BNL, Upton, Long Island, New York, USA
Caylar Scientific Instrumentation, Villebon-sur-Yvette, France
University Paris Sud, Orsay, France
Low Energy RHIC electron Cooling (LEReC) is planned during a 7.7 - 20 GeV/n run with Au+79 starting in 2019 (200 GeV/n center-of-mass typical), to explore the existence and location of the QCD critical point. An electron accelerator for LEReC is being constructed to provide a beam to cool both the blue & yellow RHIC ion beams by co-propagating a 10 - 50 mA electron beam of 1.6 - 2.7 MeV. For effective cooling of the ion beam, the electron and ion beam energies must be matched with 10-4 accuracy. As the energy of the RHIC ion beam can be known to <1×10-4, the absolute energy of the electron beam must also be measured to 10-4 accuracy. A 180° bend transport magnet will be used as an energy spectrometer for the electron beam providing fields in the range of 180 - 325 gauss. A Nuclear Magnetic Resonance (NMR) gaussmeter has been customized to measure the field in the magnet (to as low as 143 gauss) with an accuracy of 50 milligauss and a noise floor of < 20 milligauss. The concept of the magnetic spectrometer and details and commissioning performance of the NMR instrument are presented in this paper.
