Berlin 2005 – scientific programme
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A: Atomphysik
A 4: Precision Spectroscopy of Atoms and Molecules II
A 4.1: Invited Talk
Friday, March 4, 2005, 16:30–17:00, HU 3075
3He magnetometer for neutron EDM experiments — •Stefan Baeßler1, Werner Heil1, Vinzenz Kirste1, Yury Sobolev1, Vladimir Lobashev2, Wolfgang Kilian3, Herbert Rinneberg3 und Frank Seifert3 — 1Institut für Physik, Universität Mainz — 2Institute of Nuclear Research, Troitsk — 3Physikalisch-Technische Bundesanstalt Berlin
We report on a 3He-magnetometer that is capable of detecting tiny magnetic field fluctuations and gradients on a femtotesla level in an experiment which measures the electric dipole moment (EDM) of the neutron. The precession frequency of 3He atoms is detected in two different ways: One is based on the Ramsey technique of separated oscillating fields, and here the spin polarization of the 3He atoms is detected optically at the end of the Ramsey cycle. The second approach is to detect the spin precession signal directly with a SQUID. The 3He gas is polarized by means of optical pumping and stored in two flat cylindrical vessels of V ∼ 4 liter in a sandwich type arrangement around a twin-chamber type storage bottle for ultra-cold neutrons.
In order to have a high accuracy of the SQUID detection of the spin precession a long transverse relaxation time T2 of the 3He spins and a high signal to noise ratio (SNR) of the SQUID is needed. We obtained T2 ∼ 1 h and SNR ∼ 3000 Hz−1/2 which allows us to reach an accuracy in the magnetic field measurement of 3 fT per neutron storage cycle of 150 seconds. This accuracy is sufficient for a planned EDM experiment.