Performance of the Primary Cs-Standard of the Physikalisch-Technische Bundesanstalt

Abstract

First the main characteristics of the caesium beam time and frequency standard CS1 of the PTB are summarized. Then current research work on the improvement of CSI is reported: (1) Reduction of the mean beam velocity and the velocity range in the beam; (2) detection of small asymmetries of the Ramsey resonance, e.g., due to a shifted Rabi resonance; (3) development of improved analyser deflection systems. The efficiencies of beam polarizers using quadrupole magnets or hexapole magnets, or combinations of both, have been studied for CS1 achieving the reduction of the mean beam velocity to about 100 m/s and the half-width velocity range in the beam to about 16%. For the analyser a shaped quadrupole magnet or a combination of hexapole and quadrupole magnets should be advantageous. The square root of the sum of squares of the uncertainty contributions of CS1 amounts to 0.26 · 10-13, the official relative uncertainty of CS1 being 1 · 10-13.