Impurity Lines Research Articles

Impurity Ions Mn<sup>2+</sup> and Fe<sup>3+</sup> as Paired Spin Labels for the Study of Structural Transformations in Phyllosilicates by the ESR Method

Impurity paramagnetic ions Mn2+ and high spin Fe3+ (S = 5/2) are shown to be very informative “paired spin labels” to investigate structural transformations in natural aluminosilicate clay minerals by ESR spectroscopy. Second derivative ESR (SD ESR) enables to detect minor narrow lines of the ions against the background of intense broad lines of other paramagnetic impurities. Complex SD ESR spectra of the ions are explained by the Jahn-Teller effect and hyperfine interactions with OH-groups. SD ESR spectra before and after heating (620°C and 900°C) proved transformations of octahedral crystal cells accompanied by the loss of the OH-groups, displacement of the ions to equivalent positions.

Boron powder injection experiments in WEST with a fully actively cooled, ITER grade, tungsten divertor

Reactor relevant fusion devices will use tungsten (W) for their plasma facing components (PFCs) due to its thermomechanical properties and low tritium retention. However, W introduces high-Z impurities into the plasma, degrading its performance. Different wall conditioning methods have been developed to address this issue, including coating of W PFCs with layers of low-Z material. Wall conditioning by boron (B) powder injection using an impurity powder dropper (IPD) is being studied in WEST. Two series of experiments were conducted since the installation of the new ITER grade full W divertor. During the first series in 2023 ∼ 1 g of B powder was injected in total at a maximum rate of ∼ 58 mg/s, both of which are three times greater than respective values in the initial WEST powder injection experiments. The second series of experiments included injection of B and BN powders for comparison of their effects on plasma performance. The presence of an instantaneous conditioning effect is suggested by visible spectroscopy measurements of low-Z impurity lines and a rollover of total radiated power past an injection rate of ∼ 20 mg/s was observed. Presence of B coating layer formation is supported by the evolution of the average radiance of visible lines of B, W and oxygen (O). To understand B transport, an interpretative modeling workflow is employed, utilizing the SOLEDGE-EIRENE fluid boundary plasma code and the Dust Injection Simulator (DIS) code. Parameters like B perpendicular diffusivity and recycling coefficients are varied to match experimental results to see if the initial assumption of B sticking to the PFCs immediately after the contact with the wall is adequate for correctly modelling its distribution on the PFCs.

Wavelength calibration and spectral analysis of vacuum ultraviolet spectroscopy in EAST

A vacuum ultraviolet (VUV) spectroscopy with a focal length of 1 m has been engineered specifically for observing edge impurity emissions in Experimental Advanced Superconducting Tokamak (EAST). In this study, wavelength calibration for the VUV spectroscopy is achieved utilizing a zinc lamp. The grating angle and charge-coupled device (CCD) position are carefully calibrated for different wavelength positions. The wavelength calibration of the VUV spectroscopy is crucial for improving the accuracy of impurity spectral data, and is required to identify more impurity spectral lines for impurity transport research. Impurity spectra of EAST plasmas have also been obtained in the wavelength range of 50–300 nm with relatively high spectral resolution. It is found that the impurity emissions in the edge region are still dominated by low-Z impurities, such as carbon, oxygen, and nitrogen, albeit with the application of full-tungsten divertors on the EAST tokamak.

Vacuum-Ultraviolet spectrometer system for impurity emission measurement on a Compact Torus Injection System of EAST

Recently, a compact torus injection (CTI) system was developed for central fueling on experimental advanced superconducting tokamak (EAST). As impurity generated by the interaction between CTI plasma and the electrode material can dilute the fuel particle, it is important to measure impurity content in CTI and evaluate the effect of impurity on the plasma before the application of CTI to EAST. A vacuum-ultraviolet (VUV) spectrometer that utilizes a concave holographic grating with 1200 groove mm-1 was developed and installed on EAST-CTI for impurity emission measurement and transport study. The mainly parts of the spectrometer are an entrance slit, a concave holographic grating with 1200 groove mm-1 and a charge coupled device (CCD). The spectrometer is designed to image the spectra of 50–460 nm by turning the grating. Preliminary experimental results were obtained from the recent EAST-CTI campaign. Impurity line spectra from 50 to 460 nm wavelength range were measured and identified for several impurity species, such as iron, copper, chromium, oxygen, carbon and fluorine. For example, spectra in the intervals of 150 nm to 300 nm contained strong Fe lines. Helium spectra are also measured in the form of He I and He II spectral lines as helium is the main component of the plasma. The results show that the VUV spectrometer is capable of measuring impurity radiations on EAST-CTI and will be a useful tool for impurity behavior study.

Electron Temperature Measurements Using a Two-Filter Soft X-ray Array in VEST.

A multichannel soft X-ray (SXR) array has been developed to measure the electron temperature in the Versatile Experiment Spherical Torus (VEST). To estimate electron temperature using the two-filter method applied to SXR intensity, we designed a pinhole camera that has two photodiode arrays with different metallic filters. We also adopted a filter wheel and tested various filter parameters to find the optimal filter set. Through tests, the combination of aluminum and beryllium was found to be the most suitable for the current experimental conditions in VEST. The filtered SXR signals were acquired with a low-noise preamplifier, exhibiting sufficient signal-to-noise ratios for electron temperature estimation based on the intensity ratio of two signals obtained with different filters. The estimated electron temperature from the developed two-filter SXR array showed reasonably matched levels and consistent trends with Thomson scattering measurements. Error contribution from impurity line emission is also discussed.

Development of space-resolved EUV spectrometers working at 5–138 Å for profile observation of high-Z impurity ions in EAST plasma

In order to observe the radial profile of impurity line emission in a short wavelength range and to study the transport of metallic impurity ions intrinsically existing in plasma, two pairs of space-resolved extreme ultraviolet (EUV) spectrometers working at 5–138 Å were newly established on EAST tokamak. A back-illuminated complementary metal oxide semiconductor (CMOS) detector with a small pixel size of 6.5 × 6.5 μm2 and a varied-ling-spacing (VLS) concave holographic grating with a central density of 2400 grooves/mm allows the EUV spectrometers have good spectral resolution. A precise wavelength calibration is performed with cubic polynomial fitting using well-known emission lines from light impurity ions. The radial intensity profile of Cu XX at 12.570 Å and Cu XXI at 10.392 Å were observed successfully by space-resolved EUV spectrometers during H-mode discharge. The rapid change in the W XXXIII radial profile during the impurity burst period was clearly observed with sufficient intensity. The results show that the newly developed space-resolved EUV spectrometers have excellent performance in impurity diagnostics.

First-principles study of metals, metalloids and halogens doped monolayer MoSe2 to tune its electronic properties

Owing to their small band-gap characteristics, two-dimensional transition metal dichalcogenides (TMDCs) have garnered a lot of attention. Herein, we studied the electronic as well as structural properties of doped monolayered MoSe2 with different dopants at the selenium (Se) site employing the density functional theory (DFT) using generalized gradient approximation (GGA). To ascertain bonding nature electron localization function (ELF) was used and Phonon spectra computations were done for dynamical stability tests. We systematically explored the electronic properties of monolayer MoSe2 doped with X-atoms (X comprises of metals Li, Be, Al; metalloids B, Si; non-metals (NMs) C, N, P, O and the NM atoms belonging to halogen group (F, Cl). We compared our outcomes with available experimental and other calculated results in the literature. The appearance of impurity lines in the energy gap causes to diminish the band gaps of doped MoSe2. The change in doping site and dopant element results in a significant reduction in the bandgap of doped MoSe2. To gain more insight into the electronic properties of X-doped MoSe2 monolayer, the partial density of states (PDOS) of the dopants and neighbour Mo atoms are attached to the band structures. Our results give pleasing data regarding the optimization of bandgap which shows that halogen dopant provided n-type doping while the rest of the elements provided p-type doping in MoSe2, which helps to understand the electrical conductivity in addition to their utilization in semiconductor and other optoelectronic devices. We are optimistic that the findings in this work will help experimentalists to carry out their research on a real-world application, which will also widen the investigation of transition-metal dichalcogenides (TMDs) in other sectors.

EUV/VUV Spectroscopy for the Study of Carbon Impurity Transport in Hydrogen and Deuterium Plasmas in the Edge Stochastic Magnetic Field Layer of Large Helical Device

The ergodic layer in the Large Helical Device (LHD) consists of stochastic magnetic fields exhibiting a three-dimensional structure that is intrinsically formed by helical coils. Spectroscopic diagnostics was employed in the extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) wavelength ranges to investigate emission lines of carbon impurities in both hydrogen (H) and deuterium (D) plasmas, aiming to elucidate the impact of distinct bulk ions on impurity generation and transport in the edge plasmas of the LHD. The emission intensity of carbon CIII, CIV, CV, and CVI lines is significantly higher in the D plasma compared to the H plasma, indicating a greater sputtering rate of carbon materials in the D plasma, resulting in a higher quantity of carbon impurities originating from the divertor plates. A Doppler profile measurement of the second order of CIV line emission (1548.20 × 2 Å) was attempted using a 3 m normal-incidence VUV spectrometer in the edge plasma at a horizontally elongated plasma position. The flow velocity reaches its maximum value close to the outermost region of the ergodic layer, and the observed flow direction aligns with the friction force in the parallel momentum balance. The flow velocity increases with the electron density in H plasmas, suggesting that the friction force becomes more dominant in the force balance at higher density regimes. This leads to an increase in the impurity flow, which can contribute to the impurity screening. In contrast, the flow velocity in the D plasma is smaller than that in the H plasma. The difference in flow values between D and H plasmas, when the friction force term dominates in the momentum balance, could be attributed to the mass dependence of the thermal velocity of the bulk ions.

Behavior and Fractionation of Low-Volatile Impurities in a DC Arc in the Analysis of Zirconium by Atomic Emission Spectrometry

We studied the effect of chemically active fluorine-containing additives AlF3, BaF2, and ZnF2 on the character of evaporation of some low-volatile elements from a refractory matrix in the crater of a DC arc electrode in the analysis of zirconium by atomic emission spectrometry. The additives cause the formation of volatile fluorides of low-volatile elements and their fractional evaporation with respect to the base element evaporation. Impurity fluorides rapidly and completely evaporate during the first 30 s of arcing, and only after that the intensive evaporation of the base begins. Such fractionation increases significantly the intensity of the spectral lines of impurities, decreases the background intensity, and, consequently, improves the limits of determination of low-volatile elements in zirconium oxide. Zinc fluoride is the most effective of the studied additives. Using zinc fluoride, we lowered the limits of determination of low-volatile elements by two orders of magnitude compared to the limits of determination in zirconium oxide without additives and improved the reproducibility of the results of determinations.

Performance improvement of space-resolved extreme ultraviolet spectrometer by use of complementary metal-oxide semiconductor detectors at the Experimental Advanced Superconducting Tokamak.

Two pairs of space-resolved extreme ultraviolet (EUV) spectrometers working at 5-138 Å with different vertical observation ranges of -7 ≤ Z ≤ 19 and -18 ≤ Z ≤ 8cm have been newly developed to observe the radial profile of impurity line emissions and to study the transport of high-Z impurity ions intrinsically existing in EAST tokamak plasmas. Both spectrometers are equipped with a complementary metal-oxide semiconductor (CMOS) detector (Andor Marana-X 4.2B-6, Oxford Instruments) with sensitive area of 13.3 × 13.3mm2 and number of pixels equal to 2048 × 2048 (6.5 × 6.5 µm2/pixels). Compared to the currently operating space-resolved EUV spectrometers with a charge-coupled detector (CCD: 1024 × 255 pixels, 26 × 26 µm2) working at 30-520 Å, this spectrometer's performance was substantially improved by using the CMOS detector. First, the spectral resolution measured at full width at half maximum was improved in the whole wavelength range, e.g., Δλ1/2_CMOS = 0.092 Å and Δλ1/2_CCD = 0.124 Å at C VI 33.73 Å and Δλ1/2_CMOS = 0.104 Å and Δλ1/2_CCD = 0.228 Å at Mo XXXI 115.999 Å, thus enabling a more accurate analysis of spectra with complicated structure such as tungsten unresolved transition array in the range 45-65 Å. Second, the temporal resolution was largely improved due to the high-speed data acquisition system of the CMOS detector, e.g., Δt_CMOS = 15 ms/frame and Δt_CCD = 200 ms/frame at routine operation in the radial profile measurement. Third, signal saturation issues that occurred when using the old CCD sensor during impurity accumulation now disappeared entirely using the CMOS detector due to lower exposure time at high readout rates, which largely improved the observation performance in similar impurity burst events. The above-mentioned performance improvements of the space-resolved EUV spectrometer led to a rapid change in the W XXXIII (52.22 Å) radial profile during a single cycle of low-frequency sawtooth oscillation with fst = 5-6Hz at a sufficient detector count rate.

Experimental results from x-ray imaging crystal spectrometer utilizing double crystal assembly in Korea Superconducting Tokamak Advanced Research (KSTAR)

A double crystal assembly (DCA) for multiple atomic spectra measurements, including helium-like Ar and hydrogen-like Ar, and other impurity lines are applied for the x-ray imaging crystal spectrometer in Korea Superconducting Tokamak Advanced Research. The DCA expands measurable wavelengths much wider so that cross comparisons of the ion temperature and toroidal rotation between two different atomic states are possible. The recent experimental comparison studies for the ion temperature and toroidal rotation of helium-like Ar and hydrogen-like Ar from the DCA are reported.

Impurity temperatures measured via line shape analysis in the island scrape-off-layer of Wendelstein 7-X

Impurity temperatures have been determined by a spectroscopic line shape analysis for several species in the divertor scrape-off-layer of the stellarator Wendelstein 7-X (W7-X). Examples include spectral lines from intrinsic elements (C II and C III, He I) as well as from seeded impurities (Ar II, N II) through the divertor gas inlet system. Both Doppler broadening and Zeeman splitting are found to contribute significantly to the impurity line shapes. Zeeman splitting arises due to the confining magnetic field in W7-X and complicates the line shape appearance. By attributing Doppler widths to each of the various Zeeman components, however, we demonstrate that reliable ion temperature values can be derived provided that the presence of the magnetic field is properly accounted for. The spectrally highly resolved lines are analyzed by means of a multi-parameter, least-squares fit routine, which accounts for Doppler broadening, Zeeman splitting, as well as the instrumental broadening of the spectrometer used to measure the spectral line shapes. By spectral fitting of the Zeeman features, it is also found that the line shape analysis can yield values for the local magnetic field, which can be used to localize the impurity radiation approximately provided that the line emission is dominant in a small area intersected by the lines of sight of the spectrometer.

Intensity calibration including pile-up effect in PHA spectra measurements at W7-X

The pulse-height-analysis (PHA) is a technique used at fusion devices for measurements of content and intensity of the X-ray spectrum. At the stellarator W7-X, this method is applied together with the application of silicon drift detectors for observation of the radiation in the energy range from about 0.5 to 20 keV [, ]. To receive quantitative information on plasma impurity concentration, several factors should be taken into account. Firstly, the detector response curve which includes the transmission of filters and detector thickness. In this case, the response was determined from the knowledge of the detector’s geometry and characteristics of materials used, as calibration measurements with a standard X-ray radiation source were not possible. Secondly, the geometry parameters which define the observation cone of view, and finally, the pile-up effect which is a crucial point in intensity calibration. The pile-up effect can be minimized by settings of the lower values of the digital filter peaking time in X-ray signal processor (DXP), but often it is a compromise between energy resolution and temporal resolution of the time-dependent X-ray intensity signal. The information about the number of lost photons can be derived from the knowledge of the number of photons incoming to the detector and the number of photons observed in a spectrum. For the PHA system dedicated to W7-X, the loss of the pulses which undergo pileup is determined by values of the parameters: input count rate — ICR and output count rate — OCR, both delivered by the DXP. It is always taken into account in the intensity spectra calibration which allows to study the changes in impurity line intensity and hence to determine the impurity concentration.

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 diagnostics

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.

A compact electron beam ion trap in support of high-temperature plasma diagnostics based on conduction-cooled superconducting coils.

Spectroscopic diagnostics of future fusion reactor plasmas require information on impurity line emissions, especially for relevant high-Z metal elements (e.g., tungsten). These materials will be widely used as plasma facing components for their high heat tolerance and low sputtering yield. Based on an electron beam ion trap, a compact impurity spectra platform is developed to mimic the high-temperature environment of a fusion reactor. The proposed platform can deliver a focused e-beam at energies over 30 keV using a confining magnetic field of ∼1.0T generated by two superconducting coils (NbTi). Cooled by a closed-loop cryocooler, the coils can avoid the usage of a complicated cryogenic system involving the handling of liquid helium. For spectroscopic studies of highly charged ions, a spherically curved crystal spectrometer is proposed to measure a wavelength range around 2-4 Å covering the typical wavelength range expected to be emitted by metal ions in a fusion plasma. This paper reports the design and development progress of the platform.

Tunable high resolution spectrometer for H-alpha and visible spectroscopy in ITER

A tunable-band high resolution spectrometer (HRS) was designed to study the fine structure of H-alpha and impurity lines in order to separate the divertor stray light (DSL) and the scrape-off layer (SOL) emission required for H-alpha and visible spectroscopy diagnostics in ITER. The spectral resolution not worse than ~0.01 nm is needed to resolve similar Zeeman lines in the SOL and DSL components shifted with a small offset due to some difference of the magnetic field in the divertor and at the ITER first walls. HRS optical design is based on the pseudo-autocollimation scheme with a pair of coplanar holographic gratings and spatially separated back-reflected optical beam. This scheme provides independence of a dispersion versus the wavelength in the whole spectral range, together with acceptable F-number up to f/4.5 of the input/output lenses. Grating and back-reflection mirror units are mount to the motorized rotational platforms with remote control realized in LabView software.The HRS prototype was manufactured and tested to verify the design characteristics. The main parameters: spectral range, inverse linear dispersion, spectral resolution and contrast were measured at 65˚ and 75˚ light incidence angles to the gratings. The inverse linear dispersions are 0.206 nm/mm and 0.13 nm/mm respectively, with 0.01 nm spectral resolution at 65˚ angle measured by scientific-grade PCO edge 4.2 CMOS camera. Close-wavelength contrast of 1:6•10−6 was measured at δλ = 2.5 nm spectral distance from the He-Ne laser line. The total spectral range is 400..700 nm with a tunable sub-band of 1.3÷2.7 nm spectral width defined by the position of holographic gratings.

Predissociation and pressure dependence in the low frequency far wing of the Wulf absorption band of ozone near 1.2 µm

The weak low frequency tail of the ozone Wulf band is newly studied by high sensitivity cavity ring down spectroscopy (CRDS) in the 7920–8700 cm−1 range. Although strongly obscured by impurity lines, the ozone absorption signature shows up in the recorded spectra as two mostly unresolved absorption bands. These two bands with maximum near 8154 and 8450 cm−1 are hot bands from the (020) and (100) ground state vibrational levels reaching the same predissociated 3A2(000) upper state of 16O3. The observed bands include a mostly structureless continuum and lines exhibiting a clear broadening due to the predissociation of the 3A2(000) upper state. On the basis of assignments of the rotational structure available in the literature for the 3A2(000)-X1A1(000) cold band centered near 9553 cm−1, seventy-four relatively narrow lines could be rotationally assigned to the 3A2(000)-X1A1(020) and 3A2(000)-X1A1(100) hot bands. A line shape analysis, performed using a Voigt profile, provided the width of the Lorentzian component. Additional recordings performed at various pressures for 18 lines allowed to disentangle the pressure and predissociation contributions to the fitted Lorentzian widths. As a result, the newly derived pressure broadening coefficients of the considered rovibronic transitions are found to be similar to those of the rovibrational infrared bands. All the lines studied are affected by significant predissociation due the spin-orbit coupling between the 3A2(000) level and high lying dissociative vibrational levels of the X1A1 electronic ground state. The resulting set of predissociation widths for sixty lines ranges between 9 × 10−3 and 0.2 cm−1 corresponding to upper state lifetime of 560 and 25 ps, respectively. The reported results are discussed in relation with previous experimental and theoretical studies.

Experimental and simulation study of impurity transport response to RMPs in RF-heated H-mode plasmas at EAST

Spatial profiles of impurity emission measurements in the extreme ultraviolet (EUV) spectroscopic range in radiofrequency (RF)-heated discharges are combined with one-dimensional and three-dimensional transport simulations to study the effects of resonant magnetic perturbations (RMPs) on core impurity accumulation at EAST. The amount of impurity line emission mitigation by RMPs appears to be correlated with the ion Z for lithium, carbon, iron and tungsten monitored, i.e. stronger suppression of accumulation for heavier ions. The targeted effect on the most detrimental high-Z impurities suggests a possible advantage using RMPs for impurity control. Profiles of transport coefficients are calculated with the STRAHL one-dimensional impurity transport code, keeping $\nu /D$ fixed and using the measured spatial profiles of $\textrm{F}{\textrm{e}^{20 + }}$ , $\textrm{F}{\textrm{e}^{21 + }}$ and $\textrm{F}{\textrm{e}^{22 + }}$ to disentangle the transport coefficients. The iron diffusion coefficient ${D_{\textrm{Fe}}}$ increases from $1.0- 2.0\;{\textrm{m}^2}\;{\textrm{s}^{ - 1}}$ to $1.5- 3.0\;{\textrm{m}^2}\;{\textrm{s}^{ - 1}}$ from the core region to the edge region $(\rho \gt 0.5)$ after the onset of RMPs. Meanwhile, an inward pinch of iron convective velocity ${\nu _{\textrm{Fe}}}$ decreases in magnitude in the inner core region and increases significantly in the outer confined region, simultaneously contributing to preserving centrally peaked $\textrm{Fe}$ profiles and exhausting the impurities. The ${D_{\textrm{Fe}}}$ and ${\nu _{\textrm{Fe}}}$ variations lead to reduced impurity contents in the plasma. The three-dimensional edge impurity transport code EMC3-EIRENE was also applied for a case of RMP-mitigated high-Z accumulation at EAST and compared to that of low-Z carbon. The exhaust of ${\textrm{C}^{6 + }}$ toward the scrape-off layer accompanying an overall suppression of heavier ${\textrm{W}^{30 + }}$ is observed when using RMPs.

A Nodal Model for Tokamak Burning Plasma Space-Time Dynamics

Fusion alpha heating introduces new phenomena into plasma dynamics and control. On the worrisome side is the well-known fact that the dependence of the predominantly central fusion heating mechanism, coupled with the less appreciated fact of the predominantly plasma edge location of bremsstrahlung and impurity line and recombination radiation cooling and of ion orbit loss cooling, suggests the possibility of a thermal runaway fusion power excursion in the plasma core. On the encouraging side is the fact that the fusion alpha energy is transferred first to heat the core electrons and produce electron cyclotron radiation that is transferred instantaneously, predominantly to outer plasma regions and the surrounding material wall, reducing its availability for further heating of core plasma ions. This paper discusses the temporal and spatial dependence of the various heating and cooling mechanisms involved in the burn dynamics of a fusion plasma, introduces a spatially coarse nodal space-time calculation model (suitable for dynamics and controller calculations) for the analysis of burning plasmas, and identifies the research needed to fully evaluate the parameters of such a model.

Identification of forbidden emission lines from highly ionized tungsten ions in VUV wavelength range in LHD for ITER edge plasma diagnostics

Abstract Magnetic-dipole (M1) lines of W29+~W39+ were successfully observed in the vacuum-ultraviolet (VUV) wavelength range of 500–900 A in the Large Helical Device (LHD). Tungsten ions are distributed in the NBI-heated LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. It is found that W37+ line at 646.7 A and W38+ lines at 532.9 A and 559.1 A are emitted when the central electron temperature ranges from 2 to 3 keV with relatively high intensity and isolated from other intrinsic impurity lines. The result is the first observation of the M1 forbidden lines of tungsten ions in the VUV wavelength range in fusion plasma experiments. Observation of the W37+ and W38+ lines could improve the tungsten diagnostics in ITER edge plasmas because they are expected to be distributed in the edge plasmas around the last closed flux surface including the scrape-off layer in ITER.