Ion retention, blocking and monitoring within the KATRIN experiment

The KATRIN (KArlsruhe TRItium Neutrino) experiment aims to measure the effective neutrino mass with an unprecedented design sensitivity of 0.2% eV at the 90% confidence level. The electron antineutrino is produced in tritium beta decay together with the beta-electron and a positive ion. Magnetic fields guide charged particles through the energy-analyzing retarding spectrometers towards the KATRIN detector. The antineutrino mass can be determined by fitting the energy spectrum of the electrons near the kinematic endpoint of 18.6 keV. In this method, ions act as a background source as they further ionize residual gas and produce secondary electrons. We have tested the ion-blocking mechanisms implemented in the source and transport section, where ions are blocked with positive potentials created by ring electrodes, and found the preferred settings with the highest blocking efficiency. Some ions finally strike electrodes along the beamline, creating a current that allows us to monitor the tiny ion flux in the spectrometer section. We will share results from these tests and prospects for future operations.