Sphere on a vibrating reed for measurements of turbulence in superfluid helium

A modification of the vibrating reed, in which a massive sphere is made to oscillate at the end of a cantilevered beam, has been used for measurements in superfluid helium. The apparatus operates in the same way as a conventi onal vibrating reed with capacitive detection and drive. However, when oper ating submerged in the liquid, the frequency changes give information on th e superfluid fraction, and the dissipation can be used to obtain informatio n on the change of liquid flow, from laminar to turbulent. The spherical ge ometry allows an exact calculation of all parameters in the laminar regime, so departures due to the turbulence can be better quantified. The method h as been found to work well in practice. and some measurements on the turbul ent regime in the superfluid are presented (C) 2000 Elsevier Science S.A. A ll rights reserved.