Title
LSRH cesium beam No. 2
Authors
LSRH
Date of Issue
1960
Linked Datasets
Device Type
frequency
Operating Principle
beam
Reference Species
cesium
Quantum Transition
hyperfine
(F=3,mF=0) <-> (F=4,mF=0)
Reference Frequency
9 192 631 770 Hz
Fabrication Source
noncommercial
Host Institution
LSRH
Status Timeline
Development: 1959-1960
Operational: 1960-06–1966
Technical Design aspects: size, design etc.
Total length: 600 cm. Interaction length: 408 cm. Diameter of vacuum tank: 25 cm. (Kartaschoff et al. 1960a; Kartaschoff et al. 1960b)
Beam geometry: Asymmetrical beam geometry without a central collimating slit; the beam was defined by the edges of the gaps of the A and B magnets. The positions of the source and detector were adjustable perpendicular to the beam, allowing velocity selection of slower atoms and a corresponding reduction of the resonance linewidth. (Kartaschoff et al. 1960a)
Source: Cesium beam source with a beam cross-section of 0.7 × 10 mm at the source and detector. The source used metallic cesium in a heated oven operated at approximately 100–125 °C. (Kartaschoff et al. 1960a; Kartaschoff 1964)
Detector: hot-tungsten-ribbon ionizer followed by a mass-spectrometer system and a seventeen-stage secondary-electron multiplier using Cu-Be dynodes. The electron multiplier was constructed by the Applied Physics Department of ETH Zurich. (Kartaschoff et al. 1960b)
Microwave cavity: U-shaped resonant microwave cavity with a quality factor Q ≈ 10⁴. The horizontal section was 408 cm long and the two sections interacting with the atomic beam were 5 cm long in the direction of the beam. The cavity could be tuned externally over a range of approximately 2 MHz. (Kartaschoff et al. 1960a; Kartaschoff et al. 1960b)
The A and B state-selection magnets were Ticonal permanent magnets producing a field of approximately 9500 Oe. Their gaps were 15 cm long and 4 mm wide. (Kartaschoff et al. 1960a)
Microwave excitation was produced by a klystron phase-locked to a multiple of an 8.5 MHz quartz oscillator. The oscillator was frequency-modulated at 20 Hz, and the detected atomic signal generated a correction signal used to servo the quartz oscillator to the center of the atomic resonance. (Kartaschoff et al. 1960a)
Technical specifications: stability, precision
Accuracy / uncertainty: <1E-10, preliminary (Kartaschoff et al. 1960b); ±3E-11 (Kartaschoff 1962); ±1.1E-11 (Kartaschoff 1964)
Reproducibility: better than ±2E-11, zero-field extrapolated frequency (Kartaschoff et al. 1960a)
Stability: 2.7E-11 @ 4.6 s under good conditions, quartz reference (Kartaschoff 1962); 2.5E-11 @ 4.6 s, 3.8E-12 @ 360 s, rubidium reference (Kartaschoff 1964)
Precision of accuracy tests: ≈±3E-11 with quartz auxiliary reference; ≈±5E-12 with Varian rubidium auxiliary reference (Kartaschoff 1964)
Line width: 40 Hz without velocity selection; 24 Hz with velocity selection (Kartaschoff et al. 1960a); normally ≈35 Hz, adjustable through velocity selection (Kartaschoff 1962)
Q: ≈2.6E8 for the atomic resonance at the normal 35 Hz linewidth; microwave cavity Q ≈1E4 (Kartaschoff 1962; Kartaschoff 1964)
The improvement reflects both modifications to the instrument, particularly the magnetic shielding, and improved measurement of systematic effects; the introduction of a Varian rubidium standard as an auxiliary reference allowed tests previously limited by the quartz reference to be made with substantially greater precision.
Modification History
End of June 1961: The Permalloy shielding of the C-field region was modified. The resulting inadequate shielding produced a frequency offset of approximately 8 × 10⁻¹¹ relative to the NBS standard during part of 1961–1962. (Kartaschoff 1962; Bonanomi et al. 1964)
Spring 1962: The Permalloy shielding of the interaction region was replaced by a more stable demagnetizable Armco-iron shielding system. The improved shielding reduced the residual magnetic field and the estimated uncertainty associated with the C-field to approximately 1.2 × 10⁻¹². (Kartaschoff 1962; Kartaschoff 1964; Bonanomi et al. 1964)
End of April 1962: Cavity No. 1 was replaced by cavity No. 2. The new cavity could be reversed end-for-end, allowing systematic frequency shifts caused by phase differences between the two oscillating fields to be tested experimentally. (Kartaschoff 1964)
Usage History
From June 1960 until approximately 1966, the instrument served as the primary frequency standard for the Neuchâtel time service and was used for regular calibrations of the quartz clocks of the Neuchâtel Observatory. (Kartaschoff 1962; Kartaschoff 1964; LSRH 1967)
The instrument was regularly compared with atomic frequency standards in other laboratories through VLF transmissions, including standards at the National Bureau of Standards, National Physical Laboratory, Cruft Laboratory at Harvard University, CNET, and the U.S. Naval Observatory. (Kartaschoff et al. 1960a; Kartaschoff 1962; Kartaschoff 1964)
Direct comparisons with other cesium standards demonstrated agreement at the level of a few parts in 10¹² on several occasions. (LSRH 1967)
Product
kartaschoff1962
kartaschoff1960
kartaschoff1960a
bonanomi1964
kartaschoff1964
RecherchesAuLSRH
Identifiers
https://libra.unine.ch/handle/20.500.14713/99847