M. Sturm

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.

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.

First tritium results of the KATRIN test experiment trap

Abstract The TRAP experiment (TRitium Argon frost Pump) has been built at the Tritium Laboratory Karlsruhe (TLK) as a test rig for the Cryogenic Pumping Section (CPS) of the KArlsruhe TRItium Neutrino Experiment (KATRIN). TRAP employs a heterogeneous layer of pre-condensed argon to adsorb hydrogen isotopes at ~ 4.2 K. This paper presents results obtained in the first three tritium experiments with TRAP.

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%.

Investigation of Durability of Optical Coatings in Highly Purified Tritium Gas

Abstract Anti-reflection coated windows are part of Raman spectroscopy systems for tritium analytics in the KATRIN experiment and fusion-related applications. Damages of such windows were observed after three months of exposure to highly purified tritium gas in the LOOPINO facility. In this work, the origin of the damages was investigated, identified and eliminated. Coating samples manufactured by various physical vapor deposition methods have been tested for durability by exposure to pure tritium gas and subsequent visual inspection. Electron beam deposited coatings showed indications for damage after 17 days of tritium exposure in contrast to samples manufactured by ion assisted deposition or sputtering. An improved coating layout of the sample cell is presented for reliable long-term monitoring of tritium gas using Raman spectroscopy.

Status of the neutrino mass experiment KATRIN

Abstract One of the most important questions in fundamental physics and cosmology are the origin and the masses of fundamental particles, in particular the neutrino masses. KATRIN will allow a model-independent measurement of the neutrino mass scale with an expected sensitivity of 0.2 eV/c2 (90% CL). KATRIN will use a source of ultrapure molecular tritium and is currently being built up at the site of KIT, thereby making use of the unique expertise of the Tritium Laboratory Karlsruhe. This paper presents the status of the KATRIN experiment, with the focus on its Calibration and Monitoring System, which is the last component being subject to R&D.

Experimental Performance Test of Key Components of the KATRIN Outer Tritium Loop

Abstract One of the main tasks of the Tritium Laboratory Karlsruhe (TLK) is the operation of the Windowless Gaseous Tritium Source (WGTS) of the Karlsruhe Tritium Neutrino (KATRIN) experiment, which will perform an absolute measurement of the neutrino mass with a sensitivity of 200 meV/c2 (90% confidence level). While the Inner Loop system of KATRIN provides a stabilized tritium throughput of 40 g day−1 in the WGTS, the outer loop is required for tritium clean-up, purification, and accountancy. The ability of the outer loop to supply tritium has been investigated using feed gas samples of different compositions. This paper will describe the gas processing tests which were done with batches of approximately 1 mol of tritium each and 20 mol in total, processed on a day-to-day basis in the TLK tritium loop. It is shown, that an isotopic tritium purity of > 98% can reliably supplied to the KATRIN experiment. This is sufficient to maintain the required isotopic tritium purity of > 95% in the KATRIN inner loop.

The Five Phases to Standard Tritium Operation of KATRIN

Abstract By an international collaboration the KArlsruhe TRItium Neutrino experiment KATRIN is currently being installed and commissioned at Karlsruhe Institute of Technology (KIT), the site selection that makes sure of the unique expertise and infrastructure of Tritium Laboratory Karlsruhe (TLK). KATRIN requires a strong windowless gaseous source of almost pure molecular tritium (95%) and a throughput of 40 g tritium (1.5·1016 Bq) per day, stabilized to the 0.1% level. Since the last large components have been delivered in summer 2015, the collaboration is now focusing on the commissioning of the whole KATRIN experiment. A particular challenge is the commissioning with tritium, which will mark the point of no return regarding the contamination of the large magnet cryostats and tritium loop components. We have developed a 5-phase plan that covers all necessary work to be done for the safe and reliable standard tritium operation of KATRIN.