spherical Tokamak Power Plant

The center post is the most critical component as an inboard part of the toroidal field coil for the low aspect ratio tokamak. During the discharge it endures not only a tremendous ohmic heating owing to its carrying a rather high current but also a large nuclear heating and irradiation owing to the plasma operation. All the severe operating conditions, including the structure stress intensity and the stability of the structure, largely limit the maximum allowable current density. But in order to contain a very high dense plasma, it is hoped that the fusion power plant system can operate with a much high maximum magnetic field BT ≥12 T-15 T in the center post. A new method is presented in this paper to improve the maximum magnetic field up to 17 T and to investigate the possibility of the normal conducting center post to be used in the future fusion tokamak power plant.     

Current in the Edge of Small Size Divertor Tokamak

The scheme of poloidal (parallel) currents calculation is presented and compared to the two-dimensional code results both for the core region and for the Scrape-Off layer (SOL). A method of reduction of the two-dimensional equation for potential to one-dimensional ordinary differential equation is suggested. Also the impact of neutral beam injection (NBI) in plasma edge of small size divertor tokamak (SSDT) is studied.     

EAST-ICRF传输线驻波电流测量

为了测量托卡马克放电期间离子回旋加热系统的传输线电流值,利用电流探针搭建了传输线电流测量系统。对传输线电流测量原理进行简单介绍,并对电流探针的特性进行分析研究,确保电流探针的性能。将实验中用电流探针测得的传输线电流值与电压探针拟合计算得到的传输线电流值进行了对比,验证了传输线电流测量系统的可靠性。     

Experiment and Operation of a LHCD—35kV／2.8MW／1000s High—Voltage Power Supply on HT—7 Tokamak

A-35kV/2.8MW/1000s high-voltage power supply(HVPS) for HT-7 superconducting tokamak has been built successfully.The HVPS is scheduled to run on a 2.45 GHz/1MW lower hybrid current drive(LHCD)^[1] system of HT-7 superoonducting tokamak before the set-up of HT-7 superconducting tokamak in 2003.The HVPS has a series of advantages such as good steady and dynamic response,logical computer program controlling the HVPS without and fault,operationa panel and experimental board for data acquisition.which both are grounded distinctively in a normative way to protec the main body of HVPS along with its attached equipments from dangers.Electric power cables and other control cables are disposed reasonably,to prevent singals from magnetic interference and ensure the precision of signal transfer.This paper involves the experiment and operation of a 35kV/2.8 MW/1000s HVPS^[2] for 2.45 GHz/1 MW LHCD system.The reliability and feasibility of the HVPS has been demonstrated in comparison with experimental results of original design and simulation data.     

Absolute Measurements of the Magnetic Field Generated by Different Coils in the Center of EGYPTOR Tokamak

The present work is devoted to measure the absolute magnetic field produced by different coils in the EGYPTOR tokamak using a calibrated pickup coil. Scaling these measurements in different equations connected with the discharge currents from each supply system are performed. The pickup coil used in the present study is well calibrated with Helmholz coils at the IPP in Prague, Czech Republic. A 0.2% deviation has been found between an evaluation done in the present study and the calibration using Helmholz coils. Experimental measurements of the toroidal magnetic field are in good agreement with calculations to within 2%. Very low values of stray magnetic field components arising from TF and OH coils are recorded which proves that the compensation coils for these components are sufficient.