In the near future, expanding demand on electric power of the metropolis will force us to introduce very high density energy transport systems of considerable distance because appropriate site for GW class power plant is now quite limited and only found in a furtherest corner of the main land. This article discusses some engineering problems on refrigeration of expected superconducting or cryoresistive cables. With the present status of fidelity of cryogenic machineries in mind, we did not try to get the optimum values for main parameters of cooling pipes in haste, for instance, diameter, mass flow rate, distance between refrigerating plants and so on. The stresses are put on the points that technical restrictions from first stage cooling-down and safeguard design against faults of coupled system of cryogen and electric power are the main factors to determine the size of the cooling pipe. The main issue is to select out the best combination of conductor, cryogen and phase of the cryogen. Usage on two phase flow is limited to the pipes of less than 1-km length. Comparison between supercritical and sub-cooled flow is a delicate one because cooling abilities of both is approximately the same, but sub-cooled flow is the choice in respect of local thermal stability. Several rough sketches for the long range refrigerating systems are put forth in the article. In view of thermal stability, there exists a dilemma, that is, if we adopt two phase flow, systems are locally more stable but put in hazard in its full length operation. A design to reconciliate this dilemma is presented.
Superconducting apparatus which are used or to be used in High Energy Physics are reviewed. Large superconducting dc magnets in the world are tabulated with their main parameters. Special features on each magnet are discussed. Superconducting quadrupole magnets and bending magnets which are intended to use in real high energy beam lines are also discussed. A brief description on the problems in applications of ac superconductivity such as accelerator magnets is given. In the final section, a prospect of use of such superconducting apparatus in High Energy Physics of Japan is also given.