Calibration of a Laser-Raman-System using gas samples of all hydrogen isotopologues for KATRIN

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to measure the effective electron anti-neutrino mass via high-precision spectroscopy of the energy spectrum of the β-electrons from tritium decay near the 18.6 keV endpoint. In order to achieve the design sensitivity of m(νₑ) = 0.2 eV (90% C.L.), KATRIN uses a high-luminosity Windowless Gaseous Tritium Source (WGTS), which is temperature and activity stabilised on the part-per-mille level. Due to technical reasons, the molecular T₂ inside the WGTS will always contain residues of other hydrogen isotopologues (H₂, HD, D₂, HT and DT). As the gas composition influences the shape of the β-spectrum, it must be considered in the neutrino mass analysis and hence continuously monitored. At the Tritium Laboratory Karlsruhe (TLK), tritium-compatible Laser Raman systems (LARA) were developed in order to meet the performance requirements of KATRIN. For quantitative composition analysis, the system- and isotopologue-specific response function must be obtained. The main focus of this work is the direct experimental validation of the KATRIN-relevant calibration factors for the radioactive isotopologues T₂, HT and DT. This was done by the design and construction of the Tritium Hydrogen Deuterium (TRIHYDE) experiment, which is capable of providing accurate gas samples of all six hydrogen isotopologues in chemical equilibrium, using a manometric method. Detailed investigations of the initial sample purity and the reaction kinematics of the radio-induced self-equilibration, e.g. T₂ + HD $\rightleftharpoons$ HT + DT, were carried out. It was shown that the experimentally derived calibration factors and theoretical values based on ab initio calculations agree within 2% for all six isotopologues; thus validating the already excellent accuracy of the source gas composition monitoring of the WGTS. In addition, a double fold reduction of the calibration uncertainty for the homonuclear isotopologues was achieved. In summary, using the TRIHYDE facility it was possible, for the first time, to prepare accurate gas samples of all six hydrogen isotopologues with tritium content on a technical scale, thus giving a valuable tool to further expand tritium analytics to in-situ calibration, characterisation and development of existing and forthcoming methods

Speed of Sound Measurement of Hydrogen Isotopologues Containing Tritium for Reference Gas Sample Verification

Accurate gas samples containing tritiated molecules are essential for the development of tritium monitoring tools and to study tritium-induced reaction dynamics. We prepared gas samples that may contain any of the six hydrogen isotopologues by manometrically mixing high-purity homonuclear isotopologues and forming the remaining isotopologues by chemical equilibration. In order to independently verify the relative isotopologue concentrations to the manometrically derived composition and thus validate the accuracy of the produced gas samples, we measured the effective speed of sound (SoS) in the gas mixtures, which are highly sensitive to small deviations in the relative molar fractions due to the large difference in the individual SoSs. We found that deviations between the manometrically derived and measured SoSs are on a 0.1% level, demonstrating the accuracy of the sample production procedure and the suitability of SoS measurements for inline composition monitoring in tritium applications

µRA : A New Compact Easy-to-Use Raman System for All Hydrogen Isotopologues

We have developed a new compact and cost-efficient Laser-Raman system for the simultaneous measurement of all six hydrogen isotopologues. The focus of this research was set on producing a tool that can be implemented in virtually any existing setup providing in situ process control and analytics. The “micro Raman (µRA)” system is completely fiber-coupled for an easy setup consisting of (i) a spectrometer/CCD unit, (ii) a 532 nm laser, and (iii) a commercial Raman head coupled with a newly developed, tritium-compatible all-metal sealed DN16CF flange/Raman window serving as the process interface. To simplify the operation, we developed our own software suite for instrument control, data acquisition, and data evaluation in real-time. We have given a detailed description of the system, showing the system’s capabilities in terms of the lower level of detection, and presented the results of a dedicated campaign using the accurate reference mixtures of all of the hydrogen isotopologues benchmarking µRA against two of the most sensitive Raman systems for tritium operation. Due to its modular nature, modifications that allow for the detection of various other gas species can be easily implemented

The Generation and Analysis of Tritium-substituted Methane

An unavoidable category of molecular species in large-scale tritium applications, such as nuclear fusion, are tritium-substituted hydrocarbons; these form by radiochemical reactions in the presence of (circulating) tritium and carbon (mainly from the steel of vessels and tubing). Tritiumsubstituted methane species, CQ$_4$ (with Q = H , D , T), are often the precursor for higher-order reaction chains, and thus are of particular interest. Here we describe the controlled production of CQ$_4$ carried out in the CAPER facility of the Tritium Laboratory Karlsruhe (TLK), exploiting catalytic reactions and species-enrichment via the CAPER-integral permeator. CQ4 was generated in substantial quantity (>1000 cm$^3$ at ~850 mbar, with CQ$_4$ - content of up to ~20 %). These samples were analyzed using laser Raman and mass spectrometry, to determine the relative isotopologue composition and to trace the generation of tritiated chain-hydrocarbons.Comment: 10 pages, 4 figures. This article has been accepted for publication in Fusion Science and Technology, published by Taylor & Franci

First observation of tritium adsorption on graphene

In this work, we report on the first-ever studies of graphene exposed to tritium gas in a controlled environment. The single layer graphene on $\textrm{SiO}_2$/Si substrate was exposed to 400 mbar of $\textrm{T}_2$ for a total time of ~55 h. The resistivity of the graphene sample was measured in-situ during tritium exposure using the Van der Pauw method. After the exposure, the samples were scanned with a confocal Raman microscope to study the effect of tritium on the graphene structure as well as the homogeneity of spectral modifications. We found that the sheet resistance increases by three orders of magnitude during the exposure. By Raman microscopy, we demonstrate that the graphene film can withstand the bombardment from the beta-decay of tritium, and primary and secondary ions. Additionally, the Raman spectra after tritium exposure are comparable with previously observed results in hydrogen-loading experiments carried out by other groups. By thermal annealing we could demonstrate, using Raman spectral analysis, that the structural changes were partially reversible. Considering all observations, we conclude that the graphene film was at least partially tritiated during the tritium exposure.Comment: Submitted to Nanoscale Advances (RSC), 14 pages, 4 figure

Calibration strategy and status of tritium purity monitoring for KATRIN

<p> </p> <p>The KATRIN (Karlsruhe Tritium Neutrino) experiment aims to measure the mass of the electron anti-neutrino with a sensitivity of 200 meV/<em>c</em>2 by measuring the spectrum of the beta electrons close to the kinematic endpoint region. For monitoring the isotopic composition in the gaseous tritium source a custom-made Laser-Raman-System (LARA) has been developed at the Tritium Laboratory Karlsruhe.</p> <p>The two approaches used to calibrate the LARA system for trueness <3 % are: i) theoretical intensities together with a spectral intensity standard and ii) highly accurate gas mixtures. Latest efforts have improved the in-situ calibration via spectral standard with re-calculated theoretical uncertainties and uncertainty analysis. Recently, the TRIHYDE experiment has been setup which enables cross-checking of the calibration via gas mixtures of all six hydrogen isotopologues and further studies of systematic effects.</p> <p>This poster presents the benefits and status of both complementary approaches.</p

Accurate Reference Gas Mixtures Containing Tritiated Molecules: Their Production and Raman-Based Analysis

Highly accurate, quantitative analyses of mixtures of hydrogen isotopologues—both the stable species, H2, D2, and HD, and the radioactive species, T2, HT, and DT—are of great importance in fields as diverse as deuterium–tritium fusion, neutrino mass measurements using tritium β-decay, or for photonuclear experiments in which hydrogen–deuterium targets are used. In this publication we describe a production, handling, and analysis facility capable of fabricating well-defined gas samples, which may contain any of the stable and radioactive hydrogen isotopologues, with sub-percent accuracy for the relative species concentrations. The production is based on precise manometric gas mixing of H2, D2, and T2. The heteronuclear isotopologues HD, HT, and DT are generated via controlled, in-line catalytic reaction or by β-induced self-equilibration, respectively. The analysis was carried out using an in-line intensity- and wavelength-calibrated Raman spectroscopy system. This allows for continuous monitoring of the composition of the circulating gas during the self-equilibration or catalytic evolution phases. During all procedures, effects, such as exchange reactions with wall materials, were considered with care. Together with measurement statistics, these and other systematic effects were included in the determination of composition uncertainties of the generated reference gas samples. Measurement and calibration accuracy at the level of 1% was achieved.Peer Reviewe

First operation of the KATRIN experiment with tritium

The determination of the neutrino mass is one of the major challenges in astroparticle physics today. Direct neutrino mass experiments, based solely on the kinematics of β β -decay, provide a largely model-independent probe to the neutrino mass scale. The Karlsruhe Tritium Neutrino (KATRIN) experiment is designed to directly measure the effective electron antineutrino mass with a sensitivity of 0.2 eV 0.2 eV (90% 90% CL). In this work we report on the first operation of KATRIN with tritium which took place in 2018. During this commissioning phase of the tritium circulation system, excellent agreement of the theoretical prediction with the recorded spectra was found and stable conditions over a time period of 13 days could be established. These results are an essential prerequisite for the subsequent neutrino mass measurements with KATRIN in 2019