Tritium Supply and Processing for the First KATRIN Tritium Operation

The main task of the Tritium Laboratory Karlsruhe (TLK) in 2018 was the commissioning and First Tritium (FT) operation of the windowless gaseous tritium source (WGTS) of the Karlsruhe Tritium Neutrino (KATRIN) experiment. It was paramount to enable the FT measurement run of the KATRIN experiment, to yield first scientific results with the complete KATRIN beamline.

The aim of KATRIN is to determine the mass of the electron-antineutrino by precise spectroscopy of the tritium β-spectrum close to its maximum energy of 18.6 keV. KATRIN uses an ultraluminous source (WGTS) and a high-resolution electrostatic spectrometer. While the inner loop system of KATRIN has the task of providing stabilized tritium circulation with a throughput of 40 g·day⁻¹ for the WGTS, the outer loop incorporates the entire TLK infrastructure for tritium cleanup, purification, and accountancy prior to reinjection of tritium into the inner loop.

For KATRIN’s FT run, ≈5 × 10¹³ Bq (2.3 × 10⁻² mol) of tritium was provided in 3.2 mol of deuterium. In contrast to the high isotopic purity of >95% tritium necessary for future KATRIN operation, a concentration of 7 × 10⁸ Bq·m⁻³ (resulting in 0.5% nominal source luminosity) had to be kept constant during the entire FT campaign. This required a processing scheme deviating from the later KATRIN outer loop processing procedure.

This paper describes the procedures used to supply the KATRIN inner loop with its FT gas. Furthermore, experience gained during operation of the different gas processing steps and tritium accountancy is presented.