Varian, Inc.

Alexander M J Hudson

Knut G Mehr

Thomas M Barbara

Sean T Burns

Atholl A V Gibson

According to some embodiments, low-temperature (cryogenic) nuclear magnetic resonance (NMR) probe fixed capacitors include thermally-conductive dielectric layers serving to thermally connect the capacitors to a cryogenic heat sink. For example, a sapphire layer may be metalized on opposite sides to form copper capacitor plates, and along an edge to form a copper heat sink contact. Heat generated by RF currents during an operation of an NMR circuit including such a capacitor is discharged through the thermally-conductive dielectric to the heat sink. Cooling cold-probe circuit components such as capacitors through thermally-conductive capacitor dielectrics allows reducing perturbations introduced into the circuit by components such as heat sinks.

Cryogenic NMR probe capacitors with dielectric heat sinks

The vacuum properties of a cryogenic NMR probe maintained at a desired operating temperature by a cold head heat exchanger are improved by a separate heat exchanger operating below the temperature of the cold head heat exchanger for maintaining cryo-pumping surfaces at a temperature below said selected operating temperature.

Efficiently cryo-pumped NMR cryogenic probe

The thermal performance and vacuum properties of a cryogenic NMR probe are improved when thermal control is implemented by conductive heat transfer to a cold head cooled by a heat exchanger to below the selected operating temperature. The heat load is manipulated by locating a heater to produce a more nearly constant heat load in conjunction with pulsed RF power and in one embodiment transferring such heater power through a common thermal path. In another embodiment, the heater power is conductively transferred directly to the heat exchanger.

Cryogenic NMR probe

According to one aspect, the low-frequency (e.g. lock channel) performance of a nuclear magnetic resonance (NMR) saddle-shaped, distributed-capacitance radio-frequency (RF) coil is improved by connecting a pair of auxiliary inductors across a plurality of leads extending upward from the coil upper ring. The upward-extending leads can be formed from the same foil as a main coil structure. The auxiliary inductors are separated from the coil window, so that magnetic susceptibility discontinuities introduced by the auxiliary inductors can be compensated for. In one embodiment, two half-toroid auxiliary inductors are positioned to form a full toroid shape. Some lost high-frequency performance can be recovered by using a split capacitance band positioned over the lower coil ring. The split capacitance band allows capacitance tuning while maintaining an RF current path close to the coil window.

NMR RF coils with improved low-frequency efficiency

A split capacitance-tuning band of a nuclear magnetic resonance (NMR) distributed-capacitance radio-frequency (RF) coil includes a fixed band and a longitudinally-movable (sliding) band, both disposed to overlap a central coil structure. The fixed band is situated along the boundary of the RF coil window. The movable band can move between a proximal position abutting the fixed band and various distal positions. The fixed band provides an RF current path close to the RF coil window, while the movable band allows tuning the coil capacitance and resonance frequency by varying the area of overlap between the movable band and the central coil structure. A longitudinal coupling member is attached to the movable band and to an actuator piston disposed under a probe lower insulator. A chip capacitor is connected between the coupling member and the actuator piston, to provide RF insulation for the movable capacitance band.

Growing community of inventors

Palo Alto, CA, United States of America

Alexander M J Hudson