GB2533170A - Inclined nuclear magnetic resonance cryostat - Google Patents

Abstract

A nuclear magnetic resonance cryostat 100 for exposing a sample to a magnetic field, wherein the cryostat comprises a housing 102, an access hole 104 extending into the housing along an access direction 108 and configured for accommodating the sample. There is a magnet arrangement (300 figure 3) at least partially arranged in the housing for generating the magnetic field in the access hole, a cooling arrangement (302 figure 3) in the housing configured for cooling at least part of the magnet arrangement and a support 106 configured for supporting the housing. The access direction 108 is inclined by an acute angle α with regard to a vertical direction 110 when the support 106 rests on a horizontal ground 112.

Description

DESCRIPTION

INCLINED NUCLEAR MAGNETIC RESONANCE CRYOSTAT BACKGROUND ART

[0001] The present invention relates to a nuclear magnetic resonance (NMR) cryostat, a nuclear magnetic resonance measurement device, and a method of operating a nuclear magnetic resonance cryostat.

[0002] EP 0,905,436 discloses a cryostat for a superconducting magnet with a warm clear bore for NMR applications. The cryostat comprises a nitrogen tank and a helium tank housing the magnet. An intermediate shield is provided as well. An NMR system provides access to a room temperature bore of the cryostat for introducing an NMR probe to the magnet centre. The probe usually comprises a sample and radio-frequency coils for inducing transverse magnetization.

[0003] Figure 4 illustrates a conventional NMR cryostat 400.

[0004] NMR cryostat 400 comprises an NMR magnet 402 which need to be cooled to a low temperature of for instance 4.2K or less to maintain their windings in a superconducting state, and therefore have to be contained within a cryostat 400. A cross section of a typical arrangement can be seen in Figure 4. A central bore tube 404, co-axial with the bore of the magnet 402, provides access for room temperature shims, NMR probe and top tube, which provides sample access and other utilities. The liquid helium vessel 406 communicates with the outside world through neck tubes 408. This allows normal helium boil off to escape as well as providing for pressure release during a magnet quench. The arrangement is cryogenically efficient since the cold helium gas leaving the cryostat 400 through the neck tubes 408 intercepts heat load conducted down the neck tube material, which is typically stainless steel. Two or more neck tubes 408 are used to enable the magnet weight to be suspended on the necks without obstructing access to the bore tube 404, otherwise extra tie rods and associated heat load are required to compensate for the offset load. In the NMR cryostat 400 shown in Figure 4, two helium neck tubes 408 are shown, one for supplying liquid helium, and the other one for draining evaporated gaseous helium. The cryostat 400 has to be mounted some -1 -distance above the floor to allow the room temperature shim and/or an NMR probe to be inserted from underneath. The ceiling has to be some distance above the necks 408 to allow access for current leads and a helium transfer syphon. These factors determine the minimum ceiling height of the room the NMR system is located in. The cryostat 400 is mounted on multiple vibration isolating pads (not shown in Figure 4) which are arranged to prevent block of access to the magnet bore. Therefore, the cryostat 400 is mounted on three vibration isolating pads spaced at equal distances round the circumference of the cryostat 400 on top of legs designed to give the appropriate floor clearance. These vibration isolating pads are expensive.

[0005] Thus, conventional NMR cryostats require a relatively large mounting space and/or are relatively complex in construction.

DISCLOSURE

[0006] It is an object of the invention to provide an NMR cryostat which is simple in construction and convenient in use. The object is solved by the independent claims. Further embodiments are shown by the dependent claims.

[0007] According to an exemplary embodiment of the present invention, a nuclear magnetic resonance cryostat for exposing a sample to a magnetic field is provided, wherein the cryostat comprises a housing, an access hole extending into the housing along an access direction and configured for accommodating the sample, a magnet arrangement at least partially arranged in the housing for generating the magnetic field in the access hole, a cooling arrangement in the housing configured for cooling at least part of the magnet arrangement, and a support configured for supporting the housing, wherein the access direction is inclined by an acute angle with regard to a vertical direction when the support rests on a horizontal ground.

[0008] According to another exemplary embodiment of the present invention, a nuclear magnetic resonance measurement device for carrying out a nuclear magnetic resonance measurement of a sample is provided, wherein the 30 measurement device comprises a nuclear magnetic resonance cryostat having the above-mentioned features, and a detection unit configured for detecting a detection -2 -signal in response to exposing the sample to the magnetic field.

[0009] According to yet another exemplary embodiment of the invention, a method of operating a nuclear magnetic resonance cryostat having the above-mentioned features is provided, wherein the method comprises arranging the support to rest on a horizontal ground so that the access direction is inclined by an acute angle with regard to a vertical direction.

[0010] In the context of the present application, the term "nuclear magnetic resonance" (NMR) particularly denotes a spectroscopic method of analyzing a sample in which nuclear spins of material of the sample are predominantly aligned along a predefined spatial direction which is defined by a strong magnetic field generated by a magnet arrangement of an NMR cryostat. Upon superposing a smaller dynamic radio frequency (RE) field by a corresponding probe (which may have an RF coil), switching of the direction of nuclear spins of material of the sample may be accomplished, which results in a detectable signal. Analyzing this signal allows then to determine information indicative of at least one property of the sample, in particular one or more chemical properties.

[0011] In the context of the present application, the term "sample" may particularly denote a material under analysis which is exposed to the static magnetic field and the superposed dynamic RE field within an NMR cryostat. In this context, the sample may be at room or ambient temperature, for instance at or around 300 K. The sample may be accommodated in (or pumped through) an interior of a sample holder such as a tube. In addition to the sample, also an air pocket may be contained in the sampler holder located above the sample as a consequence of gravity. The sample may be a fluidic sample, i.e. a gaseous sample and/or a liquid sample, optionally comprising solid particles. However, also purely solid samples may be analyzed by NMR.

[0012] In the context of the present application, the term "housing" may particularly denote an exterior casing of the NMR cryostat within which at least and at least partially the magnetic arrangement, the cooling arrangement, a sample 30 and/or a probe may be located during analysis. Such an external casing may form instance constitute at least partially the outermost shell of the NMR cryostat. -3 -

[0013] In the context of the present application, the term "magnet arrangement" may particularly denote one or more magnetic elements configured for generating the large static magnetic field to which the sample is exposed during an NMR analysis. For instance, the static magnetic field generated by such a magnet arrangement may be at least 0.1 Tesla, in particular at least 1 Tesla, more particularly at least 10 Tesla. In order to generate such huge magnetic fields, it is advantageous to use superconductive materials for constituting the one or more magnetic elements which, upon being supplied with an electric supply current, generate high magnetic field values.

[0014] In the context of the present application, the term "cooling arrangement" may particularly denote a provision at least partially within the housing for reducing the temperature of the one or more magnetic elements of the magnet arrangement below ambient temperature (for instance below room temperature), in particular below liquid nitrogen temperatures, more particularly to or below liquid helium temperatures (i.e. at or below 4.2 K). Materials usable for constituting the one or more magnetic elements are superconductive only at very low temperatures. However, in another embodiment, it is also possible to constitute the at least one magnetic element from a high temperature superconductive material so that, in such a scenario, cooling the at least one magnetic element to a higher temperature of, for instance, at or around liquid nitrogen temperatures (77 K) may be sufficient.

[0015] In the context of the present application, the term "support" may particularly denote an arrangement which allows to hold the housing with enclosed components (magnetic arrangement and cooling arrangement) at a certain position and/or in a certain orientation. Holding the housing with enclosed components at the predefined position and/or in the predefined orientation may in particular involve holding the housing at a fixed orientation and/or a fixed position. Thus, in particular the change of the orientation of the housing may be disabled by a correspondingly configured support, i.e. disabling a user to adjust the orientation of the housing with respect to a ground plane or a vertical direction. However, in another embodiment, it is also possible that the support is configured to allow the user to adjust the orientation of the housing with respect to a vertical direction or a ground plane.

[0016] In the context of the present application, the term "access direction" may -4 -particularly denote a direction (in particular a straight direction) along which the access hole, via which a user may access an interior of the housing (for instance for inserting a component into the interior of the housing or removing a component from an interior of the housing) extends. In order to conveniently handle such components (in particular a sample, more particularly in a sample holder such as a tube, and/or a probe for generating an RE field, etc.) the access hole may extend into an exterior of the housing along a linear direction or a substantially linear direction.

[0017] In the context of the present application, the term "acute angle" may particularly denote an angle which is larger than 00 (i.e. inclination with regard to vertical direction) and smaller than 90° (i.e. inclination with regard to horizontal direction). In other words, the orientation of the access direction with regard to a vertical direction (defined by the direction of the gravity force or a direction perpendicular to a planar ground plane) may differ from both a purely horizontal alignment and a purely vertical alignment. In contrast to this, the extension of the access hole orientation may be between a horizontal and a vertical direction.

[0018] According to an exemplary embodiment, an NMR cryostat is provided having an orientation of its access hole which is (in particular permanently) oblique or slanted with regard to a vertical direction so that the cryostat fits in small spaces without compromising user convenience and measurement accuracy. On the one hand, such an NMR cryostat has the advantage that the convenience for a user to access the access hole within the housing is significantly increased, because the user does not have to handle a component from a horizontal top plane or a horizontal bottom plane, but in contrast to this may have a better view on and mechanical access to the inclined access hole. This allows a user to insert an NMR sample (such as a liquid sample with a filling height of for example 20 mm to 30 mm) in a sample holder (such as a glass tube having a length of for instance 100 mm) in a convenient and safe way. Furthermore, this decreases the required height of a room into which the NMR cryostat is to be located. Hence, the NMR cryostat of a corresponding embodiment is compatible with a smaller ceiling height as compared to conventional NMR cryostats. Therefore, the flexibility of locating the NMR cryostat in rooms is increased and the demand for room height is decreased. However, the described embodiment simultaneously and synergetically allows to -5 -overcome problems resulting from an air pocket above a for instance liquid sample, which air pocket would, in a purely horizontal arrangement, cause problems in a core region of the NMR cryostat and would thereby deteriorate the accuracy of the analysis results, or would require an enormous amount of liquid sample. In contrast to this, the inclined arrangement according to an exemplary embodiment allows to keep the vertical component of the sample orientation large enough so as to keep small remaining influences of the air pockets above the sample acceptable without an unreasonable increase of the required amount of sample for the NMR experiment. At the same time, the inclined arrangement allows to conveniently handle sample, probes, etc. [0019] In principle, the issues that conventional NMR cryostats with a purely vertical orientation require a relatively large mounting space and/or are relatively complex in construction could be addressed by mounting the magnet and cryostat with the bore tube purely horizontally. However high resolution NMR samples are usually liquid solutions contained within a partially filled sample tube. If the sample tube was oriented fully horizontal, part of the air pocket would be within the active zone of the probe, and this would deteriorate the accuracy of an NMR measurement. Thus, an inclined orientation with regard to not only a purely vertically orientation but also with regard to a purely horizontal orientation has significant advantages.

[0020] In the following, further exemplary embodiments of the cryostat, the measurement device, and the method will be explained.

[0021] In an embodiment, the access hole extending partially into or fully through the housing may delimit an ambient temperature sample accommodation volume.

[0022] In an embodiment, the access hole is a through hole fully extending through the entire housing so as to form two opposing and interconnected access openings in the housing. The provision of the access hole as a through-hole centrally extending through the housing has the advantage that access to the interior of the housing is enabled for a user from two opposing sides, thereby allowing to handle various components independently from one another by servicing both an upper access opening and a lower access opening. However, it should be -6 -said that other exemplary embodiments allow to constitute the access hole as a blind hole, so that only one surface portion of the housing needs to be accessed by a user for handling components such as a probe and/or a sample. The access hole may also be configured as two opposing blind holes, preferably in flush with one another.

[0023] In an embodiment, the NMR probe, which may be inserted via one of the two opposing access openings may be located permanently, exchangeably or semipermanently within the NMR cryostat. The NMR probe may contain an RF (radio frequency) transmitter and an RF transceiver, wherein each of which may be embodied as a coil surrounding the sample during the NMR measurement. By powering such a coil, nuclear spins of sample material may be switched or turned upside down, and the response of the sample on the application of the exciting RF signal may be detected as a detection signal. For example, such an RF system may operate at a frequency of 400 MHz.

[0024] In an embodiment, one of the access openings is configured for receiving at least the sample and the other one of the access openings is configured for receiving at least a nuclear magnetic resonance probe. In particular, an upper access opening may allow to insert a sample (for instance a sample holder) from an upper position of the housing into the cryostat. This allows a user to visually inspect insertion of the in many cases sensitive sample into the housing. Independently of the sample supply, the lower access opening may allow to insert or exchange a probe (for instance a probe serving as a generator for generating a smaller dynamic RF field for switching nuclear spins. Thus, such a probe or other components may be easily exchanged via the lower access opening without the need of previously taking out the sample from the housing. This allows to obtain reproducible and highly accurate analysis results.

[0025] In an embodiment, the magnet arrangement comprises at least one superconductive magnet element. By using one or more superconductive materials, extremely high magnetic fields can be generated to thereby obtain a high precision of the NMR analysis results characterizing the sample.

[0026] In an embodiment, the magnet arrangement comprises magnet wire joints -7 -located at a bottom of at least one magnetic element of the magnet arrangement so as to remain permanently immersed in cooling medium of the cooling arrangement. In particular, the magnet wire joints may be located at a base of the at least one superconductive magnetic element so as to remain permanently immersed in cooling medium of the cooling arrangement. The inclined orientation of the access hole relative to a vertical direction or a normal direction with regard to a planar ground plane on which the NMR cryostat rests involves challenges with regard to the location of the magnet wire joints supplying the at least one magnetic element of the magnet arrangement with electric current for generating the static magnetic field.

The reason for this is that it should, under such circumstances, be reliably prevented that the magnet wire joint is exposed to a temperature above which superconductivity of the material of the magnet wire joints breaks down. This can for instance occur when the magnet wire joint is no longer immersed within a liquid helium bath which ensures the maintenance of such low temperatures. Therefore, the magnet wire joints can be arranged within a cooling chamber of the cooling arrangement so that they always remain below a liquid helium level. In view of the inclined orientation of the for instance substantially rotationally symmetric (more particularly cylindrical) geometry of the housing, the magnet wire joints may be located asymmetrically in a bottom portion of the cooling chamber in which the at least one magnetic element is located. In other words, the magnet wire joints may be located in a bottom corner region of the main cooling chamber so as to remain permanently immersed in main cooling medium. This is shown in Figure 3.

[0027] In an embodiment, the cooling arrangement comprises a pre-cooling chamber and a main cooling chamber, wherein the pre-cooling chamber is configured for accommodating precooling medium (in particular liquid nitrogen) and at least partially surrounds at least part of the main cooling chamber configured for accommodating main cooling medium (in particular liquid helium). The precooling medium may have a boiling temperature (or boiling point) above a boiling temperature (or boiling point) of the main cooling medium. The precooling chamber may be a chamber accommodating a precooling medium such as liquid nitrogen as a thermal shield for thermally shielding an inner main cooling chamber which is, in turn, radially located between the access hole and the precooling chamber. It is also possible that a vacuum chamber is arranged within the casing which thermally -8 -decouples or isolates the precooling chamber from the main cooling chamber and the cooling chambers from the environment. Although it is preferred to use liquid nitrogen as precooling medium and liquid helium as main cooling medium, other cooling media such as liquid oxygen or liquid hydrogen may be used as well, provided that the boiling temperature of the precooling medium is higher than that of the main cooling medium. It is also possible that a precooling chamber and precooling medium are omitted.

[0028] In an embodiment, the main cooling chamber comprises at least one main cooling neck, in particular exactly one main cooling neck, extending out of the housing and being in fluid communication with the main cooling medium. The main cooling neck may establish an external flange or access provision for supplying the main cooling medium to the main cooling chamber or removing evaporated main cooling medium from the main cooling chamber. It is highly preferred that, according to an exemplary embodiment, exactly one main cooling neck is provided allowing for a simplified construction. Further preferably, this main cooling neck may be arranged at the uppermost end of the inclined housing. For a given neck circumference, and hence heat load, a single neck has much lower hydraulic impedance compared to the same total amount of neck tube material split between two or more necks. This allows the minimum pressure build up during a quench, and hence the least stringent and most cost effective pressure vessel requirements. It also gives the lowest overall cost of the necks.

[0029] In an embodiment, a center of gravity of the magnet arrangement and the main cooling chamber is substantially in-line with the exactly one main cooling neck. In particular, an extrapolation of the extension (preferably a vertical extension) of the main cooling neck may include the center of gravity of the magnet arrangement and the main cooling chamber. Such a highly advantageous arrangement allows to obtain a high stability of the cryostat which, in turn, allows to construct the support from simple components, for instance allowing to use one or more lightweight support elements.

[0030] In an embodiment, the precooling unit comprises at least one precooling neck, in particular exactly two precooling necks, extending out of the housing and being in fluid communication with the precooling medium. The provision of such a -9 -precooling neck or necks allows to get access to the precooling chamber to supply precooling medium into the precooling chamber and to remove evaporated precooling medium from the precooling chamber.

[0031] In an embodiment, the exactly two precooling necks are substantially in-line with a plane comprising a center of gravity of the precooling chamber. When the two precooling necks extend each along one linear direction (preferably a vertical direction), in particular both directions being parallel to one another, they define together a plane. For stability reasons, it has turned out highly advantageous to configure and locate the precooling chamber within this plane. This contributes to the opportunity to use simple supports reducing complexity of the cryostat and its weight.

[0032] In an embodiment, the support comprises at least one vibration isolating pad, in particular exactly one vibration isolating pad. Such a vibration isolating pad can be used to vibrationally decouple the cryostat from the ground, thereby reducing the risk of undesired quenching of the magnets. Vibrations may involve a heat introduction which, in turn, may result in an increase of the temperature within the cryostat. Thus, provision of the at least one vibration isolating pad increases safety of operation. However, such advantageous vibration isolating pads involve complexity and weight into the cryostat. Highly advantageously, an exemplary embodiment of the invention allows to use a very small number of vibration isolating pads, for instance only a single vibration isolating pad. This reduces complexity in weight of the cryostat.

[0033] In an embodiment, the exactly one vibration isolation pad is located below a center of gravity of the cryostat. More precisely, a vertical extension of the vibration isolation pad defines a direction which flushes with the center of gravity of the cryostat. In other words, when extrapolating this direction upwardly from the vibration isolation pad, the extrapolated line would intersect the center of gravity of the cryostat. This center of gravity may therefore be located directly vertically above the vibration isolation pad. By locating the single vibration isolating pad below a center of gravity of the entire cryostat, highly appropriate properties in terms of vibration isolation can be obtained while at the same time allowing for a proper mechanical stability of the entire cryostat.

[0034] In an embodiment, the support additionally comprises at least one lightweight support element, in particular exactly two lightweight support elements. While less than three (and even a single) vibration isolating pads are sufficient for a cryostat according to an exemplary embodiment, the mechanical stability and protection against undesired tilting of the housing under the influence of the gravity force can be further improved by the provision of one or more additional lightweight support elements assisting the small number of vibration isolation pads in supporting the housing. However, such support elements may be provided with a simple construction and a light weight, thereby obtaining a cryostat with reduced complexity and small weight.

[0035] In an embodiment, the acute angle is in a range between 20° and 70°, in particular between 30° and 60°, for instance substantially 45°. When the acute angle is selected in the described ranges, a proper trade-off between a suppression of the disturbing effect of a gas pocket above a sample on the one hand and the required height of a room in which the cryostat is located on the other hand may be obtained.

When the acute angle is at or above 20°, in particular at or above 30°, challenges with the only partially sample filled sample tube and with the resulting air pocket in the detection volume are still feasible, and an amount of (in particular liquid) sample required for performing the NMR measurement is still acceptably low.

Simultaneously, when the acute angle is at or below 70°, in particular at or below 60°, the advantages in terms of reduced mounting space are particularly significant in practical use of the NMR cryostat.

BRIEF DESCRIPTION OF DRAWINGS

[0036] Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawings. Features that are substantially or functionally equal or similar will be referred to by the same reference signs.

[0037] Figure 1 illustrates a three-dimensional view of a nuclear magnetic resonance measurement device comprising a nuclear magnetic resonance cryostat according to an exemplary embodiment of the invention.

[0038] Figure 2 illustrates another three-dimensional view of the nuclear magnetic resonance cryostat according to Figure 1.

[0039] Figure 3 illustrates a cross-sectional view of the nuclear magnetic resonance cryostat according to Figure 1 and Figure 2.

[0040] Figure 4 illustrates a cross-sectional view of a conventional nuclear magnetic resonance cryostat.

[0041] The illustration in the drawing is schematic.

[0042] Before, referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on 10 which exemplary embodiments of the invention have been developed.

[0043] An exemplary embodiment provides an NMR cryostat with magnet and inclined orientation. Such an NMR cryostat may overcome the need for more than one main cooling neck with associated pressure vessel. More generally, neck and main cooling medium (in particular helium) manifold costs can be reduced. In exemplary embodiments, there is no more a need for more than one expensive vibration isolation pad. Accessibility to the top of an access hole in a bore tube extending into the housing can be significantly improved. A large clearance between the base of the cryostat and the floor for probe and/or RT shim access is obtained. Accessibility to the underside of the cryostat for probe changing can be also improved significantly. The conventional need for excessive ceiling height no longer exists. These and other benefits can by realized in particular by mounting the cryostat such that the access hole or bore tube is between about 200 and about 700 (most preferably at roughly 45°) to horizontal.

[0044] Figure 1 illustrates a three-dimensional view of a nuclear magnetic resonance measurement device 150 comprising a nuclear magnetic resonance cryostat 100 according to an exemplary embodiment of the invention. Figure 2 illustrates another three-dimensional view of the nuclear magnetic resonance cryostat 100. Figure 3 illustrates a cross-sectional view of the nuclear magnetic resonance cryostat 100 according to Figure 1 and Figure 2.

[0045] The nuclear magnetic resonance cryostat 100 of the nuclear magnetic resonance measurement device 150 is configured for exposing a liquid sample (for instance a biological sample with a protein to be analyzed) to a strong magnetic field of for example several Tesla. The cryostat 100 comprises an exterior or outer housing 102 which may be made for instance of stainless steel. A tubular access hole 104, which is circumferentially delimited by a bore tube 320 shown in Figure 3 is configured as a through hole and extends through the entire substantially cylindrical housing 102 along a slanted access direction 108. The fluidic sample is to be accommodated within a sample tube which, in turn, is to be accommodated within the access hole 104 during carrying out the NMR experiment. Also an NMR probe (not shown) containing an RE transmitter (for instance operating at a frequency of several 100 MHz) and an RF detector is to be accommodated within the access hole 104. The access hole 104 is a through hole fully extending through the entire housing 102 so as to form two opposing access openings 114, 200. An upper one of the access openings 114 is configured for receiving the sample. A lower one of the access openings 200 is configured for receiving the nuclear magnetic resonance probe.

[0046] A magnet arrangement 300, which is schematically illustrated in Figure 3, is arranged inside the housing 102 and is configured for generating the magnetic field in the access hole 104 to which the liquid sample is to be exposed during the NMR experiment. The magnet arrangement 300 comprises one or more tubular superconductive magnet elements. The magnetic field generated by the magnetic element(s) is obtained by applying a high electric current to the one or more magnetic element(s). In order to benefit from the superconductive property of the magnet element(s) at low temperatures, it has or they have to be cooled to a low temperature where they show superconductive behaviour.

[0047] For the latter purpose, a cooling arrangement 302 is positioned within the housing 102 and is configured for cooling the magnet arrangement 300 to a low temperature where the magnet element(s) is/are superconductive. The cooling arrangement 302 comprises a radially outer pre-cooling chamber 308 and a radially inner main cooling chamber 306 and a vacuum space in which both the precooling chamber 308 and the main cooling chamber 306 are accommodated. The main cooling chamber 306 is radially sandwiched between the precooling chamber 308 and the bore tube 320. The pre-cooling chamber 308 acts as a heat shield and accommodates liquid nitrogen as precooling medium at a temperature of approximately 77 K. The main cooling chamber 306 serves for cooling the magnet arrangement 300 and accommodates liquid helium as main cooling medium at a temperature of approximately 4.2 K. By this configuration, it can be ensured that the magnetic element(s) immersed in the liquid helium remain(s) safely at a temperature at which it is/they are superconductive.

[0048] As can be taken from Figure 3, the magnet arrangement 300 comprises magnet wire joints mounted at a bottom position of the superconductive magnetic element(s) so as to remain permanently immersed in cooling medium of the cooling arrangement 302. The magnet wire joints are also located in a bottom corner region 308 of a main cooling chamber 306 so as to remain permanently immersed in main cooling medium. In view of the arrangement of the magnet wire joints in the bottom corner regions 308 and as a consequence of the inclined orientation of the cryostat 100, it can be ensured that the magnetic wire joints remain in a superconductive state even when the filling level with liquid helium is very low. This is an efficient protection against undesired quenching.

[0049] The main cooling chamber 308 comprises exactly one main cooling neck 116 extending vertically out of a top end of the housing 102 and being in fluid communication with the main cooling medium. Thus, liquid helium may be filled into the main cooling chamber 306 and evaporated gaseous helium may leave the main cooling chamber 306 via the main cooling neck 116. Advantageously, a center of gravity 310 of the magnet arrangement 300 and the main cooling chamber 308 is substantially in-line with the exactly one main cooling neck 116. This contributes to the stabilization of the cryostat 100. The inclined configuration of the NMR cryostat 100, in particular when provided with single main cooling neck 116, reduces the hydraulic impedance without compromising on the cryogenic performance of the NMR cryostat 100. It is thus possible to manufacture the NMR cryostat 100 with reasonable effort without any negative impact on the NMR measurement accuracy.

[0050] The precooling unit 308 comprises exactly two precooling necks 118 extending vertically out of a top end of the housing 102 and being in fluid communication with the precooling medium. Thus, liquid nitrogen may be filled into the precooling chamber 304 and evaporated gaseous nitrogen may leave the -14-precooling chamber 304 via the precooling necks 118. Advantageously, the two parallel tubular precooling necks 118 are substantially in-line with a plane comprising a center of gravity of the precooling chamber 308. In other words, referring to Figure 3, the center of gravity of the precooling chamber 308 is located within a vertical plane defined by the two parallel precooling necks 118. This also contributes to the stabilization of the cryostat 100.

[0051] Figure 3 shows an inside of the NMR cryostat 100 and shows in particular that ambient temperature access hole 104 is thermally insulated from the low temperature of the cooling media. For this purpose, a vacuum chamber 302 is 10 provided.

[0052] A support 106 mechanically supports the housing 102 in a bottom region and bridges a gap between the bottom end of the housing 102 and a ground 112. When the support 106 rests on horizontal ground 112 such as the planar floor of a room (as in Figure 1 to Figure 3), the access direction 108 (i.e. the central axis of the tubular access hole 104 and the tubular bore tube 320) is inclined by an acute angle a=45° (other angular values are possible) with regard to a vertical direction 110 which is defined by the direction of the gravity force (as indicated by g in Figure 1 and Figure 3). In the illustrated embodiment, the support 106 consists of a single vibration isolating pad 120 and exactly two lightweight support elements 122. The exactly one vibration isolation pad 120 is located in a central position of a bottom of the housing 102 and exactly vertically below a center of gravity 220 of the cryostat 100 (see Figure 2) so that the cryostat 100 is prevented from tilting. The single vibration isolation pad 120 is assembled to the inclined housing 102 at the housing's 102 lowermost position (see particularly Figure 2 and Figure 3). As can be taken best from Figure 2, center of gravity 220 of the entire NMR cryostat 100 is located directly above the vibration isolating pad 120. In other words, an extrapolation of a central vertical axis of the vibration isolating pad 120 (see reference numeral 230) intersects the center of gravity 220 of the entire NMR cryostat 100. In this context, the center of gravity 220 of the entire NMR cryostat 100 denotes the center of gravity of all mass components of the NMR cryostat 100 (in particular including magnets, shield components and coolant chambers) as well as an average filling of the NMR cryostat 100 with the corresponding coolants (for instance half-filled liquid nitrogen chamber, half-filled liquid helium chamber). This arrangement of the vibration isolating pad 120 relative to the center of gravity 220 ensures that the entire NMR cryostat 100 is advantageously not prone to oscillate. As a further consequence, the single vibration isolating pad 120 in combination with the additional lightweight support elements 122 is sufficient for supporting the NMR cryostat 100 with high stability.

[0053] The vibration isolating pad 120 may be configured, for instance, with a pneumatic (i.e. gas-based), hydraulic (i.e. liquid-based), and/or mechanical (for instance spring-based or elastic material based) mechanism for damping vibrations from being coupled from the environment into the housing 102 while carrying the weight of the housing 102 and the components in its interior. For example, the vibration isolating pad 120 may be embodied as a stability providing foot with an inflatable bag as vibration insulator which may be inflated with air so that the rest of the NMR cryostat 100 rests on an air cushion formed by the vibration isolating pad 120. The mentioned vibrations, if they were able to couple into the housing 102 without damping, may result in an undesired oscillation of components within the housing 102, in particular cooling chambers 306, 308 and central bore tube 320 delimiting the access hole 104 which, in turn, may result in artefacts in an NMR spectrum. For example, one or more artificial spikes may be generated in the NMR spectrum at one or multiple vibration frequencies, wherein such artificial signals may undesirably mask the actual sample signal. Thus, vibrations coupling into the NMR cryostat 100 may deteriorate resolution and accuracy of the NMR spectrum. This undesired effect can be suppressed by the vibration isolating pad 120. The lightweight support elements 122 may for instance be made of an elastic material such as rubber, or may comprise an elastomeric pad cooperating with one or more gas cushions. They assist the vibration isolating pad 120 in supporting the housing 102 and the components therein, but are significantly lighter and cheaper than the vibration isolating pad 120.

[0054] For comparison purposes, Figure 1 also shows a user 160 standing next to the NMR cryostat 100. As can be taken from Figure 1, adult user 160 may have a height being close to that of the NMR cryostat 100. In particular, the height of the NMR cryostat, h, may be between 1 m and 2 m, in particular between 1,5 m and 2 m. It can also be taken from Figure 2 that an ordinary ceiling height, H, of for instance 2,4 m is sufficient to operate the NMR cryostat 100. As can be taken from Figure 1, the distance, d, between the horizontal ground 112 and the lowermost end of the housing 102 may be in a range between 50 mm and 300 mm, in particular between 100 mm and 200 mm. The acute angle a between the vertical direction 110 and the access direction 108 is, in the shown embodiment, substantially 45°. A user 150 may therefore conveniently insert a sample holder via top access opening 114.

The central vibration isolating pad 120 is accompanied by two lateral lightweight support elements 122, thereby allowing to provide the support 106 with low complexity.

[0055] Figure 2 shows the lower access opening 200 which is simply accessible by user 160 due to the inclined orientation of the rotationally symmetric cylindrical housing 102 with its central through-bore defining the access hole 104. Therefore, the inclined orientation not only reduces the required height below ceiling in a room in which the NMR cryostat 100 shall be operated, but simultaneously improves usability of the NMR cryostat 100. It has turned out that with a suitably inclined NMR cryostat 100, a slight asymmetry of a gas pocket above a sample in the access hole 104 is still acceptable and does not significantly deteriorate the analysis accuracy.

[0056] As can be taken furthermore from Figure 1, the nuclear magnetic resonance measurement device 150 also comprises a detection unit 152 configured for detecting a detection signal in response to exposing the sample to the magnetic field. The detection unit 152 controls the NMR measurement by controlling the magnet arrangement 300 to generate a high static magnetic field of several Tesla. The detection unit 152 can furthermore control the RF coil of the NMR probe to generate a high frequency field capable of switching nuclear spins in the liquid sample contained in the access hole 104 of the nuclear magnetic resonance cryostat 100. After having switched nuclear spin orientation, the NMR probe may detect the response of the liquid sample by detecting a corresponding detection signal which is supplied to detection unit 152 for evaluation. Via input/output unit 154 communicatively coupled to the detection unit 152, a user may input control commands, and the result of the NMR measurement may be displayed to the user.

[0057] Figure 1 illustrates easy access to the top of the cryostat 100 for sample changing without the need for a stand. The size of the cryostat 100 is consistent with that required for Greywolf 400 MHz through 700 MHz magnets. There is sufficient clearance to allow servicing. Figure 2 shows open access for probe changing. The single main vibration isolating pad 120 can also be seen in Figure 2. Figure 3 shows the general internal arrangements. The magnet, not shown in detail, is located at the bottom of the helium (inner) vessel, i.e. in main cooling chamber 306. The centres of gravity of the magnet/helium vessel, and optionally of gas cooled shield assemblies, are approximately in line with the main cooling neck 116. This means that minimal radial rods are sufficient to centre the helium vessel or main cooling chamber 306 within the cryostat 100, so reducing or minimizing the conducted heat load. There is a single large diameter helium vessel neck or main cooling neck 116, which for a given neck heat load provides a small or even the minimum hydraulic impedance in the event of a quench. The two nitrogen vessel necks or precooling necks 118 are roughly in line with a plane through the centre of gravity of the nitrogen vessel or precooling chamber 308. It may happen that the balance is not perfect at all times since nitrogen is relatively dense and the centre of gravity will slowly change as it evaporates. Internal bracing of the nitrogen vessel to the outer vacuum case is advantageous. However nitrogen evaporation is dominated by thermal radiation and the conducted heat load is insignificant. A single, high quality, vibration isolation pad 120 is located roughly under the centre of gravity 220 of the cryostat/magnet assembly. Two further lightweight supports 122 further strengthen stability as the nitrogen vessel or precooling chamber 308 empties, probes are changed and samples are swapped. However, these take very little weight so as to provide good vibration isolation at small cost. Magnet wire joints are mounted at the base of the magnet on one side so they remain immersed in liquid helium at all times. Greywolf magnets are advantageous in this respect since they already use joints on the base of the magnet.

[0058] It should be noted that the term "comprising" does not exclude other elements or features and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims (17)

1. CLAIMS1. A nuclear magnetic resonance cryostat (100) for exposing a sample to a magnetic field, wherein the cryostat (100) comprises: a housing (102); an access hole (104) extending into the housing (102) along an access direction (108) and configured for accommodating the sample; a magnet arrangement (300) at least partially arranged in the housing (102) for generating the magnetic field in the access hole (104); a cooling arrangement (302) in the housing (102) configured for cooling at least part of the magnet arrangement (300); a support (106) configured for supporting the housing (102); wherein the access direction (108) is inclined by an acute angle (a) with regard to a vertical direction (110) when the support (106) rests on a horizontal ground (112).
2. 2. The cryostat (100) according to claim 1, wherein the access hole (104) is a through hole fully extending through the entire housing (102) so as to form two opposing access openings (114, 200).
3. 3. The cryostat (100) according to claim 2, wherein one of the access openings (114) is configured for receiving at least the sample and the other one of the access openings (200) is configured for receiving at least a nuclear magnetic resonance probe.
4. 4. The cryostat (100) according to any of claims 1 to 3, wherein the magnet arrangement (300) comprises at least one superconductive magnet element.
5. 5. The cryostat (100) according to any of claims 1 to 4, wherein the magnet arrangement (300) comprises magnet wire joints located at a bottom of at least one 30 magnetic element of the magnet arrangement (300) so as to remain permanently immersed in cooling medium of the cooling arrangement (302).
6. 6. The cryostat (100) according to any of claims 1 to 5, wherein the cooling arrangement (302) comprises a pre-cooling chamber (308) and a main cooling chamber (306), wherein the pre-cooling chamber (308) is configured for accommodating precooling medium, in particular liquid nitrogen, and at least partially surrounds at least part of the main cooling chamber (306) configured for accommodating main cooling medium, in particular liquid helium.
7. 7. The cryostat (100) according to claims 5 and 6, wherein the magnet wire joints are located in a bottom corner region (308) of the main cooling chamber (306) so as to remain permanently immersed in main cooling medium.
8. 8. The cryostat (100) according to claim 6 or 7, wherein the main cooling chamber (308) comprises at least one main cooling neck (116), in particular exactly one main cooling neck (116), extending out of the housing (102) and being in fluid communication with the main cooling medium.
9. 9. The cryostat (100) according to claim 8, wherein a center of gravity (310) of the magnet arrangement (300) and the main cooling chamber (308) is substantially in-line with the exactly one main cooling neck (116).
10. 10. The cryostat (100) according to any of claims 6 to 9, wherein the precooling unit (308) comprises at least one precooling neck (118), in particular exactly two precooling necks (118), extending out of the housing (102) and being in fluid communication with the precooling medium.
11. 11. The cryostat (100) according to claim 10, wherein the exactly two precooling necks (118) are substantially in-line with a plane comprising a center of gravity of the precooling chamber (308).
12. 12. The cryostat (100) according to any of claims 1 to 11, wherein the support (106) comprises at least one vibration isolating pad (120), in particular exactly one vibration isolating pad (120).
13. 13. The cryostat (100) according to claim 12, wherein the exactly one vibration isolation pad (120) is located below a center of gravity (220) of the cryostat (100). -20 -
14. 14. The cryostat (100) according to any of claims 1 to 13, wherein the support (106) comprises at least one lightweight support element (122), in particular exactly two lightweight support elements (122).
15. 15. The cryostat (100) according to any of claims 1 to 14, wherein the acute angle (a) is in a range between 20 ° and 70°, in particular between 30° and 60°, for instance substantially 45°.
16. 16. A nuclear magnetic resonance measurement device (150) for carrying out a nuclear magnetic resonance measurement of a sample, wherein the measurement device (150) comprises: a nuclear magnetic resonance cryostat (100) according to any of claims 1 to 15; a detection unit (152) configured for detecting a detection signal in responseto exposing the sample to the magnetic field.
17. 17. A method of operating a nuclear magnetic resonance cryostat (100) according to any of claims 1 to 15, wherein the method comprises arranging the support (106) to rest on a horizontal ground (112) so that the access direction (108) is inclined by an acute angle (a) with regard to a vertical direction (110). -21 -