The object of this paper is to show a brief review of superconducting LINAC. Characteristics of super-LINAC, results of cavity experiments, and present status of some projects for constructing the super-LINAC are given. Basic parameters for design and construction are also briefly discussed.
Following the brief description of the basic principles of dilution cooling briefly, recent developments of dilution refrigeration are reviewed. In order to realize the idea of dilution refrigeration as perfectly as possible, following factors are important; to make the efficient heat exchangers which have low flow-impedance and small thermal boundary resistance, to reduce the amount of He4 in the circulating He3 and to eliminate heat input into the mixing chamber, especially vibration of the cryostat originating in mechanical pumps. Three types of heat exchangers-continuous or tube-in-tube heat exchanger, sintered copper heat exchanger and copper foil heat exchanger are described. Almost pure He3 can be circulated by use of the novel design of still which suppresses the He4 film-flow. The lowest temperature which has been achieved so far by the dilution refrigerator is 5.5mK in the continuous operation and 4.5mK in the singlecycle operation. This value is very close to the theoretical limiting temperature of the dilution refrigerator. Experiments which combine the continuous dilution refrigeration with the adiabatic demagnetization and the adiabatic compression of He3 are also presented.
A 1kW refrigerator-liquefier for the Japanese Hydrogen Bubble Chamber was constructed and test operations with the chamber have been carried out for three times. In the first run, the refrigerator-liquefier which is Simple Linde type was confirmed that it could afford about 60 liters of liquid hydrogen per hour or the equivalent refrigerant. In the later two runs, the bubble chamber was cooled down to the liquid hydrogen temperature at the rate of less than 5°K per hour and filled up with 220 liters of liquid hydrogen. Many bubble chamber photographs were taken under the various thermodynamical conditions. An automatic bubble chamber temperature control system which regulates the direct two-phase hydrogen flow from the refrigerator-liquefier is now under testing.