The types of the oscillations of very low temperature circulation systems are reviewed. Despite the considerable success of the techniques which were developed in '60s to analyse the dynamical and transient behaviors of cryogenic systems, the incompetence thereof to predict exactly the modes of oscillations and instabilities of the He systems operated around the critical point now becomes gradually aparent. The chief aim of this review is to clarify where they fail and suggest how we can save them. The evidences which show the abnormally swift diffusion of enthalpy along supercritical He channels are presented. The relationship between oscillation modes and inhomogenuities of temperature, density and velocity of He coolant is stressed.
This paper continues from part-1 to study on the cooling of superconducting magnets by the use of He II. In this part, the fact that the cooling efficiency in He II increases drastically by pressurizing the liquid is illustrated by examples. We also give examples in which the performances of magnet quenching currents and minimum propagating currents were improved by He II. On the other hand, we envisage several problems of instability on the lowered temperature region, such as the Kapitza resistance between the stabilizing material and the superconductor, and the a.c. loss caused by increased magnetization. The demerits, however, are probably overcome by the excellent cooling abilities of He II, especially of the pressurized He II. Finally, basic ideas of conceptual designs of superconducting troidal field coils in Torus II Supra (France) and NUMAK (U.S.A.) projects are introduced focusing on the cooling manner by means of the subcooled He II at 1.8K.