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M. Klopf, J. Erhart, G. Konrad, T. Soldner:
"aSPECT: Improvement of the high voltage electrodes";
Poster: DPG spring meeting 2013 (Hadronic and Nuclear Physics), Dresden; 04.03.2013 - 08.03.2013.

The purpose of the retardation spectrometer aSPECT is to determine the anti-neutrino electron angular correlation coefficient a with high precision, by measuring the integral proton spectrum in free neutron decay. The precise measurement of the correlation coefficient a serves as a test of the validity of the Standard Model.
The analysis of the decay protons is based on a precise energy measurement, by means of an electrostatic filter. Hereby the independence of the background from the filter potential is a basic prerequisite for the determination of a. However, in previous measurements with aSPECT some dependencies have been found. The background, first mainly caused by strong discharge phenomena, has already been significantly reduced by the re-design of several electrodes. In order to reach our design accuracy in a, we have to further suppress this dependency. We therefore improved the shape of our high voltage electrodes to further reduce the electric field and thereby the probability for field emission. The theoretical background of such discharge phenomena as well as the optimization of the high voltage electrodes will be presented.