WO1998030917B1

WO1998030917B1 - Thermal buffering of cross-coils in high-power nmr decoupling

Info

Publication number: WO1998030917B1
Application number: PCT/US1997/023645
Authority: WO
Filing date: 1997-12-19
Publication date: 1998-10-08

Abstract

A transverse rf saddle coil (30) for use in NMR is affixed in intimate thermal contact on one surface of a ceramic coilform (23) of high thermal conductivity. The probe is mostly for use with solid samples at high fields where the axis of the coilform is not aligned with the main field. An orthogonal rf coil (1) is mounted in intimate thermal contact to the first saddle coil (30) via a ceramic spacer or coilform (2). The coilform is cooled by high-velocity gas flow and is also often associated with bearing exhaust gas from a high speed sample spinner. The two coils are tuned to different rf frequencies with circuits capable of supporting high rf currents. The rf coils (30, 1) may be magnetically compensated and expansion controlled, and passive geometric compensation of magnetic susceptibility effects from a sample spinner stator may also be incorporated. Novel coil mounting techniques, including metallurgical bonds to ceramics and capturing by dielectric clam-shells, are also disclosed.

Claims

AMENDED CLAIMS

[received by the International Bureau on 14 August 1998 (14.08.98); original claims 1, 17 and 28 amended; original claims 4, 20 and 31 cancelled; remaining claims unchanged (4 pages)]

1. An NMR probe for use in an external field B₀, said probe comprising: a cylindrical ceramic coilform not in fixed alignment parallel to said B₀, a dipolar transverse rf coil affixed in thermal contact with the inside of said coilform, a second rf coil mounted on the outside of said coilform, rf tuning capacitors and coupling means connected to said rf coils, said rf coils further characterized as having essentially zero mutual inductance, said thermal contact further characterized as having thermal conduction greater than 4,000 W/m²K, said coilform further characterized as comprised substantially of silicon nitride, magnesia, alumina, zirconia, forsterite, or beryllia, said rf coupling means further characterized as capable of supporting rf currents in at least one of said rf tuning capacitors in excess of 2 amperes at resonance.

2. An NMR probe as in 1 in which said coilform is also a portion of a high-speed sample spinner.

3. An NMR probe as in 1 in which one of said rf coils is a solenoid.

5. An NMR probe as in 1 wherein said first coil is capacitively segmented and includes at least four chip capacitors for tuning and segmenting.

6. An NMR probe as in 1 wherein said first coil comprises substantially an A-B-A

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15. An NMR probe as in 7 wherein said conductor pattern is plated first with a compensating metal and then with copper or silver, where said compensating metal is an alloy comprised primarily of one or more from the following: W, Ir, Re, Mo, Rh, Hf.

16. An NMR probe as in 11 in which said transverse rf coil is a capacitively segmented coil capable of generating uniform rf magnetic field transverse to the axis of said coilform, said second coil is a solenoid, said coilform is further characterized as comprised substantially of silicon nitride, and said sample spinner is further characterized as comprising two parallel gas supply tubes on opposite sides of said coilform.

17. An NMR probe for use in an external field B₀, said probe comprising: a cylindrical ceramic coilform, a transverse rf coil in intimate thermal contact with the outside of said coilform, said transverse coil further characterized as including at least four chip capacitors for tuning and segmenting, a cylindrical dielectric spacer in thermal contact with the outside of said transverse rf coil, a second rf coil in thermal contact with the outside of said spacer, rf tuning capacitors and coupling means connected to said rf coils, said rf coils further characterized as having essentially zero mutual inductance, said coilform further characterized as comprised substantially of silicon nitride, magnesia, alumina, zirconia, forsterite, or beryllia, at least one of said rf tuning capacitors further characterized as capable of supporting rf currents in excess of 2 amperes at resonance.

18. An NMR probe as in 17 in which said coilform is also a portion of a sample spinner.

19. An NMR probe as in 17 in which said second rf coil is a solenoid.

21. An NMR probe as in 17 wherein said first coil comprises substantially an A-B-A sandwich, where A represents either Ag or Cu, and B represents a copper-based alloy containing at least 4% nickel, not more than 0.05% (Fe+Mn), and at least 0.5% additional alloying content from the following set: Al, Cr, Mo, Nb, Re, Ta, Ti, Si, Sn, V, W.

22. An NMR probe as in 17 in which said dielectric spacer is further characterized as a ceramic clamshell.

23. An NMR probe as in 22 in which said second rf coil is metallurgically bonded to said clamshell spacer at more than one point.

24. An NMR probe as in 17 further characterized as comprising a third rf coil electrically isolated from said second rf coil via a second cylindrical dielectric spacer, said third rf coil having essentially zero mutual inductance to said transverse and second rf coils.

25. An NMR probe as in 18 wherein said sample spinner may be aligned at various angles with respect to said B₀.

26. An NMR probe as in 25 wherein said sample spinner is further characterized as comprising bearing compensation rings having positive magnetic susceptibility greater than 30 ppm SI volumetric units.

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27. An NMR probe as in 26 in which said transverse rf coil is a capacitively segmented coil capable of generating uniform rf magnetic field transverse to the axis of said coilform, said second rf coil is a solenoid, said coilform is further characterized as comprised substantially of silicon nitride, and said sample spinner is further characterized as comprising two parallel gas supply tubes on opposite sides of said coilform.

28. A clad rf coil wire for use on a ceramic or glass coilform, said wire comprising: a core wire and a highly conductive thick cladding, said core wire further characterized as comprised substantially of one or more from the following: W, Ir, Re, said cladding further characterized as comprised substantially of copper or silver, having thickness greater than 0.1 mm but less than 1 mm, and being bonded to said core, said rf coil wire further characterized as having a ratio of thick cladding to core mass per unit length such that the bulk magnetization of said coil is substantially less than that of pure copper.

29. A coil wire as in 28 wherein said core wire contains less than 30% but not less than 3% rhenium with the balance being substantially tungsten.

30. A coil wire as in 29 wherein said thick cladding is protected with an oxidation- resistant plating less than 1.0 micron thick.

32. An NMR probe for use in an external field B₀, said probe comprising: a generally cylindrical ceramic coilform surface, thin patches of active braze alloy chemically bonded to said surface,

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