A neutrino is a subatomic particle similar to an electron but has no electrical charge and a very small mass, which was once thought to be zero. One of the most abundant particles in the universe, neutrinos have very little interaction with matter, and they are incredibly difficult to detect. They remain a mystery, despite decades-long efforts to discover their mass.
Understanding what gives a neutrino its mass could help scientists formulate an explanation of the universe beyond the Standard Model (currently, the best theory to describe the most basic building blocks of the universe). And because of their abundance, identifying the neutrino mass would be important for understanding the current cosmological models and the formation of cosmic structures.
Located at the Karlsruhe Institute of Technology (KIT) in Germany, the aim of the KATRIN experiment is to determine the absolute mass of the neutrino. It took almost 16 years from the first design to a completed KATRIN platform to attain the sensitivity required to resolve the minute effects of measuring neutrinos. The new technologies that were developed include a tritium source and a detector (spectrometer) to measure the energy of the released electrons.
The KATRIN experiment begins with a tritium source that generates gaseous tritium, a highly radioactive isotope of hydrogen. As the tritium (3H) undergoes radioactive decay into helium isotopes (3He), beta-electrons (e-) and electron antineutrinos (ν̄), it emits also pairs of particles of one electron and one neutrino. These pairs are guided to the detector by superconducting magnets to be measured.
Because KATRIN scientists cannot directly measure the mass of neutrinos, they measure electrons to calculate neutrino properties based on electron properties. A few of the electron-neutrino pairs emitted by the tritium source have the electron taking nearly all the energy — leaving only a tiny amount for the neutrino (most pairs share their energy load equally). These rare pairs are the ones measured by KATRIN, as the miniscule amount of energy left for the neutrino must include its rest mass. Once KATRIN accurately measures the electron’s energy, the scientists can calculate the neutrino’s energy – and its mass.
World’s Largest UHV Vessel
The main spectrometer, the largest ultra-high-vacuum (UHV) vessel in the world, with a residual gas pressure in the range of 10-11 mbar (similar to the surface of the moon), contains a dual-layer electrode system comprising 23,000 wires to shield the inner volume from charged particles. The spectrometer selects the highest-energy electrons before they reach the detector.
Essentially an electron transport and tritium retention system in an extreme vacuum environment, the KATRIN experiment poses comprehensive technical challenges for a vacuum valve solution in terms of leak tightness and functional stability. Felix Jordan, VAT Key Account Manager Research, outlines the requirements for a vacuum valve solution: “The VAT valves developed by the VAT team for KATRIN needed to take into account the radiation levels, extreme temperatures, and the ultra-high vacuum environment.”
Vacuum Valves for Extreme Conditions
The VAT series 10.8 gate valves, designed specifically for UHV environments, and the VAT series 54.1 all-metal angle valves, designed for extreme UHV conditions with high-radiation levels and high temperatures, were selected for KATRIN.
The 10.8 UHV Gate Valves feature VATLOCK sealing technology which provides reliable sealing without any friction at the gate seal. The gate seals are made of temperature-resistant, high-performance elastomers vulcanized directly to the gate – for maximum durability and optimal sealing performance. A key element of the VATLOCK is that it is locked in closing position, eliminating any risk of vacuum loss due to pneumatic failure.
The 54.1 UHV All-Metal Angle Valves eliminate the risk of premature aging of seals in areas with higher radiation exposure. These valves are characterized by a unique hard-on-hard sealing technology (no elastomers). Thanks to the patented FLEX VATRING seal, a greater number of closing cycles can be performed with these valves than with conventional hard-on-hard sealing designs. This extends the time between maintenance periods to such a degree that the valves in the KATRIN experiment are virtually maintenance-free. Due to their outstanding sealing properties, these valves are also used in extremely high vacuum (XHV) applications.
"Due to VAT’s clean vacuum procedures these valves were delivered already baked out to avoid any system contamination”, adds Felix Jordan, VAT Key Account Manager Research. "They provide the physically neutral characteristics – exerting zero influence on the complex experiment’s environment – that are required in such extreme applications. We are excited about the results KATRIN will achieve."