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 F₁ 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 F₂ 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·Q²_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 F₁ 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.

Description

[0001]This application claims Paris convention priority to DE 10 2009 046 321.6 filled Nov. 3, 2009, the entire disclosure of which is hereby incorporated by referenceBACKGROUND OF THE INVENTION [0002]The invention relates to a cryo probe head for the transmission and / or reception of radio-frequency signals for nuclear magnetic resonance measurements, with at least one heat exchanger for cooling one or more heat sources, in particular, components of the cryo probe head, wherein a cryogenic fluid is supplied to the heat exchanger and the heat exchanger has at least one contact element that ensures a connection with good thermal conduction between the cryogenic fluid and the heat source.[0003]Such a configuration is known from DE 103 40 352 A1.[0004]In a configuration for measurement by means of nuclear magnetic resonance, a probe head is placed in the strong steady-state magnetic field of a typically superconducting magnet. The sample to be measured is introduced into this. The probe...

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Benefits of technology

[0028]In an especially preferred embodiment of the inventive device, the container and the inflow conduit are constituted such that VB>20·VZ, preferably 70·VZ≦VB≦150·VZ applies. These values have proven useful in practice.

[0029]In a further advantageous embodiment, a closed-loop control device is provided that controls the device for setting the inflow quantity of the first cryogenic fluid F1 into the container and controls the volume component VL of liquid cryogenic fluid in the container in relation to the volume component VG of gaseous cryogenic fluid at a definable value. The ratio between VL and VG has a considerable influence on the stability of the cooling and the damping of undesirable vibrations. It is therefore a major advantage to be able to influence this ratio by means of a closed-loop control mechanism.

[0030]It is advantageous if, in the embodiment described above, the closed-loop control device controls the inflow quantity of the first cryogenic fluid F1 into the container depending, in particular, on the heat quantity dissipated from the heat sources through the contact element to the heat excha...

Problems solved by technology

Because the nuclear spin signals are generally very weak, there are easily prone to interference.

Operation of cryocoolers requires a number of items of auxiliary equipment such as compressors, heat sinks, pumps, etc., which makes installation and operation correspondingly costly both in terms of maintenance effort and operating costs.

Moreover, the use of rotating or linearly moving components in the equipment leads to transmission of mechanical vibrations into the probe head.

Mechanical vibrations that are transmitted to the probe head can have a considerable adverse influence on the NMR signal.

Both cooling by evaporation of a fluid cryogen and cooling with cryogenic gases in cryocoolers are used in standard commercial NMR detection systems, although considerable disadvantages are encountered in systems according to the state of the art.

In evaporation cooling, an extreme density change of the fluid can arise within the cooling system due to the phase transition, possibly causing the fluid to undergo a velocity change in the conduits, which can result in formation of pressure waves or thermoacoustic vibrations that are propagated through the system and can result in mechanical vibrations.

Nucleate boiling is...

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