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

TL;DR

This study demonstrates high-precision laser Raman spectroscopy for monitoring tritium purity and isotopic composition during long-term circulation in a test loop, simulating conditions of the KATRIN neutrino-mass experiment.

Contribution

It introduces a novel setup for in-situ Raman measurements of circulating tritium, achieving 0.1% precision suitable for KATRIN's requirements.

Findings

Tritium sample circulated for over three weeks with 770 g throughput.

Observed formation of tritiated and deuterated methanes due to isotope exchange.

Achieved measurement precision of 0.1% for T2 Q1-branch.

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 CT_(4-n)X_n (X=H,D; n=0,1) were observed. Both effects are caused by hydrogen isotope exchange reactions and gas-wall interactions, due to tritium {\beta} decay. A precision of 0.1% was achieved for the monitoring of the T_2 Q_1-branch, which fulfills the requirements for the KATRIN experiment and demonstrates the feasibility of high-precision Raman measurements with tritium inside a glove box.