Freiburg 2008 – scientific programme

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T: Fachverband Teilchenphysik

T 88: Niederenergie-Neutrinophysik und Suche nach Dunkler Materie III

T 88.8: Talk

Wednesday, March 5, 2008, 18:35–18:50, KGI-HS 1098

Background electrons in MAC-E filters — •Ferenc Glück for the KATRIN collaboration — Universität Karlsruhe

Small background level is an important requirement for the precise and reliable neutrino mass measurements (Mainz, Troitsk, KATRIN) using MAC-E filters (electrostatic spectrometers with magnetic adiabatic collimation). Background experiments done with the Mainz spectrometer show that a substantial part of the background is due to low energy secondary electrons coming from the electrodes. The magnetic flux going through the detector is usually not connected with the electrodes, therefore the electrons can reach the detector only by radial motion (perpendicular to the field lines). According to trajectory calculations and to general arguments, the electrons have no radial motion in axisymmetric system; only with non-axisymmetric fields is the radial electron motion possible. Thus, the background level could increase with increasing deviation from axial symmetry. In addition, deviation from adiabaticity in the presence of non-axisymmetric fields also increases the radial electron motion, and therefore the background level. The trajectory calculations with non-axially symmetric fields yield qualitative explanations for most of the background experiments in Mainz. The background at the KATRIN main spectrometer, due to its optimal adiabaticity and axial symmetry conditions, is expected to be small.