Speaker
Description
Superfluid helium (He II) serves as a crucial refrigerant for cooling superconducting resonators, enabling the attainment of remarkably high acceleration gradients in particle accelerators. The presence of quantum vortices in He II attenuates second sound waves and influences heat transfer. Consequently, a comprehensive understanding of the attenuation of second sound waves by quantum vortices is pivotal for comprehending heat transfer in He II and can also aid in identifying surface defects in superconducting resonators. To address this, we devised and constructed an interferometry-based test bed for visualizing second sound waves. He II is procured by depressurizing liquid helium in a tank, which is connected at its base to a square stainless steel channel. Two viewports are positioned in the middle of the channel, while corresponding viewports are provided in the outer cavity, allowing the passage of a laser through the He II. At the channel’s base, a heater induces the production of second sound waves and quantum vortices in He II through thermal drive. Utilizing the M-Z interference method, object light traverses He II via the viewports and interferes with reference light, producing interference fringes that are captured by a high-speed camera. A heating pulse from the heater generates second sound waves in the He II, transmitting temperature fluctuations to the viewports and causing distortion of the interference fringes. Through this process, we have successfully obtained clear interferometric images of second sound waves, represented by deformed interferometric fringes. By comparing these with the undeformed fringes, we have inverted the information regarding the temperature field in the imaged region. We also conducted a one-dimensional simulation of the channel and compared it with the experimental results, showing a good consistency between the two.
| Submitters Country | China |
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