Development of 3He magnetometer for ultra-sensitive measurements of high magnetic fields in Penning traps

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High precision mass measurements nowadays aim to reach a relative mass uncertainty better than 10-11 for tests of fundamental interactions and symmetries. The mass is usually determined in Penning traps via the measurement of the free-space cyclotron frequency of the stored ions assuming the magnetic field is known with similar accuracy. Standard nuclear magnetic resonance methods, however, fail to measure the field with such high accuracy. Our approach (proposal) is based on the measurement of the free induction decay of gaseous, nuclear spin-polarized 3He after a resonant radio-frequency pulse excitation. The essential point is that coherent spin-precession times of several minutes for nuclear spin-polarized 3He can be obtained in typical Penning trap fields of > 4 Tesla. From the measured Larmor frequency (> 100 MHz) the local magnetic field across the sample spins can be determined to an accuracy of better than 10-11. Such a device can be miniaturized to fit next to a Penning trap that allows ultra-sensitive magnetic field monitoring and measurements of magnetic field gradients (gradiometer). The 3He gas is spin-polarized in-situ using a new, non-standard variant of the metastability exchange optical pumping.