A Permanent-Magnet Array to Maintain 3He Gas Polarization Inside a Glass Vessel for Applications in High-Energy Laser Physics

We designed and tested an array of permanent magnets (PMA) consisting of two rings with a Halbach-type magnetization pattern, which are stacked at an optimum distance such that its field homogeneity is sufficiently high to maintain the nuclear polarization of
³
He gas for future laser experiments. The design included the magnetic layout, the selection of appropriate magnets, and the calculation of the expected relaxation time for the polarized gas. After assembly, we measured the magnetic field in the center region of the PMA. We transferred polarized gas samples from the magnetized transport box into the PMA and determined the relaxation time with four magnetic field sensors in a gradiometric arrangement, detecting the decay of the stray field of the polarized gas on the order of 100 nT in a background field of 1.3 mT. The extracted polarization lifetime of about 21 h is sufficient for the planned experiments at high-power laser facilities.