EAST托卡马克的中性束注入方案

高能中性束注入(Neutral beam injection,NBI)是核聚变装置托卡马克采用的芯部辅助加热和非感应电流驱动主要手段之一.本文介绍了国家大科学工程全超导托卡马克实验装置(Experimental advanced super-conductingtokamak,EAST)上的高能NBI加热方案及注入器的工程要求,并讨论了中性束在EAST等离子体中的传输等相关问题.     

Divertor detachment operation in helium plasmas with ITER-like tungsten divertor in EAST

Detachment in helium (He) discharges has been achieved in the EAST superconducting tokamak equipped with an ITER-like tungsten divertor. This paper presents the experimental observations of divertor detachment achieved by increasing the plasma density in He discharges. During density ramp-up, the particle flux shows a clear rollover, while the electron temperature around the outer strike point is decreasing simultaneously. The divertor detachment also exhibits a significant difference from that observed in comparable deuterium (D) discharges. The density threshold of detachment in the He plasma is higher than that in the D plasma for the same heating power, and increases with the heating power. Moreover, detachment assisted with neon (Ne) seeding was also performed in L- and H-mode plasmas, pointing to the direction for reducing the density threshold of detachment in He operation. However, excessive Ne seeding causes confinement degradation during the divertor detachment phase. The precise feedback control of impurity seeding will be performed in EAST to improve the compatibility of core plasma performance with divertor detachment for future high heating power operations.     

Improvement of divertor triple probe system and its measurements under full graphite wall on EAST

Full graphite wall of experimental advanced superconducting tokamak (EAST) has been developed in the spring of 2008. A new divertor triple probe diagnostics system (DTPDs) is built for EAST during this upgrade. The tip shape and connected structure of the probe are optimized for variational magnetic field directions and DTPDs maintenance. The experiment has been carried out with a full graphite wall for EAST, and near double-null diverted plasma is achieved successfully. The evolutions of electron temperature, density, particle flux and power densities along the divertor targets have been obtained with DTPDs.     

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.     

Kinetic equilibrium reconstruction for the NBI-and ICRH-heated H-mode plasma on EAST tokamak

The equilibrium reconstruction is important to study the tokamak plasma physical processes.To analyze the contribution of fast ions to the equilibrium,the kinetic equilibria at two time-slices in a typical H-mode discharge with different auxiliary heatings are reconstructed by using magnetic diagnostics,kinetic diagnostics and TRANSP code.It is found that the fast-ion pressure might be up to one-third of the plasma pressure and the contribution is mainly in the core plasma due to the neutral beam injection power is primarily deposited in the core region.The fast-ion current contributes mainly in the core region while contributes little to the pedestal current.A steep pressure gradient in the pedestal is observed which gives rise to a strong edge current.It is proved that the fast ion effects cannot be ignored and should be considered in the future study of EAST.     

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.     

The implementation of magnetics verification in EAST plasma control system

Experimental advanced superconducting tokamak (EAST) is an experimental device aiming at steady state plasma operation for fusion research. The values of many discharge parameters, such as plasma shape, position and current must be directly acquired or indirectly evaluated from the magnetic measurements, so the accuracy of magnetic measurements plays an important role in reliable plasma control performance. A method for verifying the key magnetic measurements in real time for each shot is described in this paper. Such magnetics verification will prevent the discharge from a key magnetic signal failure and ensure the quality of a successful discharge. The diagnostics verification algorithm has been implemented in the plasma control system for the EAST. The implementation details and its application in the recent experiment are presented in this paper.     

Machine learning application to predict the electron temperature on the J-TEXT tokamak

The reliability of diagnostic systems in tokamak plasma is of great significance for physics researches or fusion reactor. When some diagnostics fail to detect information about the plasma status, such as electron temperature, they can also be obtained by another method: fitted by other diagnostic signals through machine learning. The paper herein is based on a machine learning method to predict electron temperature, in case the diagnostic systems fail to detect plasma temperature. The fully-connected neural network, utilizing back propagation with two hidden layers, is utilized to estimate plasma electron temperature approximately on the J-TEXT. The input parameters consist of soft x-ray emission intensity, electron density, plasma current, loop voltage, and toroidal magnetic field, while the targets are signals of electron temperature from electron cyclotron emission and x-ray imaging crystal spectrometer. Therefore, the temperature profile is reconstructed by other diagnostic signals, and the average errors are within 5%. In addition, generalized regression neural network can also achieve this function to estimate the temperature profile with similar accuracy. Predicting electron temperature by neural network reveals that machine learning can be used as backup means for plasma information so as to enhance the reliability of diagnostics.     

Electron Cyclotron Emission Imaging on the EAST Tokamak

An upgraded electron cyclotron emission imaging (ECEI) system consisting of new optics lenses with necessary electronics for receiving and processing signals for two dimension (2D) ECEI diagnostics was installed on EAST. Hyperboloid lens were adopted in the new system to optimize the spatial resolutions. The mixers array of sixteen elements measured the plasma electron cyclotron emission at eight frequencies simultaneously, and the profiles of the electron temperature and its fluctuation in an area of 20 cm (vertical) × 6 cm (horizontal) could then be analyzed. Eevolution of sawtooth precursor and crash in EAST was observed.     

Present Status of the Electron Cyclotron Emission Measurements on HT-7 and EAST

Present status of the diagnostics for electron cyclotron emission measurements on both HT-7 and EAST is reported. A 16-channel heterodyne radiometer system and a 20-channel grating polychromator, have been installed on HT-7 and EAST. A 32-channel heterodyne ra- diometer system, with a wider frequency coverage and better spatial resolution, is being built. In order to provide a reliable electron temperature profi, an in-situ absolute calibration system is currently being built. With the ECE measurements, study on the electron heat transport and the anomalous Doppler resonance is conducted.     

An Experimental Platform for the Study on Magnetic Reconnection in Laboratory Plasmas

In order to investigate electron dynamics near the electron diffusion region in magnetic reconnection process, an upgrade in the Linear Magnetized Plasma (LMP) device is accomplished at the University of Science and Technology of China. Radio frequency (RF) helicon discharge is used to generate a quasi-stationary plasma, and a time-dependent magnetic field is applied to the plasma, which exhibits an X-type neutral point in vacuum. A two-dimensional sophisticated mobile platform is built up, providing a high spatial resolution, below 0.5mm, for the diagnostics.     

Numerical analysis of the static performance of an annular aerostatic gas thrust bearing applied in the cryogenic turbo-expander of the EAST subsystem

The EAST superconducting tokamak,an advanced steady-state plasma physics experimental device,has been built at the Institute of Plasma Physics,Chinese Academy of Sciences.All the toroidal field magnets and poloidal field magnets,made of NbTi/Cu cable-in-conduit conductor,are cooled with forced flow supercritical helium at 3.8 K.The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of coils,structures,thermal shields,bus-lines,etc.The high-speed turbo-expander is an important refrigerating component of the EAST cryogenic system.In the turbo-expander,the axial supporting technology is critical for the smooth operation of the rotor bearing system.In this paper,hydrostatic thrust bearings are designed based on the axial load of the turbo-expander.Thereafter,a computational fluid dynamics-based numerical model of the aerostatic thrust bearing is set up to evaluate the bearing performance.Tilting effect on the pressure distribution and bearing load is analyzed for the thrust bearing.Bearing load and stiffness are compared with different static supply pressures.The net force from the thrust bearings can be calculated for different combinations of bearing clearance and supply pressure.     

Development and Integration of a Data Acquisition System for SST-1 Phase-1 Plasma Diagnostics

Long pulse(of the order of 1000 s or more) SST-1 tokamak experiments demand a data acquisition system that is capable of acquiring data from various diagnostics channels without losing useful data(and hence physics information) while avoiding unnecessary generation of a large volume data.SST-1 Phase-1 tokamak operation has been envisaged with data acquisition of several essential diagnostics channels.These channels demand data acquisition at a sampling rate ranging from 1 kilo samples per second(KSPS) to 1 mega samples per second(MSPS).Considering the technical characteristics and requirements of the diagnostics,a data acquisition system based on PXI and CAMAC has been developed for SST-1 plasma diagnostics.Both these data acquisition systems are scalable.Present data acquisition needs involving slow plasma diagnostics are catered by the PXI based data acquisition system.On the other hand,CAMAC data acquisition hardware meets all requirements of the SST-1 Phase-1 fast plasma diagnostics channels.A graphical user interface for both data acquisition systems(PXI and CAMAC) has been developed using LabVIEW application development software.The collected data on the local hard disk are directly streaming to the central server through a dedicated network for post-shot data analysis.This paper describes the development and integration of the data acquisition system for SST-1 Phase-1 plasma diagnostics.The integrated testing of the developed data acquisition system has been performed using SST-1 central control and diagnostics signal conditioning units.In the absence of plasma shots,the integrated testing of the data acquisition system for the initial diagnostics of SST-1 Phase-1 operation has been performed with simulated physical signals.The primary engineering objective of this integrated testing is to validate the performance of the developed data acquisition system under simulated conditions close to that of actual tokamak operation.The data acquisition is synchronized with a clock and trigger provided by the central timing system.     

Polarization and Mode Control of EAST 140 GHz ECRH&CD System

The 140 GHz electron cyclotron heating and current drive (ECRH&CD) project was launched in 2011 on EAST tokamak facility, which is designed to launch 4 MW of total power for the duration up to 1,000 s into the plasma. The heating and current drive efficiencies depend on the wave coupling mode in plasma and the coupling performance relies on polarization characteristics of injected beam, so polarization control is necessary for efficient plasma heating and current drive. Two polarizer miter bends will be used to control the wave polarization for each transmission line on EAST ECRH&CD system, any required wave polarization can be produced by adjusting the mirror rotation angle of each polarizer miter bend. This work mainly shows the calculated polarizer mirror settings as a function of the injection angles for pure second extraordinary harmonic mode coupling.     

Relativistic effect on synergy of electron cyclotron and lower hybrid waves on EAST

In recent experiments on EAST,the electron temperature at the center can be raised to 9.7 keV by injecting electron cyclotron(EC)and lower hybrid(LH)waves simultaneously.With such strong core electron heating,the relativistic effect could play an important role in the interactions between the plasma and waves.In order to explore the relativistic effect on synergy between the EC and LH waves on EAST,ray-tracing/Fokker-Planck simulations are conducted to investigate electron heating for a typical discharge with a center electron temperature of 9.7 keV.It is found that the relativistic effect can cause the EC wave to deposit its power deeper in the plasma core,where the synergy between the EC and LH waves occurs and enhances the absorption of the LH waves.As a result,a high center electron temperature can be achieved.     

Realization of minute-long steady-state H-mode discharges on EAST

In the 2016 EAST experimental campaign,a steady-state long-pulse H-mode discharge with an ITER-like tungsten divertor lasting longer than one minute has been obtained using only RF heating and current drive,through an integrated control of the wall conditioning,plasma configuration,divertor heat flux,particle exhaust,impurity management,and effective coupling of multiple RF heating and current drive sources at high injected power.The plasma current (Ip ～ 0.45 MA) was fully-noninductively driven (Vloop ＜ 0.0 V) by a combination of ～2.5 MW LHW,～0.4 MW ECH and ～0.8 MW ICRF.This result demonstrates the progress of physics and technology studies on EAST,and will benefit the physics basis for steady state operation of ITER and CFETR.     

托卡马克等离子体杂质密度的光谱法测量研究

本文介绍了基于托卡马克等离子体被动光谱诊断获得杂质密度的方法。通过被动光谱诊断测量获得杂质线辐射的空间多道弦积分强度分布,利用强度标定系数转换为绝对光亮度分布;通过测量弦与等离子体位形,将弦积分的强度分布反演变换为径向体发射率。根据线辐射强度激发截面求出对应电离态的离子密度,最后采用杂质输运程序模拟计算得出总密度分布。以东方超环(Experimental Advanced Superconducting Tokamak,EAST)托卡马克装置上软X射线-极紫外光谱(Soft X-ray and Extreme Ultraviolet Spectrometers,XEUV)诊断测量到的Mo XXIX-Mo XXXII为例,描叙了获得Mo杂质密度分布的过程,获得的总误差小于10%。     

Design and implementation of power and phase feedback control system for ICRH on EAST

Ion cyclotron wave resonance heating(ICRH) is one of the most important auxiliary methods to heat plasma in the Experimental Advanced Superconducting Tokamak(EAST). Several megawatts of power is transmitted through separate coaxial lines and coupled with the plasma through arrays of loop antennas. The parameters of the ICRH system, including the injected power and phasing between antenna straps, are critical to the coupling efficiency of the power as well as the resulting impact on the heating efficiency. In this paper, we present a system for feedback control of the phase between the current straps and the ICRH power on EAST. The feedback control system was tested using both a matched dummy load and a plasma load, and it successfully maintained stable operation in the 2016 EAST campaign. Good control of the injected power and wave phases was achieved during edgelocalized mode operation.     

Modeling of divertor power footprint widths on EAST by SOLPS5.0/B2.5-Eirene

The edge plasma code package SOLPS5.0 is employed to simulate the divertor power footprint widths of the experimental advanced superconducting tokamak(EAST)L-mode and ELM-free H-mode plasmas.The divertor power footprint widths,which consist of the scrape-off layer(SOL)widthλ_q and heat spreading 5,are important physical parameters for edge plasmas.In this work,a plasma current scan is implemented in the simulation to obtain the dependence of the divertor power footprint width on the plasma current I_p.Strong inverse scaling of the SOL width with I_p has been achieved for both L-mode and H-mode plasmas in the forms ofλ_(q,L-mode)=4.98×I_p~(-0.68)andλ_(q,H-mode)=1.86×I_p~(-1.08).Similar trends have also been demonstrated in the study of heat spreading with S_(L-mode)=1.95×I_p~(-0.542)and S_(H-mode)=0.756×I_p~(-0.872).In addition,studies on divertor peak heat load and the magnetic flux expansion factor show that both of them are proportional to plasma current.The simulation work here can act as a way to explore the power footprint widths of future tokamak fusion devices such as ITER and the China Fusion Engineering Test Reactor(CFETR).     

Observation and characterization of the effect of electron cyclotron waves on toroidal rotation in EAST L-mode discharges

The change in the toroidal rotation of plasma caused by electron cyclotron wave (ECW) injection has been observed in EAST.It is found that the response of the rotation is similar for all possible ECW toroidal injection angles.The core toroidal rotation velocity increases in the co-current direction along with a rise in the plasma temperature and stored energy.The profile of the electron temperature,ion temperature and toroidal rotation velocity gradually become peaked.The change in toroidal rotation in the core increases with the ECW injection power.Different behavior is observed when the ECWs are injected into low hybrid current drive (LHCD) target plasmas,where the electron temperature and rotation profile become peaked,while the ion temperature profile flattens after ECW injection,suggesting different transport characteristics in energy and momentum.