Initial studies of a linear motor for generating quantum turbulence in He-II with a drawn grid

Abstract

Studies of quantum turbulence (QT) require a means of generating well-characterised QT. For systems containing negligible normal fluid density this must be achieved without simultaneously introducing extraneous heating due, for example, to friction between mechanical components. Methods relying on oscillating objects produce negligible extraneous heating, but suffer from the disadvantages of both spatially and temporally nonuniform velocity. In addition, the vibrating grid goes back and forth through the QT it has itself created. Hence the characteristic length scale is subject to uncertainty. We are therefore developing a one-dimensional linear motor to draw a grid steadily, once, through He-II at mK temperatures. Frictionless magnetic bearings are used to levitate the moving elements in contrast to other designs, precluding mechanical dissipation. Details of the design and of the initial tests, and a quantitative comparison of theoretical and actual cryogenic performance, will be presented and discussed.