Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 90: Surface Dynamics: Experiments
O 90.9: Vortrag
Donnerstag, 23. März 2017, 12:30–12:45, WIL C107
A test experiment to determine the long term behaviour of surface work functions — •Matthias Wecker and KATRIN Collaboration — Karlsruhe Institute of Technology (KIT), ITeP/TLK, Postfach 3640, 76021 Karlsruhe
The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to determine the effective mass of neutrinos with a sensitivity of 200 meV/c2 (90% C.L.). This requires the precise measurement of the β-spectrum from tritium-decay close to the endpoint at 18.6 keV. The energy is analysed with the Main Spectrometer, a electrostatic high-pass filter with a filter width of 0.93 eV. The filter voltage of 18.6 kV has to be known with 60 mV accuracy. Thus, the plasma potential in the windowless gaseous tritium source (WGTS), where the β-electrons are produced, has to be known with the same precision. The rear end of the WGTS is electrically terminated by the Rear Wall, a gold-coated stainless steel disk. Superconducting solenoids around the beam-pipes produce a strong magnetic field (3.6 - 6 T) that guides the β-electrons to the spectrometer. The field also connects the plasma in the WGTS with the Rear Wall. Thus, inhomogeneities and fluctuations in the potential of the Rear Wall directly translate into an uncertainty of the WGTS potential, thus limiting the ultimate sensitivity of KATRIN. Exposure to ambient air before its subsequent operation in vacuum can lead to such changes of the work function. This talk introduces a new experiment at KIT for the in-situ determination of the work function. Initial results will be presented. We acknowledge the support of KSETA, the BMBF (05A14VK2) and the Helmholtz Association.