The Muon g-2 Experiment at Fermilab (E989) has been designed to determine the muon
anomalous magnetic moment to a precision of 140 parts per billion (ppb), a four-fold
improvement over the Brookhaven E821 measurement. Key to this precision goal is
the absolute determination of the magnetic field of the experiment's muon storage
ring to better than 70 ppb.
The magnetic field will be measured and monitored by nuclear magnetic resonance (NMR)
probes, which are mounted on a trolley and pulled through the muon storage region when
muons are not being stored. These trolley probes will be calibrated in terms of the
free-proton Larmor precession frequency $\omega_{p}$ by a specially-constructed NMR
absolute calibration probe. In E821, the uncertainty in the field measurement was
170 ppb, of which 50 ppb was due to the absolute probe. In E989, these uncertainties
will be reduced to 70 ppb and 35 ppb, respectively. To meet these stringent requirements,
a new calibration probe has been designed and is currently under construction, along with
a so-called plunging probe. This plunging probe will be used to transfer the calibration
to the trolley probes. This poster will present the design, fabrication, and testing of
the absolute and plunging probes, along with the calibration procedure.