[Moller] Design and performance of an in-vacuum, magnetic field mapping system

[Jay Benesch]

Seems relevant to hybrid, at least for ideas.  48 pages.  7 of 9 authors 
at Argonne.

https://arxiv.org/abs/2003.06244


Design and performance of an in-vacuum, magnetic field mapping system 
for the Muon g-2 experiment
S. Corrodi, P. De Lurgio, D. Flay, J. Grange, R. Hong, D. Kawall, M. 
Oberling, S. Ramachandran, P. Winter
(Submitted on 13 Mar 2020)

     The E989 Muon g-2 experiment at Fermilab aims to measure the 
anomalous magnetic moment, aμ, of the muon with a precision of 140 
parts-per-billion. This requires a precise measurement of both the 
anomalous spin precession frequency, ωa, and the average magnetic field 
in terms of the equivalent, free proton Larmor frequency, ωp. The 
measurement of ωp with a total systematic uncertainty of 70 
parts-per-billion involves a combination of various NMR probes. There 
are 378 probes in fixed locations constantly monitoring field drifts. A 
water-based probe provides the calibration in terms of ωp. A crucial 
element for the multi-step measurement of ωp is the regular mapping of 
the magnetic field over the muon storage region. The former E821 
experiment at Brookhaven employed an in-vacuum field mapping system 
equipped with 17 NMR probes, which was developed by the University of 
Heidelberg. We have refurbished and upgraded this system with new probes 
and electronics. The upgrades include a new communication scheme 
incorporating time-division multiplexing to separate the important NMR 
reference clock from the data communication. The addition digitization 
of the NMR signals replaced the hardware-implemented zero-crossing 
counting of the E821 system. The digitized signals offer new 
capabilities in the NMR frequency analysis and its related systematic 
uncertainties. While the mechanical systems that move the field mapper 
around the ring have been mostly refurbished, the motion control system 
was completely replaced with a custom-built electronics centered around 
a commercial Galil motion controller. Both the field mapping NMR system 
and its motion control were successfully commissioned at Fermilab and 
have been in reliable operation during the first data taking periods. 
This article provides details of the upgrades of the field mapper and 
its performance.