Doppler-cooled ions in a compact reconfigurable Penning trap

We report the design and experimental demonstration of a compact, reconfigurable Penning ion trap constructed with rare-earth permanent magnets placed outside of a trap vacuum enclosure. We describe the observation of Doppler laser cooling of ions in a permanent magnet Penning trap. We detail a method for quantifying and optimizing the trap magnetic-field uniformity in situ using a thermal beam of neutral $^{40}\mathrm{Ca}$ precursor atoms. Doppler laser cooling of $^{40}\mathrm{Ca}^{+}$ is carried out at 0.65 T, and side-view images of trapped ion fluorescence show crystalline order for both two- and three-dimensional arrays. Measured $^{40}\mathrm{Ca}^{+}$ trap frequencies confirm the magnetic-field characterization with neutral $^{40}\mathrm{Ca}$. The compact trap described here enables a variety of cold ion experiments with low size, weight, power, and cost requirements relative to traditional electromagnet-based Penning traps.