EUV Spectrometer Research Articles

Characterization of optical depth for laser produced plasma extreme ultraviolet source

This study investigates the emission mechanism of laser-produced plasma extreme ultraviolet source (LPP-EUV). In the experiment, the EUV radiation is generated by a 1064 nm laser interacting with slab Sn target. The EUV emission is characterized by EUV energy monitors and an EUV spectrometer. The dependency of CE on laser intensity and plasma relative optical depth is explored by a plasma emission-absorption layer model. The dependency is confirmed by an optical interferometry measurement of plasma electron density for the first time. Our work provides a method for characterizing and optimizing the optical depth of laser driven EUV source.

Using the Cartwheel CME to Predict Off-limb Observations of CMEs for New and Upcoming UV and EUV Spectrometers

Coronal mass ejections (CMEs) expel multithermal, magnetized plasma from the Sun, and when directed toward Earth, can cause extensive damage to space and ground-based electronics. To better understand the triggering, acceleration, and evolution of CMEs, it is critical to study CME plasma properties close to the Sun. High-resolution ultraviolet and extreme ultraviolet (UV-EUV) spectroscopy can give the most detailed plasma diagnostics of CMEs in the low solar corona. Unfortunately, very few spectrally resolved observations of CMEs in the low solar corona exist. However, with the recent launch of the Spectral Imaging of the Coronal Environment on board Solar Orbiter and the upcoming missions, including the EUV High-Throughput Solar Telescope (EUVST) on Solar-C and the Multi-slit Solar Explorer (MUSE), we will have the opportunity to obtain unprecedented, spectrally resolved CME observations. Using the only full EUV spectral observation of a CME by the Hinode/EUV Imaging Spectrometer, we predict the spectra that SPICE, EUVST, and MUSE are expected to observe during an off-limb CME eruption to investigate the diagnostic capabilities of each instrument. Finally, we provide a list of density-sensitive and temperature-sensitive ratios for CME plasma diagnostics along with the expected spectral atlas for each instrument to facilitate observing sequence planning.

Line identification of extreme ultraviolet spectra from aluminum ions in EAST Tokamak plasmas

Extreme ultraviolet (EUV) spectra emitted from aluminum in the 5-340 Å wavelength range were observed in Experimental Advanced Superconducting Tokamak (EAST) discharges. Several spectral lines from aluminum ions with different degrees of ionization were successfully observed with sufficient spectral intensities and resolutions using three fast-time-response EUV spectrometers. The line identification uses three independent state-of-art computational codes for the atomic structure calculations, which provide the wavelengths and the collisional and radiative transition rate coefficients. These programs are hullac (Hebrew University—Lawrence Livermore Atomic Code), autostructure, and fac (Flexible Atomic Code). Using three different codes allows us to resolve some ambiguities in identifying certain spectral lines and assess the validity of the theoretical predictions.

Analysis of E3 Transitions in Ag-like High-Z Ions Observed with the NIST EBIT

We report measurements and identification of the E3 4f7/2,5/2-5s1/2 transitions and E1 allowed transitions in Ag-like W (Z = 74), Re (Z = 75), and Ir (Z = 77). The spectra were recorded at the NIST EBIT using a grazing-incidence EUV spectrometer. The present measured wavelengths and theoretical predictions using GRASP2K calculations confirm previous observations of the same E3 transitions in Ag-like W. Our collisional–radiative model using the NOMAD code offers an insight into the population kinematics for Ag-like ions of heavy elements. We discuss the observed spectra and comparisons of the measured and simulated spectral lines.

Observation of coherent mode induced by a molybdenum dust on EAST

The influence of a molybdenum dust buildup on plasma edge turbulence has been studied in the EAST tokamak. The motion of the dust from the upper divertor region is detected by a fast visible CCD camera, the XUV spectrometer arrays, and the EUV spectrometer. The MoXV emission intensity sharply increases compared with the spectral lines of various ionization states of other elements, which implies that the dust particles are the molybdenum impurities. The radial distribution of Mo14+ ion simulated by a simplified 1D transport model indicates that the molybdenum dust mainly deposits in the pedestal bottom region. Moreover, it is observed that the coherent mode (CM) appears at ρ = 0.94 after the molybdenum impurities enter the main plasma region. The influx of molybdenum impurities results in increasing pedestal electron density and decreasing pedestal electron temperature in contrast to that before the event of impurities dropping. It is also found that the electron density gradient in the pedestal increases when the ablation of the molybdenum impurities is observed in the pedestal region. The qualitative experimental results indicate that the onset of CM is likely related to the increase of the density gradient and edge collisionality in the pedestal. In comparison to the density gradient, the enhancement of CM amplitude largely depends on the increase of the edge collisionality.

Responsivity calibration of the extreme ultraviolet spectrometer in the range of 175-435 Å

We reported the relative responsivity calibration of the grazing-incidence flat-field EUV spectrometer between 175 and 435 Å by means of two methods. The first method is implemented by measuring the diffraction efficiency of the grating with synchrotron radiation light source. Considering the transmission efficiency and quantum efficiency of the other optical components in the spectrometer, the total responsivity was then obtained. The second one was carried out by measuring line emissions from C3+, N4+ and O3+ ions at Shanghai high temperature super conductor electron beam ion trap (SH-HtscEBIT). The EUV spectra were also simulated theoretically via a collisional radiative model. In the calculation, the second-order relativistic many-body perturbation theory approach based on the flexible atomic code was used to calculate the energy levels and transition rates; the close-coupling R-matrix approach and relativistic distorted wave method were utilized to calculate the collision strength of electron impact excitation. In comparison with the spectroscopic measurements at EBIT device, the differences between the measured and simulated relative line intensities were obtained. The responsivity calibration for the spectrometer was then achieved by a 3rd degree polynomial function fitting. Our measurement shows that the responsivity between 175 and 435 Å varies by factor of ∼ 46. The two results of calibration demonstrated a consistency within an average deviation of 24%. In addition, an evaluation of our calculations on C iv, N v and O iv line emissions in this wavelength region was given.

EUV data processing methods of the Solar Auto-Calibrating EUV Spectrometers (SolACES) aboard the International Space Station

ContextSince 2008, the Solar Auto-Calibrating EUV Spectrometer (SolACES) experiment monitors the solar EUV radiation. SolACES is part of the SOLAR mission, a device mounted on the COLUMBUS module on the International Space Station (ISS). The SolACES device is capable of measuring the EUV radiation of the full solar disk, with three grazing incidence spectrometers, covering the spectral range from 17 to 135nm. IssueDegradation and ageing effects of hardware components are a major issue in the field of EUV measurements. In addition, propellant pollution from ISS logistic vehicles strongly complicate the instrumental operation as well as the data evaluation. To correct these effects, two double ionization chambers have been mounted onto the device frame. These are considered as a primary radiometric detector standard. By refilling the ionization chambers, the absolute EUV flux can be measured. Efficiency changes, being a severe issue in the field of measurements of EUV radiation, can corrected via an in-situ auto-calibration. The use of this method requires a thorough understanding of electron multiplier degradation and processes inside an ionization chamber. AimsThe main focus of this paper lies on the correction of hardware ageing effects in the spectrometer readout, as well as on the usage of ionization chamber measurements for absolute calibration. Additionally, we intend to demonstrate the long term stability of the in-orbit calibration principle of EUV spectrometers with double ionization chambers. MethodsIn this paper, we first briefly present the instrument and its components. Second, we list, explain, and correct various degradation effects within the spectrometer units. The core part are the adjustments between spectrometer and ionization chamber data, for calibration purposes. Results and perspectivesThe proof of concept of the in-orbit calibration, via ionization chambers, is given, by intercomparison of EUV data from SolACES with other experiments, over almost one decade. The presented data can be used for further investigations in climate modelling, as well as contribute to a SSI composite.

EMC3‐EIRENE Simulation of Impurity Transport in Comparison with EUV Emission Measurements in the Stochastic Layer of LHD: Effects of Force Balance and Transport Coefficients

AbstractThe transport properties and line emissions of the intrinsic carbon in the stochastic layer of the Large Helical Device have been investigated with the three‐dimensional edge transport code EMC3‐EIRENE. The simulations of impurity transport and emissivity have been performed to study the dedicated experiment in which the carbon emission distributions are measured by a space‐resolved EUV spectrometer system. A discrepancy of the CIV impurity emission between the measurement and simulation is obtained, which is studied with the variation of the ion thermal force, friction force and the perpendicular diffusivity in the impurity transport model. An enhanced ion thermal force or a reduced friction force in the modelling can increase the CIV impurity emission at the inboard X‐point region. Furthermore, the impact of the perpendicular diffusivity Dimp is studied which shows that the CIV impurity emission pattern is very sensitive to Dimp. It is found that the simulation results with the increased Dimp tend to be closer to the experimental observation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Extreme Ultraviolet Radiation Measurement for Planetary Atmospheres/Magnetospheres from the Earth-Orbiting Spacecraft (Extreme Ultraviolet Spectroscope for Exospheric Dynamics: EXCEED)

The Sprint-A satellite with the EUV spectrometer (Extreme Ultraviolet Spectroscope for Exospheric Dynamics: EXCEED) was launched in September 2013 by the Epsilon rocket. Now it is orbiting around the Earth (954.05 km×1156.87 km orbit; the period is 104 minutes) and one has started a broad and varied observation program. With an effective area of more than 1 cm2 and well-calibrated sensitivity in space, the EUV spectrometer will produce spectral images (520–1480 Å) of the atmospheres/magnetospheres of several planets (Mercury, Venus, Mars, Jupiter, and Saturn) from the Earth’s orbit. At the first day of the observation, EUV emissions from the Io plasma torus (mainly sulfur ions) and aurora (H2 Lyman and Werner bands) of Jupiter have been identified. Continuous 3-month measurement for Io’s plasma torus and aurora is planned to witness the sporadic and sudden brightening events occurring on one or both regions. For Venus, the Fourth Positive (A1 Π-X1 Σ +) system of CO and some yet known emissions of the atmosphere were identified even though the exposure was short (8-min). Long-term exposure from April to June (for approximately 2 months) will visualize the Venusian ionosphere and tail in the EUV spectral range. Saturn and Mars are the next targets.

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∼650Å. The two-dimensional measurement is performed by scanning the observation chord horizontally. A rectangular plasma region of 520 × 700 mm2 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 Å), C V (40.27 Å), C VI (33.73 Å) and Fe XX (132.85 Å) located at different radial positions are presented with simple analysis on the magnetic field structure of LHD.

Electron-impact induced fluorescence for EUV spectrometer–detector calibration

EUV-Spectra of electron-impact induced fluorescence from rare gases were recorded for an impact energy of 3.5keV intending their application in the first step for spectrometer wavelength scale calibrations. The spectra are in the investigated range of 165–314nm in good agreement with previously measured and calculated spectra. Nearly all observed lines could be identified including 196 new lines. 183 lines mainly for krypton and xenon could not be identified. The spectra are presented and discussed. A compendium of 1670 lines and their identification is added as supplementary tables. The spectra show a number of strong lines which are well suited for spectrometer wavelength scale calibrations and once their intensity relation is deduced can be used for a sensitivity determination of a spectrometer–detector combination as described in the introductory and experimental sections of the paper.

Edge and Core Impurity Transport Study with Spectroscopic Instruments in LHD

Impurity transport was investigated at both edge and core regions in large helical device (LHD) with developed spectroscopic instruments which can measure one- and two-dimensional distributions of impurities. The edge impurity behavior was studied recently using four carbon resonant transitions in different ionization stages of CIII (977Å), CIV (1548Å), CV (40.3Å) and CVI (33.7Å). When the line-averaged electron density, ne, is increased from 1 to 6 × 1013 cm−3, the ratio of (CIII+CIV)/ne increases while the ratio of (CV+CVI)/ne decreases. Here, CIII+CIV (CV+CVI) expresses the sum of CIII (CV) and CIV (CVI) intensities. The CIII+CIV indicates the carbon influx and the CV+CVI indicates the emissions through the transport in the ergodic layer. The result thus gives experimental evidence on the impurity screening by the ergodic layer in LHD, which is also supported by a three-dimensional edge particle simulation. The core impurity behavior is also studied in high-density discharges (ne ≤ 1× 1015 cm−3) with multi H2-pellets injection. It is found that the ratio of V/D (V: convection velocity, D: diffusion coefficient) decreases after pellet injection and Zeff profile shows a flat one at values of 1.1–1.2. These results confirm no impurity accumulation occurs in high-density discharges. As a result, the iron density, nFe, is analyzed to be 6 × 10−7 ( = nFe/ne) of which the amount can be negligible as radiation source even in such high-density discharges. One- and two-dimensional impurity distributions from space-resolved VUV and EUV spectrometers newly developed for further impurity transport study are also presented with their preliminary results.

Model prediction of impurity retention in stochastic magnetic boundary and comparison with edge carbon emission in LHD

Impurity retention (screening) potential in the edge region with stochastic magnetic field in LHD (large helical device) is studied numerically using the three-dimensional edge transport code, EMC3-EIRENE, and experimentally applying VUV and EUV spectrometers. The code predicts an impurity retention regime at high densities, where the friction force dominates over the thermal force. The carbon radiation intensities from each charge state are measured in experiments, and compared with the modelling results. The density dependencies of the calculated and measured radiation intensities agree well with each other, confirming the impurity retention in the edge region of LHD. Geometrical advantages of the stochastic field line structure in this concern are also discussed.

On-line spectrometer for FEL radiation at FERMI@Elettra

A key diagnostic task in a free-electron laser (FEL) facility is the energy spectrum acquisition, both during the development and characterization of the source, and for the definition of the experimental conditions for the users that have to know it at each FEL shot. Since FERMI@Elettra is operated at low repetition rate (10–50 Hz), the spectrum can be easily obtained for each pulse. The design of a shot-to-shot online EUV and soft X-ray spectrometer for the FERMI@Elettra FEL facility is presented. The instrument is a grazing-incidence flat-field spectrometer equipped with a variable-line-spaced plane grating giving a constant deviation of the FEL radiation. The optical layout is detailed both to the FEL-1 (40–100 nm) and FEL-2 (10–40 nm) facilities.

Establishing HZ43 A, Sirius B, and RX J185635–3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC

Establishing HZ43 A, Sirius B, and RX J185635–3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC

Behavior of CIII to CVI Emissions during the Recombining Phase of LHD Plasmas

Carbon emissions of CIII-CVI during the recombining phase of the Large Helical Device (LHD) plasma are studied to understand their behaviors. To achieve this, four resonance transitions of CIII (977 A: 2 s2 1S-2s2p 1P), CIV (1548 A: 2s 2S-2p 2P), CV (40.27 A: 1s2 1S-1s2p 1P), and CVI (33.73 A: 1s 2S-2p 2P) are observed using absolutely calibrated VUV monochromators and EUV spectrometers. A one-dimensional impurity transport code has been used to calculate spectral emissivity under the consideration of measured ne and Te profiles. The temporal evolution of line emissions has been calculated and compared with the measured data. The comparison shows that the carbon density is 3 % of the electron density. However, a discrepancy between the calculated and measured values has been noticed in CIII and CIV emissions. It has been argued that three-dimensional structures of CIII and CIV emissions are likely to be the reason for this difference, which is based on the presence of relatively high-density and high-temperature plasmas in edge ergodic layer in LHD. It is also found that the CV and CVI emissions during the recombining phase increase with electron density, whereas these are nearly constant during steady state phase. This strongly suggests the disappearance of the edge particle screening effect in the recombining phase.

Spectroscopy on magnetically confined plasmas using electron beam ion trap spectrometers

Multiple spectrometers originally designed for and used at the University of California Lawrence Livermore National Laboratory’s electron beam ion trap have found use at various magnetically confined plasma facilities. Three examples will be described. First is a soft X-ray/EUV grating spectrometer (6–150 Å), which is operating at the National Spherical Torus Experiment. Second is an EUV spectrometer with wavelength coverage up to 400 Å, which has just recently started operating at the Sustained Spheromak Physics Experiment. The last is a high-resolution transmission-grating spectrometer for visible light that has been used at the Compact Toroid Injection Experiment and is currently at the Alcator C-Mod tokamak.PACS Nos.: 39.30.+w, 52.55.–s, 32.30.Rj, 07.60.Rd, 52.70.La

Quiet sun XUV and EUV spectroscopy

The two XUV–EUV spectrometers on SOHO have collected a large amount of data in the 6000–10 6 K solar plasma temperature range. These data have allowed us to greatly enhance our knowledge of the processes acting in the solar atmosphere, from the chromosphere to the corona. Some results on the quiet Sun structure (network, quiet Sun versus coronal hole), on the dynamics (velocities, waves, transient events), and the main characteristics of the quiet Sun atmosphere are presented and discussed.

Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC

The absolute calibration of space-borne instruments in the soft X-ray regime rests strongly on model spectra of hot white dwarfs. We analyze the Chandra LETG+HRC-S observations of the white dwarfs HZ43 A and Sirius B and of the neutron star RX J185635-3754 in order to resolve current uncertainties in the soft X-ray spectral fluxes and photospheric parameters of the three stars. We have obtained improved parameters for which fit the observations from the optical to the soft X-ray regime. Our approach allows us to quote their absolute spectral fluxes at selected wavelengths which may aid the calibration of other space-borne instruments.

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 x-ray 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 coefficient 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 x-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 Hα 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.