Magnus Schlösser

Monitoring of all hydrogen isotopologues at tritium laboratory Karlsruhe using Raman spectroscopy

We have recorded Raman spectra for all hydrogen isotopologues, using a CW Nd:YVO4 laser (5 W output power at 532 nm) and a high-throughput (f/1.8) spectrograph coupled to a Peltier-cooled (200 K) CCD-array detector (512 × 2048 pixels). A (static) gas cell was used in all measurements. We investigated (i) “pure” fillings of the homonuclear isotopologues H2, D2, and T2; (ii) equilibrated binary fillings of H2 + D2, H2 + T2, and D2 + T2, thus providing the heteronuclear isotopologues HD, HT, and DT in a controlled manner; and (iii) general mixtures containing all isotopologues at varying concentration levels. Cell fillings within the total pressure range 13–985 mbar were studied, in order to determine the dynamic range of the Raman system and the detection limits for all isotopologues. Spectra were recorded for an accumulation period of 1000 s. The preliminary data evaluation was based on simple peak-height analysis of the ro-vibrational Q1-branches, yielding 3σ measurement sensitivities of 5 × 10−3, 7 × 10−3, and 25 × 10−3 mbar for the tritium-containing isotopologues T2, DT, and HT, respectively. These three isotopologues are the relevant ones for the KATRIN experiment and in the ITER fusion fuel cycle. While the measurement reported here were carried out with static-gas fillings, the cells are also ready for use with flowing-gas samples.

Monitoring of tritium purity during long-term circulation in the KATRIN test experiment LOOPINO using Laser Raman Spectroscopy

Abstract The gas circulation loop LOOPINO has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK) to perform Raman measurements of circulating tritium mixtures under conditions similar to the inner loop system of the neutrino-mass experiment KATRIN, which is currently under construction. A custom-made interface is used to connect the tritium containing measurement cell, located inside a glove box, with the Raman setup standing on the outside. A tritium sample (purity > 95 %, 20 kPa total pressure) was circulated in LOOPINO for more than three weeks with a total throughput of 770 g of tritium. Compositional changes in the sample and the formation of tritiated and deuterated methanes CT4-nXn (X=H,D; n=0,1) were observed. Both effects are caused by hydrogen isotope exchange reactions and gas-wall interactions, due to tritium β decay. A precision of 0.1 % was achieved for the monitoring of the T2 Q1-branch, which fulfils the requirements for the KATRIN experiment and demonstrates the feasibility of high-precision Raman measurements with tritium inside a glove box.

Automated Quantitative Spectroscopic Analysis Combining Background Subtraction, Cosmic Ray Removal, and Peak Fitting

An integrated concept for post-acquisition spectrum analysis was developed for in-line (real-time) and off-line applications that preserves absolute spectral quantification; after the initializing parameter setup, only minimal user intervention is required. This spectral evaluation suite is composed of a sequence of tasks specifically addressing cosmic ray removal, background subtraction, and peak analysis and fitting, together with the treatment of two-dimensional charge-coupled device array data. One may use any of the individual steps on their own, or may exclude steps from the chain if so desired. For the background treatment, the canonical rolling-circle filter (RCF) algorithm was adopted, but it was coupled with a Savitzky–Golay filtering step on the locus-array generated from a single RCF pass. This novel only-two-parameter procedure vastly improves on the RCFs deficiency to overestimate the baseline level in spectra with broad peak features. The peak analysis routine developed here is an only-two-parameter (amplitude and position) fitting algorithm that relies on numerical line shape profiles rather than on analytical functions. The overall analysis chain was programmed in National Instruments LabVIEW; this software allows for easy incorporation of this spectrum analysis suite into any LabVIEW-managed instrument control, data-acquisition environment, or both. The strength of the individual tasks and the integrated program sequence are demonstrated for the analysis of a wide range of (although not necessarily limited to) Raman spectra of varying complexity and exhibiting nonanalytical line profiles. In comparison to other analysis algorithms and functions, our new approach for background subtraction, peak analysis, and fitting returned vastly improved quantitative results, even for “hidden” details in the spectra, in particular, for nonanalytical line profiles. All software is available for download.

Design implications for laser Raman measurement systems for tritium sample-analysis, accountancy or process-control applications

Abstract In this paper we discuss the implementation of Raman spectroscopy for compositional analysis, and monitoring and control of tritium-carrying gas flows. Specifically, we discuss how the criteria for the detection and handling of tritium impact on the conceptual design and actual system suitability and performance in applications such as the KATRIN experiment or the ITER fuel cycle, which require real-time, in-line monitoring and control.

Enhanced sensitivity of Raman spectroscopy for tritium gas analysis using a metal-lined hollow glass fiber

Abstract The precise compositional analysis of tritium-containing gases is of high interest for tritium accountancy, e.g. in future fusion power plants. Raman spectroscopy provides a fast and contact-free gas analysis procedure with high precision, thus being an advantageous tool for the named purpose. In this paper, it is shown that the sensitivity achieved with conventional Raman systems (in 90° or forward/backward configurations) can be enhanced by at least one order of magnitude by using a metal-lined hollow glass fiber as the Raman cell. This leads to the ability to detect low partial pressures of tritium within short measurement intervals (< 0.5 mbar in < 0.5 s).

Raman spectroscopy at the tritium laboratory Karlsruhe

Abstract Raman spectroscopy is employed successfully for analysis of hydrogen isotopologues at the Tritium Laboratory Karlsruhe (TLK). In this paper, we summarize the recent achievements in the further development on this technique, and the various applications for which it is used at the TLK. Further, we show that Raman spectroscopy has evolved as a versatile, highly accurate key method for quantitative analysis complementing the portfolio of analytic techniques at the TLK.

In-Line Calibration of Raman Systems for Analysis of Gas Mixtures of Hydrogen Isotopologues with Sub-Percent Accuracy

Highly accurate, in-line, and real-time composition measurements of gases are mandatory in many processing applications. The quantitative analysis of mixtures of hydrogen isotopologues (H2, D2, T2, HD, HT, and DT) is of high importance in such fields as DT fusion, neutrino mass measurements using tritium β-decay or photonuclear experiments where HD targets are used. Raman spectroscopy is a favorable method for these tasks. In this publication we present a method for the in-line calibration of Raman systems for the nonradioactive hydrogen isotopologues. It is based on precise volumetric gas mixing of the homonuclear species H2/D2 and a controlled catalytic production of the heteronuclear species HD. Systematic effects like spurious exchange reactions with wall materials and others are considered with care during the procedure. A detailed discussion of statistical and systematic uncertainties is presented which finally yields a calibration accuracy of better than 0.4%.

CAPER as Central and Crucial Facility to Support R&D with Tritium at TLK

Abstract The CAPER facility at TLK originally devoted to R&D on tokamak exhaust processing has been significantly upgraded over the last years. Beside new R&D on highly tritiated water, CAPER is presently largely used to support satellite experiments, mainly those dedicated to R&D on advanced analytics. Mutation from R&D to part of the TLK tritium infrastructure necessitated new features to be installed in order to facilitate and optimize tritiated mixtures preparation and sample filling, and to enable satellites experiments to discharge their waste gas to CAPER for clean-up. This paper presents recent CAPER mutations to become a central and key facility at TLK.

How to make Raman-inactive helium visible in Raman spectra of tritium-helium gas mixtures

Abstract Raman spectroscopy, a powerful method for the quantitative compositional analysis of molecular gases, e.g. mixtures of hydrogen isotopologues, is not able to detect monoatomic species like helium. This deficit can be overcome by using radioluminescence emission from helium atoms induced by β-electrons from tritium decay. We present theoretical considerations and combined Raman/radioluminescence spectra. Furthermore, we discuss the linearity of the method together with validation measurements for determining the pressure dependence. Finally, we conclude how this technique can be used for samples of helium with traces of tritium, and vice versa.

CARS spectroscopy of the

Molecular hydrogen is a benchmark system for bound state quantum calculation and tests of quantum electrodynamical effects. While spectroscopic measurements on the stable species have progressively improved over the years, high resolution studies on the radioactive isotopologues