Cooling device for cryogenic cooling of an NMR detection system with the assistance of a container filled with a cryogenic fluid

Abstract

A cryo probe head for the transmission/reception of RF signals for NMR measurements with a heat exchanger ( 1 ) for cooling heat sources ( 5 ), the heat exchanger having a contact element ( 4.2 ) for thermal connection between a cryogenic fluid and the heat source, is characterized in that the heat exchanger comprises a container having an interior volume V B into which a first cryogenic fluid F 1 that has a liquid component F 1L and a gaseous component F 1G flows through an inflow conduit ( 8 ) and from which a second cryogenic fluid F 2 that has liquid component F 2L and a gaseous component F 2G flows out through an outflow conduit ( 9 ). The inflow conduit has a flow cross-section Q Z and a circumference U Z from which a characteristic conduit volume V Z =4·Q 2 Z /U Z results, wherein V B >10·V Z , and the outflow conduit has a flow diameter Q A wherein Q A ≧Q Z . The contact element is in close thermal contact with both the liquid volume component V L of the cryogenic fluid and with the heat source. A device for setting the inflow quantity of the first cryogenic fluid F 1 into the container is provided that ensures a state F 1L /F 1G >F 2L /F 2G during operation. In this way, vibrations due to the cooling process can be largely reduced and the consumption of cryogenic fluid minimized.

1 . A cryo probe head for the transmission and/or reception of radio-frequency (=RF) signals in nuclear magnetic resonance (=NMR) measurements, the probe head comprising:
 at least one heat source;   at least one heat exchanger for cooling said at least one heat source, said heat exchanger being structured to accept a cryogenic fluid, said heat exchanger having at least one contact element that ensures a connection with good thermal conduction between the cryogenic fluid and said heat source, said heat exchanger having a container with an interior volume V B , said container structured as a buffer reservoir for the cryogenic fluid, wherein said container defines an inflow conduit leading to said interior volume, said inflow conduit structured to accept input flow of a first cryogenic fluid F 1  into said interior volume, the first cryogenic fluid having a liquid component F 1L  and a gaseous component F 1G , said container also defining an outflow conduit communicating with said interior volume, said outflow conduit structured to accept output flow of a second cryogenic fluid out of said interior volume, the second cryogenic fluid having a liquid component F 2L  and a gaseous component F 2G , wherein said inflow conduit has a flow cross-section Q Z  and a circumference U Z  defining a hydraulic diameter D hyd, Z =4·Q Z /U Z  and an associated characteristic conduit volume V Z =Q Z ·D hyd, Z , with V B >10·V Z , said outflow conduit having a flow diameter Q A , wherein Q A ≧Q Z , said contact element being in close thermal contact with both the liquid volume component V L  of the cryogenic fluid in said container and with said heat source; and   a device for setting an inflow quantity of the first cryogenic fluid F 1  into said container, said device structured to establish and maintain an operation state of the cryo probe head for which F 1L /F 1G >F 2L /F 2G .   
     
     
         2 . The cryo probe head of  claim 1 , wherein said container and said inflow conduit are constituted such that V B >20·V Z  or 70·V Z ≦V B ≦150·V Z . 
     
     
         3 . The cryo probe head of  claim 1 , further comprising a closed-loop control device, said control device regulating said device for setting the inflow quantity of the first cryogenic fluid F 1  into said container to maintain the volume component V L  of liquid cryogenic fluid in said container at a definable value relative to a volume component V G  of gaseous cryogenic fluid. 
     
     
         4 . The cryo probe head of  claim 3 , wherein said closed-loop control device controls an inflow quantity of the first cryogenic fluid F 1  into said container as a function of a quantity of heat transferred from said heat source through said contact element to said heat exchanger, wherein V G >V L  or V G ≧5V L . 
     
     
         5 . The cryo probe head of  claim 3 , wherein said closed-loop control device controls an inflow quantity of the first cryogenic fluid F 1  into said container such that F 2L ≈0. 
     
     
         6 . The cryo probe head of  claim 3 , further comprising a temperature sensor, said temperature sensor structured to measure a temperature of said heat source, said temperature sensor having an output signal fed to said closed-loop control device as an input signal for closed-loop control of the inflow quantity of the first cryogenic fluid F 1  into said container. 
     
     
         7 . The cryo probe head of  claim 1 , further comprising a level sensor for measurement of a current level of the volume component V L  of liquid cryogenic fluid in said container. 
     
     
         8 . The cryo probe head of  claim 7 , wherein the fluid inflow is increased by said device for setting the inflow quantity of the first cryogenic fluid F 1  into said container in response to signaling that a current level of the volume component of liquid cryogenic fluid has fallen below a settable level. 
     
     
         9 . The cryo probe head of  claim 7 , wherein the fluid inflow is reduced or blocked by said device for setting the inflow quantity of the first cryogenic fluid F 1  into said container in response to attainment of or to exceeding of a maximum liquid level, wherein fluid inflow is opened or increased in response to reaching or dropping below a minimum liquid level. 
     
     
         10 . The cryo probe head of  claim 1 , further comprising a closed-loop temperature control of said heat source, said temperature control comprising a closed-loop control device and a heater that is thermally well connected to said heat source. 
     
     
         11 . The cryo probe head of  claim 1 , wherein said heat source is directly connected to a lower cover of said container, wherein said lower cover performs a function of said contact element and is therefore made of a material with a lowest possible thermal resistance and a wall thickness that is as small as possible. 
     
     
         12 . The cryo probe head of  claim 1 , wherein said heat source is directly connected to an upper cover of said container, upper and side covers of said container performing a function of said contact element and therefore consisting of a material with a lowest possible thermal resistance and a wall thickness that is as large as possible. 
     
     
         13 . The cryo probe head of  claim 12 , wherein said heat exchanger has two or more contact elements. 
     
     
         14 . The cryo probe head of  claim 1 , wherein said heat source is directly connected to an upper cover of said container, an interior of said container accommodating said contact element of good thermal conduction, wherein said contact element is permanently connected to said upper cover of said container and is immersed in the liquid fluid V L , said contact element being disposed directly below said heat source, wherein said upper cover has a smallest possible wall thickness. 
     
     
         15 . The cryo probe head of  claim 1 , wherein said contact element protrudes from a top of said heat exchanger, is attached to an upper cover of said heat exchanger, and has a good thermal connection to said heat source, wherein a lower part of said contact element is immersed in the liquid fluid V L  so that a best possible thermal connection between said heat source and the liquid fluid V L  is thereby ensured. 
     
     
         16 . The cryo probe head of  claim 1 , wherein said contact element is connected to a thermally insulating fastening element which is constituted such that an upper part of said contact element is separated from the liquid fluid V L  and only a lower part remains immersed in the fluid V L . 
     
     
         17 . The cryo probe head of  claim 1 , wherein the heat source is attached above the fluid level to a side wall of said container, said side wall performing a function of said contact element and therefore being made from a material with a lowest possible thermal resistance and a wall thickness that is as large as possible 
     
     
         18 . The cryo probe head of  claim 1 , wherein said heat source is attached below the fluid level to a side wall of said container, said side wall thereby performing a function of said contact element and therefore being made of a material with a lowest possible thermal resistance and a wall thickness that is as small as possible. 
     
     
         19 . A serial connection of multiple said heat exchangers of  claim 1 , wherein an outflow of an i-th heat exchanger constitutes an inflow of an (i+1)-th heat exchanger. 
     
     
         20 . The serial connection of multiple heat exchangers of  claim 19 , wherein at least a last heat exchanger in a series is equipped with closed-loop temperature control and/or closed-loop level control.