MAS probehead with a thermally insulated sample chamber
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 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 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.
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 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 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 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 1 spatially separated from the gas stream at the second variable temperature T 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 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 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 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 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 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 1 between −120° C. and 400° C.; and
maintaining the pressurized gas stream at the second variable temperature T 2 between 10° C. and 30° C.