Abstract: A .sup.3 He-.sup.4 He dilution refrigerator comprises an upper mixing chamber for mixing liquid concentrated .sup.3 He and superfluid .sup.4 He, and a lower segregating chamber for separating concentrated .sup.3 He and superfluid .sup.4 He. An auxiliary chamber is situated between the mixing chamber and the segregating chamber. A connecting duct extends between the segregating chamber and the auxiliary chamber. The upper part of the auxiliary chamber communicates with the upper part of the mixing chamber for flow of concentrated .sup.3 He into the latter; and the lower part of the auxiliary chamber communicates with the lower part of the mixing chamber for flow of dilute .sup.3 He to the lower part of the auxiliary chamber.

Abstract: .sup.3 He-.sup.4 He refrigerator in which superfluid .sup.4 He is circulated by a thermomechanical pumping device which is based on the fountain pump effect and which is constructed from several series-arranged fountain pumps.

Abstract: A superleak in which a heat exchanger having a superleak structure is included in order to drastically reduce heat leak in the flow direction during operation.

Abstract: A .sup.3 He-.sup.4 He dilution refrigerator is provided with two interconnected mixing chambers arranged at different levels. One end of a superleak opens into concentrated .sup.3 He contained in the upper mixing chamber, while the other end opens into a portion of the apparatus containing dilute .sup.3 He for the supply of superfluid .sup.4 He, via the superleak, to the upper mixing chamber under the influence of the osmotic differential pressure prevailing across the superleak.