Shu-chen Liu

Quantum Turbulence:decay of Grid Turbulence in a Dissipationless Fluid: Kelvin Wave Cascade Theory, Magnetically Shielded Superconducting Linear Motor, Superfluid Helium-4 and Calorimetry Technique Shu-chen Liu

QUANTUM TURBULENCE : DECAY OF GRID TURBULENCE IN A DISSIPATIONLESS FLUID We produced grid turbulence in liquid helium at 520 mK to compare with classical experiments and theories. Above T = 1 K, with viscosity present, it has been shown that grid turbulence is equivalent to homogeneous isotropic turbulence in a classical fluid. We seek to investigate the nature of grid turbulence when viscosity is zero. Specifically, in the absence of viscosity in a quantum fluid, through what path does the turbulence decay? To produce grid turbulence, a magnetically shielded superconducting linear motor was designed and built to accelerate and decelerate the grid rapidly in a short distance (~ 1 mm), and achieve glide speeds up to 1 m/s, when driven with the properly shaped current pulse. We measured the decay of the turbulence produced by calorimetry technique. Recent theory suggests the decay occurs through a Kelvin-wave cascade on the vortex lines which couples the initially large turbulent eddies to the short wavelength phonon spectrum of the liquid, yielding a characteristic rate of temperature rise. Initial measurements support the Kelvin wave cascade theory.