Electron Heating of LHCD Plasma in HT-7 Tokamak

Electron heating via lower hybrid current drive （LHCD） has been investigated in HT-7 superconducting tokamak. Experiments show that the central electron temperature Te0, the volume averaged electron temperature 〈 Te 〉 and the peaking factor of the electron temperature QTe = Teo/〈 Te 〉 increase with the lower hybrid wave （LHW） power. Simultaneously the electron heating efficiency and the electron temperature as the function of the central line-averaged electron density （ne） and the plasma current （Ip） have also been investigated. The experimental results are in a good agreement with those of the classical collision theory and the LHW power deposition theory.     

The Study of Heat Pulse Propagation on HT—7 Tokamak

The propagation of heat pulses originating from sawtooth activity has been studied on the HT-7 tokamak.Two theoretical models are used for determining electron heat diffusivity from the experimental data measured by a diagnostic system of soft x-ray diode-array.The results show that one model caaled dipole model is more suitable for HT-7 tokamak.In order to improve the signal-to-noise(S/N) ratio of the original signals,over a few tens of sawteeth are averaged to generatc nicc wavcforms.The apace-time evolution is found to be diffusive in character,which is consistent with the theoretical model.The electron heat diffusivity determined from heat pulse propagation is larger than determined from background plasma power balance.The variation of Xe in different discharge phases has been also discussed.     

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.     

Recent Progress of HT-7U Superconducting Tokamak

HT-7U is a superconducting tokamak. which is being constructed in Institute of Plasma Physics, Chinese Academy of Sciences. The mission of the HT-7U project is to develop a scientific and engineering basis of the steady state operation of advanced tokamak.The engineering design of the device has been optimized. The R&D program is going on. Short samples of the conductor and a CS model coil were tested. All the TF and PF coils will be manufactured and tested in Institute of Plasma Physics. Therefore, a 600-meter long jacketing line for cable-in-conduit conductors along with two winding machines, a set of VPI equipment and a test facility for the TF and PF coils are ready in ASIPP now. In this paper, the recent progress of the HT-7U is described.     

The Positions and Number of Flux Loops and Magnetic Probes for the HT—7U Superconducting Tokamak

The plasma shape and other paremeters such as βp,li is important for the tokamak deveice where the palsma has a non-circular cross-section of sufficient elongation.The measuered signals of magnetic probes and flux loops are used to reconstruct the plasma shape and the current profile in device operation and plasma shape feed back control system.So the number and positions of magnetic probes and flux loops provides the basis of the plasma reconstruction.This paper instroduce how to use EFIT code (equilibrium fitting code)to determine the number and positions of the magnetic probes and flux loops.The simulation result is given also.     

Temperature Distribution at the Lower Hybrid Wave Antenna on the Superconducting Tokamak HT－7

The radiation constant of the plasma and the temperature distribution at the Lower Hybrid Wave(LHW) antenna on the superconducting tokamak HT-7 axe calculated from the engineering point of view and the result provides an important reference to the design of a new antenna.     

Plasma Shape and Current Control Simulation of HT-7U Tokamak

This paper describoes the discharge simulation of HT-7U tokamak plasma equilibrium and plasma current by solving MHD equations and surface average transport equations using an equilibrium evolution code. The simulated result shows the evolution of plasma parameter versus time .The simulated result can play an important role in the design of the plasma equilibrium and control system of a tokamak.     

The Circulating Current Analysis and Parameter Design of Interphase—Reactor of HT—7U Toroidal Power Supply

This paper analyzes the circulating current which is produced by HT-7U superconducting toroidal power supply-two sets of two-reverse-star converter with an interphase-reactor in parallel running on the basis of the output voltage mathematical equation of three-phaase semi-wave converter circuit.A new iden of omitting interphase-reactor between two converters is proposed,and the parameter design of interphase-reactor of HT-7 toroidal power supply is presented.Simulated results demonstrate the validity of this new project.     

Poloidal Field Control for the HT—7U Superconducting Tokamak

Controlling the poloidal field(PF) in the HT-7U superconducting tokamak is critical to the realization of the mission of advanced tokamak research.Plasma start-up,plasma position,shape,current control and plasma shape reconstruction have been performed as a part of its design process.The PF coils have been designed to produce a wide range of plasmas,Plasma start-up can be achieved for multiple conditions.Fast controlling coils for plasma position inside the vacuum vessel are sued for controloling the plasma vertical position on a short timescale.The PF coils control the plasma current and shape on a slower timescale,VXI(VME bus extensions for Instrumentation)Bus system and DSP(Digital Signal Processor is a basic unit of the feedback control system),the response time of which is about(2-4)ms.The basic unit of this system ,the shape-controlling algorithms of a few critical points on plasma boundary and real-time equilibrium fitting(RTEFIT)will be described in this paper.     

Experimental Study on LHCD Efficiency in HT-7 Tokamak

Lower Hybrid Current Drive (LHCD) experiments on HT-7 Tokamak have been carried out by scanning the following two parameters: central line averaged electron density (0.5～2.0)×10~(19)cm~(-3) and toroidal magnetic field (B_t=1.62～2.0T). The dependence of current drive efficiency on these parameters has been studied and the     

Experimental Study of Diagnosis Neutral Beam for HT-7 Tokamak

Parametrical effect on plasma discharge and beam extraction in the diagnosis neutral beam （DNB） system for HT-7 tokamak was studied experimentally. Useful results with an improved beam quality were obtained.     

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.     

Feedback Control Systems on HT-7 Tokamak

1. IntroductionThe construction of HT－7 Tokamak is a 5－layerstructure, including a cryostat and a vacuum vessel, the screen of an outer and an inner copper shellwith a liquid nitrogen cooling, and a superconducting magnet with a forced flow of helium cooling.Theplasma is screened by two layers of copper with athickness of l.5 cm. [1] A simple structure is shownin Fig.1.For the vertical field being difficult to pass throllghthe double copper shells less than 400 ms, it is difficult for plas…     

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.     

Investigation of Ion Temperature Characteristics in the HT-7 Tokamak

Characteristics of ion temperature measured with charge-exchange recombination spectroscopy （CXRS） were studied in Ohmic, lower-hybrid-wave （LHW） driven and ion...     

Hard X-Ray PHA System on the HT-7 Tokamak

A new hard X-ray pulse-height analysis （PHA） system has been established on HT-7 tokamak for long pulse steady-state operation. This PHA system consists of hard X-ray diagnostics and multi-channel analysers （MCA）. The hard X-ray diagnostics consists of a vertical X-ray detector array （CdTe） and a horizontal X-ray detector array （NaI）. The hard X-ray diagnostics can provide the profile of power deposition and the distribution function of fast electron during radio frequency （RF） current drive. The MCA system is the electronic part of the PHA system, which has been modularized and linked to PC through LAN. Each module of MCA can connect with 8 X-ray detectors. The embedded Ethernet adapter in the MCA module makes the data communication between PC and MCA very convenient. A computer can control several modules of MCA through certain software and a hub. The RAM in MCA can store 1024 or more spectra for each detector and therefore the PHA system can be applied in the long pulse discharge of several minutes.     

Fast Thermography for HT-7U Superconducting Tokamak

1. IntroductionThe tokamak configuration is the most favorable approach for the confinement of nuclear fusionplasma with magnetic field. But the tokamak suffers from three main limitations at present f disruption, pulsed operation and low fi values. HT--7U isa full superconducting tokamak device designed toaddress these three problems, especially for an advanced steady--state operation. FOr disruption study,It is very important to know the temperature profilesacross the first wall during dis…