NMR spectrometer with refrigerator cooling
An NMR spectrometer comprising an NMR magnet system ( 27 ) disposed in a helium tank of a cryostat and an NMR probe head ( 11 ) disposed in a room temperature bore of the cryostat, which contains a cooled RF resonator ( 9 ) for receiving NMR signals from a sample to be investigated, and a cooled pre-amplifier ( 10 ), wherein the NMR probe head ( 11 ) is cooled by a common multi-stage compressor-operated refrigerator ( 2 ), wherein the refrigerator ( 2 ) comprises a cold head and several heat exchangers ( 5, 6 ) at different temperature levels, wherein the refrigerator ( 2 ) is disposed at a spatial separation from the cryostat in a separate, evacuated and thermally insulated housing ( 1 ) and wherein at least one cooling circuit with cooling lines, which are thermally insulated by a transfer line ( 13, 14 ) is disposed between the housing ( 1 ) containing the heat exchangers ( 5, 6 ) and the NMR probe head ( 11 ), is characterized in that additional cooling lines to an LN 2 tank ( 18 ) or radiation shield ( 21 ) disposed in the cryostat and surrounding the helium tank are provided, and the refrigerator ( 2 ) also cools the LN 2 tank ( 18 ) or the radiation shield ( 21 ). The inventive NMR spectrometer comprises a simple and inexpensive device for matching the holding time of LN 2 to that of LHe through cooling the LN 2 tank using the refrigerator provided for cooling the NMR probe head and without great expense.
1. An NMR spectrometer for investigating a sample, the spectrometer comprising:
a cryostat having a room temperature bore;
a helium tank disposed in said cryostat;
an NMR magnet system disposed in said helium tank;
an NMR probe head disposed in said room temperature bore, said probe head having a cooled RF resonator for receiving NMR signals from the sample and a cooled pre-amplifier;
an evacuacted and thermally insulated housing disposed outside of said cryostat;
a multi-stage compressor-operated refrigerator disposed in said housing, said refrigerator having a cold head and several heat exchangers at different temperatures;
a least one cooling circuit having first cooling lines communicating with said refrigerator and communicating with said probe head to cool said probe head with said refrigerator;
at least one transfer line, disposed between said housing and said probe head and structured to thermally insulate said cooling lines;
a LN 2 tank or radiation shield disposed in said cryostat and surrounding said helium tank; and
second cooling lines communicating with said refrigerator and said helium tank or radiation shield by means of which said refrigerator cools said LN 2 tank or radiation shield.
2. The NMR spectrometer of claim 1 , wherein-said refrigerator cools said LN 2 tank or radiation shield but does not cool said helium tank.
3. The NMR spectrometer of claim 1 , wherein said first and second cooling lines have a common thermally insulated section within said transfer line which comprises at least 50% of an overall length of said transfer line.
4. The NMR spectrometer of claim 3 , wherein said common section comprises approximately 90% of said overall transfer line length.
5. The NMR spectrometer of claim 3 , wherein cooling lines with a lowest energy level are thermally shielded by at least one cooling line radiation shield at a higher energy level and within said common thermally insulated section.
6. The NMR spectrometer of claim 1 , wherein said transfer line comprises vibration-damping components for decoupling said refrigerator from said NMR probe head or said cryostat.
7. The NMR spectrometer of claim 1 , wherein a cooling circuit is provided between said housing and said cryostat having a return path at a temperature level of approximately 77 K.
8. The NMR spectrometer of claim 1 , wherein two cooling circuits are provided between said housing and said NMR probe head, wherein one cooling circuit thereof has a return path temperature of approximately 77K.
9. The NMR spectrometer of claim 8 , wherein said one cooling circuit at 77 K cools a pre-amplifying electronics in said NMR probe head.
10. The NMR spectrometer of claim 1 , wherein a common cooling circuit is provided between said housing, said cryostat, and said NMR probe head having a return path temperature of approximately 77 K.
11. The NMR spectrometer of claim 10 , wherein said common cooling circuit cools a pre-amplifying electronics in said NMR probe head and said LN 2 tank or radiation shield in said cryostat.
12. The NMR spectrometer of claim 8 , wherein said one cooling circuit is operated with gaseous helium coolant.
13. The NMR spectrometer of claim 1 , wherein a cooling circuit extending between said housing and said NMR probe head has a return path temperature of approximately 15K and is operated with gaseous helium coolant.
14. The NMR spectrometer of claim 1 , wherein said refrigerator comprises at least one stage exchanger along which at least one coolant is guided to pre-cool said coolant to a defined temperature.
15. The NMR spectrometer of claim 1 , wherein said refrigerator is a Gifford-McMahon cooler.
16. The NMR spectrometer of claim 15 , wherein said refrigerator is a pulse tube cooler.
17. The NMR spectrometer of claim 1 , wherein said compressor of said refrigerator additionally drives at least one of said cooling circuits.
18. The NMR spectrometer of claim 1 , wherein a circuit cooling said LN 2 tank or radiation shield comprises a valve for regulating a coolant flow and a heat exchanger which is in thermal contact with said LN 2 tank or radiation shield.
19. The NMR spectrometer of claim 1 , wherein said cooling circuits form a helium circuit with at least one branch in a forward and/or return path.