Robin Größle

We present a novel device for the inline activity monitoring of gaseous tritium, named “Gaseous Tritium Activity Monitoring with Scintillators” (GaTAMOS). Unlike established methods that often rely on liquid scintillation or plastic scintillators with limited chemical resistance, this system utilizes a chemically inert, inorganic Terbium-activated Gadolinium Oxysulfide (Gd2O2S:Tb) ceramic. A specialized soldering technique was developed to join the ceramic scintillator to a stainless-steel flange, achieving a vacuum-tight seal (95% of residual contamination within minutes. The proposed system offers a compact, robust, and cost-effective alternative to ionization chambers or BIXS systems for process monitoring in tritium handling facilities.

To study thermodynamic properties and dynamic phase space behavior of hydrogen isotopologues (Q2) at cryogenic temperatures and at high density, the Tritium Absorption InfraRed Spectroscopy 2 (T2ApIR) experiment has been set up and commissioned at Tritium Laboratory Karlsruhe (TLK). In the frame of the experiment, Q2 behavior in different phases, ortho/para states, temperatures (10 K - 300 K) and pressures (up to 2.5 bar a) will be investigated with optical methods, infrared and Raman spectroscopy. The facility consists of a fully tritium compatible cryostat, which includes an optical cell, ortho/para converter and windows for optical and spectroscopic studies. The cryostat can be cooled below the H2 triple point by a two-stage cryocooler and contains openings in the cryogenic shielding for the optical access. The challenge of combining these scientific requirements in a design with high amounts of tritium (14 g), in a limited space, all while maintaining the TLK safety philosophy was solved by the presented design. The experiment is ready to be fully integrated into the TLK closed loop tritium infrastructure. This contribution reports a comprehensive overview of the commissioning phase of the experimental facility and the results of the firstcommissioning experiments, including cryogenic performance tests, commissioning experiments with non-radioactive gases, and tests of the analytical instruments.

The tangential momentum accommodation coefficient (TMAC) describes to what degree the interaction of a molecule with a surface is specular or diffuse and is therefore an important quantity for gas dynamics simulations and tritium processing in future fusion power plants. To the best of our knowledge, up to now, no TMAC values for tritium can be found in literature: neither ab initio calculated nor experimentally obtained. At the Tritium Laboratory Karlsruhe (TLK), with a license to handle up to 40 g of tritium, we have set up a cryogenic viscosity measurement apparatus (Cryo-ViMA) experiment aimed at measuring the viscosity of tritium. The Cryo-ViMA setup is based on a spinning rotor gauge, with a stainless steel rotor. The measurement principle and accuracy have been verified using helium, hydrogen, and deuterium. In this measurement, the normalized deceleration rate (DCR) of the spinning rotor is measured as a function of the pressure of the surrounding dilute gas. In addition to the viscosity, the analysis of the data acquired in this manner allows access to the velocity slip coefficient (VSC), from which the TMAC can be extracted as described in (Tekasakul et al., 1996). Therefore, the measurement data from (Wydra, 2025) will be used in this article to calculate the VSC and the TMAC. The Cryo-ViMA setup allows for cooling over a wide temperature range using evaporated liquid nitrogen. With slow thermal cycling, this system enables a high-resolution measurement of the temperature dependence of the TMAC between 110 and 300 K. The results of these measurements show that for the VSC, the values for H₂ and D₂ range from 1.25 to 1.4, depending on the temperature, whereas for T₂, the VSC is approximately 1.15. This leads to values for the TMAC for H₂ and D₂ between 0.80 and 0.87, whereas the TMAC of T₂ is much closer to one with 0.93. Moreover, the results show that a simple extrapolation of the value for tritium from the other hydrogen isotopologues is insufficient.

Experimental values for the viscosity of the radioactive hydrogen isotopologue tritium are still unknown in literature. Existing values from ab initio calculations disregard quantum mechanic effects and are therefore only good approximations for room temperature and above. To fill in these missing experimental values, a measurement setup has been designed, to measure the viscosity of gaseous hydrogen and its isotopologues (H$_2$, HD, HT, D$_2$, DT, T$_2$) at cryogenic temperatures. In this paper, the first results with this Cryogenic Viscosity Measurement Apparatus (Cryo-ViMA) of the viscosity of gaseous hydrogen between 200 K to 300 K are presented.

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.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims at measuring the effective electron neutrino mass with a sensitivity of 0.2 eV/c², i.e., improving on previous measurements by an order of magnitude. Neutrino mass data taking with KATRIN commenced in early 2019, and after only a few weeks of data recording, analysis of these data showed the success of KATRIN, improving on the known neutrino mass limit by a factor of about two. This success very much could be ascribed to the fact that most of the system components met, or even surpassed, the required specifications during long-term operation. Here, we report on the performance of the laser Raman (LARA) monitoring system which provides continuous high-precision information on the gas composition injected into the experiment’s windowless gaseous tritium source (WGTS), specifically on its isotopic purity of tritium—one of the key parameters required in the derivation of the electron neutrino mass. The concentrations c_x for all six hydrogen isotopologues were monitored simultaneously, with a measurement precision for individual components of the order 10⁻³ or better throughout the complete KATRIN data taking campaigns to date. From these, the tritium purity, ε_T, is derived with precision of −3 and trueness of −3, being within and surpassing the actual requirements for KATRIN, respectively.

The IR spectra of liquid hydrogen isotopologues (Q₂ = H₂, D₂, T₂, HD, HT, DT) are dominated by the interaction induced absorption. Therefore, the complexity tremendously increases with the number of different isotopologues in the sample. As we aim for a system independent calibration of IR absorption spectroscopy against all six isotopologues and three ortho–para ratios, we need a minimal and complete set of descriptors to predict the spectra and to decrease the needed calibration effort. For this, we grouped the absorption lines into three groups: absorption on monomers, phonons, and molecular dimers. In particular, molecular dimers contribute to the absolute number of absorption lines in the spectra of mixed isotopologues. To develop and test the set of descriptors, we make use of three spectra: a pure H₂ sample, a pure D₂ sample, and a mixed H₂–D₂ sample. We show a detailed analysis of these three spectra in the first and second vibrational branch in the range from 2000 cm⁻¹ to 9000 cm⁻¹. The set of descriptors found within this work can be used to identify and predict all lines in this range for liquid H₂–D₂mixtures.

The presented method allows us to quantify and correct the systematic influence of a rolling circle filter for quantitative spectroscopic measurements.

Fusion facilities like ITER and DEMO will circulate several kilograms tritium and deuterium per day in their fuel cycle. For the separation of the hydrogen isotopologues the Isotope Separation System (ISS), based on cryogenic distillation, was developed at Tritium Laboratory Karlsruhe (TLK). One challenge is to find and develop an in situ and real time method to analyse the isotopologic composition of the column content. Calibration tests with IR absorption spectroscopy (FTIR) with chemically equilibrated samples have been performed at the Tritium absorption IR Spectroscopy Experiment (TApIR). From this previous work and from literature, it is known that the dependence between IR absorbance and the concentrations is non-linear. This makes it impossible to extrapolate the calibration from equilibrium to non-equilibrium samples. This work shows a full D₂, H₂, and HD calibration with samples in and off the high temperature. This enables us now to measure composition of inactive liquid hydrogen samples with an accuracy of better than 5%. In addition, one of the main challenges on the way to a calibration with tritiated mixtures is shown, the IR absorbance at molecular dimers, which tremendously increases the complexity of IR absorption spectra.

An integral part of the fuel cycle of future fusion facilities is the isotope separation system (ISS). The Tritium Laboratory Karlsruhe (TLK) is currently developing a system to monitor the concentration of all six hydrogen isotopologues Q₂ (H₂, HD, D₂, HT, DT, T₂) in the liquid phase in the cryogenic distillation process of the ISS. Liquid inactive Q₂ were already successfully analyzed under cryogenic conditions via infrared (IR) absorption spectroscopy and calibration data for D₂ is provided by previous experiments at TLK. The new experiment T₂ApIR (Tritium Absorption Infrared Spectroscopy Experiment) is designed to be fully tritium compatible to perform a complete calibration of the IR absorption measurement system with all six hydrogen isotopologues in the liquid phase under conditions similar to the ISS. This provides a unique non-invasive, inline and real-time measurement system for isotopologic concentration determination, ready for implementation in the cryogenic distillation column.