Line identification of boron and nitrogen emissions in extreme-and vacuumultraviolet wavelength ranges in the impurity powder dropping experiments of the Large Helical Device and its application to spectroscopic diagnostics

An impurity powder dropper was installed in the 21 st campaign of the Large Helical Device experiment(Oct. 2019–Feb. 2020) under a collaboration between the National Institute for Fusion Science and the Princeton Plasma Physics Laboratory for the purposes of real-time wall conditioning and edge plasma control. In order to assess the effective injection of the impurity powders,spectroscopic diagnostics were applied to observe line emission from the injected impurity. Thus,extreme-ultraviolet(EUV) and vacuum-ultraviolet(VUV) emission spectra were analyzed to summarize observable impurity lines with B and BN powder injection. Emission lines released from B and N ions were identified in the EUV wavelength range of 5–300 ? measured using two grazing incidence flat-field EUV spectrometers and in the VUV wavelength range of 300–2400 ? measured using three normal incidence 20 cm VUV spectrometers. BI–BV and NIII–NVII emission lines were identified in the discharges with the B and BN powder injection, respectively. Useful B and N emission lines which have large intensities and are isolated from other lines were successfully identified as follows: BI(1825.89, 1826.40) ?(blended), BII 1362.46 ?, BIII(677.00, 677.14,677.16) ?(blended), BIV 60.31 ?, BV 48.59 ?, NIII(989.79, 991.51, 991.58) ?(blended), NIV765.15 ?, NV(209.27, 209.31) ?(blended), NVI 1896.80 ?, and NVII 24.78 ?. Applications of the line identifications to the advanced spectroscopic diagnostics were demonstrated, such as the vertical profile measurements for the BV and NVII lines using a space-resolved EUV spectrometer and the ion temperature measurement for the BII line using a normal incidence 3 m VUV spectrometer.     

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.     

Measurement of the first Townsend's ionization coefficient for atmospheric pressure neon by a dielectric barrier discharge

Fast photography and optical emission spectroscopy are implemented in a 5 mm neon gap dielectric barrier discharge (DBD) at atmospheric pressure with quartz glass used as the dielectric layer. Results show that it starts with a Townsend discharge and ends at a sub-normal glow discharge in neon DBD. Based on the Townsend discharge, the first ionization coefficient of neon is measured. The measurements are consistent with those at low pressure. Optical emission spectroscopy indicates that the spectra are mainly composed of atomic lines of neon, molecular bands and molecular ion bands originating from inevitable gas impurities (mainly nitrogen). Moreover, spectral lines emitted from atomic neon corresponding to the transitions (2p⁵ 3p → 2p⁵ 3s) are predominant. Although the second positive system of N₂(C³Π_u → B³Π_g) is observed, their intensities are too weak compared with neon's spectrum. The molecular nitrogen ion line of 391.4 nm is observed. It reveals that Penning ionization between high energy neon excited states and the inevitable gas impurities plays an important role in the value of the α coefficient.     

Spatially-resolved flat-field soft X-ray spectrometer on experimental advanced superconducting tokamak

A space- and time-resolved flat-field soft X-ray spectrometer with the wavelength range of 1–13 nm has been developed to study impurity behavior on the Experimental Advanced Superconducting Tokamak (EAST). Using an entrance slit, a varied line spacing grating (2400 grooves/mm at the grating center), and a charged coupled device (CCD) system, time evolution of profiles of impurity line emissions were recorded. The spectral resolution of the spectrometer is 0.006 nm at 5 nm when the width of entrance slit is set at 0.03 mm. The best spatial resolution obtained is 24.5 mm with the height of slit at 1.0 mm. The spectrometer is placed 8000 mm away from the plasma center and the observed spatial range covers 0–450 mm from the equatorial plane of EAST. The first experimental results were obtained from the recent EAST campaign. The system was shown to be capable of observing spectral lines from both intrinsic low-Z impurities (C, O, et al.) and highly ionized medium- and high-Z impurities (Fe, Cr, Ni, Cu, et al.). Spectral lines from the full wavelength range (1–13 nm) can be obtained by moving the position of the CCD. Spectra with the wavelength intervals of 1–2 nm show strong metal lines for H-mode discharges. Time evolutions of C VI (3.373 nm) and O VIII (1.897 nm) lines are presented and detail analysis is performed combining electron density intensity, D_α and soft X-ray and extreme ultraviolet (XUV) radiation intensities. Evolutions of profiles of C VI (3.373 nm) and O VIII (1.897 nm) at core plasma were also shown, indicating that the spectrometer can be applied for impurity transport studies,     

Spectroscopic studies of fuel recycling and impurity behaviors in the divertor region of Wendelstein 7-X

The first divertor operation phase(OP1.2 a) was carried out on Wendelstein 7-X in the second half of 2017.Fuel recycling and impurity behaviors in the divertor region were investigated by employing a newly built ultraviolet–visible–near infrared overview spectroscopy system.The characteristic spectral lines of the working gases(hydrogen and helium),intrinsic impurities(carbon,oxygen and iron),and seeded impurities(neon and nitrogen) were identified and analyzed.The divertor electron temperature and density were measured using He I(667.8,706.5,and 728.1 nm) line intensity ratios.The Hα(656.3 nm),He I(587.6 nm),C II(514.5 nm),and O I(777.2 nm) emissions were investigated over a wide range of operating conditions.The results showed that fuel and impurity emissions in the divertor region exhibit a strong dependence on magnetic topology and plasma conditions.The levels of Hα,He I,C II,and O I emissions are all reduced moving from the standard configuration to the high mirror configuration,and even further reduced for the high iota configuration,which is associated with decreasing connection length in these island divertor configurations.The H/He influx ratio shows that the plasma is a mixture of helium and hydrogen.The neutral and impurity influxes from the divertor target tend to increase with increasing divertor electron temperature.     

Line identification of boron and nitrogen emissions in extreme- and vacuum-ultraviolet wavelength ranges in the impurity powder dropping experiments of the Large Helical Device and its application to spectroscopic diagnostic

An impurity powder dropper was installed in the 21st campaign of the Large Helical Device experiment (Oct. 2019–Feb. 2020) under a collaboration between the National Institute for Fusion Science and the Princeton Plasma Physics Laboratory for the purposes of real-time wall conditioning and edge plasma control. In order to assess the effective injection of the impurity powders, spectroscopic diagnostics were applied to observe line emission from the injected impurity. Thus, extreme-ultraviolet (EUV) and vacuum-ultraviolet (VUV) emission spectra were analyzed to summarize observable impurity lines with B and BN powder injection. Emission lines released from B and N ions were identified in the EUV wavelength range of 5–300 Å measured using two grazing incidence flat-field EUV spectrometers and in the VUV wavelength range of 300–2400 Å measured using three normal incidence 20 cm VUV spectrometers. BI–BV and NIII–NVII emission lines were identified in the discharges with the B and BN powder injection, respectively. Useful B and N emission lines which have large intensities and are isolated from other lines were successfully identified as follows: BI (1825.89, 1826.40) Å (blended), BII 1362.46 Å, BIII (677.00, 677.14, 677.16) Å (blended), BIV 60.31 Å, BV 48.59 Å, NIII (989.79, 991.51, 991.58) Å (blended), NIV 765.15 Å, NV (209.27, 209.31) Å (blended), NVI 1896.80 Å, and NVII 24.78 Å. Applications of the line identifications to the advanced spectroscopic diagnostics were demonstrated, such as the vertical profile measurements for the BV and NVII lines using a space-resolved EUV spectrometer and the ion temperature measurement for the BII line using a normal incidence 3 m VUV spectrometer.     

Measurement of tungsten impurity spectra with a two-crystal X-ray crystal spectrometer on EAST

Spectral measurement of tungsten (W) impurity is essential to study impurity transport. Therefore, an X-ray crystal spectrometer (XCS) on EAST was used to measure the line spectra from highly ionized W ions. On EAST, both poloidal XCS and tangential XCS have been developed to measure the plasma temperature as well as the rotation velocity. Recently, He-like and H-like argon spectra have also been obtained using a two-crystal setup. W lines are identified in this study. Through a careful analysis, the W lines of 3.9336, 3.9321, and 3.664 Å are found to be diffracted by He-like or H-like crystals. The lines are confirmed with the NIST database. We also calculated the ion temperature with Doppler broadening of these lines. The ion temperature from the W lines is entirely consistent with that from Ar line spectra. The measurement of these W line spectra could be used to study W impurity transport in future work.     

Preliminary results of in situ laser-induced breakdown spectroscopy for the first wall diagnostics on EAST

Post-mortem methods cannot fulfill the requirement of monitoring the lifetime of the plasma facing components(PFC) and measuring the tritium inventory for the safety evaluation.Laserinduced breakdown spectroscopy(LIBS) is proposed as a promising method for the in situ study of fuel retention and impurity deposition in a tokamak.In this study,an in situ LIBS system was successfully established on EAST to investigate fuel retention and impurity deposition on the first wall without the need of removal tiles between plasma discharges.Spectral lines of D,H and impurities(Mo,Li,Si,...) in laser-induced plasma were observed and identified within the wavelength range of 500-700 nm.Qualitative measurements such as thickness of the deposition layers,element depth profile and fuel retention on the wall are obtained by means of in situ LIBS.The results demonstrated the potential applications of LIBS for in situ characterization of fuel retention and co-deposition on the first wall of EAST.     

Quantitative analysis and time-resolved characterization of simulated tokamak exhaust gas by laser-induced breakdown spectroscopy

Tokamak exhaust is an important part of the deuterium-tritium fuel cycle system in fusion reactions. In this work, we present a laser-induced breakdown spectroscopy (LIBS)-based method to monitor the gas compositions from the exhaust system in the tokamak device. Helium (He), a main impurity in the exhaust gas, was mixed with hydrogen (H2) in different ratios through a self-designed gas distribution system, and sealed into a measurement chamber as a standard specimen. A 532 nm wavelength laser pulse with an output power of 100 mJ was used for plasma excitation. The time-resolved LIBS is used to study the time evolution characteristics of the signal strength, signal-to-background ratio (SBR), signal-to-noise ratio (SNR) and relative standard deviation (RSD) of the helium and hydrogen characteristic lines. The Boltzmann two-line method was employed to estimate the plasma temperature of laser-induced plasma (LIP). The Stark-broadened profile of He I 587.56 nm was exploited to measure the electron density. From these studies, an appropriate time was determined in which the low RSD% was consistent with the high signal-to-noise ratio. The He I 587.56 nm and Hα emission lines with good signal-to-noise ratio were extracted from the spectrum and used in the external standard method and internal standard method for quantitative analysis. The test results for mixed gas showed that the average relative error of prediction was less than 11.15%, demonstrating the great potential of LIBS in detecting impurities in plasma exhaust gas.     

Impurity effects on reduced-activation ferritic steels developed for fusion applications

Reduced-activation steels are being developed for fusion applications by restricting alloying elements that produce long-lived radioactive isotopes when irradiated in the fusion neutron environment. Another source of long-lived isotopes is the impurities in the steel. To examine this, three heats of reduced-activation martensitic steel were analyzed by inductively coupled plasma mass spectrometry for low-level impurities that compromise the reduced-activation characteristics: a 5-ton heat of modified F82H (F82H-Mod) for which an effort was made during production to reduce detrimental impurities, a 1-ton heat of JLF-1, and an 18-kg heat of ORNL 9Cr–2WVTa. Specimens from commercial heats of modified 9Cr–1Mo and Sandvik HT9 were also analyzed. The objective was to determine the difference in the impurity levels in the F82H-Mod and steels for which less effort was used to ensure purity. Silver, molybdenum, and niobium were found to be the tramp impurities of most importance. The F82H-Mod had the lowest levels, but in some cases the levels were not much different from the other heats. The impurity levels in the F82H-Mod produced with present technology did not achieve the low-activation limits for either shallow land burial or recycling. The results indicate the progress that has been made and what still must be done before the reduced-activation criteria can be achieved.     

Equilibrium Evolution in the ZaP Flow Z-Pinch

Investigations of sheared flow stabilization in a Z-pinch geometry have generated Z-pinch plasmas that exhibit long-lived stability during a quiescent period. Holographic interferometry measurements show a discrete pinch. Heat conduction analysis reveals a high temperature plasma. Internal magnetic fields are measured using Zeeman splitting of impurity carbon line emission. The measurements are consistent with a well-confined pinch plasma.     

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.     

Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave (MW) resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence (TALIF) using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy (OES). In this case, we compared the spectra intensities of a specific atomic oxygen line (844 nm) and the closest wavelength xenon line (823 nm). The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon (1% Xe) of this chemically inert gas inside the air while a further small quantity of H₂ (2%) is also added in the mixture in order to collect OH(A¬X) and NH(A-X) spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09×1017± 0.2×10¹⁷ cm ⁻³ . This is in very good agreement with the TALIF measurement, which is equal to 2.0×10¹⁷ cm ⁻³ .     

Electron spin resonance investigations on ion beam irradiated single-wall carbon nanotubes

ESR investigations on single-wall carbon nanotubes irradiated with accelerated protons, helium ions, and neon ions are reported. All spectra were accurately simulated assuming that the resonance line is a convolution of up to 4 lines originating from catalyst residues, amorphous carbon, and electrons delocalized over the conducting domains of nanotubes. The faint line observed in irradiated nanotubes at g > 2.25 was assigned to magnetic impurities. However, there are no sufficient data to confirm that this line is connected to radiation-induced magnetism in carbon nanotubes. The generation of paramagnetic defects due to the bombardment of single-wall carbon nanotubes by accelerated ions is reported. These data correlate with previous Raman and thermal investigations on the same single-wall carbon nanotubes and reveals their sensitivity to ionizing radiation. The temperature dependence of ESR spectra in the range 25-250 K was used to identify the components of the ESR spectra.     

Quantitative analysis of saindha salt using laser induced breakdown spectroscopy and cross-validation with ICP-MS

Saindha salt is considered to be more advantageous than the other edible salts for the patients suffering from diabetes,blood pressure and kidney diseases.To explore the constituent elements of this salt,laser induced breakdown spectroscopy(LIBS) has been exploited for its qualitative and quantitative analysis.The third harmonic(355 nm) of a Q-switched Nd:YAG laser has been used to produce the saindha salt plasma and the time integrated optical emission spectra were registered using a set of six miniature spectrometers covering the spectral range of 230-805 nm.The spectroscopic analysis of the emission spectra predominately revealed numerous neutral or singly ionized emission lines of Ca,Mg,Na,K,Fe,Sr,Si,Li and Al.The laser produced plasma was characterized by calculating the electron temperature from the Boltzmann plots and the electron number density from the Stark broadened line profile as a function of laser irradiance and distance from the target sample.The relative concentration of the constituent elements was extracted by the integrated line intensities of the strongest spectral line of each element using the self-calibration-LIBS(SC-LIBS) and one-line calibration free-LIBS(OLCF-LIBS) methods.For cross-validation,the LIBS results have been compared with that obtained from the inductively coupled plasma-mass spectroscopy(ICP-MS) showing good agreement.     

Characteristics of Single Cathode Cascaded Bias Voltage Arc Plasma

A single cathode with a cascaded bias voltage arc plasma source has been developed with a new quartz cathode chamber,instead of the previous copper chambers,to provide better diagnostic observation and access to the plasma optical emission.The cathode chamber cooling scheme is also modified to be naturally cooled only by light emission without cooling water to improve the optical thin performance in the optical path.A single-parameter physical model has been developed to describe the power dissipated in the cascaded bias voltage arc discharge argon plasmas,which have been investigated by utilizing optical emission spectroscopy(OES) and Langmuir probe.In the experiments,discharge currents from 50 A to 100 A,argon flow rates from 800 sccm to 2000 sccm and magnetic fields of 0.1 T and 0.2 T were chosen.The results show:(a) the relationship between the averaged resistivity and the averaged current density exhibits an empirical scaling law as η∝ j~(-0.63369) and the power dissipated in the arc has a strong relation with the filling factor;(b) through the quartz,the argon ions optical emission lines have been easily observed and are dominating with wavelengths between 340 nm and 520 nm,which are the emissions of Ar~+-434.81 nm and Ar~+-442.60 nm line,and theintensities are increasing with the arc current and decreasing with the inlet argon flow rate;and(c) the electron density and temperature can reach 2.0 × 10~(19) m~(-3) and 0.48 eV,respectively,under the conditions of an arc current of 90 A and a magnetic field of 0.2 T.The half-width of the n_e radial profile is approximatively equal to a few Larmor radii of electrons and can be regarded as the diameter of the plasma jet in the experiments.     

The effect of impurities on TL emission wavelengths of NaCl crystals

We report emission spectra during thermoluminescence of NaCl crystals doped with Eu, Sr, Ca, Cr and Ni impurities. Crystals were irradiated at ambient temperature with X- or γ-rays prior to measurement. Isometric plots in the wavelength range 200–800 nm reveal only small differences in patterns of TL emission for pure samples and samples doped with Eu, Sr and Ca. However samples doped with Cr and Ni show significant variations characterized by suppressed emission between 390 nm and 520 nm. This is discussed in terms of the efficiency of colouration of the crystals and the state of aggregation of impurity–vacancy dipoles.     

LiCl-KCl共晶熔盐的纯化

氯化锂-氯化钾共晶熔盐是电解精炼干法后处理中最常用的电解质,其含有的杂质直接影响电流效率和产物纯度。本研究分别采用高温处理、HCl气体鼓泡和恒电位电解等方法依次去除了熔盐中的易挥发物质、氧离子和金属离子等杂质,获得了较高纯度的熔盐。采用热重分析(TGA)、电化学和电感耦合等离子体原子发射光谱(ICP-AES)等方法对比了纯化前后熔盐中各杂质的含量。研究结果表明:去除易挥发杂质的最佳处理温度范围为450～650℃;去除杂质金属离子时最佳电解电位为-2.3Vvs.Ag/AgCl(摩尔分数2%),恒电位电解800s后杂质金属离子总量低于1.5×10-6 g/g(盐)。以上研究结果表明,采用高温处理、HCl气体鼓入和恒电位电解可获得纯度较高的LiCl-KCl共晶熔盐。     

Comparative Study of Plasma Parameters in Magnetic Pole Enhanced Inductively Coupled Argon Plasmas

Langmuir probe measurements of radio frequency (RF) magnetic pole enhanced inductively coupled (MaPE-ICP) argon plasma were accomplished to obtain the electron number densities and electron temperatures. The measurements were carried out with a fixed RF frequency of 13.56 MHz in a pressure range of 7.5 mTorr to 75 mTorr at an applied RF power of 10 W and 100 W. These results are compared with a global (volume average) model. The results show good agreement between theoretical and experimental measurements. The electron number density shows an increasing trend with both RF power and pressure while the electron temperature shows decreasing trend as the pressure increases. The difference in the plasma potential and floating potential as a function of electron temperature measured from the electrical probe and that obtained theoretically shows a linear relation with a small difference in the coefficient of proportionality. The intensity of the emission line at 750.4 nm due to 2p 1 → 1s 2 (Paschen’s notation) transition closely follows the variation of n e with RF power and filling gas pressure. Measured electron energy probability function (EEPF) shows that electron occupation changes mostly in the high-energy tail, which highlights close similarity of 750.4 nm argon line to n e .     

Space-time Resolved Spectroscopic System Based on a Rotating Hexahedral Mirror for Measurement of Visible and Ultraviolet Spectral Line Emissions

By using a rotating hexahedral mirror placed in front of the objective lens and two sets of visible and ultraviolet monochromators coupled with a branchy quartz fiber bundle, a space-time resolved spectroscopic system has been developed on the HT-7 superconducting tokamak. A center monitoring system has been used including a Helium-Neon laser and a photodiode detector to indicate the absolute position of the measurement in order to reduce the error caused by the uncertain emissive position of the plasma. By using the asymmetric Abel inversion, the space-time resolved local emission coefficients of the spectroscopic line emissions have been obtained. Presented in this article are simultaneous measurements of two spectral line emissions such as CV-227.1 nm and OV-278.1 nm during a single plasma discharge on the HT-7. Experimental results indicate that the time resolution is better than 3 ms, the space resolution is better than 1.5cm, the ratio of signal to background is better than 10：1, and the relative error of chord-integrated emission profile is less than 10%. Compared to traditional multichannel detecting systems, this system has considerably improved measurement efficiency, reduced uncertainty, and is therefore suitable for transport studies of global particles and impurities.