The cryogenic Lagrangian exploration module: A rotating cryostat for the study of quantum vortices in helium II via particle seeding

The study of quantum vortex dynamics in He II offers great potential for advancing quantum-fluid models. Bose-Einstein condensates, neutron stars, and even superconductors exhibit quantum vortices, whose interactions are crucial for dissipation in these systems. These vortices have quantized velocity circulation around their cores, which, in He II, are of atomic size. They have been observed indirectly, through methods such as second sound attenuation or electron bubble imprints on photosensitive materials. Over the past twenty years, decorating cryogenic flows with particles has become a powerful approach to studying these vortices. However, recent particle visualization experiments often face challenges with stability, initial conditions, stationarity, and reproducibility. Moreover, most dynamical analyses are performed in 2D, even though many flows are inherently 3D. We constructed a rotating cryostat with optical ports on an elongated square cupola to enable 2D and 3D Lagrangian and Eulerian studies of rotating He II flow. Using this setup, individual quantum vortices have been tracked with micron-sized particles, as demonstrated by Peretti et al. [Sci. Adv. 9, eadh2899 (2023)]. The cryostat and associated equipment-laser, cameras, sensors, and electronics-float on a 50 μm air cushion, allowing for precise control of the experiment's physical parameters. The performance during rotation is discussed, along with details on particle injection.