Abstract: A pulse tube refrigerator comprising a cold head, wherein the cold head comprises at least one pulse tube (6) and at least one regenerator (7); the cold head having a cold end (8) and a warm end (5), each end being provided with respective heat exchangers (12, 13); wherein refrigerant is supplied (3) to the cold head; and wherein the warm end heat exchanger (13) is provided with a secondary cooling mechanism (16, 17) to improve the efficiency of the PTR.

Abstract: A cryogenic chamber comprising an outer vacuum vessel (9), an inner cryogen vessel (11), a turret (40) housing a neck tube (8) itself providing external access to the inner cryogen vessel (11), and a pulse tube refrigerator (20) itself comprising at least one pulse tube and at least one regenerator tube. The pulse tube refrigerator is located within a vacuum contained between the outer vacuum vessel (9) and the inner cryogen vessel (11) and the pulse tube refrigerator (20) and the neck tube (8) share a single turret (40). The cooling stage(s) (6, 7) of the pulse tube refrigerator (20) is/are rigidly mechanically connected to the neck tube (8) by highly conductive thermal links. The pulse tube(s) and regenerator tube(s) are displaced away from the neck tube and from each other.

Abstract: The present invention relates to pulse tube refrigerators for recondensing cryogenic liquids. In particular, the present invention relates to the same for magnetic resonance imaging systems. In many cryogenic applications components, e.g. superconducting coils for magnetic resonance imaging (mri), superconducting transformers, generators, electronics, are cooled by keeping them in contact with a volume of liquified gases (e.g. helium, neon, nitrogen, argon, methane). In a first aspect, the present invention provides a pulse tube refrigerator PTR pulse tube refrigerator (PTR) arrangement within a cryogenic apparatus, wherein a regenerator tube of the PTR is finned. In this configuration the fins or baffles, are believed to increase the surface area available for distributed heat transfer from the helium atmosphere to the regenerator.

Abstract: A pulse tube refrigerator system comprises a pulse tube refrigerator and a compressor coupled together via a high pressure line and a low pressure line. Cryogenic fluid is transferred to the PTR via the high pressure line and returned to the compressor via the low pressure line. The system further comprises an acoustic tuning device coupled to the low pressure line between a low pressure output from the PTr and a lower pressure input to the compressor, such that noise and vibration in the PTR system are reduced.

Abstract: A multiple port rotary valve for flow switching comprises a rotor (2), a stator (7), a compressor supply (8) and a compressor return (6). Gas is supplied via the compressor supply throughout a switching cycle such that the rotor is lifted away from the stator (7). The valve further comprises a balance ram to counteract the effect of the differential pressure produced by the compressor supply, such that a gas seal is formed at the rotor/stator interface.

Abstract: An active shield magnet has a plurality of screening coils which each have a small number of turns in comparison with the number of turns of the main magnet coil assemblies and which are connected in series in a closed loop to reduce the effect of disturbing influences in a working volume of the magnet.

Abstract: A magnet assembly suitable for use in magnetic resonance imaging has a first superconducting coil assembly for generating a first magnetic field and a second superconducting coil assembly for generating a second magnetic field. The first and second superconducting coil assemblies are connected in series and each generate magnetic fields whose corresponding components are of substantially the same order of magnitude. The assemblies are arranged so that a resultant, uniform magnetic field is generated in a working volume, and the second magnetic field substantially opposes the first magnetic field externally of the magnet assembly. The resultant magnetic field prevailing externally of the magnet assembly is maintained within preset limits during normal operation of the assembly in which the current in the superconducting coils is substantially constant.