The Cryogenic Lagrangian Exploration Module: a rotating cryostat for the study of quantum vortices in Helium II via particle seeding

TL;DR

The Cryogenic Lagrangian Exploration Module (CryoLEM) addresses the challenge of visualizing and characterizing quantum vortices in HeII with high spatial dimensionality and reproducible initial conditions. It combines a rotating optical cryostat at saturated vapor pressure with eight optical ports, solid-particle seeding (H$_2$/D$_2$ in He), and high-speed imaging for 2D2C, 2D3C, and 3D3C measurements, enabling detailed Lagrangian and Eulerian analyses of rotating HeII flows. Key contributions include the design and demonstrated stability of the rotating cryostat on an air-bearing table, cryogenic performance metrics, an integrated particle-injection system, and a scalable data-control pipeline (Node-RED/InfluxDB/Grafana) for real-time monitoring and post-processing. The system enables controlled exploration of canonical rotation, counterflow, and vortex-lattice dynamics, with implications for understanding quantum turbulence, Kelvin waves, and vortex reconnection in HeII, and provides a versatile platform for validating quantum-fluid models in a 3D experimental regime.

Abstract

The study of quantum vortex dynamics in HeII 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 HeII, 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 2D2C, 2D3C, and 3D3C Lagrangian and Eulerian studies of rotating HeII 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 $μ$m air cushion, allowing for precise control of the experiment's physical parameters. The performance during rotation is discussed, along with details on particle injection.

Figures (11)

• Figure 1: Experimental cell with optical ports. The helium reserve is located above the optical access ports, and thermometer data can be transmitted through a reconfigured optical port (here, the bottom port). (a) Inner cell, which contains the liquid helium. (b) $77$ K intermediate jacket in thermal contact with the nitrogen reservoirs. (c) $300$ K layer.
• Figure 2: (a) Schematic view of the modified orange cryostat with the experimental cell. It has been modified by adding a cold valve, which allows filling the core of the cryostat with liquid helium from the reservoir, and a solenoid valve that permits releasing the evaporated helium gas from the reservoir to the top of the pumping line. The main modifications include the presence of the experimental cell with eight optical accesses at the bottom of the chimney, and the addition of particle injection capillaries that run from the top of the chimney to the middle of the experimental cell. In gray: pressure control apparatus. (b) Experimental setup zoomed in on the experimental cell. White rods schematically represent the vortex lattice present in rotating superfluid helium.
• Figure 3: Typical temperature profile during experiments. In blue : temperature of the bottleneck between the cryostat chimney and the cell ($T_{exch}$). The fluctuations observed in the green "Experiments" region are due to particle injections ($300$ K gas) between each experimental run acquisition. Stable temperature is obtained thanks to pressure regulation.
• Figure 4: Superfluid-Gas interface position as a function of time is shown. A double plot compares the luminosity-based data and the PTV-based data, which overlap quite significantly as shown in the insert. Consequently, both methods yield a similar surface velocity of $v_{surf}\simeq -11$$\mu$m.s$^{-1}$. A film is recorded during the experiment with a laser sheet orthogonal to the camera, capturing particles floating in the superfluid. The luminosity-based data is obtained by summing the pixel intensities horizontally and identifying the peak intensity. The PTV-based data is directly derived from the PTV tracks with the highest altitudes.
• Figure 5: Rotational motion of the entire experimental apparatus is presented. The stators of the rotating table and the rotating gasket are not blurred, as they remain stationary within the laboratory reference frame.