Abstract: A dilution refrigerator includes a still; a mixing chamber; a pump to pump coolant from the still through a still outlet port and a heat exchanger connected between the still and mixing chamber whereby coolant flows under the assistance of the pump from the still to the mixing chamber and from the mixing chamber to the still through respective first and second adjacent paths in the heat exchanger. An access path extends to the mixing chamber. A probe is provided for insertion along the access path, the probe having a displacer which substantially fills the cross-section of the access path in use. Any coolant from the mixing chamber which flows along the access path past the displacer can flow from the access path into the still. The still outlet port is separate from the access path.

Abstract: An apparatus employing a method for measuring the temperature of a sensor (Rx) having a resistance which varies in accordance with the temperature of the sensor, using a switching sequence to apply a parasitic voltage correction signal to the input of an amplifier in the measurement circuit whereby the sensor generates an offset response signal which is amplified and adjusted to substantially minimize the amplified offset response signal. The temperature of the sensor is calculated from the amplified response signal in accordance with a predetermined algorithm.

Abstract: An rf magnetic field pulse generator for generating a pulse train comprising a plurality of rf magnetic field pulses for use in an NMR investigation, the generator comprising(i) an amplifier (5) for generating an rf signal, the amplifier having an input for receiving a supply voltage;(ii) a transmitter coil (42) connected to an output of the amplifier, the transmitter coil being adapted to transmit the rf magnetic field pulses in response to the rf signal;(iii) a switched voltage regulator (4) for regulating the supply voltage by charging a local storage capacitor; and(iv) a controller (13) for causing the switched voltage regulator to charge the local storage capacitor only when a magnetic field pulse is not being transmitted.

Abstract: A refrigerator for cooling a sample (16,17) comprising a reservoir (1) for storing gaseous .sup.4 He when in use; a cooler (13) for cooling gaseous .sup.4 He from the reservoir; and a helium vessel (18,19) for containing .sup.4 He, the .sup.4 He in the helium vessel being in fluid communication with the reservoir (1) via the cooler (13). The sample (16,17) is mounted, in use, in thermal contact with the .sup.4 He in the helium vessel whereby the .sup.4 He in the helium vessel provides a path for heat to transfer from the sample to the cooler.

Abstract: An rf coil assembly for use in an NMR investigation, the assembly comprising(1) a transmitter coil (10) adapted to transmit an rf magnetic field suitable for the NMR investigation into a working region and comprising a plurality of serially connected winding elements (1-4); and(2) a receiver coil (9) electrically separate from the transmitter coil and adapted to receive an rf signal from the working region and comprising a plurality of serially connected winding elements (5-9).Winding elements of one coil are interleaved and substantially coaxial with winding elements of the other coil, and at least one of the coils comprises one or more winding elements which are counter-wound with respect to the other winding element(s) in the coil.

Abstract: A refrigerator for cooling a sample comprises a container for holding liquid helium refrigerant to cool the sample. First cooling means is provided for cooling a condensation region with liquid helium coolant whereby helium refrigerant condenses on the condensation region and collects in the container. A sorption pump pumps gaseous helium refrigerant from the container. Second cooling means is provided for cooling the sorption pump with the liquid helium coolant. The first and second cooling means are connected in series with a source of the liquid helium coolant.

Abstract: A proof mass support system has a pair of alignment coils for controlling the rest position of an elongate proof mass. The alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of the proof mass. The relative strength of the electric currents are tuned in the alignment coils to cause the proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by the alignment coils. In an alternative, one or more anti-rotation coils may be arranged to apply a restoring force to the proof mass when electric currents pass therethrough. The proof mass is formed so as to cooperate with the restoring force which acts against rotation of the proof mass away from a predetermined orientation. The system is typically provided as part of a superconducting accelerometer or gravity gradiometer.

Abstract: A magnetic field generating assembly for use in NMR apparatus comprises a pair of first magnets arranged coaxially with like poles facing each other and axially spaced apart. At least one second magnet is positioned between the first magnets and with its axis coaxial with the first magnets. The axial positions and strengths of the magnets are arranged such that a working region is defined radially spaced from the magnets and extending substantially parallel with the axis of the magnets. The magnetic field within the working region is suitable for obtaining NMR information from material in the working region and exhibits a radial gradient which is substantially uniform in the axial direction.

Abstract: A proof mass support system has a pair of alignment coils for controlling the rest position of an elongate proof mass. The alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of the proof mass. The relative strength of the electric currents are tuned in the alignment coils to cause the proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by the alignment coils. In an alternative, one or more anti-rotation coils may be arranged to apply a restoring force to the proof mass when electric currents pass therethrough. The proof mass is formed so as to cooperate with the restoring force which acts against rotation of the proof mass away from a predetermined orientation. The system is typically provided as part of a superconducing accelerometer or gravity gradiometer.

Abstract: A sample holding device (30) for a dilution refrigerator having a still (16), a mixing chamber (22), and a heat exchanger (26) connected between the still and mixing chamber whereby coolant flows from the still to the mixing chamber and from the mixing chamber to the still through respective first and second adjacent paths in the heat exchanger and wherein the mixing chamber has a tubular portion (27), the sample holding device comprising a tube for insertion in the tubular portion of the mixing chamber and having means (34) for holding a sample within the tubular portion, the tube having an aperture (36) adjacent the sample holding means communicating in use between the interior of the tube and the interior of the tubular portion and another aperture (37) positioned in use to communicate between the interior of the tube and the second path in the heat exchanger.

Abstract: A magnetic field generating assembly having at least two magnetic fields in the same sense. The generators are arranged such that, in use in a working region external to the generators, the resultant magnetic field exhibits a gradient extending in a first direction and at least second order variations in the fields in directions transverse to the first direction within the working region are substantially balanced such that an NMR experiment can be performed on a sample within the working region in accordance with the related method. The magnetic electrical field generators are substantially coaxial electrical coils, wherein the axis extends in the first direction.