  The technical properties of helium II ('superfluid' helium) are presented in
view of its applications to the cooling of superconducting devices,
particularly in particle accelerators. Cooling schemes are discussed in terms
of heat transfer performance and limitations. Large-capacity refrigeration
techniques below 2 K are reviewed, with regard to thermodynamic cycles as well
as process machinery. Examples drawn from existing or planned projects
illustrate the presentation. Keywords: superfluid helium, cryogenics
