9 October 2020
Objective
In the frame of the Kibble balance project (previously Watt balance), g has to be determined at the center of mass of the involved mass. It is then necessary to transfer the g absolute value obtain with the atom gravimeter to the location of this mass. For that purpose, we characterize the gravity variations in the two neighboring rooms in which the two experiments are located.
Laboratories
Two identical concrete pillars (6 m × 5,5 m × 2 m) have been built in these two rooms especially designed for metrology. They are sustained by four 12 m long concrete legs deeply fixed into the stable Fontainebleau sand layer. This structure guarantees the stability in height and tilt and acts as a low pass filter for vibrations.
Mapping
On these pillars, we performed a 3D gravity mapping with a relative gravimeter Scintrex CG-5. Based on this mapping, we developped a local gravity model allowing to determine gravity differences between any points of the two rooms with an associated uncertainty of 3 µGal (1 µGal = 10-8 m.s-2).
- Gravity horizontal model
- Gravity differencies on the two pillars at 52 cm with respect to the center point of the gravimetry pillar (GR).
Gravity monitoring of the site
The gravity stability is regularly checked, by measuring gravity differences between unoccupied stations and with the continuous gravity variations measured with a second relative gravimeter operating since 2013. This device is a superconducting iGrav, that has been calibrated with the atom gravimeter. Its small drift (<2 µGal/an) allows to confirm the proper functioning of the atom gravimeter, especially in between two measurement campaigns outside the laboratory, and to be free from gravity variation models to study and improve the performances of the atom gravimeter. Finally, it also allows to deliver a continuous gravity signal, calibrated by the absolute gravimeter, to the Planck constant measurements performed by the Watt balance.
Continuous gravity signal for the Planck constant determination
The last Planck constant determination with the LNE Kibble balance took part in spring 2017 (M. Thomas et al. Metrologia 54 (2017) 468-480). This measurement has been taken into account in the SI revision including a new definition for the kilogram, which occurred in 2018.
- Earth gravity variations during the Planck constant determination with the LNE Kibble balance in spring 2017
- The green lines frame the Kibble balance measurement session. The iGrav signal (black) is calibrated by the CAG signal (red). In blue is represented the iGrav residual signal
Publications
M. Thomas, D. Ziane, P. Pinot, R. Karcher, A. Imanaliev, F. Pereira Dos Santos, S. Merlet, F. Piquemal and P. Espel
"A determination of the Planck constant using the LNE Kibble balance in air"
Metrologia 54, 468 (2017)
M. Thomas, P. Espel, D. Ziane, P. Pinot, P. Juncar, F. Pereira Dos Santos, S. Merlet, F. Piquemal and G. Genevès,
"First determination of the Planck constant using the LNE watt balance"
Metrologia 52, 433-443 (2015)
S. Merlet, P. Gillot, T. Farah, Q. Bodart, J. Le Gouët, P. Cheinet, C. Guerlin, A. Louchet-Chauvet, N. Malossi, A. Kopaev, O. Francis, G. d’Agostino, M. Diament, G. Genevès, A. Clairon, A. Landragin et F. Pereira dos Santos
"Détermination de l’accélération de la pesanteur pour la balance du watt du LNE"
Revue Française de Métrologie 36, 11-27 (2014)
Z. Jiang, et al.
"On the gravimetric contribution to the redefinition of the kilogram"
Metrologia 50, 452-471 (2013)
O. Francis, et al.
"The European Comparison of Absolute Gravimeters 2011 (ECAG-2011) in Walferdange, Luxembourg: results and recommendations"
Metrologia 50, 257-268 (2013)
Z. Jiang, et al.
"The 8th International Comparison of Absolute Gravimeters 2009: the first Key Comparison (CCM.G-K1) in the field of absolute gravimetry"
Metrologia 49, 666-684 (2012)
Z. Jiang, V. Pálinkás, O. Francis, P. Jousset, J. Mäkinen, S. Merlet, M. Becker, A. Coulomb, K. U. Kessler-Schulz, H. R. Schulz, Ch. Rothleitner, L. Tisserand and D. Lequin
"Relative Gravity Measurement Campaign during the 8th International Comparison of Absolute Gravimeters (2009)"
Metrologia 49, 95-107 (2012)
G. D’Agostino,S. Merlet, A. Landragin and F. Pereira Dos Santos
"Perturbations of the local gravity field due to mass distribution on precise measuring instruments: a numerical method applied to a cold atom gravimeter"
Metrologia 48, 299-305 (2011)
S. Merlet, A. Kopaev, M. Diament, G. Geneves, A. Landragin et F. Pereira Dos Santos
"Micro-gravity investigations for the LNE watt balance project"
Metrologia 45, 265, (2008)
G. Genevès, P. Gournay, A. Gosset, M. Lecollinet, F. Villar, P. Pinot, P. Juncar, A. Clairon, A. Landragin, D. Holleville, F. Pereira Dos Santos, J. David, M. Besbes, F. Alves, Luc Chassagne and S. Topçu
"The BNM Watt Balance Project"
IEEE transaction on Instrumentation and Measurement 54, 850-853, (2005)
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