Producing Towed Grid Quantum Turbulence in Liquid He

• Published in: Journal of low temperature physics 2007-08, Vol.148 (3-4), p.281-285
• Main Authors: Liu, Shu-chen, Labbe, Greg, Ihas, Gary G
• Format: Article
• Language: English
• ISSN: 0022-2291
• DOI: 10.1007/s10909-007-9381-2

To produce turbulence in a pure quantum liquid, a superconducting linear motor has been built to tow a grid through a channel of superfluid helium at 20 mK. The design was developed using a computer simulation which considered the critical aspects of the cryogenic and electrical environment. This resulted in a single superconducting solenoid motor with an armature moving through its center. This light insulating armature is constructed of 3 phenolic tubes separated by two hollow cylindrical niobium cans placed 26 mm apart, with the turbulence-producing grid attached to one end. A conducting section on the armature, composed of one of the Nb cylinders and silver paint coating part of the phenolic rod, is inside a closely fitting capacitor made of two semi-cylindrical copper sheets. This capacitor, coupled to a bridge circuit, measures the armature position. When driven with the properly shaped current pulse (also determined by simulation), a magnetic field is produced that accelerates the rod (and grid) quickly, moves the rod and grid at near constant speed for at least 10 mm, and then quickly decelerates it. With LabView, complex pulse shapes are applied to the superconducting solenoid to produce the desired motion. The decay of turbulence is detected by the calorimetry technique in the isolated cell after the grid is pulled. Results of tests at 4.2 K (normal, classical liquid) and in superfluid down to 1.3 K, show that the motor preforms adequately in this temperature regime.