EAST电磁环境下辐射量热诊断系统屏蔽接地研究

介绍了东方超环(EAST)磁约束聚变实验装置中辐射量热诊断系统的屏蔽接地措施,并对整个系统的接地方案进行了研究。通过采用封闭的屏蔽支撑盒、双屏蔽传输电缆、串并混合单点接地等措施,有效避免了多道之间的共振和地回路,保证了测量系统在复杂电磁环境下的正常工作。     

Evidence of vapor shielding effect on heat flux loaded on flowing liquid lithium limiter in EAST

A lithium (Li) vapour layer was formed around a flowing liquid Li limiter to shield against the plasma incident power and reduce limiter heat flux in the EAST tokamak. The results revealed that after a plasma operation of a few seconds, the layer became clear, which indicated a strong Li emission with a decrease in the limiter surface temperature. This emission resulted in a dense vapour around the limiter, and Li ions moved along the magnetic field to form a green shielding layer on the limiter. The plasma heat flux loaded on the limiter, measured by the probe installed on the limiter, was approximately 52% lower than that detected by a fast-reciprocating probe at the same radial position without the limiter in EAST. Additionally, approximately 42% of the parallel heat flux was dissipated directly with the enhanced Li radiation in the discharge with the liquid metal infused trenches (LIMIT) limiter. This observation revealed that the Li vapour layer exhibited an excellent shielding effect to liquid Li on plasma heat flux, which is a possible benefit of liquid-plasma-facing components in future fusion devices.     

Structural design of cryogenic component support for EAST （HT-7U）

EAST is a full superconducting tokamak with an elongated plasma cross-section. It consists of superconducting poloidal field (PF) magnet system, toroidal field (TF) magnet system, vacuum vessel with inner parts, thermal shields and cryostat vessel. The mission of the project is to widely investigate both physics and technologies of advanced tokamak operations, especially the mechanism of power and particle handling for steady-state operations. The cryogenic component is mainly composed of superconducting TF and superconducting PF coils that ensure the ability of sustaining magnetic field for plasma confinement, control and shaping in steady-state. This report describes the process of the structure design of cryogenic component support for EAST.     

A real-time neutron-gamma discriminator based on the support vector machine method for the time-of-flight neutron spectrometer

A new neutron-gamma discriminator based on the support vector machine(SVM) method is proposed to improve the performance of the time-of-flight neutron spectrometer. The neutron detector is an EJ-299-33 plastic scintillator with pulse-shape discrimination(PSD) property. The SVM algorithm is implemented in field programmable gate array(FPGA) to carry out the real-time sifting of neutrons in neutron-gamma mixed radiation fields. This study compares the ability of the pulse gradient analysis method and the SVM method. The results show that this SVM discriminator can provide a better discrimination accuracy of 99.1%. The accuracy and performance of the SVM discriminator based on FPGA have been evaluated in the experiments. It can get a figure of merit of 1.30.     

Manufacturing and testing of W/Cu mono-block small scale mock-up for EAST by HIP and HRP technologies

ITER-like W/Cu mono-block plasma-facing components (PFCs) will be used in vertical target regions of the experimental advanced superconducting tokamak (EAST) divertor. The first W/Cu mono-block small scale mock-up with five W mono-blocks has been manufactured successfully by technological combination of hot isostatic pressing (HIP) and hot radial pressing (HRP). The joining of a W mono-block and a pure copper interlayer was achieved by means of HIP technology and the bonding strength was over 150 MPa. The good bonding between the pure copper interlayer and a CuCrZr cooling tube was obtained by means of HRP technology. In order to understand deeply the process of HRP, the stress distribution of the mock-up during HRP process was simulated using ANSYS code. Ultrasonic Nondestructive Testing (NDT) of the W/Cu and Cu/CuCrZr interfaces was performed, showing that excellent bonding of the W/Cu and Cu/CuCrZr interfaces. The thermal cycle fatigue testing of the mock-up has been carried out by means of an e-beam device in Southwest Institute of Physics, Chengdu (SWIP) and the mock-up withstood 1000 cycles of heat loads up to 8.4 MW/m² with the cooling water of 2 m/s, 20 °C, 0.2 MPa.     

Reconstructions of velocity distributions from fast-ion D-alpha(FIDA) measurements on EAST

2D fast-ion velocity-space distributions have been reconstructed from two-view fast-ion D-alpha(FIDA) measurements on experimental advanced superconducting tokamak(EAST). To make up for the sparse data and incomplete velocity-space coverage with the dual-view, we use nonnegativity and null-measurements as prior information to reconstruct the velocity distribution in experiments with co-and counter-current neutral beam injection. An improved reconstructed fast-ion distribution is achieved by combining the existing O-and B-port FIDA measurements with the proposed A-port FIDA view. To further improve the reliability of FIDA-based reconstructions on EAST, based on real multi-view FIDA measurements on EAST in the near future, various bases will be studied further.     

EAST托卡马克新型积分器系统控制器的研制

为了满足EAST托卡马克的实验需求,提升积分器系统的可维护性和可测试性,研制了新型积分器系统控制器。该控制器采用ARM微控制器和轻量级IP协议栈,实现了积分器系统的网络化控制。所提供的参数设置指令可远程设置和读取积分器板卡上放大器的放大倍数,而控制指令则提供了初始化、标准信号积分、脉冲积分、积分保持、标定和探针测试功能。经实验和EAST现场测试,该积分器系统控制器可满足EAST装置的实验要求。     

Design,Analysis and R＆D of the EAST In-Vessel Components

In-vessel components are important parts of the EAST superconducting tokamak. They include the plasma facing components, passive plates, cryo-pumps, in-vessel coils, etc. The structural design, analysis and related R＆D have been completed. The divertor is designed in an up-down symmetric configuration to accommodate both double null and single null plasma operation. Passive plates are used for plasma movement control. In-vessel coils are used for the active control of plasma vertical movements. Each cryo-pump can provide an approximately 45 m^3/s pumping rate at a pressure of 10^-1 Pa for particle exhaust. Analysis shows that, when a plasma current of 1 MA disrupts in 3 ms, the EM loads caused by the eddy current and the halo current in a vertical displacement event （VDE） will not generate an unacceptable stress on the divertor structure. The bolted divertor thermal structure with an active cooling system can sustain a load of 2 MW/m^2 up to a 60 s operation if the plasma facing surface temperature is limited to 1500 ℃. Thermal testing and structural optimization testing were conducted to demonstrate the analysis results.     

Numerical Simulation Approaches to Evaluating the Electromagnetic Loads on the EAST Vacuum Vessel

Numerical simulation approaches are developed to compute the electromagnetic forces on the EAST vacuum vessel during major disruptions and vertical displacement events, with the halo current also considered. The finite element model built with ANSYS includes the vacuum vessel, the plasma facing components and their support structure, and the toroidal and poloidal field coils. The numerical methods are explained to convince of its validity. The eddy current induced by the magnetic flux variation and the conducting current caused by the halo current are also presented for discussion. The electromagnetic forces resulting from the numerical simulation are proven to be useful for structure design optimization. Similar methods can be applied in the upgrades of the EAST device.     

Study on the Dynamic Performance of the Helium Turboexpander for EAST Subsystems

An increase of the cooling capacities in the liquid helium temperature area is required by Experimental Advanced Superconducting Tokamak(EAST) due to the extension of its subsystems in the near future.Limited by the heat exchangers,cryogenic pipes,and cryogenic valves,it is difficult to enlarge the present EAST helium system.10~2 W@4.5 K level helium cryogenic systems are needed in view of feasibility and economy.A turboexpander is the key component of a helium cryogenic system.In this article,a hydrostatic gas lubricated cryogenic helium turboexpander for a 900 W@4.5 K cryogenic helium system was developed for the EAST updated subsystem by the Institute of Plasma Physics,Chinese Academy of Sciences and the Institute of Cryogenic and Refrigeration of Xi'an Jiaotong University.The main components,such as gas bearings,expansion wheel,shaft,and brake wheel,were briefly presented.The dynamic performance of the journal and thrust gas bearings was investigated numerically.The rotordynamic performance of the developed turboexpander was studied experimentally.The results show that the axial and radial load capacities supplied by the journal gas bearing and thrust gas bearing are enough to balance the axial force and radial force of the rotor.A 43%overspeed operation was achieved,which validated the reasonable design of the turboexpander.     

Development of a Data Acquisition Control System for the First NBI on EAST

Neutral beam injection （NBI） heating is one of the most efficient auxiliary plasma heating methods for fusion devices. The data acquisition control system （DACS） with PXI （pe- ripheral component interconnect extensions for instrumentation） data acquisition card for the first NBI system in the experimental advanced superconducting tokamak （EAST） is presented in this paper. As an important sub-system, DACS is designed to obtain physical measurement signals in the EAST NBI system and to deal and store these data with the Lempel-Ziv-Oberhumer （LZO） lossless data compression algorithm, as well as offer convenient data call-back and access inter- faces to the user for examining and analyzing the data. Experimental results show that accurate data will ensure that researchers correctly analyze it and then properly adjust the experimental parameters or operation, so DACS should take a large step in improving experimental efficiency. Tile hardware and software sections are briefly presented in this paper, and now this system has been tested to be able to work reliably and steadily.     

Modelling of carbon erosion and re-deposition for the EAST movable limiter

The movable limiter at the mid-plane of the Experimental Advanced Superconducting Tokamak(EAST)with carbon coatings on the surface was exposed to edge plasma to study the material erosion and re-deposition.After the experiments,the carbon erosion and re-deposition is modelled using the 3D Monte Carlo code ERO.The geometry of the movable limiter,3D configuration of the plasma parameters and electromagnetic fields under both limiter and divertor configurations have been implemented into the code.In the simulations,the main uncertain parameters such as carbon concentrationρ_c in the background plasma and cross-field transport coefficient D_⊥in the vicinity of surface according to the'funneling model',have been studied in comparison with experiments.The parameterρ_c mainly influences the net erosion and deposition profiles of the two sides of the movable limiter,while D_⊥mostly changes the profiles on the top surface.     

Upgrade of the Distributed Time-Keeping and Synchronization System for EAST

The distributed time-keeping and synchronization system(DTSS)underwent an upgrade for EAST during the last shutdown.The upgraded DTSS,designed based on PXI bus and reconfigurable I/O devices,synchronizes all other sub-systems by using a reference clock and trigger.It can produce a uniform clock up to 80 MHz,provide a delayed trigger from 1 ms to6872 s in 1 ms steps with 10 ns accuracy,and acquire the outputs of itself for self-inspection.The new DTSS was successfully applied in the 2012 spring EAST campaign,and has proven to be stable and reliable,giving an effective performance.The system structure and software development will be illustrated in detail in this paper.     

Development and Preliminary Commissioning Results of a Long Pulse 140 GHz ECRH System on EAST Tokamak(Invited)

A long pulse electron cyclotron resonance heating(ECRH)system has been developed to meet the requirements of steady-state operation for the EAST superconducting tokamak,and the first EC wave was successfully injected into plasma during the 2015 spring campaign.The system is mainly composed of four 140 GHz gyrotron systems,4 ITER-Like transmission lines,4 independent channel launchers and corresponding power supplies,a water cooling,control &inter-lock system etc.Each gyrotron is expected to deliver a maximum power of 1 MW and be operated at 100-1000 s pulse lengths.The No.1 and No.2 gyrotron systems have been installed.In the initial commissioning,a series of parameters of 1 MW 1 s,900 k W 10 s,800 k W 95 s and650 k W 753 s have been demonstrated successfully on the No.1 gyrotron system based on calorimetric dummy load measurements.Significant plasma heating and MHD instability suppression effects were observed in EAST experiments.In addition,high confinement(H-mode)discharges triggered by ECRH were obtained.     

Construction and Implementation of the Online Data Analysis System on EAST

In order to obtain diagnostic data with physical meaning,the acquired raw data must be processed through a series of physical formulas or processing algorithms.Some diagnostic data are acquired and processed by the diagnostic systems themselves.The data processing programs are specific and usually run manually,and the processed results of the analytical data are stored in their local disk,which is unshared and unsafe.Thus,it is necessary to integrate all the specific process programs and build an automatic and unified data analysis system with shareable data storage.This paper introduces the design and implementation of the online analysis system.Based on the MDSplus event mechanism,this system deploys synchronous operations for different processing programs.According to the computational complexity and real-time requirements,combined with the programmability of parallel algorithms and hardware costs,the OpenMP parallel processing technology is applied to the EAST analysis system,and significantly enhances the processing efficiency.     

Primary Results of Lithium Coating for the Improvement of Plasma Performance in EAST

First lithium coating associated with ion cyclotron range of frequency (ICRF) plasma was performed successfully in EAST. Results in reduction of both residual impurity and deuterium in the vacuum vessel were obtained. Particularly the partial pressure of deuterium after the lithium coating was reduced by about a factor of 5. Impurity radiation in the plasma was reduced and electron temperature increased by about 50%. Moreover, reproducible plasma discharges with high parameters, such as higher plasma current and density, could be easily obtained. These results showed that plasma performance was improved. Even though only 2 g of lithium were injected, the effective lifetime of the Li film was raised up to 40 shots.     

Development of Distributed Control System for Neutral Beam Injector on EAST

A distributed control system of Neutral Beam Injector(NBI) on the Experimental Advanced Superconducting Tokamak(EAST-NBI) is briefly presented in this paper.The control system is developed in accordance with the experimental operational characteristics of the EASTNBI.The NBI control system(NBICS),which is based on the computer network technologies and classified according to the control levels,consists of three levels:a remote monitoring layer,a server control layer,and a field control layer.The 3-layer architecture is capable of extending the system functions and upgrading devices.The timing system provides the reference clock of the synchronization and interlock for the EAST-NBI system.An interlock system ensures the safety of the experiment operators and field devices.Both of the ion sources of the beamline are designed to operate independently.This lays an important foundation for developing a control system for the second beamline on EAST.Experimental results demonstrate that the NBICS meets functional requirements of the EAST-NBI control,and makes experimental operations visual and automatic.     

The design and the manufacturing process of the superconducting toroidal field magnet system for EAST device

The toroidal field (TF) magnet system of EAST (HT-7U), which consists of 16 superconducting coils enclosed in steel cases, has been manufactured to generate the magnetic field of 3.5 T at the plasma center to maintain plasma in a tokamak configuration with a current up to 1 MA. The TF coils have an approximately D-shape geometry of 2.6 m wide and 4.0 m high, and operate at a maximum field of 5.8 T. The conductor used in the TF coil is NbTi/Cu cable-in conduit (CIC) conductor, and its operating current is 14.3 kA.In March 2006, the first cooling down of the EAST device has been carried out successfully. The total of TF magnet system has been cooled down from room temperature to 4.5 K, and the TF system has been energized up to 8.2 kA with 5 A/s ramp rate. In September 2006, full performances of the TF magnet system have been reached, and the device of EAST has delivered its first plasma. In addition, the TF magnet system has been routinely operated with a current maintained constant on a whole day basis, for a preliminary program of more than 500 shots.In this paper, the main parts of the design, developmental tests, and the fabrication and assembly of TF coils are described in detail.     

Simulations of first-orbit losses of neutral beam injection(NBI) fast ions on EAST

Simulations of first-orbit losses of neutral beam injection(NBI) fast ions in the EAST tokamak have been studied in detail by using the orbit-following code GYCAVA and the NBI code TGCO. Beam ion losses with the wall boundary are smaller than those with the last closed flux surface boundary. In contrast to heat loads on the wall without radio frequency wave(RFW)antennas, heat loads on the wall with RFW antennas are distributed more locally near the RFW antennas. The direction of the toroidal magnetic field dramatically affects the final positions of lost fast ions, which is related to the magnetic drift. The numerical results on heat loads of beam ions corresponding to different toroidal magnetic fields are qualitatively consistent with the experimental results. Beam ion losses increase with the beam energy for the co-current NBIs and the counter-perpendicular NBI. We have studied the behavior of fast ions produced by a small section neutral beam(beamlet) by using the numerical tool NBIT. The distributions of the loss fraction of beamlet fast ions peaked near the edge of the beam section for the counter-current NBIs, and they are related to the injection angle. This indicates that the first-orbit losses can be reduced by changing the shape of beam cross section.     

RF calculation and thermal-stress analysis of the ECRH launcher on EAST tokamak

EAST is a medium sized superconducting tokamak with major radius R = 1.8 m, minor radius a = 0.45 m, plasma current I_p ≤ 1 MA, toroidal field B_T ≤ 3.5 T and expected plasma pulse length up to 1000 s. An electron cyclotron resonance heating (ECRH) launcher for four-beam injection is being installed on EAST tokamak. Four electron cyclotron wave beams which are generated from four sets of 140 GHz/1 MW/1000 s gyrotrons will be injected into the plasma by the spherical focusing mirrors and plane mobile mirrors. The focusing mirrors are spherical to focus Gaussian beams after reflection. Four plane mobile mirrors independently steer continuously in the poloidal and toroidal direction controlled by motors. With the suitable distance between mirrors and appropriate focal length of focusing mirror, the beam radius in the resonance layer of plasma is 31.145 mm. The heat from plasma radiation and metal losses is loaded on the mobile mirror. In order to decrease the temperature and thermal stress, the inner equivalent diameter of water channels is 8 mm and the suggested water velocity is 4 m/s.