Monitoring of the operating parameters of the KATRIN Windowless Gaseous Tritium Source

TL;DR

This paper details the monitoring and control systems for the KATRIN experiment's gaseous tritium source, ensuring stability and precision necessary for accurate neutrino mass measurements.

Contribution

It introduces comprehensive sensor and control systems, including a Laser-Raman setup, demonstrating their effectiveness in stabilizing key parameters within 0.1%.

Findings

Successful control of source parameters at 0.1% level

Proof-of-principle validation from large-scale tests

Enabling precise neutrino mass measurement

Abstract

The Karlsruhe Tritium Neutrino (KATRIN) experiment will measure the absolute mass scale of neutrinos with a sensitivity of $\m_{\nu}$ = 200 meV/c$^2$ by high-precision spectroscopy close to the tritium beta-decay endpoint at 18.6 keV. Its Windowless Gaseous Tritium Source (WGTS) is a beta-decay source of high intensity ($10^{11}$/s) and stability, where high-purity molecular tritium at 30 K is circulated in a closed loop with a yearly throughput of 10 kg. To limit systematic effects the column density of the source has to be stabilised at the 0.1% level. This requires extensive sensor instrumentation and dedicated control and monitoring systems for parameters such as the beam tube temperature, injection pressure, gas composition and others. Here we give an overview of these systems including a dedicated Laser-Raman system as well as several beta-decay activity monitors. We also report on results of the WGTS demonstrator and other large-scale test experiments giving proof-of-principle that all parameters relevant to the systematics can be controlled and monitored on the 0.1% level or better. As a result of these works, the WGTS systematics can be controlled within stringent margins, enabling the KATRIN experiment to explore the neutrino mass scale with the design sensitivity.