First results of CO_(2) dispersion interferometer on EAST tokamak

A dispersion interferometer(DI)has been installed and operates on the Experimental Advanced Superconducting Tokamak(EAST).This DI system utilizes a continuous-wave 9.3μm CO_(2)laser source to measure line-averaged electron densities accurately.In contrast to conventional interferometers,the DI does not require substantial vibration isolations or compensating systems to reduce the impact of vibrations in the optical path.It also employs a ratio of modulation amplitudes,ensuring it remains immune to the variations in detected intensities.Without a variation compensation system,the DI system on EAST reaches a density resolution of less than1.8×10^(-2)πrad and a temporal resolution of 20μs.The measurements made by the POlarimeterINTerferometer(POINT)system and the far-infrared hydrogen cyanide(HCN)interferometer are remarkably consistent with the DI’s results.The possibility of fringe jumps and the impact of refraction in high-density discharge can be significantly decreased using a shorter wavelength laser source.A rapid density change of 3×10^(19)m^(-3)during 0.15 s has been measured accurately in shot No.114755 of EAST.Additionally,the DI system demonstrates dependability and stability under 305 s long-pulse discharges in shot No.122054.

Design and platform testing of the compact torus central fueling device for the EAST tokamak

Compact torus(CT)injection is a highly promising technique for the central fueling of future reactor-grade fusion devices since it features extremely high injection velocity and relatively high plasma mass.Recently,a CT injector for the EAST tokamak,EAST-CTI,was developed and platform-tested.In the first round of experiments conducted with low parameter settings,the maximum velocity and mass of the CT plasma were 150 km·s^(-1)and 90μg,respectively.However,the parameters obtained by EAST-CTI were still very low and were far from the requirements of a device such as EAST that has a strong magnetic field.In future,we plan to solve the spark problem that EAST-CTI currently encounters(that mainly hinders the further development of experiments)through engineering methods,and use greater power to obtain a more stable and suitable CT plasma for EAST.

Optimization of X-mode electron cyclotron current drive in high-electron-temperature plasma in the EAST tokamak

A discharge with electron temperature up to 14 keV has been achieved in EAST.Analysis of the electron cyclotron current drive(ECCD)efficiency at high electron temperature under EAST parameters is presented using C3PO/LUKE code.Simulation results show that the ECCD efficiency of X-mode increases with central electron temperature up to 10 keV and then starts to decrease above 10 keV,at a specific magnetic field and toroidal angle.The efficiency degradation is due to the presence of the third harmonic extraordinary(X3)downshifted absorption at the low field side(LFS);even the cold resonance of X3 mode is located outside the plasma.As the electron temperature increases from 5 to 20 ke V,the X3 absorption increases from 0.9%to 96.4%.The trapping electron effect at the LFS produces a reverse Ohkawa current.The competition between the Fisch–Boozer current drive and the Ohkawa current drive results in a decrease in ECCD efficiency.ECCD efficiency optimization is achieved through two methods.One is to increase the toroidal angle,leading to X2 mode predominating again over X3 mode and the electron resonance domain of X2 mode moving far from the trapped/passing boundary.The second one is to increase the magnetic field to move away the X3 resonance layer from the plasma,hence less EC power absorbed by X3 mode.

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. Evolution of sawtooth precursor and crash in EAST was observed.

Combined Langmuir-magnetic probe measurements of type-Ⅰ ELMy filaments in the EAST tokamak

Detailed investigations on the filamentary structures associated with the type-I edge-localized modes（ELMs） should be helpful for protecting the materials of a plasma-facing wall on a future large device.Related experiments have been carefully conducted in the Experimental Advanced Superconducting Tokamak（EAST） using combined Langmuir-magnetic probes.The experimental results indicate that the radially outward velocity of type-I ELMy filaments can be up to 1.7 kms^（-1） in the far scrape-off layer（SOL） region.It is remarkable that the electron temperature of these filaments is detected to be ~50eV,corresponding to a fraction of 1/6 to the temperature near the pedestal top,while the density ~3×10^（19）m^（-3） of these filaments could be approximate to the line-averaged density.In addition,associated magnetic fluctuations have been clearly observed at the same time,which show good agreement with the density perturbations.A localized current on the order of ~100kA could be estimated within the filaments.

Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak

Neon(Ne)seeding is used to cool the edge plasma by radiation to protect the divertor tungsten(W)target in the Experimental Advanced Superconducting Tokamak(EAST).The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system.It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature.After reaching a maximum around 25 eV,the W sputtering rate starts to decrease,presenting a suppression effect.The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed.The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering.Moreover,ELM suppression is observed when Ne and W impurities enter the core plasma,which could be correlated to the enhanced turbulence transport in the pedestal.

Dependence of the internal inductance on the radial distance between the primary and secondary X-point surfaces in the EAST tokamak

In view of their advantage in long-pulse high-performance operations, low internal inductance scenarios are being developed and tested for the EAST and other tokamaks. Dependence of the internal inductance on several main plasma configuration parameters are statistically analyzed. It is found that the internal inductance of the plasma is closely related to the radial distance dRsep between the primary and secondary X-point surfaces on the outer mid-plane as well as the poloidal field of the last closed flux surface. Moreover, dRsep is alSO related to the distribution of the fast electrons driven by the injected lower-hybrid waves, which is partially responsible for the observed relation between dRsep and the internal inductance. The results here should therefore be helpful as a guide for future experiments on internal inductance control and long-pulse operations of the EAST and other tokamaks, as well as for detailed theoretical study of the underlying physics.

The Alignment and Assembly for EAST Tokamak Device

EAST （HT-7U） is a large fusion experimental device. It is a full superconducting tokamak with 1 MA of plasma current, 1000 s of plasma duration, high elongation and triangularity. It mainly consists of superconducting magnets of poloidal and toroidal field （PF ＆ TF）, vacuum vessel （VV）, thermal radiation shield （TRS） and cryostat vessel （CV）. The significant difficulty for assembly of EAST is tight installation tolerances, which are in the order of several tenth of a millimeter. In particular, the alignment of plasma facing components to the magnetic axis of the device is less than ±0.5 mm. At present, a reasonable assembly process of EAST has been defined, and based on it, the alignment method for EAST, including the survey control network, the location of the main components in different directions, the magnetic axis determination and the accurate positioning of the plasma facing components inside of the vacuum vessel and so on, has been defined by using the sophisticated optical metrology system （SOMS）. This paper describes the assembly procedure of EAST and the installation tolerances associated with the main components. Meanwhile, how to establish the assembly survey control network, magnetic axis determination methods, are introduced in detail.

Improved plasma position detection method in EAST Tokamak using fast CCD camera

To control the steady-state operation of Tokamak plasma, it is crucial to accurately obtain its shape and position. This paper presents a method for use in rapidly detecting plasma configuration during discharge of the Experimental Advanced Superconducting Tokamak device. First, a visible/infrared integrated endoscopy diagnostic system with a large field of view is introduced,and the PCO.edge5.5 camera in this system is used to acquire a plasma discharge image. Based on the analysis of various traditional edge detection algorithms, an improved wavelet edge detection algorithm is then introduced to identify the edge of the plasma. In this method, the local maximum of the modulus of wavelet transform is searched along four gradient directions, and the adaptive threshold is adopted. Finally, the detected boundary is fitted using the least square iterative method to accurately obtain the position of the plasma. Experimental results obtained using the EAST device show that the method presented in this paper can realize expected goals and produce ideal effects;this method thus has significant potential for application in further feedback control of plasma.

Online Plasma Shape Reconstruction for EAST Tokamak

An online plasma shape reconstruction, based on the offiine version of the EFIT code and MPI library, can be carried out between two adjacent shots in EAST. It combines online data acquisition, parallel calculation, and data storage together. The program on the master node of the cluster detects the termination of the discharge promptly, reads diagnostic data from the EAST mdsplus server on the completion of data storing, and writes the results onto the EFIT mdsplus server after the calculation is finished. These processes run automatically on a nine-nodes IBM blade center. The total time elapsed is about 1 second to several minutes, depending on the duration of the shot. With the results stored in the mdsplus server, it is convenient for operators and physicists to analyze the behavior of plasma using visualization tools.

Assessment of Radiation Damage to the Structural Material of EAST Tokamak

Radiation damage to structural material of fusion facilities is of high concern for safety. The superconducting tokamak EAST will conduct D-D plasma experiments with the neutron production of 10^15 neutrons per second. To evaluate the material radiation damage a programme system has been devised with the Monte Carlo transport code MCNP-4C, the inventory code FISPACT99, a specific interface, and the fusion evaluated nuclear data library FENDL-2. The key nuclear responses, i.e. fast neutron flux, displacement per atom, and the helium and hydrogen production, are calculated for the structural material SS-316L of the first wall, and the vacuum vessel, using this programme. The results demonstrate that the radiation damage to the structural material is so little that it will not lead to any significant change of material properties according to the reference design. This indicates that there is a large potential space for EAST to test advanced operation regime from the viewpoint of structural material safety.

Application of MDSplus on EAST Tokamak

EAST is a fully superconducting Tokamak in China used for controlled fusion research. MDSplus, a special software package for fusion research, has been used successfully as a central repository for analysed data and PCS （Plasma Control System） data since the debugging experiment in the spring of 2006 [1]. In this paper, the reasons for choosing MDSplus as the analysis database and the way to use it are presented in detail, along with the solution to the problem that part of the MDSplus library does not work in the multithread mode. The experiment showed that the data system based on MDSplus operated stably and it could provide a better performance especially for remote users.

The Procedure for Assembling the EAST Tokamak

Due to the complicated constitution and high precision requirements of the EAST superconducting tokamak, a meticulous assembling procedure and measurement scheme must be established. The big size and mass of the EAST machine＇s components and complicated configuration with tight installation tolerances call for a highly careful assembling procedure. The assembling procedure consists of three main sub-procedures for the assembling of the base, of the tori of the VV, the vacuum vessel TS and the TF, and of the peripheral parts respectively. Before the assembly, a reference framework has been set up by means of an industrial measurement system with reference fiducial targets fixed on the wall of the test hall. In this paper, the assembling procedure is described in detail, the survey control system of the assembly is discussed, and progress in the assembly work is also reported.

Development of a 2D spatial displacement estimation method for turbulence velocimetry of the gas puff imaging system on EAST

A gas puff imaging(GPI)diagnostic has been developed and operated on EAST since 2012,and the time-delay estimation(TDE)method is used to derive the propagation velocity of fluctuations from the two-dimensional GPI data.However,with the TDE method it is difficult to analyze the data with fast transient events,such as edge-localized mode(ELM).Consequently,a method called the spatial displacement estimation(SDE)algorithm is developed to estimate the turbulence velocity with high temporal resolution.Based on the SDE algorithm,we make some improvements,including an adaptive median filter and super-resolution technology.After the development of the algorithm,a straight-line movement and a curved-line movement are used to test the accuracy of the algorithm,and the calculated speed agrees well with preset speed.This SDE algorithm is applied to the EAST GPI data analysis,and the derived propagation velocity of turbulence is consistent with that from the TDE method,but with much higher temporal resolution.

Experimental study of core MHD behavior and a novel algorithm for rational surface detection based on profile reflectometry in EAST

Microwave reflectometry is a powerful diagnostic that can measure the density profile and localized turbulence with high spatial and temporal resolution and will be used in ITER,so understanding the influence of plasma perturbations on the reflect signal is important.The characteristics of the reflect signal from profile reflectometry,the time-of-flight(TOF)signal associated with the MHD instabilities,are investigated in EAST.Using a 1D full-wave simulation code by the Finite-DifferenceTime-Domain(FDTD)method,it is well validated that the local density flattening could induce the discontinuity of the simulated TOF signal and an obvious change of reflect amplitude.Experimental TOF signals under different types of MHD instabilities(sawtooth,sawtooth precursors and tearing mode)are studied in detail and show agreement with the simulation.Two new improved algorithms for detecting and localizing the radial positions of the low-order rational surface,the cross-correlation and gradient threshold(CGT)method and the 2D convolutional neural network approach(CNN)are presented for the first time.It is concluded that TOF signal analysis from profile reflectometry can provide a straightforward and localized measurement of the plasma perturbation from the edge to the core simultaneously and may be a complement or correction to the q-profile control,which will be beneficial for the advanced tokamak operation.

EAST 低杂波加热对同向切向中性束碰撞力矩影响的研究

为研究低杂波加热对同向切向中性束注入的束功率沉积和碰撞力矩的影响,基于低杂波加热的实验参数,使用TRANSP程序进行了模拟分析。研究结果表明,当注入功率1.3MW、能量50keV的同向切向束时,随着LHW加热束沉积功率降低,快离子电荷交换损失增加20%;离子吸收的功率占总的束沉积功率的比例由45%增加到51%。碰撞力矩与束沉积功率的比值由1.327Nm·MW^(-1)增加到1.457Nm·MW^(-1);等离子体电子温度越高,电荷交换损失和碰撞力矩与束沉积功率比值也越大,而低杂波加热期间的束碰撞力矩保持稳定。

EAST托卡马克早期H模实验边界局域模特征的统计分析

为分析EAST托卡马克早期(2010—2014年)高约束运行模式(H模)中边界局域模(ELM)与哪些参数具有强相关性,在验证有效性的基础上,采用主打击点处Dα辐射的相对涨落来定量表征边界局域模幅度,建立EAST托卡马克早期H模下ELM特征数据库。统计分析表明,ELM频率随边界安全因子的增大而减小,2010年type-ⅢELM的频率随总加热功率的增大而增大。这与其他装置或2015年以后EAST装置上得到的结果不一致,部分原因是碳杂质水平的变化。碳杂质水平是影响EAST托卡马克早期H模实验中ELM行为的重要因素之一。

EAST托卡马克钨杂质上下不对称性分布的实验研究

基于EAST托卡马克装置高性能极紫外空间分辨杂质光谱仪,本文首次开展了磁约束聚变装置高Z杂质上下不对称分布的实验研究.实验结果显示,在同向中性束注入期间,等离子体芯部环向旋转速度V_(t0)大,钨杂质上下不对称性较强,且辐射(密度)较强的一侧背离离子B×▽B漂移方向;当从上外偏滤器充气口注入氘化甲烷气体后,V_(t0)迅速下降,原有上下不对称性发生反转.因此我们针对近似条件下W^(32+)杂质离子特征线辐射不对称因子I_(u)/I_(d)与V_(t0)依赖关系开展了进一步的统计分析.结果表明,I_(u)/I_(d)正相关于V_(t0),当V_(t0)<20 km/s以下时,不对称性发生反转.上述现象从实验角度验证了漂移动理学的理论预测,说明环向旋转带来的离心力影响了杂质离子平行于磁场方向的动量守恒,作为直接诱因,造成了高Z杂质密度的上下不对称分布,进而影响辐射的分布.本文对钨杂质上下不对称性分布的实验观测为进一步开展高Z杂质极向输运的机理研究打下了坚实的基础,并为今后聚变堆高Z杂质控制提供重要的参考.

国家重大科技基础设施运行管理的改进方法与实践——以EAST全超导托卡马克核聚变实验装置为例

中国科学院合肥物质科学研究院等离子体物理研究所先后建成中国第一个圆截面超导托卡马克核聚变实验装置,以及世界上第一个非圆截面全超导托卡马克核聚变实验装置(EAST)。为持续改进EAST的运行管理,从顶层设计、组织实施和评估评价等方面分析EAST管理实践的有关探索与创新,具体包括:建立所领导、物理与实验运行部至一级系统的三级管理体系,能够更好围绕成果产出进行统一规划和分级管理;基于“计划—实施—检查—行动(PDCA)”管理理论,形成覆盖EAST运行周期的全过程管理机制;通过国内外评估制定设施中长期、近期计划,设置物理与实验运行部,负责主导EAST装置运行计划与目标的制定。另外,根据设施构成、结合运行需求设置一级系统,起用青年骨干担任负责人,分解任务、明确责任;同时,加强设施运行评估,部署实施系列改进举措,如优化基础研究组织模式和管理方式、创新国际合作模式等。根据EAST运行管理经验,对中国重大科技基础设施的运行和管理提出优化科研组织模式、完善管理方法、建设大科学工程团队、加强开放与合作等对策建议。

Optical plasma boundary reconstruction based on least squares for EAST Tokamak

Reconstructing the shape and position of plasma is an important issue in Tokamaks. Equilibrium and fitting（EFIT） code is generally used for plasma boundary reconstruction in some Tokamaks. However, this magnetic method still has some inevitable disadvantages. In this paper, we present an optical plasma boundary reconstruction algorithm. This method uses EFIT reconstruction results as the standard to create the optimally optical reconstruction. Traditional edge detection methods cannot extract a clear plasma boundary for reconstruction. Based on global contrast, we propose an edge detection algorithm to extract the plasma boundary in the image plane. Illumination in this method is robust. The extracted boundary and the boundary reconstructed by EFIT are fitted by same-order polynomials and the transformation matrix exists. To acquire this matrix without camera calibration, the extracted plasma boundary is transformed from the image plane to the Tokamak poloidal plane by a mathematical model,which is optimally resolved by using least squares to minimize the error between the optically reconstructed result and the EFIT result. Once the transform matrix is acquired, we can optically reconstruct the plasma boundary with only an arbitrary image captured. The error between the method and EFIT is presented and the experimental results of different polynomial orders are discussed.