Modification of Boundary Parameters and Fluctuations by IBW and LHCD in the HT-7 Tokamak

Measurements of boundary parameters and their fluctuations have been performed in ohmic (OH) plasma and Ion Bernstein Wave (IBW) and Lower Hybrid Current Drive (LHCD) enhanced confinement plasma using a pneumatically driven Langmuir probe array on HT-7 toka-maX. In the enhanced confinement plasma~ the gradients of electron density and temperature become higher and a transport barrier comes into being in the vicinity of the limiter. The boundary potential shows a clear modification in the same region. The fluctuation levels are significantly depressed and the coherences between fluctuations are reduced evidently in the enhanced plasma.Meanwhile, we obtained the spectral features and the poloidal phase velocity of fluctuations us-ing a two-point correlation technique and found obvious modifications of the turbulence and the poloidal flow. The results suggest that the improved confinement in the IBW and LHCD enhanced plasma is at least partially due to the modification of the boundary parameters and the suppression of the boundary fluctuations and fluctuation induced fluxes.     

基于LabVIEW的多通道数据采集系统

采用NI PCI-MIO-16E-1数据采集卡为硬件平台,以LabVIEW为开发软件,采用NI-DAQmx驱动程序和TDMS高速数据流文件,开发了一套多通道数据采集系统。最高可实现16道信号同时采集,同时实现数据的实时后处理、在线监测和实时图形显示。该系统在现代测控、自动化和大型科学实验研究中具有重要的应用价值。     

Design of Amplifier Circuit for the HT-7 Tokamak Thomson Scattering System

Thomson scattering diagnostic is important for measuring electron temperature and density profiles. To improve the signal-to-noise ratio, a silicon avalanche photodiode （APD） with high quantum efficiency, high sensitivity, and high gain up to 100 was adopted to measure the Thomson scattering spectrum. A preamplifier, which has low noise, high bandwidth, and high sensitivity, was designed with suitable transimpedance. Using AD8367 as the post-amplifier, good performance of the APD readout electronics have been obtained. A discussion is presented on the performance of the amplifier using a laser diode to simulate the Thomson scattering light. The test results indicate that the designed circuit has a high amplifying factor and fast rising edge. So reduction of the integral gate of the CAMAC ADC converter can improve the signal-to-noise ratio.     

Observation of Pedestal Plasma Turbulence on EAST Tokamak

Pedestal plasma turbulence was experimentally studied by microwave reflectometry on EAST tokamak. The characteristics of edge pedestal turbulence during dithering L-H transition, ELM-free H-mode phase and inter-ELM phase have recently been studied on EAST. An edge spatial structure of density fluctuation and its dithering temporal evolution is observed for the first time on the EAST tokamak during the L-H transition phase. A coherent mode usually appears during the ELM-free phase prior to the first ELM on EAST tokamak. The mode frequency gradually decreases as the pedestal evolves. Analysis shows that the coherent mode is in the pedestal region inside the separatrix. In plasma with type-III ELMs, a precursor mode before ELM is usually observed. The frequency of the precursor was initially about 150 kHz and gradually decreased till the next ELM. The mode amplitude increases or shows saturation before ELM. In the plasma with compound ELMs composed of high and low frequency ELMs, the precursor was also observed before the high frequency ELM while the harmonic oscillations with frequencies of 20 kHz, 40 kHz and 60 kHz appear before the low frequency ELM.     

Soft x-ray Diode-array Diagnostic System for HT-7 Superconducting Tokamak

1. IntroductionEnergy loss caused by radiation of hightemperature plasma is produced during collisions between electrons and ions through the processes ofbrernsstrahlung radiation, recombination radiation,line radiation, and cyclotron radiation. A large portion Of radiation belongs to the ultra-soft and softx-ray regions of spectrum and carries a plenty ofphysical information in the plasma. Moreover, softx-ray (SXR) radiation emitted from any point inplasma can arrive outside of the plasma w…     

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).     

HT-7托卡马克装置上微波辐射测量研究

15道组成的电子回旋辐射温度测量系统，已安装在HT-7装置上，可以测量98GHz～124GHz来自于HT-7托卡马克等离子体的电子回旋辐射波的强度，从而获得电子温度。和其他电子温度诊断，如软x射线能谱记数，汤姆逊散射诊断以及边界静电探针相比，具有较好的时间分辨并可以给出电子温度分布。实验结果显示，在欧姆放电条件下，可以给出电子温度的时间演变，并在大于1．8T的纵场条件下，给出等离子体电子温度的分布。     

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.     

Experimental Determination of the ICRF Power Depositing on the Electrons in HT-7

This paper reports for the first time an experimental study on the power deposition profile of the ion cyclotron range frequencies （ICRF） power depositing on electrons in HT-7. The fast Fourier transform （FFT） analysis and the break in slope （BIS） method are utilized to obtain the information of the power deposition. The results indicate that the electrons were heated directly, and the electrons absorbed around 20% of the input power of the discharge of interest.