Laser-Induced Fluorescence Imaging of a Magnetically Confined, Spin-Polarized Ultracold Neutral Plasma

Ultracold neutral plasmas (UCNPs), created by photoionization of a cold gas, are an excellent platform for studying neutral plasmas in far more complex environments such as plasma in the Sun’s atmosphere, white dwarf stars, and inertial-confinement fusion devices. Magnetized UCNPs are of current interest because of the interplay of magnetization and strong coupling, connection to plasma confinement, and modification of recombination dynamics in strong fields. We recently demonstrated the magnetic confinement of UCNPs at the null of a biconic cusp, or quadrupole magnetic field, with confinement times of up to 0.5 ms. Here, we describe our use of laser-induced fluorescence imaging of a magnetically confined UCNP to obtain spatially resolved measurements of ion density, hydrodynamic flow velocity, temperature, and spin polarization. Our observations demonstrate the ions are highly spin-polarized immediately after plasma creation, and the spin polarization is long-lived throughout plasma expansion and confinement.