Temperature control system for an MR system with a permanent magnet arrangement

Abstract

The invention relates to a temperature control system for an NMR magnet system, comprising a permanent magnet arrangement with a central air gap for generating a uniform static magnetic field in a measurement volume inside the central air gap, an NMR sample head for transmitting HF pulses and receiving HF signals from a measurement sample, an NMR frequency lock comprising a frequency detection in the NMR sample head and an HO coil for changing the amplitude of the static magnetic field, and a shim system in the central air gap for further homogenizing the magnetic field in the measurement volume, wherein a first isolation chamber thermally shields the permanent magnet arrangement and the first isolation chamber comprises means for regulating a temperature T1 of the first isolation chamber, the shim system, the HO coil and the NMR sample head are arranged in the central air gap outside the first isolation chamber, and at least one heat conductor is arranged between the shim system and the HO coil on the one hand and the permanent magnet arrangement on the other hand.

Description

Technical Field

[0001] The invention relates to temperature regulation of an NMR (Nuclear Magnetic Resonance) magnet system, comprising a permanent magnet arrangement with a central air gap for generating a uniform static magnetic field in a measurement volume inside the central air gap, an NMR sample head for emitting HF (high frequency) pulses and receiving HF signals from the measurement sample, an NMR frequency lock comprising a frequency detection in the NMR sample head and an HO coil for varying the amplitude of the static magnetic field, and a shimming system in the central air gap for further homogenizing the magnetic field in the measurement volume.

[0002] Such a temperature-adjustable NMR magnet system is known, for example, from US 2011 / 0137589 A1 (=reference [1]). Background Art

[0003] In general terms, the present invention relates to temperature regulation of permanent magnet systems, particularly for benchtop NMR instruments.

[0004] In permanent magnets, the magnetic field generated depends on the ferromagnetic properties of the permanent magnet material used. These properties are in turn highly temperature-dependent. Taking neodymium iron boron magnets as an example, the temperature coefficient of the coercive field strength is about -0.6% / K and the temperature coefficient of the remanence is about 0.1% / K. Therefore, it is important to thermally regulate the permanent magnet arrangement very accurately, especially when using the permanent magnet arrangement for high-resolution NMR with sub-hertz line widths. It is necessary to keep the temperature (T) stable for a sufficiently long time, preferably to minimize temperature fluctuations to 1 / 1000K, in order to avoid drifts or fluctuations of the B0 field, which may lead to broadening of the resonance lines when accumulating spectra to improve the signal-to-noise ratio (S / N) or line distortions when the magnetic field strength changes during the acquisition period. At the same time, the measurement conditions should be ensured with the lowest possible magnet temperature, preferably in the room temperature range (standard is 298K), so that NMR measurements can be achieved without temperature regulation of the sample. If the magnet temperature is further reduced, the generated B0 field can be maximized and the thermally excited relaxation of the magnet is slowed down. Ideally, the B0 field should be at least 1.5 T, preferably 1.9 T or higher.

[0005] Some currently commercially available devices do not have a variable measurement sample temperature, but instead measure the measurement sample at the operating temperature of the magnet. If a very hot / cold measurement sample is inserted, this can lead to detrimental changes in the B0 homogeneity through temperature gradients generated in the magnet system. Furthermore, the measurement time is extended by the time required to reach thermal equilibrium in the measurement sample, which, without active temperature regulation, is much longer than, for example, with the aid of a temperature-regulated gas flow.

[0006] According to some publications, instead of measuring the sample, a vacuum-insulated flow cell is inserted into the tabletop device and the measured sample temperature is set and regulated outside the magnet. This can lead to a significant loss of S / N due to the reduction in the measured sample volume. As an alternative, a flow cell that is not thermally insulated is used. It is then accepted that the measured sample temperature in the measuring area and at the outlet may differ significantly from the temperature in the inlet. This can lead to serious problems, for example in the case of solution precipitation, for example when the solution is supersaturated in the temperature range of the magnet.

[0007] Specific prior art

[0008] Magnet temperature regulation:

[0009] US 8,461,841 B2 (=reference [2]) describes an NMR device with a permanent magnet which is brought to the desired temperature through a bore by means of a temperature-regulating fluid. A temperature sensor is used to monitor the magnet temperature and the flow rate and temperature of the fluid are adjusted accordingly. However, this device does not allow precise temperature regulation in the mK range.

[0010] US 6,489,873 B1 (=reference [3]) discloses a temperature control system for an open permanent magnet system based on a yoke, wherein the permanent magnet arrangement is mounted in thermal contact with a C-shaped yoke via a plurality of thermoelectric heat pump devices. At least one temperature sensor is connected to an electronic control circuit. In this arrangement, too, precise temperature control in the mK range is not possible, since there is no closed chamber.

[0011] US 6,566,880 B1 and WO 2000 / 016117 A1 (=reference [4]) describe a magnetic resonance tomograph equipped with a permanent magnet assembly mounted on a magnetic yoke. The tomograph also includes gradient coils. Each permanent magnet assembly is in thermal contact with a plate having good thermal conductivity and arranged between the permanent magnet assembly and the gradient coils. In addition, there is a temperature control with temperature sensors which are connected to the plate and which control a thermoelectric heat pump. This is still an open system, the temperature control device is intended to limit the heat input via the gradient circuit.

[0012] GB 2512328 A (=reference [5]) describes an NMR system with a permanent magnet, which is equipped with temperature sensors and directly heats the magnet via a heating plate. The sensors are mounted at different locations on the magnet and send information to a controller which in turn actuates the heating plate.

[0013] US 8,030,927 B2 (=reference [6]) describes a tomography device with a permanent magnet, wherein a magnet temperature controller is provided for maintaining temperature stability inside the magnet. The magnet temperature controller comprises a pipeline having a liquid circulating therein or a gas circulating therein and a temperature controller which is connected in series with the pipeline in order to regulate the temperature of the liquid or the gas. Compared with references [3] to [5], more precise temperature regulation can be achieved here due to the fluid circulation. However, the input of gradient coils or shim coils is not taken into account.

[0014] Thermal Isolation:

[0015] US 7,297,907 B2 (=reference [7]) describes a method for active thermal isolation of an NMR permanent magnet, which is located in an envelope ("thermally isolated virtual envelope") relative to a sample located inside the magnet bore. A so-called "active shield" is used, in which a temperature-regulating liquid is passed between two components to be thermally separated. It is also disclosed that the magnet assembly can also include a passive isolation layer. However, the described shim coils can include active shim elements, which can be positioned directly around the magnet. Therefore, the purpose of this arrangement is not to limit the heat input into the magnet material by the current in the H0 coil and / or the shim coil. Although no temperature values ​​are explicitly stated, it can be assumed that in this arrangement large temperature differences between the measured sample and the magnet should be thermally separated. However, no effort is made to achieve exact temperature regulation of the magnet.

[0016] Another magnet configuration is known from US 2013 / 0207657 A1 (=reference [8]). However, this document does not disclose the provision of a temperature-adjustable barrier or separation between the measurement sample and the pole piece or between the pole piece and the magnet material.

[0017] Shimming with Temperature Control:

[0018] The magnetic field is electronically shimmed using a plurality of shim coils which, when energized, generate different field gradients in the measurement volume.

[0019] US 9,285,441 B1 (=reference [9]) describes a magnetic field correction system for NMR applications. In particular, it relates to electronic shimming in order to achieve a uniform magnetic field in the field of view. Although this document addresses the problem of temperature changes in the magnet system and the shimming system, in particular magnetic field drift, according to reference [9], this is not solved by a temperature control system, but by purely adjusting the current through the shimming coils.

[0020] US 2011 / 0037467 A1 (=reference

[10] ) describes a solution to a similar problem in MR imaging. When the temperature in the shim material changes, the homogeneity of the static magnetic field changes. Therefore, a temperature sensor is proposed on the shim, which sends information to a controller, which determines the inhomogeneity from this. Here, too, no temperature control system for shimming is provided.

[0021] Temperature control using heat pumps and heat exchangers:

[0022] US 2018 / 0038924 A1 (=reference

[11] ) discloses an NMR system for high-temperature measurements. For this purpose, the sample head is equipped with a thermal insulation portion facing the magnet. The insulation portion or thermal barrier comprises a heat sink, for example consisting of a heat pipe or a heat pump (Peltier element), and a thermal insulation portion in the form of a wall. In addition, the pole shoes of the permanent magnet can be temperature-controlled to prevent temperature gradients in the magnet. A gas flow (VT gas flow) for temperature-controlling the measurement sample is also shown.

[0023] US 2016 / 0077176 A1 (=reference

[12] ) describes an NMR sample head box comprising a first removable connector made of a non-magnetic material. The connector is reversibly connected to a heat exchanger in order to keep the connector substantially at a predetermined temperature. However, the subject matter is not magnet temperature regulation.

[0024] Reference [1] cited at the outset describes an arrangement of the same type and a method for generating a uniform magnetic field having the features mentioned at the outset. Reference [1] discloses that only the temperature of the magnet is directly regulated. Indirect temperature regulation, in particular at intermediate locations between the magnet and / or the pole shoe and the shim system, is not described. The device for magnet temperature regulation described in reference [1] (according to the block diagram) is only connected to the magnet itself and not to the shim system or the pole shoe. No thermal packaging of the magnet system is provided either. The problem of thermal and mechanical coupling is not discussed in detail in the document. Summary of the invention

[0025] In contrast, the object of the present invention is to improve the temperature control system for an NMR magnet system of the type mentioned at the outset using technical means that are as simple as possible, in order to avoid the above-mentioned disadvantages of known arrangements of the same type. The NMR device improved by the invention should in particular provide the following possibilities:

[0026] 1. Set the variable measurement sample temperature,

[0027] 2. Produce large shim current changes in a short time without causing the magnet system to drift for a long time,

[0028] 3. Ability to induce fast changes of current in the H0 coil and allow a large maximum amplitude of the locking range, without the magnet system reacting to this with slow drifts and changing field gradients,

[0029] 4. An increased field stability compared to devices according to the prior art, in particular when changing the measurement sample,

[0030] 5. Regulating the temperature of the permanent magnet so that a constant temperature or, if necessary, a stable temperature gradient can be achieved in the magnet, in particular independently of heat input based on uniform field currents or in the area of ​​the measuring chamber, i.e. on the inner side of the permanent magnet, which is essential for field stability in the measuring chamber but can also be affected by external influences such as room temperature or solar radiation on the device.

[0031] Brief description of the invention:

[0032] This task - which is relatively demanding and complex when considered in detail - is achieved by the present invention in a surprisingly simple and effective manner in that, in a temperature control system for an NMR magnet system of the type defined at the outset, a first isolation chamber thermally shields the permanent magnet arrangement, the first isolation chamber comprises one or more means for regulating the temperature T1 of the first isolation chamber, a shim system, an H0 coil and an NMR specimen head are arranged outside the first isolation chamber in a central air gap and at least one heat conductor is arranged between the shim system and the H0 coil on the one hand and the permanent magnet arrangement on the other hand.

[0033] The invention is primarily concerned with achieving a temperature control of a permanent magnet system that is as “sensitive” as possible, with an accuracy of a few mK.

[0034] According to the invention, this object is achieved in particular by an NMR magnet system, in which the permanent magnet is arranged in an internally and externally closed system. The magnet is completely surrounded by an isothermal wall and is therefore protected from heat input from different sides by active shielding. The permanent magnet has an inner contour with a cross section that is at least partially rectangular, polyhedral, elliptical or circular, in which the shim system, the HO coil and the NMR measuring head are arranged.

[0035] The mechanism for regulating the temperature T1 is arranged on the wall of the first insulating chamber so that the heat is transferred to the magnet inertia in the form of a low-pass system based on radiation, heat conduction in the gas and possible convection in the chamber. The mechanism is preferably realized by a heating foil, which is mounted on the surface of the outer wall over a large area. As an alternative, the wall is constructed as a good thermal conductor and is only locally loaded with heat, which is diffused through the wall.

[0036] The material of the inner wall, i.e., the surface of the inner contour of the adjacent magnet arrangement of the first isolation chamber, is preferably made of a material with good thermal conductivity and / or adjacent to a heat conductor. Ideally, at least a part of the surface includes the heat conductor. This is conducive to the uniform distribution of heat in the internal space of the first isolation chamber and allows thermal regulation to be achieved through a source / sink outside the air gap. This is particularly advantageous if heat is locally input, for example, through dissipation in a shim coil or an H0 coil.

[0037] The heat conductor has the function of thermally shielding the magnet and actively regulating the temperature of the inner wall and the inner contour of the magnet arrangement through the temperature T2 of the heat conductor.

[0038] The magnet temperature is indirectly regulated because there should be only a few low-thermal-conductivity contact points between the magnet and the wall (i.e., the fixing points of the magnet relative to the housing). The magnet temperature is preferably between 15 °C and 35 °C.

[0039] The average temperature of the magnet itself is set to the temperature TM. It applies that: if T1 ≠ T2, then T1 < TM < T2 or T1 > TM > T2, and if T1 = T2, then TM = T1 = T2. TM can preferably be set to an accuracy of 0.1 K, especially 0.01 K, and particularly preferably 0.001 K. The temperature TR of the space surrounding the MR spectrometer is between the lowest temperature TRmin and the highest temperature TRmax during operation, i.e., TRmin ≤ TR ≤ TRmax, and for the magnet temperature TM, it applies that: TRmin ≤ TM ≤ TRmax.

[0040] Compared with the prior art where the magnet is actively heated to a temperature higher than the room temperature TR, such as 40 °C, the present invention allows for measuring a measurement sample at room temperature without additional sample temperature regulation. Thus, the equilibration time after inserting the measurement sample is greatly shortened and NMR measurements can be performed significantly faster.

[0041] Another advantage is that the NMR spectrometer has faster temperature regulation and no longer drifts after installation (i.e., after being switched on) because the thermal conductivity of the magnet material is very low. It has been proven advantageous that the target temperature of the magnet can thus be kept as close as possible to the storage temperature of the switched-off measuring device.

[0042] An important difference between the present invention and known devices lies in the regulation of the temperature T2 of the heat conductor, which is "observed" by the inner contour of the magnet. In addition, it is novel to provide a thermal isolation part between the sample temperature regulation chamber and the shim system. As can be seen from the above-cited literature, in devices according to the prior art, the isolation part is arranged between the measurement sample and the inner wall of the sample temperature regulation chamber, but especially inside the transmit / receive coil.

[0043] Preferred embodiments and extensions of the present invention:

[0044] An embodiment of the temperature control system according to the invention is particularly preferred, in which one or more means for regulating the temperature T2 of the heat conductor are arranged outside the first isolated chamber. The central air gap corresponds to the bore of the magnet, in the center of which a sample head with a measuring chamber and an RF (radio frequency) coil is arranged. A shimming system with an integrated H0 coil is arranged radially outside and is arranged adjacent to the permanent magnet arrangement. The heat generated by the current through the shimming system and the H0 coil is carried away by the heat conduction system and released to the environment via a heat exchanger. The temperature control device adjusts the temperature of the heat conductor to a temperature T2. This ensures that if T2>T1, the heat input in the direction of the permanent magnet remains constant, or if T1>T2, the heat absorption from the permanent magnet remains constant. Preferably, T2=T1, so that there is no temperature change inside the chamber and in particular inside the magnet. In this case, TM=T1=T2 and no heat is transferred from the magnet system to the first isolated chamber. This is particularly advantageous because the initial (e.g. mechanical or ferromagnetic) shimming of the magnet can be carried out independently of the temperature control and possible temperature gradients inside the magnet.

[0045] An advantageous development of this embodiment provides that the first insulating chamber surrounding the permanent magnet arrangement has a wall which comprises at least two thermally distinguishable surfaces which each have at least one sensor for determining a surface temperature T1i of the surface and have mutually independent thermal regulation.

[0046] Also advantageous is an embodiment of the invention in which at least one of the means for regulating the temperature T1 of the first insulating chamber or the temperature T2 of the heat conductor is a thermoelectric element and has a heat exchanger. Thermoelectric elements, such as Peltier elements, enable particularly precise setting of the temperature T1 / T2. In particular, the thermoelectric elements allow cooling and heating equally, which allows efficient and very fast regulation and provides the possibility of also absorbing a greater heat flow from the system.

[0047] A further advantageous embodiment of the invention is characterized in that the wall of the first insulating chamber is simultaneously designed as a shielding arrangement for magnetically shielding the magnetic field from the outside space, i.e. is made of one or more ferromagnetic materials and preferably comprises a passive thermal insulation on the outside of the first insulating chamber. In addition, the wall can also simultaneously constitute an HF shield.

[0048] Also advantageous is an embodiment of the temperature control system according to the invention, characterized in that the heat conductor comprises a homogenizing body and a heat conducting device. The homogenizing body is made, for example, of a material that conducts heat well (Cu) and serves to distribute the heat as evenly as possible over its entire surface, thereby minimizing temperature gradients.

[0049] In a preferred development of this embodiment, the heat conducting device comprises at least one heat pipe. Heat pipes or heat conduits transfer heat more effectively than pure heat conductors.

[0050] In another preferred embodiment, the homogenization body consists of a heat sink / 3D heat spreader, ie a non-cylindrical heat pipe, which transfers heat more effectively than a pure heat conductor and thus allows for comparable homogenization at a low overall height.

[0051] Alternatively or additionally, in other embodiments, the homogenization body can be thermally connected to the shim system and the H0 coil. This allows the elimination of the dissipation of the shim / H0 current from the air gap of the magnet and helps to achieve a temperature in the measurement space that is as constant as possible without a device for setting the temperature of the measurement sample.

[0052] A configuration is also preferred in which at least a part of the homogenization body is arranged between the shim system and the permanent magnet arrangement.

[0053] The homogenization body is arranged in particular between the shim system and the permanent magnet system in order to distribute the temperature T2 uniformly over the adjacent magnets.

[0054] Other embodiments are characterized in that the means for regulating the temperature T2 in the central air gap comprise a heater and / or a temperature sensor and / or a thermoelectric element for measuring the temperature T2 and are thermally connected to the shim system and / or the heat conduction system.

[0055] One class of embodiments of the present invention is characterized in that the first isolation chamber is surrounded by a second isolation chamber, the second isolation chamber is at temperature T3 and the temperature T3 inside the second isolation chamber is isolated from the ambient temperature TR outside the second isolation chamber by means of the second isolation chamber.

[0056] Such a cascade of insulating chambers has the result that the temperature stability of the temperature T1 at the wall of the first chamber and / or the temperature T2 of the heat conduction system is set at least one order of magnitude higher than the stability of the temperature T3 in the intermediate space.

[0057] In this case, in particular, T3 is stabilized to an accuracy of better than ±1 K, preferably better than ±0.1 K, and T1 and T2 are stabilized to an accuracy of better than ±0.1 K, preferably better than ±0.01 K, ideally to ±0.001 K.

[0058] The following applies here: TRmin≤T3≤TRmax.

[0059] Furthermore, it is preferably applicable that T1 > T3 , since in this case the temperature T1 can be adjusted by heating to T3 relative to the heat sink, and no thermoelectric elements are required to achieve a constant temperature T1 of the wall of the first insulating chamber.

[0060] In a preferred extension of such embodiments, there is a temperature regulating device for the second isolation chamber, which regulates the temperature T3 inside the second isolation chamber towards the ambient temperature TR outside the second isolation chamber.

[0061] Preferably, the temperature T1 of the inner wall of the first temperature regulating system and / or the temperature T2 of the heat conducting system is less than or greater than the temperature T3 in the intermediate space, in particular the temperature difference is at least 2 K. Thus, the temperatures T1 and T2 can be regulated very precisely towards as constant a background and a constant heat flow of the first isolation chamber and the heat conducting system relative to the second isolation chamber can be ensured.

[0062] Particularly preferred is an embodiment where T3 < T1. In this case, the temperature regulation of T1 can be achieved only by means of heating elements and there is no need to use thermoelectric elements because cooling is never required.

[0063] If thermoelectric elements are used to regulate the temperature T2, the heat exchanger can exchange heat with the temperature T3 or with the ambient air at room temperature. The configuration for regulating T3 increases the regulation accuracy based on cascading. The configuration for regulating the room temperature makes it difficult to achieve a particularly stable regulation of the temperature T2 independently of the room temperature and possible thermal radiation (such as due to sunlight), but allows a large heat flow to be dissipated effectively without the risk of heating one or more walls of the first isolation chamber and in particular a large temperature gradient inside the second isolation chamber.

[0064] Particularly advantageous is a class of embodiments of the present invention, wherein the sample head has one or more means for setting the temperature TS of the measurement sample in the measurement volume, and the temperature can be set independently of the temperature T1 / T2 of the wall surrounding the permanent magnet arrangement. This air flow is used for the temperature regulation of the measurement sample, which results in an additional temperature input in the air gap of the NMR magnet system in addition to the shim coils, and this must be carried away by the heat conducting system.

[0065] Preferably, the temperature TS of the measurement sample is set in the range of -40 to +150 °C by means of a temperature-regulated sample temperature regulating air flow (VT air flow). When the measurement sample temperature is changed, there is a very large change in the heat input into the magnetic resonance system because the magnet has a large inertia due to the poor thermal conductivity of the magnet material, so this can lead to a very slow change in the magnetic field strength, but especially a change in the magnetic field homogeneity. A similar situation can also occur during the setting of the electrical shimming, but not in the static (shimmed) state. Therefore, for efficient operation, it is particularly important to decouple this heat source / sink from the magnet as effectively as possible, which is achieved in the preferred embodiment by the active regulation of the temperature T2 and the combination of the heat conducting system and the homogenizing body.

[0066] A development of this type of embodiment is advantageous in which an isolation system is provided between the shim system and at least one HF coil of the NMR specimen head, and a purge gas flow (purge gas) preferably temperature-regulated to temperature TF flows through the NMR specimen head, the shim system or the H0 coil.

[0067] Preferably, the sample temperature regulating gas flow (VT gas flow) and at least a portion of the purge gas flow are mixed before leaving the spectrometer.

[0068] As an alternative, the isolation system can be designed as a Dewar, ie evacuated.

[0069] Furthermore, a magnetic resonance spectrometer equipped with a temperature control system according to the invention can be characterized in that the absolute temporal stability of the temperature T3 at least at the location of the temperature sensor is at T3= <t3>The range is ±1K, preferably ±0.1K.

[0070] The absolute temporal stability of the at least one temperature T1i is at least at the location of the corresponding temperature sensor T1i= <t1i>The range is ±0.1K, preferably ±0.01K, and ideally ±0.001K.

[0071] The absolute temporal stability of the temperature T2 at least at the location of at least one temperature sensor is at T1 = <t2>The range is ±0.1K, preferably ±0.01K, and ideally ±0.001K.

[0072] The relative difference between the two temperatures T1i and T1j on the surface surrounding the magnet arrangement is less than 1 K, preferably less than 0.1 K and ideally less than 0.01 K.

[0073] The NMR sample head comprises as usual a measurement sample chamber which accommodates the measurement sample in operation and which can optionally be made of a material with low thermal conductivity (e.g. glass, quartz, Teflon, ...). The sample head comprises a first transmitting / receiving coil which surrounds or is surrounded by the measurement sample chamber. Preferably, the measurement head also comprises a network for tuning different resonance frequencies on the first transmitting / receiving coil.

[0074] Furthermore, the sample head optionally comprises a second transmitting / receiving coil, on which a further measuring core, such as a locking frequency, can be tuned. In another embodiment, the measuring head comprises a further measuring sample, which has a substance which is detected by the second or third transmitting / receiving coil and serves as a reference signal for the locking.

[0075] The permanent magnet material is usually, for example, neodymium iron boron, samarium cobalt, etc., and may optionally further include ferromagnetic materials such as iron, cobalt iron, etc.

[0076] Usually, pole shoes are arranged on the magnet, which pole shoes are attached to the magnet on the measuring head side.

[0077] The magnet system and the isothermal wall comprise "means for regulating the temperature", such as heaters, thermoelectric elements with heat sinks (heat exchangers) or similar means.

[0078] Further advantages of the invention are apparent from the description and the drawings. The features already described above and still to be described below can also be used according to the invention individually or in any combination of a plurality. The embodiments shown and described are not to be understood as an exhaustive description, but rather have exemplary characteristics for describing the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The invention is illustrated in the accompanying drawings and explained in detail with reference to exemplary embodiments. The accompanying drawings are as follows:

[0080] Figure 1 A schematic vertical sectional view showing a first embodiment of a temperature regulation system according to the present invention, the temperature regulation system having a first insulating chamber, a temperature regulator and a heat conductor;

[0081] Figure 2 A permanent magnet arrangement with temperature control according to the invention is shown, with additional T2 control, thermal insulation and closed air gap;

[0082] Figure 3 An embodiment of the present invention is shown with a second isolated chamber, a closed air gap and additional T3 adjustment;

[0083] Figure 4 An embodiment with two isolated chambers, an open air gap, T1, T2 and T3 regulation and with temperature regulation of the heat conductor towards ambient temperature is shown;

[0084] 5 shows a schematic vertical cross-sectional view of an embodiment of the present invention of an NMR sample head having a thermal isolation system and a temperature-regulated purge gas flow and a temperature-regulated VT gas flow for temperature regulation of the sample;

[0085] FIG6 shows a cross-sectional view of a sample head having a shim system, a heat conductor and a homogenizing body; and

[0086] Figure 7 A schematic vertical section through a temperature control system according to the prior art is shown. DETAILED DESCRIPTION

[0087] Figure Figure 1 6 respectively show preferred embodiments of the temperature control system according to the present invention in schematic diagrams of different details, and Figure 7 A conventional arrangement according to the prior art is shown.

[0088] Such a temperature control system for an NMR magnet system comprises: a permanent magnet arrangement structure 1 with a central air gap 2 for generating a uniform static magnetic field in a measurement volume inside the central air gap 2; an NMR sample head 3 for transmitting HF pulses through an HF coil 13 and receiving HF signals from a measurement sample 0; an NMR frequency lock including a frequency detection in the NMR sample head 3 and an HO coil for changing the amplitude of the static magnetic field; and a shim system 4 in the central air gap 2 for further homogenizing the magnetic field in the measurement volume.

[0089] For reasons of position and clarity, the H0 coils are not shown separately in all figures of the patent drawings and therefore do not have their own reference numerals. In the schematic vertical sections, the H0 coils spatially overlap (for the observer) with the schematically shown shim system 4 .

[0090] In such an arrangement according to the prior art, the permanent magnet arrangement can be directly or indirectly temperature-controlled, but due to the lack of thermal separation the waste heat of the shim system and the H0 coil is always transferred directly or indirectly into the magnet.

[0091] The present invention improves these arrangements known per se and expands them by the following elements that are essential to the invention:

[0092] The temperature regulation system according to the present invention is characterized in that a first isolation chamber 5 thermally shields and surrounds a permanent magnet arrangement structure 1, the first isolation chamber 5 comprises one or more mechanisms 6 for regulating the temperature T1 of the first isolation chamber 5, a shim system 4, an H0 coil and an NMR sample head 3 are arranged in a central air gap 2 outside the first isolation chamber 5, and at least one heat conductor 7 is arranged between the shim system 4 and the H0 coil on the one hand and the permanent magnet arrangement structure 1 on the other hand.

[0093] A first particularly simple embodiment of the invention is Figure 1 It is schematically shown in FIG.

[0094] Since the thermal conductivity of the magnet and the pole shoe materials is usually relatively poor, in the case of point-like temperature control, temperature gradients can occur in the magnet material, which have a negative impact on the NMR measurement. For the same reason, people want to avoid convection. Therefore, according to the present invention, heaters and Peltier elements on the magnet, as described in the prior art, are abandoned. Instead, uniform heat radiation and heat conduction are sought through the medium surrounding the magnet (usually fluid / gas / insulator). Therefore, in a preferred embodiment, the regulation of the magnet temperature is abandoned, and instead the environment is completely and uniformly temperature-controlled. In particular, the walls in the air gap are also temperature-controlled.

[0095] For initial temperature adjustment, further temperature control mechanisms can be arranged directly on the magnet and / or the pole piece, but are deactivated again after the startup phase after the MR spectrometer is switched on. Such additional temperature control elements are advantageous in that the time for initial temperature adjustment of the magnet is significantly shortened.

[0096] Figure 2 A preferred embodiment of the system according to the invention is shown, in which the first insulating chamber 1 is additionally surrounded to the outside by a passive thermal insulation 9. Towards the sample head area, i.e. inside the inner contour of the magnet, at least one shim system 4 and a heat conduction system with at least one heat conductor 7 are provided. The heat conductor 7 is thermally connected to a means 8 for regulating the temperature T2 of the heat conductor 7, which means can be a heater or a thermoelectric element with a heat exchanger to the environment. T2 is set to a temperature between 15° C. and 35° C., as is T1. Passive insulation can also be installed on the side facing the magnet system or on one or both sides of the heat conductor 7 and serves to increase the inertia of the magnet temperature and to limit the heat flow to the environment.

[0097] The heat conductor 7 may include a material having good heat conductivity (such as Cu, Al, Al 2 O 3 , ...) and / or a heat conducting device 17 in the form of a heat pipe in which a fluid is present, which evaporates or condenses inside the heat pipe depending on the temperature and can thus carry away heat. The heat conductor 7 is arranged between the shim system 4 and the magnet, so that it forms a thermal shield between the permanent magnet arrangement 1 and the shim system and thus constitutes a part of the first insulating chamber inside the inner contour of the permanent magnet.

[0098] In a preferred embodiment, the central air gap 2 with the NMR sample head 3 is closed to the outside. This is not a hermetic closure, but the opening to the outside is designed in such a way that a minimum exchange of air between the environment and the air gap is ensured. Thus, when an NMR sample tube is inserted, the gap to the housing is preferably limited to 1 / 10 mm.

[0099] Thus, in particular if the dissipation caused by the shim system and the current in the H0 coil is discharged via the heat conductor, a temperature close to T2 is generated in the air gap 2, which is close to temperature T1, preferably the same as temperature T1. This is advantageous because the measurement sample temperature is thus close to room temperature during operation and the time to reach a constant measurement sample temperature after the measurement sample is inserted is as short as possible.

[0100] The shim system 4 comprises a plurality of shim coils (not shown in detail in the drawings) and is preferably thermally coupled to a heat conducting system. In addition, this embodiment with a closed measuring head can advantageously be operated with the aid of a locked sample, so that the locked sample also comprises a second transmitting / receiving coil, which surrounds the locked sample and / or can generate an HF signal in the locked sample and receive an HF signal from the locked sample, and the locked sample also comprises at least one further (also not shown) HO coil, which is thermally coupled to the heat conducting system and is adjusted to the frequency change in the locked sample by a changing current. The energization of the HO coil leads to heat input into the magnet region, so that thermal shielding of the shim system 4 has proven to be particularly advantageous here. This heating caused by adjusting the current in the shim coil leads, for example, to poor convergence of the shim algorithm. Adjustment of the current in the HO coil can lead to "shimming" of the magnet due to the thermal gradient generated in the magnet material. In an alternative embodiment, the shim system and / or the HO coil are not coupled to a heat conductor. The heat generated by the electrical dissipation can be discharged from the air gap in an uncontrolled manner, for example, via further heat conductors and released to room temperature, for example, by means of a heat exchanger.

[0101] Figure 3 Show Figure 2 In this embodiment, a second insulating chamber 11 is additionally present, which surrounds the first insulating chamber 5. In this example, a thermoelectric element with a heat exchanger for the air inside the second insulating chamber 11 is also shown as a means 8 for adjusting the temperature T2. The second insulating chamber 11 is adjusted to a temperature T3 by means of a temperature control device 12, preferably also here by means of a thermoelectric element and a heat exchanger for the room temperature.

[0102] The second insulating chamber 11 ensures that the environment of the magnet can be used as a heat sink, regardless of the actual temperature in the space. As a result, the isotherm around the magnet can always be reached by heating, without having to cool the magnet. This is always sufficient for the regulation of the temperature T1, because apart from the shim system, the H0 coil and the possibly variable measurement sample temperature, no heat is input into the first insulating box and these heat sources are coupled to the heat conductor as far as possible over the entire range and therefore only involve the regulation of the temperature T2.

[0103] Peltiers (thermoelectric elements) with heat exchangers on both sides of the wall are used to adjust the temperature of the second insulation chamber 11 to T3. This also meets another important purpose: the second insulation chamber is responsible for the preliminary reduction of fluctuations in the room temperature, so that the temperature of the isothermal wall and the shim system 4 / H0 coil can be accurately adjusted to the temperature T1 and T2 without placing high demands on the ambient temperature of the spectrometer. In order to be able to reach the temperature T3 with as little power as possible, it is meaningful to provide a passive thermal insulation of sufficient size as the wall of the second insulation chamber.

[0104] Furthermore, in these embodiments, a Peltier with a heat exchanger to the second insulating chamber 11 can be provided for generating the temperature T2. This is advantageous, for example, if the temperature difference and the size of the heat exchanger are not sufficient to have a sufficient thermal range to cool the shim system 4 and / or the H0 coil and / or the heat input caused by the variable measurement sample temperature.

[0105] Preferably, the first insulating chamber 5 is made of a material that can conduct heat well. This has the advantage that the heat radiation from the outside to the magnet is as uniform as possible, so that no temperature gradient is generated on the magnet.

[0106] The second insulation chamber 11 preferably comprises means 19, such as a fan or a turbine, for circulating air inside the second insulation chamber 11. This enables a substantially uniform temperature distribution and ensures air flow through the heat exchanger.

[0107] In an alternative embodiment, Figure 4 As shown, the mechanism 8 for adjusting the temperature T2 can also be adjusted toward the external temperature. Figure 4 The sample chamber is shown open, so that in this embodiment, the sample temperature can also be adjusted. For the sake of clarity, the corresponding sample head together with the mechanisms required for temperature adjustment of the measured sample are not shown. Figure 4 5 .

[0108] If the mechanism for regulating the temperature T2 toward the outside and the NMR sample head 3 up to the top are constructed as independent chambers, the advantage is that the latter will not reach the second isolated chamber 11 under high heat load and therefore the mechanism 12 (Peltier) of the temperature regulating device for regulating the temperature T3 of the second isolated chamber 11 can be designed to be smaller. This is particularly suitable for situations where a large amount of heat load is brought about by the sample temperature regulation in addition to the dissipation of the shim system 4 / H0 coil. The thermal regulation of the shim system 4 can be carried out again in two stages, and a small additional heater is also used here. When the heat is dissipated toward room temperature, the stability of the T2 regulation can be improved by using a cascade system of thermoelectric elements.

[0109] Figure 5a and 5b A section of a schematic partial longitudinal section of a sample chamber with a shim system 4 and a heat conductor 7 is shown in two embodiments for regulating the sample temperature by means of a VT gas flow 16 .

[0110] In order to optionally adjust the temperature TS of the measurement sample (TS in the range of -40 to +150°C), a further thermal insulation system 14 is required, which separates the space for temperature adjustment of the measurement sample from the shim system 4. The further thermal insulation system is made of a material with poor thermal conductivity (e.g. vacuum, aerogel, foam, glass, plastic, ...) and optionally contains a second gas flow in the form of a temperature-regulated purge gas flow 15 (purge gas), the temperature TF of which is preferably between 15°C and 35°C.

[0111] In both embodiments shown, a central tube is additionally provided for sample temperature regulation, which surrounds the usually elongated sample tube in a cylindrical manner. Such a central tube has the advantage that, in addition to forming a channel for the VT gas flow, it can also be used to collect escaping liquid and broken glass in the event of a broken measurement sample or a leak in the flow cell / measurement sample, so that they can be removed more easily.

[0112] The thermal isolation system 14 is arranged between the HF coil 13 and the shim system 4 .

[0113] Figure 5a An embodiment is shown in which the central tube is made of a material with poor thermal conductivity and provides insulation between the purge gas and the VT gas. The area for the purge gas / fluid flow is located between the central tube and the thermal insulation, since the temperature gradient through the thermal insulation can be minimized in this way. However, in order to improve the temperature gradient inside the measurement sample, it may be more meaningful to pass the purge gas flow outside the thermal insulation, for example between the thermal insulation and the shim system, such as Figure 5b It is also conceivable to implement a combination of both configurations and to use a third gas stream with a temperature close to TS or between TS and TF.

[0114] Figure 5a An embodiment is shown in which the temperature of the measurement sample can be set directly via the temperature regulating gas. Figure 5b This is particularly useful for forming a hermetically closed sample chamber, for example for toxic measurement samples, in order to avoid contamination in the event of a rupture of the measurement sample.

[0115] Ideally, the temperature TF of the purge gas stream is approximately equal to the temperature T2 so that the heat input to the heat conductor is as low as possible.

[0116] at last, Figure 6a -c show different cross sections of embodiments of an NMR sample head 3 with a shim system 4, wherein the heat conductor 7 comprises a homogenization body 10 and a heat conducting device 17 in each case:

[0117] Figure 6a A heat conductor 7 is shown which comprises two homogenizing bodies 10 and two conduction devices 17 for transferring heat to the outside. The plate-shaped homogenizing bodies 10 have the task of conducting the heat generated in the plane to the heat conduction devices 17. Due to the relatively short paths, the material thickness of these bodies can be reduced.

[0118] exist Figure 6b In the embodiment, the heat conducting device 17 includes two heat pipes respectively, thereby significantly improving the heat conduction in the direction perpendicular to the cross section.

[0119] Figure 6c The schematic diagram shows the geometric structure of a semi-axial magnet with a concentric structure. The heat conductor is not composed of a homogenizer 10 and a heat conducting device 17 alone, but a heat pipe can be welded thereon or a hollow cylindrical heat pipe can be used to improve heat transfer in a direction perpendicular to the plane of the drawing.

[0120] The heat conductor 7 is preferably thermally connected to a homogenizing body 10. The homogenizing body is made, in particular, of a material with high thermal conductivity in order to set a temperature T2 that is as uniform as possible over the entire outer contour of the homogenizing body 10 (oriented toward the magnets).

[0121] The heat conducting device 17 is connected to the heat exchanger and is used to transfer heat into or out of the homogenizing body 10. The heat conducting device 17 is preferably made of a material with high thermal conductivity or is configured as a heat pipe.

[0122] Preferably, the shim system and / or the HO coil are directly thermally coupled to the heat conductor 7, in particular the homogenization body 10. This ensures that the dissipation generated by the current during operation can be effectively discharged from the central air gap.

[0123] An important difference from the known devices of the prior art is the regulation of the temperature T2, which is "observed" by the inner contour of the magnet. Furthermore, it is novel that a thermal insulation is provided between the sample temperature control chamber and the shim system. As can be seen from the literature cited above, in the prior art insulation is always arranged between the measurement sample and the inner wall of the sample temperature control chamber, but in particular inside the transmitting / receiving coil.

[0124] The features of all the above-described embodiments of the invention can also be combined with one another—at least for the most part.

[0125] References

[0126] Publications considered for the purpose of assessing patentability

[0127] [1] US 2011 / 0137589 A1

[0128] [2] US 8,461,841 B2

[0129] [3] US 6,489,873 B1

[0130] [4] US 6,566,880 B1 and WO 2000 / 016117 A1

[0131] [5] GB 2512328 A

[0132] [6] US 8,030,927 B2

[0133] [7] US 7,297,907 B2

[0134] [8] US 2013 / 0207657 A1

[0135] [9] US 9,285,441 B1

[0136]

[10] US 2011 / 0037467 A1

[0137]

[11] US 2018 / 0038924 A1

[0138]

[12] US 2016 / 0077176 A1

[0139] List of reference numerals:

[0140] 0 Measurement sample

[0141] 1. Permanent magnet arrangement structure

[0142] 2 Central air gap

[0143] 3 NMR sample head

[0144] 4 Shimming system

[0145] 5. First isolation chamber

[0146] 6 Mechanism for regulating temperature T1

[0147] 7 Heat Conductor

[0148] 8 Mechanism for regulating temperature T2

[0149] 9 Passive thermal insulation

[0150] 10 Homogenization

[0151] 11. Second Isolation Chamber

[0152] 12 Temperature Control Device

[0153] 13 HF Coil

[0154] 14 Thermal Isolation System

[0155] 15 Temperature regulated purge gas flow

[0156] 16 Temperature regulated VT airflow

[0157] 17 Heat conduction device

[0158] 18 Temperature sensor for measuring T1

[0159] 18' Temperature sensor for measuring T2

[0160] 18” Temperature sensor for measuring T3

[0161] 19 Mechanism for circulating air

Claims

1. A temperature regulation system for an NMR magnet system, comprising: A permanent magnet arrangement (1) having a central air gap (2) for generating a uniform static magnetic field in a measurement volume within the central air gap (2); An NMR sample head (3) for transmitting HF pulses and receiving HF signals from a measurement sample (0); an H0 coil for changing the amplitude of the static magnetic field; as well as a shim system (4) in the central air gap (2) for further homogenizing the magnetic field in the measurement volume, It is characterized in that the first insulating chamber (5) surrounds the permanent magnet arrangement (1) in a thermally shielded manner, The first insulation chamber (5) comprises one or more mechanisms (6) for adjusting the temperature T1 of the first insulation chamber (5), the shim system (4), the H0 coil and the NMR sample head (3) are arranged in the central air gap (2) outside the first insulation chamber (5), At least one heat conductor (7) is arranged between the shim system (4) and the H0 coil on the one hand and the permanent magnet arrangement (1) on the other hand, The heat conductor (7) comprises a homogenizing body (10) and a heat conducting device, wherein the homogenizing body (10) is used to evenly distribute heat over its entire surface, thereby minimizing the temperature gradient, and The homogenizing body (10) is thermally connected to the shim system (4) and the H0 coil.

2. The temperature control system according to claim 1, characterized in that: One or more mechanisms (8) for adjusting the temperature T2 of the heat conductor (7) are arranged outside the first isolation chamber (5).

3. The temperature control system according to claim 2, characterized in that: A first insulating chamber (5) surrounding the permanent magnet arrangement (1) has a wall comprising at least two thermally separated surfaces, each of which has at least one sensor for determining a surface temperature T1i of the wall and has mutually independent thermal regulation, one of the at least two thermally separated surfaces surrounding a central air gap (2) surrounding the measurement volume and actively thermally separating the shim system (4), the HO coil and the NMR sample head (3) from the permanent magnet arrangement (1).

4. The temperature control system according to claim 2, characterized in that: At least one of the means (6 or 8) for regulating the temperature T1 of the first insulating chamber (5) or the temperature T2 of the heat conductor (7) is a thermoelectric element and has a heat exchanger which ensures a heat flow between the walls of the first insulating chamber (5) during operation.

5. The temperature control system according to claim 3, characterized in that: The wall of the first isolation chamber (5) is designed as a shielding arrangement structure for magnetically shielding the magnetic field from the external space.

6. The temperature control system according to claim 5, characterized in that: The wall of the first insulating chamber (5) comprises a passive thermal insulation (9) on the outside of the first insulating chamber (5).

7. The temperature control system according to any one of claims 1 to 6, characterized in that: The heat conducting device comprises at least one heat pipe.

8. The temperature control system according to any one of claims 1 to 6, characterized in that: At least a part of the homogenization body (10) is arranged between the shim system (4) and the permanent magnet arrangement (1).

9. The temperature control system according to claim 2, characterized in that: The means (8) for adjusting the temperature T2 in the central air gap (2) comprises a heater and / or a thermometer for measuring the temperature T2 and is thermally connected to the shim system (4) and / or the heat conduction system.

10. The temperature control system according to any one of claims 1 to 6, characterized in that: The first isolation chamber (5) is surrounded by a second isolation chamber (11), which is at a temperature T3 and by which the temperature T3 inside the second isolation chamber (11) is isolated from the ambient temperature TR outside the second isolation chamber (11).

11. The temperature control system according to claim 10, characterized in that: A temperature regulating device (12) is provided on the outer wall of the second isolation chamber (11), and the temperature regulating device regulates the temperature T3 inside the second isolation chamber (11) to the ambient temperature TR outside the second isolation chamber (11).

12. The temperature control system according to any one of claims 1 to 6, characterized in that: The sample head (3) has means for setting a temperature TS of the measurement sample (0) in the measurement volume, said temperature TS being set independently of the temperature of the wall surrounding the permanent magnet arrangement (1).

13. The temperature adjustment system according to claim 12, characterized in that: An isolation system (14) is arranged between the shim system (4) and at least one HF coil (13) of the NMR sample head (3).

14. The temperature adjustment system according to claim 13, characterized in that: A purge gas stream (15) temperature-regulated to a temperature TF flows through the NMR sample head (3), the shim system (4) or the H0 coil.

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