Precision NMR measurement of the TRIUMF cyclotron magnetic field

Plans for separated turn operation and the need for improved stability in the present operation at TRIUMF require that drifts in the main magnet be reduced to <1 ppm. Stability of +-0.7 ppm for short periods (approx. =10 min) were achieved with modifications to the present power supply. To improve the long term stability, a high resolution, high bandwidth, absolute method for magnetic field measurement is required. This paper describes an NMR system which uses a digital frequency synthesizer controlled by a CAMAC based microprocessor to determine the NMR resonant frequency. The system has been shown to be capable of measuring the TRIUMF magnet field with a resolution of 0.1 ppm, and a 10 Hz bandwidth. This system should allow the stabilization of the beam phase directly from the magnetic field measurement, a substantial improvement over a previous method where the required phase stability was obtained by modulating the RF frequency to compensate measured phase excursions of the extracted beam