Abstract: An insulated dual-bayonet connector is provided. The connector provides simple alignment and connection for both fluid tubes of a fluid recirculation system. The connector is especially useful for closed-cycle systems, but is also useful for open-cycle gas systems where it is desired to vent a gas in a desired location remote from the item to be cooled or heated by the gas.

Abstract: Inhomogeneities in the magnetic field in the vicinity of a superconducting NMR receiver coil are avoided by placing the probe, at about room temperature, within the magnetic field, cooling rapidly to just above the critical temperature of the superconductor and then controllably cooling the coil to operating temperature at a rate of 3 K./minute or less.

Abstract: A resonant coil for nuclear magnetic spectroscopy and microscopy is provided, in which the coil is in the form of nested, interrupted loops of a conductive material forming a distributed inductive element and having a plurality of capacitive elements with capacitance distributed over the periphery of the loops. The coil is preferably formed as a thin film of a superconductive material on an electrically nonconductive substrate.

Abstract: A cryogenic refrigerator cools a heat source by cyclically concentrating and diluting the amount of .sup.3 He in a single phase .sup.3 He-.sup.4 He solution. The .sup.3 He in superfluid .sup.4 He acts in a manner of an ideal gas in a vacuum. Thus, refrigeration is obtained using any conventional thermal cycle, but preferably a Stirling or Carnot cycle. A single phase solution of liquid .sup.3 He at an initial concentration in superfluid .sup.4 He is contained in a first variable volume connected to a second variable volume through a superleak device that enables free passage of .sup.4 He while restricting passage of .sup.3 He. The .sup.3 He is compressed (concentrated) and expanded (diluted) in a phased manner to carry out the selected thermal cycle to remove heat from the heat load for cooling below 1 K.