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Submitted on 1 Jan 1981
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DEVELOPMENT AND PERFORMANCE OF PRIMARY STANDARDS AT THE PTB
K. Dorenwendt
To cite this version:
K. Dorenwendt. DEVELOPMENT AND PERFORMANCE OF PRIMARY STANDARDS AT THE PTB. Journal de Physique Colloques, 1981, 42 (C8), pp.C8-229-C8-231. �10.1051/jphyscol:1981827�.
�jpa-00221722�
JOURNAL DE PHYSIQUE
CoZZoque 6'8, suppZdment au n '2 2, Tome 42, ddcembre 2 9 8 2 page C8-229
DEVELOPMENT AND PERFORMANCE O F PRIMARY STANDARDS AT THE P T B
K. Dorenwendt
PhysikaZiseh-Technische BundesanstaZt, Braunschweig, F . R. G.
Abstract.- This article compares the main character- istics of the primary Cs-beam time and frequency standard CS1 in PTB with corresponding standards at the NBS (USA) and YRC (Canada)
.
Some unnormal changes in the performance of CS1 during the last year are reported. The concept of new standards at PTB is out- lined.Primary Cs-beam time and frequency standards are under development in several laboratories. Three of them at EJRC (Canada)
,
NBS (IJSA) and PTB (Federal Republic of Germany) are in oyyation for some years.Their uncertainties are smaller than 1.10- , respectively. The long term stability of the International Atomic Time (TAI) is depending on them. In the following table the specific characteristics of these three standards are given.
In spite of different design and operating conditions the results obtained with these standards are in agreement within the stated un- certainties. For instance, CSV and CS1 are running as clocks for several years. They are continuously compared by means of the Franco- German communication satellite SYMPHONIE. Frequency differences of less than 5.10-l4 were found during the last 12 months. Some months earlier however the differences exceeded 10-I for a short time.
During this period the cavity phase difference bias measured by beam reversal in CS1 changed by 1 ,3.1 0-13. This was never observed before or after this period and no explanation was found. Since this time a beam reversal is executed every four or five weeks. Also no ex- planation can be given for a slowly decreasing beam current in CSI.
It changed by 30 % during the last year, affecting thus the stability of our standard. The variation of cavity phase difference and the de- creasing beam current are the only irregularities stated with CS1 since the beginning of its clock-operation in mid 1978. The reasons can perhaps be found by opening the sytem. But it was decided to continue the clock-operation of CS1 as long as possible as no syste- matic errors should be caused by these effects.
Three new standards are under construction at PTB. It is expected that they will start operation during the next two years. Their main characteristics (interaction length, beam velocity, beam deflecting system, direction of C-field) will be the same as in CSI. It would be tentative to have several standards of quite different design in our laboratory. But technical difficulties and restrictions in man-
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1981827
JOURNAL DE PHYSIQUE
Institution, name of the
character- istics interaction length
beam velocity half width of velocity distri- bution
line width beam deflecting system
detection of phase difference
direction and amount of C-field
beam cross section instability (1 s)
NRC C sv
60 Hz dipole magnets double beam
perpendiculal to the beam,
NBS NBS-6
29 Hz dipole magnets double be am
perpendiculal to the beam,
4,8 A - m
PTB 2s 1
quadrupole
,
hexapole magnets beam
reversal parallel to the beam,
A 4 -
-
l i / 4 x ( 3 m mm)5.10-l2
power and means cause a limitation. Therefore the successful concept of CS1 will be used with the following minor modifications only:
The resonator will be completely under vacuum in the new standards, and one detector and one oven will be located at each side of the resonator. Thus beam reversal can be executed without opening the vacuum system. One standard will operate in an horizontal position like CS1 but two will be mounted vertically. Ry this way slow atoms with trajectories undisturbed by gravitational acceleration can be used.
The new standards will benefit from the results of two research programs. a) In order to optimize the performance of the oven and the beam deflecting magnets it is desirable to know the velocity dis- tribution of the atoms in the beam. This is achieved by chopping the beam and by measuring the time-of-flight spectrum of atoms arriving at the detector. b) A considerable contribution to the uncertainty of all standards is due to an unknown phase-gradient in the resonator.
When the paths of the atoms in the two beam directions are different, these gradients cause systematic frequency shifts leading to a wrong
determination of the cavity phase difference. In order to detect these gradients an experimental Cs-beam apparatus has been built allowing to adjust the resonator position with respect to the beam.
Different types of resonators will be tested in order to find con- figurations with minimal phase gradients for the new standards.
