Temperature-related effects in the polarization of atoms in a magnetized plasma as a promising feature towards high $^3$He nuclear polarization

Abstract

We report on further investigation of nuclear hyperpolarization of helium-3 in magnetized plasma at a magnetic field of 3.66 T and at different experimental conditions in a dual cell of relatively large volume, compared to those reported in the original polarization of atoms in a magnetized plasma (PAMP) paper by Maul $\textit{et al.}$ [Phys. Rev. A. $\textbf{98}$, 063405 (2018)]. It was found that steady-state nuclear polarizations obtained by this method strongly increase with temperature and rf gas discharge power. We managed to reach almost 8% at the highest possible temperature in our setup which is to date the highest polarization obtained by this method at 10 mbar. It was also shown that atomic oxygen in plasma, considered as an impurity, could be a good probe of plasma parameters relevant for the PAMP process, either the temperature or the metastable $^3$He density. The polarization build-up rates with the cell temperature stabilized near room temperature are found to be of the order of 1 s$^{-1}$ which is by two orders of magnitude faster than was reported in the original PAMP paper for the same filling pressure. These observations promise a further optimization of experimental conditions towards strong and fast hyperpolarization by this method.