Vacuum Ultraviolet Spectrograph Research Articles

Reinvestigation of the Herzberg-Lagerqvist-Malmberg transitions of C2 in vacuum ultraviolet region and the implications for astronomical observations.

The dicarbon radical, C2, is one of the most abundant molecules in the universe, and has been widely observed in various energetic environments. Even though numerous experimental and theoretical investigations on C2 have been done during the last two centuries, spectroscopic study of C2 in vacuum ultraviolet (VUV) region has been rare. The only three known absorption band systems in VUV region were identified by Herzberg and co-workers in 1969 by VUV spectrograph, namely the electronic transitions F1Πu(v')-X1Σg +(v″), f3Σg -(v')-a3Πu(v″) and g3Δg(v')-a3Πu(v″) (Herzberg-Lagerqvist-Malmberg transitions). In this study, we employ a two-photon resonance-enhanced four-wave mixing based VUV laser source and a time-of-flight mass spectrometer for reinvestigating the above three electronic transitions of C2 through a resonant (1VUV + 1'UV) photoionization scheme. Besides those vibronic transitions as identified by Herzberg and co-workers, many more absorption bands belonging to the electronic transitions f3Σg -(v')-a3Πu(v″) and g3Δg(v')-a3Πu(v″) are observed with their spectroscopic parameters determined. The rather astrophysically important F1Πu state is not observed here by the resonant (1VUV + 1'UV) photoionization scheme, which must be due to its fast predissociation process. Instead, our study shows that the vibronic band g3Δg(v' = 2)-a3Πu(v″ = 0) exactly overlaps with F1Πu(v' = 0)-X1Σg +(v″ = 0), which was not realized in previous studies. The potential implications of these findings to astronomical observations are discussed.

X-Ray and VUV Spectra from the Laser Plasma Produced with “Kanal-2” Facility

The paper presents experimental results obtained on “Kanal-2” facility. Laser radiation focusing on the surface of plane magnesium targets created the high temperature plasma, which emitted X-ray and vacuum ultraviolet (VUV) radiation. This radiation spectrum was investigated with two spectrographs: the mica crystal spectrograph (working range 8.2 ? - 9.6 ?) and the grazing incidence VUV spectrograph (working rage 30 ? - 130 ?). A set of beryllium stepwise attenuators appended the diagnostic complex and allowed us to get an approximated picture of a continuous spectrum within the range of 2.2 ? - 6.2 ?. The estimation of the plasma electron temperature Te from the ratio between the intensity of the dielectronic satellites and the resonance line gives Te ~ 180 eV. The ratio between the intensity of the resonance and intercombination lines gives the electron density of the emitting zone ne ~ 2 × 1019 cm-3. Some lines observed within the spectral range of 8.5 ? - 9.1 ? belong to none of the transitions of Mg ions. Perhaps the observed spectrum is determined by the transitions in so-called hollow ions of Mg, i.e. in the ions with unfilled inner shells. The spectra obtained with the grazing incidence spectrograph and with the minimum-directioned discrepancy iteration method of spectrum reconstruction from the attenuation curve in the beryllium stepwise attenuators are also presented.

Calibration of a VUV spectrograph by collisional-radiative modelling of a discharge plasma

The feasibility of inferring the plasma parameters of a Penning discharge in helium, from the experimentally observed intensities of a number of spectral lines in the visible wavelength region, is explored. The collisional-radiative model of ADAS (atomic data analysis structure) code and database has been used for this analysis. The electron density, electron temperature, ground-state atom and ion densities and also the 2 3S metastable state density are the parameters thus estimated. The results are encouraging. The derived plasma parameters are then used to obtain the intensities of a few lines in the vacuum ultraviolet (VUV) region. This has been compared with the observed VUV spectral lines, recorded simultaneously with the visible lines, using a VUV spectrometer for which intensity calibration was not available, to arrive at calibration factors. It is expected that this approach might provide an alternative to the ‘branching ratio’ method for calibration in the VUV region once the analysis is improved and the possible re-absorption of certain lines is accounted for.

Observation and interpretation of the Tm 3+ free ion spectrum

The emission spectrum of thulium produced by a vacuum spark source was observed in the wavelength range from 700 to 2320 A on the 10.7 m normal-incidence vacuum ultraviolet spectrograph at the Paris-Meudon observatory. In the unknown spectrum of Tm IV, more than 760 lines have been identified for the first time as transitions between 157 levels of 4f115d, 33 levels of 4f116p, 9 levels of 4f116s and 10 levels of the 4f12 ground configuration. A parametric interpretation of the levels has been carried out using the Cowan codes. Configuration interaction effects are discussed, in particular with the core-excited configurations 5p54f13 and 5p54f125d. Radial Slater parameters derived from 4f12 levels are larger than those pertaining to trivalent Tm ions in compounds. A selection of 105 prominent lines is given.

The spectrum of singly ionized potassium, K II

Using 10.7 m and 3 m normal-incidence vacuum ultraviolet spectrographs, we investigated the spectrum of singly ionized potassium in the regions 495–612 Å and 1247–2150 Å. More than 120 new K II lines were identified. The previous study on this spectrum was revised and extended. All levels of the 3p5 4f and 5f configurations as well as the levels of 3p5 6f based on the 3p5 2P3/2 core state have now been located. Several new levels of 3p5 3d were also located. The ionization limit was determined from the 3p5nf 1.5[4.5]5 (n=4–6) series as 255072.8±1.5 cm−1 (31.6250±0.0002 eV).

Absolute calibration of vacuum ultraviolet spectrograph system for plasma diagnostics

A space- and time-resolving vacuum ultraviolet (VUV) spectrograph system has been applied to diagnose impurity ions behavior in plasmas produced in the tandem mirror GAMMA 10 and the reversed field pinch TPE-RX. We have carried out ray tracing calculations for obtaining the characteristics of the VUV spectrograph and calibration experiments to measure the absolute sensitivities of the VUV spectrograph system for the wavelength range from 100 to 1100 Å. By changing the incident angle, 50.6°–51.4°, to the spectrograph whose nominal incident angle is 51°, we can change the observing spectral range of the VUV spectrograph. In this article, we show the ray tracing calculation results and absolute sensitivities when the angle of incidence into the VUV spectrograph is changed, and the results of VUV spectroscopic measurement in both GAMMA 10 and TPE-RX plasmas.

SPACE-RESOLVING VUV AND SOFT X-RAY SPECTROSCOPY IN THE TANDEM MIRROR GAMMA 10 PLASMA

Vacuum ultraviolet (VUV) and soft X-ray (SX) spectroscopic measurements are important means to diagnose radiation power loss, impurity ion densities and effective charge of confined plasma, Z eff , in magnetically confined plasmas such as fusion plasmas. We have constructed space- and time-resolving flat-field VUV (150–1050Å) and SX (20–350Å) spectrographs by using aberration-corrected concave gratings with varied line spacing. Absolute calibration experiments have been conducted at the Photon Factory in the High Energy Accelerator Research Organization. Absolute sensitivities of the VUV and SX spectrographs have been obtained for the two (S and P) polarization geometries. Thus, absolute intensities of emission spectra from impurity ions can be measured together with their radial distributions in plasmas. The total radiation power was determined to be less than 6 kW within ±20% of error in our normal plasma operation. Density profiles of impurity ions were reduced by using absolute emissivities of impurity lines and a collisional-radiative model. Moreover, the value of Z eff is estimated to be 1.00 in the tandem mirror GAMMA 10 plasma.

Absolute calibration of space- and time-resolving flat-field vacuum ultraviolet spectrograph under both P and S polarized light conditions for plasma diagnostics

Measurement of spectra in the wavelength range from vacuum ultraviolet (VUV) to soft x ray is an important means to diagnose impurity behavior in magnetically confined plasmas used in fusion plasmas. Recently, a space- and time-resolving flat-field grazing-incidence VUV spectrograph was constructed for the simultaneous observation of spatial, temporal, and spectral distributions of plasma radiation in the wavelength range of 150–1050 Å. Absolute calibration experiments were performed at beamline 11C and beamline 12A in the Photon Factory at the High Energy Acceleration Research Organization. The absolute sensitivity of the VUV spectrograph was measured under both P and S polarized light conditions.

Studies of Impurity Ion Spectrum in the GAMMA10 Plasma by Using Vuv Spectrograph

Measurements of spectra in the wavelength range from vacuum ultraviolet (VUV) to soft X-ray are important means to diagnose impurities in magnetically confined plasmas used in fusion plasmas such as a GAMMA 10 plasma. Recently, a space- and time-resolving flat-field grazing-incidence VUV spectrograph was constructed for the simultaneous observation of spatial, temporal and spectral distributions of plasma radiation in the wavelength range of 150-1050 Å. Absolute calibration experiments of the space- and time-resolving VUV spectrograph in the wavelength range of 450-1050 Å were performed for the first time under both S and P polarized light conditions at beamline 11C in the Photon Factory at the High Energy Accelerator Research Organization. Thus, we can obtain radial profiles of the absolute emissions from the impurities by using Abel inversion, and estimate the density of impurity ions such as oxygen, carbon and so on. From the total impurity ion densities, we can estimate Zeff. During the formation of plug potential by ECRH, the highly-ionized impurities increased as a result of rising of electron temperature. The Zeff with plug potential is larger than that without plug potential.

Absolute Calibration of Space- and Time-Resolving Flat-Field Vacuum Ultraviolet Spectrograph for Plasma Diagnostics

Measurement of spectra in the wavelength range from vacuum ultraviolet (VUV) to soft X-ray is an important means to diagnose impurities in magnetically confined plasmas used in fusion plasmas such as a GAMMA10 plasma. Recently, a space- and time-resolving flat-field grazing-incidence VUV spectrograph was constructed for the simultaneous observation of spatial, temporal and spectral distributions of plasma radiation in the wavelength range of 150–1050 Å. Absolute calibration experiments were performed at beamline 11C in the Photon Factory at the High Energy Accelerator Research Organization. The absolute efficiency of the VUV spectrograph was measured for P polarization geometry in the spectrograph.

Radiometric calibration of the vacuum-ultraviolet spectrograph SUMER on the SOHO spacecraft with the B detector

The Solar Ultraviolet Measurement of Emitted Radiation (SUMER) vacuum-ultraviolet spectrograph was calibrated in the laboratory before the integration of the instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft in 1995. During the scientific operation of the SOHO it has been possible to track the radiometric calibration of the SUMER spectrograph since March 1996 by a strategy that employs various methods to update the calibration status and improve the coverage of the spectral calibration curve. The results for the A Detector were published previously [Appl. Opt. 36, 6416 (1997)]. During three years of operation in space, the B detector was used for two and one-half years. We describe the characteristics of the B detector and present results of the tracking and refinement of the spectral calibration curves with it. Observations of the spectra of the stars alpha and rho Leonis permit an extrapolation of the calibration curves in the range from 125 to 149.0 nm. Using a solar coronal spectrum observed above the solar disk, we can extrapolate the calibration curves by measuring emission line pairs with well-known intensity ratios. The sensitivity ratio of the two photocathode areas can be obtained by registration of many emission lines in the entire spectral range on both KBr-coated and bare parts of the detector's active surface. The results are found to be consistent with the published calibration performed in the laboratory in the wavelength range from 53 to 124 nm. We can extrapolate the calibration outside this range to 147 nm with a relative uncertainty of ?30% (1varsigma) for wavelengths longer than 125 nm and to 46.5 nm with 50% uncertainty for the short-wavelength range below 53 nm.

Calibration of Time- and Space-Resolving Vacuum Ultraviolet Spectrograph for Plasma Diagnostics in the Tandem Mirror GAMMA 10

A time- and space-resolving vacuum ultraviolet (VUV) spectrograph has been developed and is applied as an impurity diagnostic in the tandem mirror GAMMA 10. The VUV spectrograph enables us to analyze the spatial distributions of plasma radiation in the wavelength range from 15 nm to 105 nm. Calibration of the VUV spectrograph was carried out in order to determine the sensitivity of the spectrograph as a function of wavelength. We also established a method of analyzing the emissivity profiles of each spectral source in a visual manner from spatially resolved VUV spectrophotograph in the GAMMA 10.

Calibration of space-resolving VUV and soft X-ray spectrographs for plasma diagnostics.

Vacuum ultraviolet (VUV) and soft X-ray measurements are important means of diagnosing impurities in magnetically confined plasmas used in fusion research. Recently, space- and time-resolving flat-field VUV (150-1050 A) and soft X-ray (20-350 A) spectrographs have been constructed by using aberration-corrected concave gratings with varied-spacing grooves which give a wide simultaneous spectral coverage on a microchannel-plate intensified detector. Calibration experiments have been performed at beamlines 11A and 11C at the Photon Factory of the High Energy Accelerator Research Organization. The relative efficiency of the VUV spectrograph has been measured for P-polarization geometry in the spectrograph. In the soft X-ray spectrograph, efficiencies have been obtained for several different points of irradiation on the grating along the groove direction and for two (S and P) polarization geometries.

C+ and C++ ion densities scaling in laser plasmas by ultraviolet photoabsorption spectroscopy

The photoabsorption of discrete transitions of C+ and C++ ions was measured with a new experiment where the absorbing medium and the backlighter are both laser-generated plasmas. A stigmatic vacuum ultraviolet spectrograph is presented. The measure of absorption coefficients is used to derive the density scaling of the two ions in selected levels.

Spectroscopic measurement of impurity transport coefficients and penetration efficiencies in Alcator C-Mod plasmas

Impurity transport coefficients and the penetration efficiencies of intrinsic and injected impurities through the separatrix of diverted Alcator C-Mod discharges have been measured using x-ray and vacuum ultraviolet (VUV) spectroscopic diagnostics. The dominant low Z intrinsic impurity in C-Mod is carbon which is found to be present in concentrations of less than 0.5%. Molybdenum, from the plasma facing components, is the dominant high Z impurity and is typically found in concentrations of about 0.02%. Trace amounts of medium and high Z nonrecycling impurities can be injected at the midplane using the laser blow-off technique and calibrated amounts of recycling, gaseous impurities can be introduced through fast valves either at the midplane or at various locations in the divertor chamber. A five chord crystal x-ray spectrometer array with high spectral resolution is used to provide spatial profiles of high charge state impurities. An absolutely calibrated, grazing incidence VUV spectrograph with high time resolution and a broad spectral range allows for the simultaneous measurement of many impurity lines. Various filtered soft x-ray diode arrays allow for spatial reconstructions of plasma emissivity. The observed brightnesses and emissivities from a number of impurity lines are used together with the mist transport code and a collisional-radiative atomic physics model to determine charge state density profiles and impurity transport coefficients. Comparisons of the deduced impurity content with the measured Zeff and total radiated power of the plasma are made.

Space-resolving flat-field vacuum ultraviolet spectrograph for plasma diagnostics

A spatial imaging vacuum ultraviolet (VUV) spectrograph has been constructed for simultaneous observation of spatial and spectral distributions of plasma radiation in the wavelength range 150–1050 Å. The spectrograph consists of an entrance slit of limited height which provides spatial resolution, an aberration-corrected concave grating with varied spacing grooves which gives a flat-field spectral output plane, and an image-intensified two-dimensional detector system. The basic characteristics of the spectrograph have been investigated by ray-tracing calculations. The expected performance has been confirmed through experiments using a dc glow discharge source on the reciprocal dispersion, the spatial resolution, or the incident angle dependence of spectral images. VUV spectra with spatial and time resolution have been obtained successfully in the GAMMA10 tandem mirror experiment.

Rotational analysis of the nonthermal NO(A 2Σ+, v′=0) distribution observed in the N2(A 3Σ+u, v′=0)+NO(X 2Π, v″=0) energy transfer reaction

A rapidly pumped discharge-flow reactor was constructed to characterize the N2(A 3Σ+u,v′)+NO(X 2Π, v″=0) energy transfer (ET) reaction. Emission spectra of the NO γ bands from the product NO A 2Σ state formed in the title reaction were collected with a 2.2 m vacuum-ultraviolet spectrograph monochromator utilizing both photographic and photoelectric techniques. The rotational structure of the γ bands resulting from the title reaction is resolved with a spectral resolution of Δλ∼0.1 Å. The product NO(A,v′) emission spectra were measured as a function of total pressure (∼0.8≤pTOTAL≤∼3.0 Torr) and initial N2(A,v′) population distribution at 298 K. The product NO(A,v′,N′) rotational distributions yield temperatures much higher than room temperature (>1600 K) and are discussed in detail. Vibrational level specific bimolecular rate constants kv′ ’s for the N2(A,4≤v′≤6)+NO reaction were measured using N2(B 3Πg–A 3Σ+u) laser-excited fluorescence detection with a fixed reaction time. The kv′ ’s are (9.5±1.0), (11.3±1.2), and (11.2±1.1)×10−11 cm3 molecule−1 s−1 for v′=4, 5, and 6, respectively. A comparison with previous measurements is presented.

Observations consistent with self-generated magnetic fields in CO2 laser-produced plasmas

The spatial structure of extreme ultraviolet (XUV) line emission from plasmas produced by nanosecond CO2 laser pulses has been examined with a slitless normal-incidence vacuum-ultraviolet spectrograph in the 200–500-Å spectral region. The anomalous structural behavior of these spectra is consistent with the existence of self-generated magnetic fields. These fields could also explain the gross plasma structure observed through picosecond interferometry.

A normal incidence, vacuum ultraviolet, spectrograph/monochromator for time resolved plasma spectroscopy

A film holder/exit slit movement for a fixed-grating, vacuum ultraviolet spectrograph is described. Film clamped on a holder lying along the Rowland circle is used conventionally in the spectrograph mode. For use as a monochromator, the exit slit moves along the film holder and a phosphor/flexible lightguide combination couples the output radiation to a photomultiplier outside the vacuum system. The spectrum is covered from 25 nm to 200 nm using two gratings. The combination instrument is suitable for time resolved spectroscopy of a transient plasma with a complicated spectrum when reliable identification of spectral lines and accurate wavelength settings are necessary.

An Inexpensive Vacuum Ultraviolet Spectrograph

The description of an inexpensive vacuum ultraviolet spectrograph is presented. A representative spectrum used in the qualitative identification of arsenic is shown for the region of 1890 Å.