Influence of impurity seeding on the plasma radiation in the EAST tokamak

Plasma radiation characteristics in EAST argon(Ar) gas and neon(Ne) gas seeding experiments are studied.The radiation profiles reconstructed from the fast bolometer measurement data by tomography method are compared with the ones got from the simulation program based on corona model.And the simulation results coincide roughly with the experimental data.For Ar seeding discharges,the substantial enhanced radiations can be generally observed in the edge areas at normalized radius ρ_(pol)~0.7–0.9,while the enhanced regions are more outer for Ne seeding discharges.The influence of seeded Ar gas on the core radiation is related to the injected position.In discharges with LSN divertor configuration,the Ar ions can permeate into the core region more easily when being injected from the opposite upper divertor ports.In USN divertor configuration,the W impurity sputtered from the upper divertor target plates are observed to be an important contributor to the increase of the core radiation no matter impurity seeding from any ports.The maximum radiated power fractions f_(rad)(P_(rad)/P_(heat)) about 60%–70% have been achieved in the recent EAST experimental campaign in 2015–2016.     

Latest Results from the Damavand Tokamak Experiments

Damavand is a small tokamak (a = 7 cm, R = 36 cm) with an elongated plasma cross section (k 2) and a poloidal divertor. Its passive coils within the vacuum chamber provide the plasma formation at the torus center and act as a passive stabilizer for the plasma current. The experimental measurements presented here are the latest results related to the Damavand discharge main behavior with graphite limiters (before the device modification) during the ohmic heating phase. In this respect, we have evaluated some of the characteristic parameters such as edge safety factor (q_a 3.1), energy confinement (_E = 0.4 ms), electron temperature (T_e = 161 eV), and so on, during normal operation of the plasma current. The assessment of disruption phase of the plasma current has been considered by estimating the characteristic parameters of thermal and current quenches to be about 6 eV and 6 MA/s, respectively. Here, also we have monitored the evolution of the line emission of impurity (C, O) ions in the central deuterium plasma. The relative density of carbon and oxygen impurity levels has been estimated to be 2.6 and 1.4%, respectively. It is concluded that the impurity radiation loss is much higher during disruption phase of plasma current.     

Development of vacuum ultraviolet spectroscopy for measuring edge impurity emission in the EAST tokamak

The dominant wavelength range of edge impurity emissions moves from the visible range to the vacuum ultraviolet(VUV) range, as heating power increasing in the Experimental Advanced Superconducting Tokamak(EAST). The measurement provided by the existing visible spectroscopies in EAST is not sufficient for impurity transport studies for high-parameters plasmas. Therefore, in this study, a VUV spectroscopy is newly developed to measure edge impurity emissions in EAST. One Seya-Namioka VUV spectrometer(McPherson 234/302) is used in the system, equipped with a concave-corrected holographic grating with groove density of 600 grooves mm~(–1). Impurity line emissions can be observed in the wavelength range ofλ=50–700 nm, covering VUV, near ultraviolet and visible ranges. The observed vertical range is Z=-350–350 mm. The minimum sampling time can be set to 5 ms under full vertical binning(FVB) mode. VUV spectroscopy has been used to measure the edge impurity emission for the 2019 EAST experimental campaign. Impurity spectra are identified for several impurity species, i.e., lithium(Li), carbon(C), oxygen(O), and iron(Fe). Several candidates for tungsten(W) lines are also measured but their clear identification is very difficult due to a strong overlap with Fe lines. Time evolutions of impurity carbon emissions of CII at 134.5 nm and CIII at97.7 nm are analyzed to prove the system capability of time-resolved measurement. The measurements of the VUV spectroscopy are very helpful for edge impurity transport study in the high-parameters plasma in EAST.     

用于双离子束注入器的杂质消除系统

研制了一套用于双离子束注入器的杂质消除系统，该系统由两台速度选择器、1台单透镜和1台双孔选束光阑组成，可实现不同荷质比的两种离子束在同时传输过程中消除杂质离子。该技术已用于1台H⁺₂和He⁺两种离子束同时传输的50 keV双离子束注入器，实现了1台加速器同时产生、传输两种离子束，并同轴注入靶内，离子束纯度好于99.9%。     

Numerical studies of the influence of seeding locations on D-SOL plasmas in EAST

Impurity seeding has been found effective for divertor detachment operations and the seeding location plays a key role in this process. In this work, we use the fluid code SOLPS-ITER to study the influence of seeding locations on divertor and scrape-off layer (D-SOL) plasmas in Experimental Advanced Superconducting Tokamak (EAST) with neon seeding. Simulation results indicate that the neon is a highly effective impurity in mitigating the heat flux and electron temperature peaks on the target of the divertor and achieving the partial detachment on both inner and outer targets. Further, by comparing results of the seeding at the private-flux region (PFR) plate (called 'TP' location) and the outer target (called 'XP' location), we find that the impurity density and power radiation for TP case are higher in core and upstream regions and lower in the divertor region than that for seeding at the XP, and the difference becomes more and more obvious as the seeding rate increases. It clearly demonstrates that the seeding at the XP location is more appropriate than at the TP location, especially in high seeding rate conditions.     

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.     

Estimate of the Deposition Profile of Carbon Pellets Using a High-Speed VUV Imaging System in the LHD

The deposition profile of the impurity pellet is measured by a two-dimensional fast- framing vacuum ultraviolet （VUV） camera system in the large helical device （LHD）. The fast framing camera selectively measures the emission from the hydrogen-like ions of carbon （C VI） with a frame rate of several kHz. From the emission profile of the hydrogen-like carbon ions, which are in the process of ionization, the initial deposition profile of the carbon is estimated using a simple one-dimensional transport model.     

An evaluation of the influence of impurity concentration and composition in concrete on activation and radiation dosein the reactor facility

The content analysis of radioactive waste and radiation dose evaluation is considered as one of the important factors in the reactor facility design.This kind of buildings consists of the concrete for the most part and uses it as the structure and shield of the building.Generally,the concrete has impurities such as cobalt,europium,nickel,and cesium with specific content depending on the production method or manufacturing company.Dominant radioactive nuclides generated from the fundamental components of concrete are considered that it is less contributed to the radiation dose because they are beta decay nuclides in general.Thus,impurities of irradiated concrete in the reactor facilities,are considered occasionally an important evaluation factor for induced activity.In this study,the influence on the activation of impurities in concrete was evaluated from the radiation dose and induced activity calculations.The calculation was evaluated at the bio-shield which is one of the areas with the highest neutron irradiation among the concrete structure in the reactor facility.The results show that radioactive nuclides with gamma decay were produced in these impurities.Moreover,the radiation dose of concrete with impurities was higher than concrete without impurities.The increased radiation dose was quantified through the content of impurities.     

Observation of the Two-Dimensional Distribution of Impurity Line Emissions Using a Space-Resolved EUV Spectrometer in LHD

A space-resolved EUV spectrometer for measuring the one-dimensional distribution of impurity line emissions in Large Helical Device (LHD) has been upgraded to measure two- dimensional distributions of impurity line emissions with an extension of working wavelength range to 30～650 A. The two-dimensional measurement is performed by scanning the observation chord horizontally. A rectangular plasma region of 520 × 700 mm 2 in vertical and horizontal sizes can be observed during a single horizontal scan. The horizontal scan requires a time duration of 5 s at least. The spatial resolution is 10 mm in the vertical direction when a spatial-resolution slit of 0.2 mm in width is adopted. Although a spatial resolution in the toroidal direction is 75 mm, it is a function of CCD exposure time and horizontal scanning speed. Two-dimensional distribution of EUV line emissions from several impurities has been successfully observed for the first time from steady discharges in LHD. In this paper two-dimensional distributions of He II (303.78 A), C V (40.27 A), C VI (33.73 A) and Fe XX (132.85 A) located at different radial positions are presented with simple analysis on the magnetic field structure of LHD.     

Impurity Measurement and Study on HL-2A Divertor Tokamak

HL-2A tokamak with two close divertors has been operated since 2003. In the experimental campaign of 2004 the divertor configuration has been successfully formed and the sillconization as a wall conditioning has been firstly done in this device. The divertor configuration can be reconstructed by the CFc code. Impurity behavior has been investigated during the experiment with divertor configuration and wall conditioning. The reduction of impurity is clear under both conditions of divertor configuration and siliconization.     

Sawtooth Activities During Impurity Injection by Laser Blow-off in HL-2A

In order to study impurity transport and their progression in the plasma, small amount of high-Z impurities were injected into HL-2A ohmic heated plasmas by laser blow-off and traced with good spatial temporal resolution by a soft X-ray camera. An analysis of the evolution of the impurities＇ radiation distribution in the plasma revealed that impurity transport in the central region was profoundly different from that outside of it. It was found that the sawteeth tended to be inverted on the central soft X-ray chord signals after the impurity injection and the soft X- ray profiles exhibited discontinuities during the movement of the impurities in the plasma central region. Detailed 2D visualization of the evolution of impurities＇ radiation using computer tomography has provided further understanding of the properties of impurity transport in the HL-2A plasma.     

Study of the tungsten sputtering source suppression by wall conditionings in the EAST tokamak

The steady fusion plasma operation is constrained by tungsten(W) material sputtering issue in the EAST tokamak. In this work, the suppression of W sputtering source has been studied by advanced wall conditionings. It is also concluded that the W sputtering yield becomes more with increasing carbon(C) content in the main deuterium(D) plasma. In EAST, the integrated use of discharge cleanings and lithium(Li) coating has positive effects on the suppression of W sputtering source. In the plasma recovery experiments, it is suggested that the W intensity is reduced by approximately 60% with the help of ～35 h Ion Cyclotron Radio Frequency Discharge Cleaning(ICRF-DC) and ～40 g Li coating after vacuum failure. The first wall covered by Li film could be relieved from the bombardment of energetic particles, and the impurity in the vessel would be removed through the particle induced desorption and isotope exchange during the discharge cleanings. In general, the sputtering yield of W would decrease from the source, on the bias of the improvement of wall condition and the mitigation of plasmawall interaction process. It lays important base of the achievement of high-parameter and longpulse plasma operation in EAST. The experiences also would be constructive for us to promote the understanding of relevant physics and basis towards the ITER-like condition.     

Impurity Measured by VUV Spectrometer and OMA on HL-2A Tokamak

Impurity is one of the key issues on a great impact to the quality of tokamak plasma.HL-2A is the first divertor tokamak in China. In this paper the experimental results are presented on impurity through the line emission measurement in the campaign in 2003 under the limiter and divertor configurations. The low-Z impurities such as carbon and oxygen are the most important components in the plasma, but their content are not so high to affect the discharge quality. The high-Z impurities such as copper and ferrum are not essential. The emission intensity of impurity is clearly decreased during the divertor configuration formed.     

在短寿命放射性医疗废物中发现长寿命杂质核素

为了确定短寿命放射性医疗废物能否清洁解控及短期的衰变贮存是否有效,本研究使用γ谱仪分析已放置了10个半衰期以上的低水平含99Tcm的放射性废物中残留的放射性核素,通过核素的全能峰定性,通过感兴趣区的净峰面积定量.经过了衰变贮存,虽然所有核素的活度浓度均低于相应的清洁解控水平,但在99Tcm废物中检出了长寿命核素137Cs、155Eu、123Tem、154Eu,其中137Cs、155Eu分析为99Tcm的母体99Mo生产过程中产生的杂质核素进入99Tcm所致,123Tem、154Eu可能为99Mo靶中杂质核素衰变而成.半衰期最长的长寿命核素137Cs的半衰期为30a,短期的衰变贮存并不能使这些长寿命核素活度显著减少,可见控制放射性药物的核纯度具有重要意义,可防止后期产生的医疗废物处置复杂化.     

结晶固体的辐射损伤与释光

从辐射与物质的作用出发,对释光现象进行了讨论,认识到结晶固体的释光效应最本质的是结晶固体中的杂质离子。它们在固体中形成的发光中心有两类,一类是辐射本质,它对辐射的释光响应正比于它所接受的辐射剂量;另一类属于非辐射本质的,全由固体中的杂质离子所决定。     

DIVIMP Modeling of Impurity Transport in EAST

Simulations of carbon impurity transport in SOL/divertor plasmas with Ohmic heating on EAST tokamak were performed using the two-dimensional（2D）Monte Carlo impurity transport code DIVIMP.The background plasmas for DIVIMP simulations were externally taken from B2.5/Eirene calculation.Besides the basic output of DIVIMP,the 2D density distributions of the carbon impurity with different ionization states and neutral carbon atoms were obtained,the2D distributions of CII and CIII emissivities from C＋1and C＋2radiation respectively were also calculated.Comparison between the measured and calculated CIII emissivities showed favorable agreement,indicating that the impurity physics transport models,as implemented in the DIVIMP code,are suitable for the EAST tokamak plasma condition.     

Spectroscopic Studies on Impurity Transport of Core and Edge Plasmas in LHD

Spectroscopic diagnostics have been extensively developed for studies of impurity and neutral particle transports at core and edge plasmas in LHD. Diagnostics of core plasmas are similar to a tokamak case, i.e., Zeff from visible bremsstrahlung, K-x-ray measurements from xray spectroscopy using Si（Li） detectors and a compact crystal spectrometer, and high-Z impurity diagnostics from VUV spectroscopy using a flat-field EUV spectrometer. A combination of impurity pellet injection and visible bremsstrahlung is an active tool for determination of the diffusion coeffici＇ent D and convective velocity V. Using this tool the spatial structures of D and V are obtained and discussed with a neoclassical effect. On the other hand, the spectroscopic method for edge diagnostics is considerably different from the tokamak case because of the existence of a thick ergodic layer in addition to the z-points necessarily included into the diagnostic chord view. In order to break this negative situation, Zeeman and polarization spectroscopy are adopted to LHD edge plasmas. As a result, 2-dimensional emission contours of HeI and Ha are successfully obtained. Laser absorption spectroscopy is tried to measure hydrogen neutrals directly. Radial profiles of edge impurities are also measured with a mirror-assembled 3 m VUV spectrometer. Recent results of and progress in LHD spectroscopy are briefly reviewed.     

强流溅射源束流杂质的分析和消除

在北京HI-13串列加速器上使用强流溅射源引出某些离子时,总是含有不必要的束流杂质。经详细分析后确定束流杂质主要是由离子源内部一个绝缘套筒造成的。本文对离子源内部结构进行了改进:在靶阴极与阳极之间的绝缘套筒上加上内外金属屏蔽帽,从而降低了束流杂质,提高了束流的纯度和强度。     

含氚废气中杂质气体去除材料研制

为去除含氚惰性废气中的CH₄、水气、O₂等杂质气体,采用溶胶凝胶法制备了65%Ni-10%Cu-25%SiO₂材料作为杂质气体消除材料,对材料进行XRD、SEM及程序升温还原表征,结果显示,少量Cu的加入增加了Ni的分散度,有助于稳定Ni的形态,避免Ni过早发生氧化。材料可以使Ar中的少量CH₄、O₂和水气得到有效的去除,在空速1000 h^-1时Ar中φ=1%CH₄和φ=1%CO₂重整时CH₄去除率达到81.5%以上,对于Ar中φ=1%O₂的去除率达到91.8%以上,对于Ar中φ=1%水气的去除率达到91.7%以上。实验还发现低浓度的CH₄可以与水气及O₂发生反应而去除,空速10000 h^-1催化φ=1%水气和φ=1%CH₄反应,CH₄的去除率均高于80.7%;空速10000 h^-1催化φ=0.67%CH₄和φ=0.33%O₂的反应,CH₄的去除率均高于84.2%。     

用同步辐射X射线荧光微区分析技术测定单晶硅中的掺杂元素As

利用同步辐射Ｘ射线微区分析技术，研究了单晶硅中掺杂元素Ａｓ浓度的定量分布，并对结果进行了讨论。