Emerging issues in helium turbulence

It has been appreciated recently that because helium has the lowest viscosity of any known material, it can be used in reaching the very highest Reynolds numbers and Rayleigh numbers. Critical helium gas, helium I and helium II are all candidates for such uses. Helium gas and helium I are classical fluids and the advantage stems solely from their low kinematic viscosity. Helium II obeys two-fluid equations and their use in turbulence investigations is under study. This article provides a brief introduction and review of this topic, outlining some of the progress already made and questions which need to be resolved as this relatively new field of investigation evolves. A summary of instrumentation available is included