Vacuum Ultraviolet Spectrometer Research Articles

Absolute calibration of the Lyman-α measurement apparatus at DIII-D.

The LLAMA (Lyman-Alpha Measurement Apparatus) diagnostic was recently installed on the DIII-D tokamak [Rosenthal et al., Rev. Sci. Instrum. (submitted) (2020)]. LLAMA is a pinhole camera system with a narrow band Bragg mirror, a bandpass interference filter, and an absolute extreme ultraviolet photodiode detector array, which measures the Ly-α brightness in the toroidal direction on the inboard, high field side (HFS) and outboard, low field side (LFS). This contribution presents a setup and a procedure for an absolute calibration near the Ly-α line at 121.6nm. The LLAMA in-vacuum components are designed as a compact, transferable setup that can be mounted in an ex situ vacuum enclosure that is equipped with an absolutely calibrated Ly-α source. The spectral purity and stability of the Ly-α source are characterized using a vacuum ultraviolet spectrometer, while the Ly-α source brightness is measured by a NIST-calibrated photodiode. The non-uniform nature of the Ly-α source emission was overcome by performing a calibration procedure that scans the Ly-α source position and employs a numerical optimization to determine the emission pattern. Nominal and measured calibration factors are determined and compared, showing agreement within their uncertainties. A first conversion of the measured signal obtained from DIII-D indicates that the Ly-α brightness on the HFS and LFS is on the order of 1020 Ph sr-1m-2s-1. The established calibration setup and procedure will be regularly used to re-calibrate the LLAMA during DIII-D vents to monitor possible degradation of optical components and detectors.

A critical comparison of vacuum UV (VUV) spectrometer and electron ionization single quadrupole mass spectrometer detectors for the analysis of alkylbenzenes in gasoline by gas chromatography: Experimental and statistical aspects

Recent advances in benchtop vacuum ultraviolet (VUV) spectrometers have yielded effective universal detectors for gas chromatography (GC). The ability of these detectors to acquire absorbance spectra from 125 nm to 430 nm poses an alternative to the gold standard of mass spectrometry (MS) as a sensitive and selective GC detector. The applications of GC/VUV extend into many areas. Featured here is the potential application of GC/VUV to the analysis of ignitable liquids, which may be found on debris from suspected arson fires. A particular compound class of interest is the alkylbenzenes, as they are a significant component in fuels such as gasoline, petroleum distillates, and aromatic solvents such as degreasers and cleaning solvents. To measure the sensitivity, selectivity and specificity of GC-VUV and GC-MS for alkylbenzenes we employed both library search methods and chemometric analysis using discriminant analysis. The GC-VUV detector was found to have superior specificity to the GC-MS detector in full scan mode. The GC-VUV detector was able to identify all alkylbenzenes correctly, including the correct identification of all structural isomers. LODs for both GC-VUV and GC-MS were found to be picograms on column.

Absolute radiometric calibration of a VUV spectrometer in the wavelength range 46–300 nm

Vacuum ultraviolet (VUV) radiation corresponds to photon energies exceeding 6.2 eV and provides access to atomic and molecular resonant transitions in various plasmas. Determining population densities of electronic levels directly connected to the ground state requires an absolute intensity calibration of the VUV spectrometer. For this purpose, synchrotron radiation from electron storage rings is the typical primary standard source associated with transport effort and operating costs. Alternatively, a complex procedure using several secondary standards and discharges directly at the setup in use can be applied. In this work, an absolute intensity calibration avoiding synchrotron radiation to cover the wavelength range 46–300 nm accessible with two detectors—a photomultiplier tube and a channel electron multiplier—is presented. A combination of different standard sources—two deuterium arc lamps, branching-ratios of a nitrogen plasma and a high current hollow cathode—is applied for the relative calibration. The absolute calibration is based on simultaneous measurements of atomic lines in a low pressure helium discharge with the VUV spectrometer and an absolutely calibrated optical emission spectrometer. Special focus is laid on the uncertainties of the relative and absolute calibration depending on the wavelength range. The applicability of the intensity calibration is demonstrated at a hydrogen plasma in the wavelength range 80–300 nm. Using the emissivity of the Lyman series, population densities of the first six excited atomic states are calculated considering opacity effects. The excellent agreement with results from the Balmer series by optical emission spectroscopy manifests the high validity of the performed absolute intensity calibration.

Comprehensive Two-Dimensional Gas Chromatography Hyphenated with a Vacuum Ultraviolet Spectrometer To Analyze Diesel—A Three-Dimensional Separation (GC × GC × VUV) Approach

Effective separation of individual components continues to pose the greatest challenge in the characterization of complex hydrocarbon mixtures. Recent research has tackled this problem using severa...

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 of λ = 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 at 97.7 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.

Local profiles of line emission of impurity ions in rotating fusion plasmas

We analyze the poloidal distribution of impurity ions, such as C V, C VI and O VIII, in fast rotating KSTAR plasmas using the impurity emission lines in the 1–7 nm wavelength range obtained from the space-resolved extreme ultra violet spectrometer. This is aided particularly by a new tomographic reconstruction technique with limited viewing angles. The vacuum and extreme ultraviolet spectrometer system at ITER and its prototypes installed at KSTAR are one of the main diagnostic systems to monitor the impurity species in fusion plasmas; however, they have an insufficient field of view to utilize the conventional reconstruction method. The new algorithm developed in this work considers a curvilinear grid of pixels mapped onto the magnetic equilibrium and a weight factor considering toroidal rotational effect on impurity species. Validation tests with poloidally asymmetric images of synthetic plasma demonstrate that this method is highly useful for emission diagnostics that have a narrow field of view. The experimental results of the spatially resolved spectra from KSTAR plasma clearly show that even the light impurities such as carbon and oxygen are significantly affected by the toroidal rotation. Accordingly, the method is expected to be utilized for estimating the poloidal density profile of each charge state of an impurity species, which will play a key role in impurity transport studies.

Application of Vacuum Ultraviolet Single-photon Ionization Mass Spectrometer in Online Analysis of Volatile Organic Compounds

Abstract A vacuum ultraviolet single-photon ionization mass spectrometer, which has the merits of broad-spectrum soft ionization, low fragment peak, low matrix influence, high sensitivity and short response time, is fit for use in the online analysis of mixed volatile organic compounds. In this review, the theory and structural composition of the single-photon ionization mass spectrometer are described, and the current research progress of sampling systems, ionization sources, and mass spectrometers are summarized. Then, a summary is provided on how online analysis has been applied to the fields of atmospheric composition observation, atmospheric chemistry research, environmental monitoring, food detection, etc. Finally, the direction and trends for future work are proposed.

Laser plasma vacuum ultraviolet light source using solid rare-gas targets

The laser plasma emission spectra in a broadband from 30 to 200 nm of solid Ar, Kr, and Xe targets are presented for the first time. The spectra are composed of a broadband continuum and lines. A broadband vacuum ultraviolet (VUV) spectrometer that can measure spectra in the wavelength range from 30 to 200 nm is developed and the measured spectra are able to be calibrated over the entire broad band. The spectral intensity integrated from 30 to 200 nm indicates that the VUV average power generated in the wavelength range is 30 mW when the laser energy is 1 J at 1 Hz. The number of photons of monochromatic light after passing through the spectrometer is estimated to be more than 5 × 106 photons/nm/pulse over the wavelength range and is considered to be useful for applications of broadband VUV spectroscopy.

Three-dimensional simulations of edge impurity flow obtained by the vacuum ultraviolet emission diagnostics in the Large Helical Device with EMC3-EIRENE

Edge carbon impurity flow in the stochastic layer of the Large Helical Device (LHD) has been investigated with the three-dimensional (3D) edge transport code EMC3-EIRENE. The simulated synthetic C3+ impurity flow profile from EMC3-EIRENE shows a reasonable agreement with the vacuum ultraviolet (VUV) measurements according to the CIV (1548.20 × 2 Å) Doppler- shift spectrum. The same horizontally outward C3+ impurity flows at the top and bottom edges of the stochastic layer are determined by the 3D magnetic field structure and the parallel C3+ impurity flow velocity. The observed up-down asymmetric structure of the C3+ impurity flow at the top and bottom edges is caused by the vertical displacement of the VUV spectrometer from the midplane. The horizontally outward shift of the magnetic axis position from 3.6 to 3.9 m leads to a change of the C3+ impurity flow direction at the top and bottom edges. For a high upstream plasma density, the transport of the C3+ impurity flow is mainly determined by the background parallel plasma flow, while a reversed C3+ impurity flow is obtained for a low upstream plasma density, due to the expansion of the thermal force dominant regions. The enhanced thermal force leads to a suppression of the impurity screening effect.

Construction of a vacuum ultraviolet transmission spectrometer

Construction of a vacuum ultraviolet transmission spectrometer

Preliminary Design for Diagnostic Port Integration at ITER Upper Port #18

ITER has many ports to install various diagnostics which view and measure various plasma parameters. One of the ports, the upper port #18 (UP18) is designed to integrate three tenant diagnostic systems: vacuum ultraviolet spectrometer, neutron activation system, and upper vertical neutron camera. The key design drivers for the port integration are requirements on neutron shielding and maintenance. In this paper, we discuss the neutron shielding design made following the as low as reasonable achievable principle in order to reduce the shut-down dose rate in the interspace and port cell which are human-accessible areas. The design choice for radiation shielding of electronics in the port cell is also discussed. The port maintenance in ITER consists of remote handling operation for the port plug and manual (or assisted-manual) operation for the interspace and port cell areas. The compatibility with the ITER maintenance strategy is investigated for UP18 and the associated issues are addressed.

Exploring the negative temperature coefficient behavior of acetaldehyde based on detailed intermediate measurements in a jet-stirred reactor

Acetaldehyde is an observed emission species and a key intermediate produced during the combustion and low-temperature oxidation of fossil and bio-derived fuels. Investigations into the low-temperature oxidation chemistry of acetaldehyde are essential to develop a better core mechanism and to better understand auto-ignition and cool flame phenomena. Here, the oxidation of acetaldehyde was studied at low-temperatures (528–946 K) in a jet-stirred reactor (JSR) with the corrected residence time of 2.7 s at 700 Torr. This work describes a detailed set of experimental results that capture the negative temperature coefficient (NTC) behavior in the low-temperature oxidation of acetaldehyde. The mole fractions of 28 species were measured as functions of the temperature by employing a vacuum ultra-violet photoionization molecular-beam mass spectrometer. To explain the observed NTC behavior, an updated mechanism was proposed, which well reproduces the concentration profiles of many observed peroxide intermediates. The kinetic analysis based on the updated mechanism reveals that the NTC behavior of acetaldehyde oxidation is caused by the competition between the O2-addition to and the decomposition of the CH3CO radical.

Vacuum Ultraviolet Spectroscopy and Mass Spectrometry: A Tandem Detection Approach for Improved Identification of Gas Chromatography-Eluting Compounds.

For wide class characterizations of volatile organic compounds (VOCs), conventional gas chromatography mass spectrometry (GC-MS)-based techniques are utilized. These GC-MS-based chemical identification approaches typically rely on library searches against ion fragmentation patterns of known compounds. Although MS library searches can often provide correct chemical identities, erroneous chemical assignments of structurally similar unknown compounds are also possible. Other detection systems, such as absorption spectrometers, have been used for VOC analysis and can provide complementary absorption data. Here, we demonstrate the analytical advantages of coupling vacuum ultraviolet (VUV) absorption spectroscopy and MS in tandem for the improved characterization of structurally similar VOCs. We also discuss technical considerations and limitations of coupling a VUV spectrometer to a quadrupole mass spectrometer. Moreover, we show that combining the isomer selectivity of VUV spectroscopy, as a nondestructive analyte detection approach, with the mass selectivity of MS in a VUV-MS detection system improves characterization of GC-eluting compounds. Utilizing GC/VUV-MS data, we demonstrate that orthogonal VUV and MS library searches improve identification of VOCs present in complex mixtures such as a mixed standard sample, a commercial perfume product, and an essential oil sample.

Formation mechanism of secondary organic aerosol from ozonolysis of gasoline vehicle exhaust.

Gasoline vehicles are a major source of anthropogenic secondary organic aerosols (SOAs). However, current models based on known precursors fail to explain the substantial SOAs from vehicle emissions due to the inadequate understanding of the formation mechanism. To provide more information on this issue, the formation of SOAs from ozonolysis of four light-duty gasoline vehicle exhaust systems was investigated with a vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS). Remarkable SOAs formation was observed and the SOAs were primarily aliphatic alkenes. PI mass spectra of the SOAs from all vehicles exhibited similar spectral patterns (a regular mass group with m/z at 98, 112, 126 …). Interestingly, most carbonyl products of aliphatic alkenes observed as major gaseous products have specific molecular weights, and the main formation pathway of SOAs can be explained well using aldol condensation reactions of these carbonyls. This is a direct observation of the aldol condensation as a dominated pathway for SOAs formation, and the first report on the composition and formation mechanism of the SOAs from the ozonolysis of gasoline vehicle exhaust is given. The study reveals that low molecular weight alkenes may play a more significant role in vehicle-induced SOAs formation than previously believed. More importantly, the PI mass spectra of SOAs from vehicles show similarities to the field aerosol sample mass spectra, suggesting the possible significance of the aldol condensation reactions in ambient aerosol formation. Since carbonyls are a major degradation product of biogenic and anthropogenic VOCs through atmospheric oxidation processes, the mechanism proposed in this study can be applied more generally to explain aerosol formation from the oxidation of atmospheric hydrocarbons.

A rapid detection method for policy-sensitive amines real-time supervision

Many organic amines that comprise a benzene ring are policy-sensitive because of their toxicity and links to social harm. However, to date, detection of such compounds mainly relies on offline methods. This study proposes an online pptv (parts per trillion by volume) level of detection method for amines, using the recently-built vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) combined with a new doping technique. Thus, the dichloromethane doping-assisted photoionization mass spectra of aniline, benzylamine, phenethylamine, amphetamine, and their structural isomers were recorded. The dominant characteristic mass peaks for all amines are those afforded by protonated amines and the amino radical-loss. The signal intensities of the amines were enhanced by 60–130 times compared to those recorded without doping assistance. Under 10s detection time, the sensitivities of aniline and benzylamine in the gas phase were determined as 4.0 and 2.7 countspptv−1, with limits of detection (LODs) of 36 and 22 pptv, respectively. Notably, the detection efficiency of this method can be tenfold better in future applications since the ion transmission efficiency of the mass spectrometer was intentionally reduced to ~ 10% in this study. Therefore, dichloromethane doping-assisted photoionization mass spectrometry has proven to be a highly promising on-line approach to amine detection in environmental and judicial supervision and shows great potential for application in the biological field.

Characterization of secondary organic aerosol from photo-oxidation of gasoline exhaust and specific sources of major components

To further explore the composition and distribution of secondary organic aerosol (SOA) components from the photo-oxidation of light aromatic precursors (toluene, m-xylene, and 1,3,5-trimethylbenzene (1,3,5-TMB)) and idling gasoline exhaust, a vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) was employed. Peaks of the molecular ions of the SOA components with minimum molecular fragmentation were clearly observed from the mass spectra of SOA, through the application of soft ionization methods in VUV-PIMS. The experiments comparing the exhaust-SOA and light aromatic mixture-SOA showed that the observed distributions of almost all the predominant cluster ions in the exhaust-SOA were similar to that of the mixture-SOA. Based on the characterization experiments of SOA formed from individual light aromatic precursors, the SOA components with molecular weights of 98 and 110 amu observed in the exhaust-SOA resulted from the photo-oxidation of toluene and m-xylene; the components with a molecular weight of 124 amu were derived mainly from m-xylene; and the components with molecular weights of 100, 112, 128, 138, and 156 amu were mainly derived from 1,3,5-TMB. These results suggest that C7-C9 light aromatic hydrocarbons are significant SOA precursors and that major SOA components originate from gasoline exhaust. Additionally, some new light aromatic hydrocarbon-SOA components were observed for the first time using VUV-PIMS. The corresponding reaction mechanisms were also proposed in this study to enrich the knowledge base of the formation mechanisms of light aromatic hydrocarbon-SOA compounds.

VUV spectroscopy in impurity injection experiments at KSTAR using prototype ITER VUV spectrometer.

The ITER vacuum ultra-violet (VUV) core survey spectrometer has been designed as a 5-channel spectral system so that the high spectral resolving power of 200-500 could be achieved in the wavelength range of 2.4-160 nm. To verify the design of the ITER VUV core survey spectrometer, a two-channel prototype spectrometer was developed. As a subsequent step of the prototype test, the prototype VUV spectrometer has been operated at KSTAR since the 2012 experimental campaign. From impurity injection experiments in the years 2015 and 2016, strong emission lines, such as Kr xxv 15.8 nm, Kr xxvi 17.9 nm, Ne vii 46.5 nm, Ne vi 40.2 nm, and an array of largely unresolved tungsten lines (14-32 nm) could be measured successfully, showing the typical photon number of 1013-1015 photons/cm2 s.

Application of VUV-PIMS coupled with GC-MS in chemical characterization, identification and comparative analysis of organic components in both vehicular-derived SOA and haze particles

Gasoline vehicle exhaust is a significant source of volatile organic compounds (VOCs) in megacities. In this study, chemical characterization of secondary aerosol particles from the oxidation of gasoline vehicular exhaust by O3, OH, and NO3 radicals and the airborne aerosol particles collected during a heavy haze episode (23–25 December 2015) in Beijing were elaborately investigated. The secondary organic aerosols (SOAs) collected from the exhaust and airborne aerosol particles were characterized with a newly built vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) after thermal desorption, and identified by gas chromatography mass spectrometry (GC-MS). The obtained photoionization mass spectra revealed that the SOAs from the oxidation of gasoline vehicular exhaust and airborne aerosol particles possess a series of common characteristic mass peaks at m/z 98, 112, 126, and 140. The components at m/z 98, 112, 126, 140 were further identified to be carbonyl species after PFBHA derivatization followed by GC-MS analyses. The carbonyl species from exhaust SOAs were found to be responsible for 51.7%, 57.5%, 36.3%, and 27.9% of the chemical components in haze particles at m/z 98, 112, 126, and 140, respectively, which indicates that these SOA components from the oxidation of gasoline vehicular exhaust are a major factor that affects the air quality in Beijing. Among the exhaust SOAs, the carbonyl species detected simultaneously in two (P(O3/OH)) or three kinds of exhaust oxidation reactions (P(O3/NO3/OH)) make a significant contributions to these carbonyl species in haze particles (10.6% for m/z 98, 18.3% for m/z 112, 23.4% for m/z 126, and 20.5% for m/z 140). These results implies that the unsaturated VOCs (i.e. alkenes) from exhaust may be one kind of important SOA precursor and that their chemical degradation in the atmosphere may have an important impact on urban air quality in heavy polluted cities such as Beijing, especially during severe winter haze weather.

Effect of impurity source locations on up-down asymmetry in impurity distributions in the ergodic layer of large helical device

A space-resolved spectroscopy using a 3m normal incidence vacuum ultraviolet (VUV) spectrometer was developed to measure the VUV emission profiles in wavelength range of 300–3200Å from impurities in the edge plasmas in Large Helical Device (LHD). The edge plasma of the LHD is characterized by stochastic magnetic fields with three-dimensional structure intrinsically formed by helical coils called the “ergodic layer”. The VUV spectroscopy has revealed that intensity profiles of the impurity emission from the ergodic layer have strong up-down asymmetries, namely, the emission intensities are quite different between top and bottom plasma edges. Observations of the up-down asymmetries are summarized on the following impurity line emissions: (1) CII 1335.71Å (2s-2p), CIII 977.02Å (2s-2p), and CIV 1548.20Å (2s-2p) from intrinsic carbon impurity ions sputtered from the carbon divertor plates, (2) NeVII 465.22Å (2s-2p), NeVIII 770.41Å (2s-2p), ArVII 585.75Å (3s-3p), and ArVIII 700.24Å (3s-3p) from Ne or Ar ions introduced in plasmas by gas puffing, and (3) WVI 639.68Å (5d-6p) from W ions introduced in plasmas by pellet injection.

Flow-modulated comprehensive two-dimensional gas chromatography combined with a vacuum ultraviolet detector for the analysis of complex mixtures

The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC×GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer’s law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120–240nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry (e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC×GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids.Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis.