1. G. Horlitz, Refrigeration of a 6.4 km circumference, 4.5 tesla superconducting magnet ring system for the electron proton collider HERA, in: “Proc. Tenth Intl. Cryo. Engr. Conf.”, Butterworth, Guildford, UK (1984) p. 377.
2. C. Trepp, Refrigeration systems for temperatures below 25 K with turboexpanders, in: “Advances in Cryogenic Engineering,” Vol. 7 Plenum Press, New York (1962) p. 251.
3. P. Grassmann, “Physikalische Grundlagen der Verfahrenstechnik”, Sauerlander, Aarau (1970) p. 142.