title: Spherical fused silica cells filled with pure helium for nuclear magnetic resonance-magnetometry.
abstract: High magnetic fields (>1 T) are measured by NMR magnetometers with unrivaled precision if the precessing spin sample provides long coherence times. The longest coherence times are found in diluted (3)He samples, which can be hyperpolarized for sufficient signal strength. In order to have minimal influence on the homogeneity and value of the measured magnetic field, the optimal container for the (3)He should be a perfect sphere. A fused silica sphere with an inner diameter of 8 mm and an outer diameter of 12 mm was made from two hemispheres by diffusion bonding leaving only a small hole for cleaning and evacuation. This hole was closed in vacuum by a CO2 laser and the inner volume was filled with a few mbars of (3)He via wall permeation. NMR-measurements on such a sample had coherence times of 5 min. While the hemispheres were produced with <1 μm deviation from sphericity, the bonding left a step of ca. 50 μm at maximum. The influence of such a mismatch, its orientation, and the immediate environment of the sample is analyzed by FEM-simulations and discussed in view of coherence times and absolute field measurements.
authors.affiliation: Institute of Physics, Johannes Gutenberg University, Staudingerweg 7, 55128 Mainz, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Maul
authors.affiliation: Institute of Physics, Johannes Gutenberg University, Staudingerweg 7, 55128 Mainz, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Blümler
authors.affiliation: Institute of Physics, Johannes Gutenberg University, Staudingerweg 7, 55128 Mainz, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Heil
authors.affiliation: Institute of Physics, Johannes Gutenberg University, Staudingerweg 7, 55128 Mainz, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Nikiel
authors.affiliation: Institute of Physics, Johannes Gutenberg University, Staudingerweg 7, 55128 Mainz, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: Otten
authors.affiliation: ifw Günter-Köhler-Institut für Fügetechnik und Werkstoffprüfung GmbH, Otto-Schott-Str. 13, 07745 Jena, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Petrich
authors.affiliation: ifw Günter-Köhler-Institut für Fügetechnik und Werkstoffprüfung GmbH, Otto-Schott-Str. 13, 07745 Jena, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmidt