Evolution of edge turbulent transport induced by L-mode detachment in the HL-2A tokamak

This paper presents the characteristics of L-mode detachment,together with the behavior of edge turbulent transport and plasma confinement on the HL-2A tokamak.Partially detached and pronounced detached states have been achieved in L-mode plasma.Stored energy was maintained before and after detachment.Edge turbulence and its transport have increased obviously in the partially detached state.In the pronounced detached state,redistribution of the density and temperature profiles due to detachment leads to low amplitude of electron temperature and pressure,as well as very weak edge turbulence and transport.Despite strong plasma radiation in the pronounced detached state,reduced edge turbulent transport contributes to maintaining stored energy in detached L-mode plasma in HL-2A.Different detachment states play an important role in the redistribution of density and temperature profiles,which requires further study.

Upgrade of an integrated Langmuir probe system on the closed divertor target plates in the HL-2A tokamak

A newly designed divertor Langmuir probe diagnostic system has been installed in a rare closed divertor of the HL-2A tokamak and steadily operated for the study of divertor physics involved edge-localized mode mitigation,detachment and redistribution of heat flux,etc.Two sets of probe arrays including 274 probe tips were placed at two ports(approximately 180°separated toroidally),and the spatial and temporal resolutions of this measurement system could reach6 mm and 1μs,respectively.A novel design of the ceramic isolation ring can ensure reliable electrical insulation property between the graphite tip and the copper substrate plate where plasma impurities and the dust are deposited into the gaps for a long experimental time.Meanwhile,the condition monitoring and mode conversion between single and triple probe of the probe system could be conveniently implemented via a remote-control station.The preliminary experimental result shows that the divertor Langmuir probe system is capable of measuring the high spatiotemporal parameters involved the plasma density,electron temperature,particle flux as well as heat flux during the ELMy H-mode discharges.

Progress of microwave diagnostics development on the HL-2A tokamak

Sets of powerful microwave diagnostic systems have been developed on the HL-2 A tokamak,including 18 subsystems with high spatial and temporal resolutions.These systems have been applied in the HL-2 A tokamak experiments to investigate the core plasma transport,turbulence,MHD,energetic particle physics and so on.In this paper,the microwave diagnostics and their applications are reviewed.Some new technologies,including GHz sampling digital correlation electron cyclotron emission(DCECE),multi-channel correlation reflectometers,and solid state terahertz interferometers,are also presented in the paper.

Preliminary Study of Ideal Operational MHD Beta Limit in HL-2A Tokamak Plasmas

Magnetohydrodynamic(MHD)n=l kink mode with n the toroidal mode number isstudied and the operational beta limit,constrained by the mode,is calculated for the equilibrium ofHL-2A by using the GATO code.Approximately the same beta limit is obtained for configurationswith a value of the axial safety factor qo both larger and less than 1.Without the stabilization ofthe conducting wall,the beta limit is found to be 0.821% corresponding to a normalized beta valueof β_N^c=2.56 for a typical HL-2A discharge with a plasma current Ip=0.245 MA,and the scaling ofβ_N^c～constant is confirmed.

Study of Plasma MHD Equilibrium in HL-2A Tokamak

EFIT(Equilibrium Fitting) code is successfully transplanted for HL-2A tokamak pa-rameters.The evolution of the equilibrium configurations for shot 2898 is simulated.It is shownthat the discharge starts with a limiter configuration and develops into a divertor configurationgradually after t=200 ms.The latter lasts until the end of the discharge at t=900 ms.Theevolution of the major plasma shape parameters such as the boundary magnetic fluxes,the posi-tions of the x-point and magnetic axis,and the minor radii obtained are calculated and comparedwith the experimental results.The agreement between the simulation and experiments are shownto be reasonable.The possibility for discharge quality improvement is discussed.

The Designed Operation of the Machine Control System on HL-2A Tokamak

The Ethernet and field-bus communications are used in the machine control system(MCS) of HL-2A. The control net, with a programmable logic controller (PLC) as its logic controlmaster, an engineering control management station as its net server, and a timing control PCconnected to a number of terminals, flexibly and freely transfers information among the nodeson it with the Ethernet transmission techniques. The PLC masters the field bus, which carriessmall pieces of information between PLC and the field sites reliably and quickly. The control netis connected into the data net, where Internet access and sharing of more experimental data areenabled. The communication in the MCS guarantees the digitalization, automation and central-ization. Also provided are a satisfactory degree of safety, reliability, stability, expandability andflexibility for maintenance.

Simulations of the effects of density and temperature profile on SMBI penetration depth based on the HL-2A tokamak configuration

Using the trans-neut module of the BOUT++ code, we study how the fueling penetration depth of supersonic molecular beam injection(SMBI) is affected by plasma density and temperature profiles. The plasma densities and temperatures in L-mode are initialized to be a set of linear profiles with different core plasma densities and temperatures. The plasma profiles are relaxed to a set of steady states with different core plasma densities or temperatures. For a fixed gradient, the steady profiles are characterized by the core plasma density and temperature. The SMBI is investigated based on the final steady profiles with different core plasma densities or temperatures. The simulated results suggest that the SMB injection will be blocked by dense core plasma and high-temperature plasma. Once the core plasma density is set to be N_(i0)= 1.4N_0(N_0= 1 × 10^(19)m^(-3)) it produces a deeper penetration depth. When N_(i0) is increased from 1.4N_0 to 3.9N_0 at intervals of 0.8N_0, keeping a constant core temperature of T_(e0)= 725 eV at the radial position of ψ = 0.65, the penetration depth gradually decreases. Meanwhile, when the density is fixed at N_(i0)= 1.4N_0 and the core plasma temperature T_(e0) is set to 365 eV,the penetration depth increases. The penetration depth decreases as T_(e0) is increased from 365 eV to 2759 eV. Sufficiently large N_(i0) or T_(e0) causes most of the injected molecules to stay in the scrape-off-layer(SOL) region, lowering the fueling efficiency.

The Power Supply System for HL-2A Tokamak's Magnetic Field

The highpower pulsed power supply system for the magnetic field of the HL-2ATokamak is described in this paper.The total output power of its eight magnetic field powersupply units of nearly 250 MW.Their highest DC output voltage and current are 3510 V and45 kA,respectively.All the units are operated in a pulsed mode.The pulse duration is 5 s,and the cyclic period is 15 min.The power supply system consists mainly of pulsed flywheelmotor generators,rectifying transformers,thyristor converters,diode rectifiers and switches.Thesystem incorporates many key technologies-supply equalization with two generators and four diodebridges,constant-angle phase triggers with a wide frequency range,current equalization,a statusdetector for the high current 6-phase converter,and advanced monitoring based on a programmablelogic computer and engineering parameter measurement.The experimental results show that theperformance of the power supply system satisfies the requirements of HL-2A experiments verywell.

Research on the phase adjustment method for dispersion interferometer on HL-2A tokamak

A synchronous demodulation system is proposed and deployed for CO_2 dispersion interferometer on HL-2 A,which aims at high plasma density measurements and real-time feedback control.In order to make sure that the demodulator and the interferometer signal are synchronous in phase,a phase adjustment(PA) method has been developed for the demodulation system.The method takes advantages of the field programmable gate array parallel and pipeline process capabilities to carry out high performance and low latency PA.Some experimental results presented show that the PA method is crucial to the synchronous demodulation system and reliable to follow the fast change of the electron density.The system can measure the lineintegrated density with a high precision of 2.0?×?10^(18)m^(-2).

High-speed VUV spectroscopy for edge impurity line emission measurements in HL-2A tokamak

A 20 cm focal length normal incidence vacuum ultraviolet(VUV_20 cm) monochromator with a fast time response has been developed for measuring edge impurity line emission in the wavelength range of 300–2000 ? on an HL-2A tokamak. An aberration corrected concave holographic grating with 1200 grooves/mm is adopted in the monochromator, which provides a wavelength dispersion of 40 ? mm^(-1). The aperture is f/4.5. A channel electron multiplier is used as a detector. The time resolution of the system is 17 μs. Wavelength calibration of the system has been done by using a hollow cathode light source in the laboratory with helium and argon gases. The obtained signals of helium and argon spectra are very strong since the inner surface of the monochromator vacuum chamber is blackened and the stray light level is then significantly reduced. The optical property of the system has been examined by scanning the width of the entrance and exit slits. The system is then installed at the mid-port of the HL-2A tokamak and typical line emissions from the HL-2A plasma are measured. Time behaviors of edge impurity line emissions are observed with the fast time response system in different plasma confinement regimes, especially in the H-mode discharges. The result shows that the VUV_20 cm system works very well to measure the edge impurity line emissions in the edge localized modes phase of H-mode discharges.

Identification of the magnetic island structure in the HL-2A tokamak

The identification of the magnetic island structure in the HL-2A tokamak is presented.First,the perturbation current as a source for the perturbation flux can be determined by using Mirnov probe measurements.By superposing the perturbation flux and the equilibrium flux reconnected by equilibrium fitting,the structure and the width of the magnetic islands can be estimated.The method has been used in the HL-2A experiments.

Analysis of Divertor Heat Flux with Infrared Thermography During Gas Fuelling in the HL-2A Tokamak

In HL-2A tokamaks,the behavior of heat flux deposited on the divertor targets has been studied during deuterium gas fuelling.The heat flux is reduced significantly after supersonic molecular beam injection(SMBI)fuelling during Ohmic and electron cyclotron resonance heating(ECRH)divertor discharges.The SMBI fuelling causes an increase in the plasma density and this change results in the experienced change of the edge properties.Most of this reduction in divertor target heat flux occurs together with a high plasma radiation region located at near the X-point.The largest reduction in heat flux profiles is observed at the outboard divertor separatrix strike point,while the heat flux far from the strike point remains almost unchanged.In particular,with SMBI multi-pulses gas fuelling,a partially detached divertor regime is observed with a highly radiating region at the X-point.With the onset of the partially detached divertor regime,a sudden drop in both heat flux and power flow on the divertor target is observed.The reduction in power load on the divertor targets is roughly equal to the increase in plasma radiation loss.

Design ofthe ECRH/ECCD Launcher System for HL-2A Tokamak

An ECRH/ECCD system with two 68 GHz/500 kW/1S gyrotrons will be built up in HL-2A tokamak. The location of the Gaussian beam waist is 580 mm away from the center of the plasmas and the beam radius is 37 mm at the center of the plasmas. Compared to the minor plasma radius (420 mm), it is small enough for localized control. The launcher system covers a wide toroidal and poloidal steering range by the two steering plane mirrors. Therefore it is possible to explore the on- and off-axis heating over half of the plasma minor cross section and the co-current drive.

Investigation of Impurity Ion Transport with Laser Blow-off in HL-2A Tokamak

非再循环的杂质被注入欧姆的 HL-2A 血浆为初次。钛和铝的杂质与改变血浆密度和电流在分泌物被注射。注射杂质离子的传送对流和散开过程在茶碱病房阶段期间是调查的品质上。结果证明杂质的运输比在它外面在血浆的中央区域是慢得多的并且它极大地在锯齿锐齿碰撞期间被提高。

Transport Simulation of ECRH H-Mode Experiments on HL-2A Tokamak

Transport simulation of ECRH H-mode experiments on HL-2A tokamak is carried out using ONETWO code,the GLF23 and PEDESTAL models,along with TORAY code for ECRH.It is found that the initial electron and ion temperature profiles affect L-H transition significantly,and larger initial temperature gradient at the edge plasma benefits the transition.The simulation results show that it is possible to achieve ECRH H-mode with appropriate initial electron and ion temperature profiles under present discharge conditions on HL-2A tokamak.In addition,the pedestal density,electron temperature and pedestal width are predicted,and the evolutions of electron and ion temperature profile are calculated.

The Real-Time,High Precision Phase Difference Measurement of Electron Density in HL-2A Tokamak

This paper introduces a real-time high precision measurement of phase difference based on Field Programmable Gate Array(FPGA) technology,which has been successfully applied to laser grating interference measurement and real-time feedback of plasma electron density in HL-2A tokamak.It can track the changes of electron density while setting the starting point of the density curve to zero.In a laboratory test,the measuring accuracy of phase difference is less than 0.1°,the time resolution is 80 ns,and the feedback delay is 180 μs.

Research on the Real-Time Phase Jump Process Method for Plasma Electron Density Measurement in HL-2A Tokamak

In the real-time plasma electron density measurement using far infrared(FIR) laser interferometry, the plasma electron density can be calculated by measuring the real time phase difference between the reference signal and the probe signal. A novel Real-time Phase Jump Process(RPJP) method is applied to the HL-2A tokamak. With this method, the phase difference precision is up to1/3600fringe(1 fringe is equal to a phase shift of 2π), and the dynamic measurement range is extensible 65536 fringes. The time resolution of the phase difference is 80 ns, while the feedback delay is 180 μs.

Edge Particle Flux with Temperature Fluctuation in the HL-2A Tokamak

在边血浆的电子温度，密度，血浆潜力和他们的变化侧面在 HL-2A 与一个互给的探查系统同时被测量。四尖端的数据的分析结果显示温度变化有相对振幅 10 15% ，交上更多的贡献到粒子流动更低(0 25 kHz ) 并且更高的频率(50 250 kHz ) 变化。在温度变化或潜在的变化之间的连贯暗示他们的联合愿望影响异常运输。当认为温度是变化时，测量散开系数是大约三次 Bohm 散开系数。有温度变化的粒子流动第一次在 HL-2A 被讨论。

Numerical Simulation and Experimental Identification of Divertor Configuration in the HL-2A Tokamak

Single- and double-null divertor configurations in HL-2A are simulated by SWEQU equilibrium code. Lower divertor discharges in the first physics campaign have been achieved by two kinds of power supply method of multipole-field coils. Single-null divertor configuration has been identified by visible photography, target probe arrays and the reconstructed magnetic surface. Magnetic separatrix and minor radius of plasma column are obtained by a reconstructed code of multiple current filaments using 18 Mirnov signals.