MAS probehead with a thermally insulated sample chamber

Abstract

An MAS probehead (1) positioned in a magnet bore (2) includes a sample chamber (3) with a stator (4) for receiving a rotor and an RF coil that radiates RF pulses into and/or receives RF signals from an NMR sample (5). A temperature-control apparatus guides gas at a first variable temperature T.sub.1 into the sample chamber and through the stator during an NMR measurement, and guides a pressurized gas stream at a second variable temperature T.sub.2 around the sample chamber. The sample chamber is surrounded by an encapsulation device (6), at least in the azimuthal direction around the axis of the magnet bore and counter to the flow direction of the pressurized gas, and is oriented to provide an air gap (7′) between the sample chamber and the magnet bore. This prevents dissipation of the gas temperature to outer parts of the probehead, and yields larger NMR measurement temperature ranges.

Claims

1. A magic angle spinning (MAS) probehead, configured for insertion into a magnet bore during operation of a nuclear magnetic resonance magic angle spinning (NMR-MAS) arrangement, comprising: a sample chamber, which comprises an MAS stator for receiving an MAS rotor and a radio frequency (RF) coil that serves to radiate RF pulses into an NMR sample and/or to receive RF signals from the NMR sample, a first gas stream at a first variable temperature T.sub.1 guided into the sample chamber and through the MAS stator during an NMR measurement, for setting the temperature of the NMR sample, and a second, pressurized gas stream at a second variable temperature T.sub.2 guided, simultaneously with the first gas stream, around the sample chamber, and an encapsulation device that surrounds the sample chamber, at least in an azimuthal direction around an axis of the magnet bore and counter to a flow direction of the pressurized gas stream, and that is oriented to form an air gap between the sample chamber and the magnet bore of the NMR-MAS arrangement.

2. The probehead as claimed in claim 1, further comprising electronic components other than the RF coil, that are located outside of the encapsulation device in the region of the pressurized gas stream at the second variable temperature T.sub.2.

3. The probehead as claimed in claim 2, wherein the electronic components comprise all electronic components of the probehead other than the RF coil, and include resonator structures and electric transmission lines.

4. The probehead as claimed in claim 1, further comprising an exhaust gas system, which guides the gas stream at the first variable temperature T.sub.1 spatially separated from the gas stream at the second variable temperature T.sub.2.

5. The probehead as claimed in claim 1, wherein the air gap is arranged in azimuthal circumferential fashion between the sample chamber and the magnet bore and is embodied to pass the pressurized gas at the second variable temperature T.sub.2 within the magnet bore.

6. The probehead as claimed in claim 5, wherein the encapsulation device and the magnet bore each have respective cylindrical forms with parallel cylinder axes, and wherein the air gap between the encapsulation device and the magnet bore is circumferentially uniform in cross section.

7. The probehead as claimed in claim 1, wherein the magnet bore extends in an axial direction, and wherein the air gap between the sample chamber and the magnet bore, for guiding the pressurized gas stream at the second variable temperature T.sub.2 radially narrows in the axial direction of the magnet bore, in an axial region of the sample chamber.

8. The probehead as claimed in claim 1, wherein the air gap between the sample chamber and the magnet bore for guiding the pressurized gas stream at the second variable temperature T.sub.2 is configured for a gas flow with a gas quantity of 2 to 50 standard liter/min.

9. The probehead as claimed in claim 1, further comprising a shielding tube surrounding the MAS stator and made of electrically conductive material for shielding against RF radiation, wherein the encapsulation device is located within the shielding tube such that the gas flow with the pressurized gas stream at the second variable temperature T.sub.2 is guided outside of the sample chamber, through an air gap between the encapsulation device and the shielding tube.

10. The probehead as claimed in claim 4, wherein the exhaust gas system extends a distance s from the MAS stator into the magnet bore, and wherein the distance s is greater than a maximum external diameter of the MAS stator.

11. The probehead as claimed in claim 10, wherein the gas flows emerging from the sample chamber are guided in thermal isolation from one another along at least a part of the distance s.

12. The probehead as claimed in claim 4, wherein the exhaust gas system is embodied to heat and/or to cool the gas flows emerging from the sample chamber.

13. The probehead as claimed in claim 12, further comprising a heating or cooling device provided in a part of the exhaust gas system distant from the MAS stator, wherein the heating or cooling device heats or cools the gas flows emerging from the sample chamber.

14. The probehead as claimed in claim 13, wherein the heating or cooling device comprises an electric heating coil or a heat exchanger configured to heat or cool gas flows emerging from the sample chamber at variable temperature T.sub.1.

15. The probehead as claimed in claim 4, further comprising a transfer system connected downstream from the exhaust gas system, such that the exhaust gas flows are guided separately from one another into the transfer system.

16. The probehead as claimed in claim 15, wherein the transfer system is configured to guide the exhaust gas flows up to a mixing chamber.

17. A method for operating an nuclear magnetic resonance (NMR) magic angle spinning (MAS) arrangement with an MAS probehead as claimed in claim 1, comprising: maintaining a temperature of the gas stream at the first variable temperature T.sub.1 between −120° C. and 400° C.; and maintaining the pressurized gas stream at the second variable temperature T.sub.2 between 10° C. and 30° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated in the drawing and will be explained in more detail on the basis of exemplary embodiments.

(2) In detail:

(3) FIG. 1 shows a very schematic vertical sectional illustration of an embodiment of the MAS probehead according to the invention with an RF shielding tube; and

(4) FIG. 2 shows a similar embodiment to FIG. 1, but without an RF shielding tube.

DETAILED DESCRIPTION

(5) The present invention considers a specifically modified probehead for an NMR spectrometer, in particular for MAS applications, in which a spatial separation, and hence also, especially, a thermal separation, of the sample chamber from temperature-sensitive assemblies outside of said chamber is obtained.

(6) The figures of the drawing, which have been kept schematic for the sake of clarity, each show a vertical sectional plane of an MAS probehead 1 according to the invention, for insertion into a magnet bore of an NMR magnet system which, just like the NMR spectrometer, is not illustrated in more detail in the drawing.

(7) During operation, the probehead 1 is disposed in a magnet bore 2 of an NMR-MAS arrangement and comprises a sample chamber 3, which contains an MAS stator 4 for receiving an MAS rotor and an RF coil that serves to radiate RF pulses into an NMR sample 5, which is situated within an MAS rotor, and/or to receive RF signals from the NMR sample 5. Additionally, channels for streams of gas providing temperature-controlled gas flows (designated herein also simply as a temperature-control apparatus) are present in order to guide gas at a first variable temperature T1 into the sample chamber 3 and through the MAS stator 4 during an NMR measurement so as to set the temperature of the NMR sample 5 and in order to simultaneously guide pressurized gas at a second variable temperature T2 around the sample chamber 3.

(8) According to the invention, the NMR probehead 1 is distinguished in relation to the known prior art in that the sample chamber 3 is surrounded by an encapsulation device 6, at least in the azimuthal direction around the axis of the magnet bore 2 and counter to the flow direction of the pressurized gas, and is disposed such that an air gap 7 is present between the sample chamber 3 and the magnet bore 2 of the NMR-MAS arrangement.

(9) In the embodiment according to FIG. 1, the MAS stator 4 is surrounded by a shielding tube 9 made of electrically conductive material for shielding against RF radiation. Here, the encapsulation device 6 is disposed within the shielding tube 9 so that the gas flow of the pressurized gas at the second variable temperature T.sub.2 is guided outside of the sample chamber 3 and through an air gap 7′ between the encapsulation device 6 and the shielding tube 9—and hence also between the sample chamber 3 and the magnet bore 2.

(10) The slightly simpler embodiment illustrated in FIG. 2 differs from the embodiment according to FIG. 1 in that the shielding tube 9 is omitted in this case. In this embodiment, the function of shielding the sample chamber 3 from external RF radiation and also of shielding the outside from the radiation in the sample chamber 3 produced by the RF coils is substantially implemented by the magnet bore 2. Therefore, the air gap 7 extends between the sample chamber 3 and the magnet bore 2.

(11) In both embodiments of the probehead 1 according to the invention illustrated in the drawing, provision is made of an exhaust gas system 8 in each case, the latter guiding the gas flows at the first variable temperature T.sub.1 and at the second variable temperature T.sub.2 from the probehead 1 in spatially separated fashion. The gas flows emerging from the sample chamber 3 are guided in a manner thermally insulated from one another along at least part of the distance s. Moreover, the exhaust gas system 8 is embodied so that the gas flows emerging from the sample chamber 3 can be heated and/or cooled and/or mixed, together or individually, depending on requirements.

(12) A heating or cooling device 10, which may be embodied as an electric heating coil, as a Peltier element or as a heat exchanger and which can be used to heat or cool gas flows emerging from the sample chamber 3, preferably the gas at variable temperature T.sub.1, depending on requirements, is provided in the part of the exhaust gas system 8 distant from the MAS stator 4.

(13) Following the exhaust gas system 8, a transfer system 11 is connected, within which the exhaust gas flows are still guided separate from one another along a distance s, in particular as far as a mixing chamber 12.

(14) A—preferably circumferential—air gap 7; 7′ is situated between the encapsulated sample chamber 3 and the shielding tube 9, an additional gas flow at room temperature being guided in said air gap such that the heat transfer between sample chamber 3 and shielding tube 9 is made more difficult thereby. The air gap 7; 7′ is designed such that the circulating air absorbs the amount of heat dissipated by the sample chamber 3. In the present case, the air gap 7; 7′ is dimensioned in the range of 0.1-1.0 mm. The principle also works for larger or smaller air gaps; what is decisive here is the flow speed at the surface to be subject to temperature control and the maximum/minimum temperature of the surface to be insulated. This narrowing distinguishes the temperature control according to the invention from the prior art, in which flush gases are likewise guided within a shielding tube. However, the flow speed of the flush gas is accelerated by the narrowing and can consequently absorb the heat or coldness of the sample chamber 3 substantially more efficiently. The airflow is approximately 2 to 50 standard liters/min, preferably 10 to 25 standard liters/min. A heat transfer to the shielding tube 9 is therefore almost entirely prevented (thermal insulation).

(15) The figures show how the sample chamber 3 is encapsulated and how the flush gas flows around the chamber.

(16) Both the gas flow at the first variable temperature T.sub.1 and the gas flow at the second variable temperature T.sub.2 are guided separately from one another to the outside. Hence, the hot/cold MAS work gases are guided from the sample chamber to the outside in thermally insulated fashion and can be mixed/heated/cooled outside where necessary. The “insulation distance” is therefore also continued above the sample chamber 3 and can, when necessary, be extended upwardly. This measure guides all gases at potentially critical temperature away from the sensitive region within the magnet.

(17) Optionally, a transfer system 11 is connected to the upper probehead interface, said transfer system continuing to guide these separated gas flows in separated fashion until said gas flows can be mixed in a mixing chamber 12 and can be heated when necessary such that the gas mixture flowing out of the probehead 1 only mixes with ambient air outside of the probehead. The transfer system 11 absorbs the gases flowing out of the shielding tube 9 and initially guides these through the HR turbines that are usually installed in spectrometers before said gases are mixed and, where necessary, heated by a heating coil so that the spectrometer does not ice over.

LIST OF REFERENCE SIGNS

(18) 1 NMR probehead 2 Magnet bore 3 Sample chamber 4 MAS stator 5 NMR sample 6 Encapsulation device 7 Air gap between sample chamber and magnet bore 7′ Air gap between probehead and magnet bore 8 Exhaust gas system 9 RF shielding tube 10 Heating or cooling device 11 Transfer system 12 Mixing chamber

LIST OF CITATIONS

Publications Considered for the Assessment of Patentability

(19) [1] U.S. Pat. No. 4,587,492 A [2] US 2010/0026302 A1 [3] US 2015/0048829 A1 [4] US 2005/0122107 A1