EP3467852A1 - Magnet assembly with cryostat and magnet coil system, with cold storage at the power connections - Google Patents

Abstract

A magnet arrangement (1) comprising a cryostat (2), a superconducting magnet coil system (3), an active cooling device (4) for the magnet coil system (3) and power supply lines (5a, 5b) for charging the magnet coil system (3) in the cryostat (2 )
wherein the power supply lines (5a, 5b) comprise at least one normally-conductive area (15a, 15b), in particular wherein the power supply lines (5a, 5b) also comprise an HTS area (16a, 16b),
wherein a plurality of cold accumulators (20) are thermally coupled to the power supply leads (5a, 5b) along the normal conducting region (15a, 15b) of the current supply leads (5a, 5b) in order to charge the magnet coil system (3) in the normally conducting region (15a, 15b) to absorb the resulting heat
is characterized in that the current supply lines (5a, 5b) in the normally conducting region (15a, 15b) have a variable cross-sectional area B along their direction of extension,
wherein the cross-sectional area B decreases from a cold end (18a, 18b) to a warm end (19a, 19b) at least over a predominant portion of the total length of the power supply leads (5a, 5b) in the normally-conducting region (15a, 15b). The invention provides a magnet arrangement in which a reduced cooling capacity is required during charging of the superconducting magnet coil system, and in normal operation a heat input into the superconducting magnet coil system is reduced.

Description

The invention relates to a magnet arrangement comprising a cryostat, a superconducting magnet coil system, an active cooling device for the magnet coil system and power supply lines for charging the magnet coil system in the cryostat,
wherein the power supply lines comprise at least one normal-conducting area, in particular wherein the power supply lines also comprise an HTS area,
wherein a plurality of cold accumulators are thermally coupled to the power supply lines along the normal conducting region of the power supply lines in order to absorb heat arising during charging of the magnetic coil system in the normally-conductive region.

Such a magnet arrangement is known from JP H04 23305 A known.

For nuclear magnetic resonance (= NMR) measurements strong magnetic fields are required, which can be generated by means of superconducting magnet coil systems. The superconducting magnet coil systems can carry large electrical losses without loss, with which the strong magnetic field strengths are generated. However, cooling to cryogenic temperatures below the critical temperature of the superconducting material in the magnetic coil system is necessary for the superconducting state. The superconducting magnet coil systems are therefore arranged in a cryostat. In order to minimize the helium consumption of the cryostat, partially active cooling means are used, e.g. Pulse tube coolers with which a cryogenic temperature can be maintained permanently and cost-effectively.

To charge a superconducting magnet coil system within a cryostat with electrical current, run in the cryostat from the space temperature-warm outer wall of the cryostat to the magnet coil system power supplies. At least a portion of these power leads is normally conducting ("normal-conducting area"); a lower portion of the power supply lines (often close to the magnetic coil system) is often also made of a high-temperature superconductor (= HTS) material. During charging, electric current flows through the power supply lines, which generates ohmic heat in the normal-conducting area. During normal operation (also called "steady state" operation) typically flows through the power supply lines no electric current ("persistent mode"), but the power supply lines represent thermal bridges that bring heat into the magnetic coil system.

Typically, the heat load during charging due to several effects (eg operation of the "Persistent Mode Switches" or ohmic dissipation in the Power supply) significantly larger than in normal operation. In order to prevent that during charging too high, resulting in a quench (loss of superconductivity) leading temperature at the magnet coil system or in the HTS region of the power supply, the active cooling device can be dimensioned so large that the heat load of the store with the cooling device can be compensated. However, this leads to high production costs and high maintenance costs, to a large size and requirements for cooling and power supply, which must be based on the peak power required during charging. Since charging typically takes only a few hours, but normal operation usually takes many weeks or months, the active cooling device is underutilized most of the time.

In the case of cryogenic containers filled with a liquid cryogen (such as liquid helium), a high coolant consumption can easily be accepted during charging, which, however, causes high costs.

From the EP 2 624 262 A2 It is known in a cryogenic cryocooler system to couple a power supply to the upper cooling stage of a two-stage cooler, and to further couple a thermal inertia member in the region of this upper cooling stage. The thermal inertia element can reduce a temperature rise when charging or discharging a cooled superconducting coil.

From the JP H04 23305 A are known power supplies for a superconducting magnet system, where heat storage material is arranged. In one embodiment, the power supply lines are tubular, and the heat storage material is disposed in the pipe, wherein the heat storage material is divided in the interior of the tube by layers of a thermally insulating material. The power supply lines are cooled with a helium gas stream.

From the GB 2 506 009 A , the US 5,317,296 , the CN 102 360 694 A and the CN 102 592 773 A separable power supplies have become known for a superconducting magnet. By separating the power supply lines after charging, heat input can be prevented during normal operation. However, this approach is technically difficult and involves high production costs.

In the US 5,302,928 For example, a superconducting magnet power supply has been disclosed that is shared between the room temperature interface and the solenoid coil and coupled to a heat sink at the point of division. A disadvantage is the line extension (lead extension), which is introduced into the current path and leads by additional contact resistance to increased ohmic resistance.

In the JP H06 231950 , the GB 2 476 716 A and the DE 10 2007 013 350 A1 have been known power supplies, which are cooled with liquid cryogens.

In the DE 69 324 436 T2 a superconducting magnet system has become known whose power supply lines at the end close to the coil are made of high-temperature superconducting material and whose hot end is not mechanically fixed.

In the U.S. 5,586,437 An MRI cryostat with an inner heat shield and an outer heat shield is described, wherein a separate cooling device is provided for cooling the outer heat shield.

Object of the invention

The invention has for its object to provide a magnet arrangement in which a reduced cooling capacity is required during charging of the superconducting magnet coil system, and in normal operation, a heat input is reduced in the superconducting magnet coil system.

Brief description of the invention

This object is achieved in a surprisingly simple and effective manner by a magnet arrangement of the type mentioned at the outset, which is characterized in that the power supply lines in the normally conducting region have a variable cross-sectional area B along their extension direction,
wherein the cross-sectional area B decreases from a cold end to a warm end at least over a predominant proportion of the total length of the current feeds in the normally conducting region.

In the context of the present invention, it is proposed to provide the power supply lines in their normal conducting region with a special geometry in order to optimize the current supply for charging requirements on the one hand and in normal operation on the other hand, along the normal conducting region of the power supply lines a plurality of cold storage thermal to the power supply lines are coupled.

When charging the superconducting magnet coil, it is important to reduce the ohmic heat generation, especially at the cold end of the power supply lines. Therefore, the invention provides, to the cold end to increase the cross-sectional area (perpendicular to the longitudinal extent or current flow direction), so that the ohmic resistance to the cold end, as far as it is due to the cross-sectional area, is lowered. This also reduces the heat development near the cold end.

In normal operation, but also during charging, it is important to reduce the heat input into the superconducting magnet coil system via the power supply lines as a thermal bridge to the space temperature-warm outer wall of the cryostat. The heat input is mainly from the warm temperature-warm outer wall of the cryostat ago. Therefore, according to the invention, the cross-sectional area of the power supply leads to the space temperature warm end down, which increases the thermal conductivity resistance, as far as it is caused by the cross-sectional area.

By the simultaneous distribution of multiple cold stores along the power supply lines in the normal-conducting area ensures that reached by the geometry of the power supply local limits in heat generation and heat input can be used over a long time, and in particular not quickly compensated by heat conduction along the power supply lines can. The cold storage slows down the equalization processes; by suitable dimensioning of the cold storage (and suitable geometry of the power supply lines), the duration of a complete charging process can be easily buffered.

This makes it possible to manage the charging with a comparatively small cooling power during the duration of the charging process, without the magnetic coil system or possibly a superconducting section of the power supply lines becoming too warm and quenching. Accordingly, a low-cost active cooling device can be used with comparatively low cooling capacity, which requires little space. In the case of a cryogenic cryostat, the cryogen consumption (coolant consumption) during loading can be minimized. At the same time, the heat input via the power supply lines in normal operation can be kept low, so that even this only a small cooling capacity is needed and incurred in normal operation only low operating costs.

The normal-line power supplies typically run from a room temperature (hot end) terminal to the solenoid system or to an HTS area (or HTS section) of the power supplies (cold end); the power supply in the HTS area then continues to the magnetic coil system.

The magnet coil system typically has a superconducting short-circuit switch for establishing a persistent mode. Preferably, the short-circuit switch can be operated with a low heating current or a low heating power, for example with 50 mW or less. The magnetic coil system is preferably formed with low-temperature superconductor (= LTS) materials (in particular NbTi or preferably Nb ₃ Sn for higher operating temperatures). Advantageously, the operating current of the magnetic coil system is low in normal operation, about 100 A or less, preferably 70 A or lower. Preferably, the magnet coil system can be charged with high charging voltages, for example 5 V or more.

The active cooling device may in particular be a pulse tube cooler or a Gifford-McMahon cooler. A preferred power consumption of the active cooling device is 2 kW or less, in particular 1.5 kW or less. Preferably, the active cooling device is operated without cooling water or air-cooled.

The cross-sectional area B of the power supply lines in the normal-conducting region typically decreases over the entire length of the normal-conducting region from the cold end to the warm end, or at least over a predominant proportion of the total length of the power supply lines in the normal-conducting region. The reduction in cross section may be continuous or in stages or in a mixed form. Sometimes exceptions are in the cross-sectional surface course, especially at junctions of Power supply parts, necessary and / or desired. Such connection points usually have a smaller cross-sectional area B ("soldering point"), more rarely a larger cross-sectional area ("soldering bead") than the surrounding power supply parts. These exceptions typically account for less than 5%, usually less than 2%, of the total length of the normal-conduction power supplies and, accordingly, have little effect on overall heat build-up in the power lines when charging the solenoid system or on the total heat input from the warm end of the solenoid Power supply forth. Preferably, the cross-sectional area B decreases from the cold end to the warm end over a proportion of at least 95%, preferably at least 98%, of the total length of the power supply lines in the normal conducting region within the cryostat.

Preferably, the active cooling device is arranged within a tube which is filled with gas during operation (in particular during charging and in normal operation); then an expansion or replacement of the active cooling device is possible without breaking the isolation vacuum of the cryostat. For example, this tube may be provided for one of the power supply lines; this is available anyway and thus the heat load does not increase further in normal operation. Likewise, this tube may be the neck tube of the cryostat, in particular wherein one of the power supply lines runs in the neck tube. Any excess cooling power available at a regenerator of the active cooling device may be used to cool the power supply by thermal contact via the gas in the tube.

Preferred embodiments of the invention

A preferred embodiment of the magnet arrangement according to the invention provides the power supply lines in the normally conducting region each have N successive subsections, with N≥2, in particular 3≤N≤7, the subsections each having a cross-sectional area Bi which is constant within a subsection,
and that the cross-sectional areas Bi decrease from the cold end to the warm end. This embodiment is structurally simple to implement; In addition, the thermal behavior during a charging process can be simulated relatively easily and the geometry of the power supply lines can be optimized accordingly. Through a large number of sections heat flow and heat development or the temperature distribution in the power supply lines can be set more accurately. Note that this setting can also be further optimized by means of the ratios Bi / Hi, with Hi: length of the subsection i (along the longitudinal direction / current flow direction). Usually also N≥3 or N≥4 applies. Typically, at least one coupled cold storage is provided per subsection. Alternatively, it is also possible to continuously change the cross-sectional area of a power supply along the extension direction.

In a preferred embodiment of this embodiment, different sections are thermally coupled to different cold storage. In this design, the cold storage only one (direct) coupling to one of the sections; a connection to other subsections is made only indirectly via the former subsection. This facilitates the formation of a strong temperature gradient in the power supply lines. For example, the cold stores may each contact the subarea approximately in the middle (with respect to the direction of extension).

In another development, at least one cold storage is thermally coupled at a transition of two sections at least, in particular wherein also at the cold end of the power supply in the normal conducting area, at least one cold storage thermally coupled is. This is usually structurally very simple. One or more cold stores at the cold end provide a particularly good protection of the superconducting magnet coil system (or an HTS area of the power supply lines).

Also preferred is an embodiment in which K stages of the thermal coupling are set up in each case along the current supply lines in the normally conducting region, wherein at least one cold accumulator is thermally coupled to the current supply lines at each stage,
with K≥2, in particular 3≤K≤7. Also advantageous is K≥3 or K≥4. By a greater number of stages of the thermal coupling, the heat flow or the temperature distribution in the power supply lines can be set more accurately. In addition, the cold storage are used thermodynamically efficient. In the case of N subsections in each case of constant cross section Bi, preference is furthermore given to K = N or K = N + 1. One stage of the thermal coupling corresponds to a contacting of a power supply by one or more cold storage at a certain length position along the power supply; different stages of the thermal coupling contact a power supply in the normal-conducting area so at different length positions.

A further development of this embodiment is advantageous in that a heavy mass Mi of cold-storing material in the at least one cold store of a respective stage of the thermal coupling decreases over the steps from the cold end to the warm end. The specific heat capacity of most cold accumulating materials (such as metals) increases strongly with higher temperature (in the cryogenic range), so that at the warm end no such large (absolute) heavy masses are needed. The term "heavy" (ie weight-generating) mass of a cold storage is used here to avoid confusion with the "thermal mass" (ie the absolute heat capacity). An embodiment in which the cryostat is designed as a cryogen-free cryostat is preferred. In this case, an increased heat load during charging can not be compensated by accepting an increased cryogen consumption during charging. The invention in this case allows the use of an active cooling device with a low cooling capacity, which is inexpensive and compact. A cryostat is considered to be cryogen-free if no anticipated operating state (ie not charging or a quench) allows cryogens to escape from the system. In this case, the magnetic coil system is typically arranged directly in the vacuum of the vacuum container (and in particular not in a cryogenic liquid cryogenic tank in which the magnetic coil system is immersed).

Also preferred is an embodiment in which at least part of the cold storage is formed as a gas-tight container, wherein a portion of the volume of the gas-tight container is filled with a vaporizable substance. In this design, thermal energy can be bound by evaporation of the (at the prevailing temperatures in operation) substance vaporizable. The vaporizable substance may be, for example, nitrogen, krypton or argon, and in a colder range also neon or helium. Note that in this design, the vaporizable (mostly liquid) substance essentially provides the "heavy mass" of the particular cold storage. It should also be noted that the container is typically made of poor thermal conductivity material, such as stainless steel or the titanium alloy 15-3-3-3. Typically, several containers are connected in series along the power supply lines.

An advantageous development of this embodiment provides that the power supply lines in the normal conducting region extend at least partially within the container. As a result, a particularly good heat flow can take place. Leaves and shields (baffles) in the containers be arranged to minimize the heat flow between the warm and cold end of the container by convection and / or heat radiation.

Furthermore, an embodiment is preferred in which at least a part of the containers is thermally coupled to a lower end via a heat-conducting element to a heat sink of the active cooling device, and the boiling point of the substance contained in the container is above the temperature of the heat sink. Heat can be slowly removed from the container (after charging) via the heat-conducting element in order to recondensate the vaporized substance, typically slowly over several hours or even several days. In particular, two tanks can be used in series, which are coupled to two different cooling stages of the active cooling device (such as a pulse tube cooler).

Also preferred is an embodiment in which at least a portion of the cold storage are formed as a metallic body. This design is particularly simple and robust. A good thermal contact between the (metallic) power supplies in normal-conducting area and the metallic bodies is easy to set up directly.

An embodiment in which a plurality of cold reservoirs designed as metallic bodies are arranged at a distance from one another in a vacuum region of the cryostat is advantageous. This avoids thermal short circuits of the cold storage in a simple manner, in particular between cold storage of different stages of the thermal coupling.

Particularly preferred is an embodiment in which there is further provided an active auxiliary cooling device, which is thermally coupled to a part (portion) of the power supply lines in the normal conducting region, in particular wherein a lowest operating temperature AT _help the Auxiliary cooling device is higher than a lowest operating temperature AT _mss the active cooling device for the magnetic coil system. With the auxiliary cooling device, the power supply lines additional heat energy can be withdrawn, especially when loading; As a result, the active cooling device (which is primarily intended to cool the magnetic coil system) can be relieved. The auxiliary cooling means typically has a AT _Helpful in a range of -70 ° C to -30 ° C, usually from -60 ° C to -50 ° C, which is relatively easy to achieve (especially low-power); however, AT _{mss is} usually between 4 K and 10 K (-269 ° C to -263 ° C). An auxiliary cooling device or a corresponding cooling coil (associated heat exchanger) is typically arranged in the vacuum container (in vacuum).

A development of this embodiment provides that the auxiliary cooling device is further thermally coupled to a radiation shield of the cryostat and / or a vacuum container of the cryostat and / or a tempering device for a sample to be examined. As a result, the active cooling device is additionally relieved, in particular during normal operation. If the auxiliary cooling device is used to cool the vacuum container of the cryostat below the ambient temperature, it is advantageous to thermally isolate the vacuum container. Particularly suitable for this purpose are e.g. Plastic foams. Thus, e.g. Condensation can be prevented.

Also preferred is an embodiment in which the cross-sectional area B changes from the cold end to the warm end by at least a factor of 3. By a factor of 3 or more (based on the majority of the power supply lines in the normal-conducting area) can already be achieved a very significant relief of the active cooling device with respect to the heat load during loading.

The use of a magnet arrangement according to the invention also falls within the scope of the present invention.
wherein the magnetic coil system is charged via the power supply lines and a charging current is selected and the variable cross-sectional area B and / or the cold storage are arranged to _load WL for a heat _load , which acts on a coldest stage of the power supply lines in the normal conducting area during charging to the maximum , and for a heat load WL _gg to this coldest stage in an equilibrium state with charged magnetic coil system:
WL _load ≤ 5 * _gg WL, WL particular _load ≤ 2 * WL _gg. The coldest stage (or stage of thermal coupling) corresponds to the area of the power supply to which the cold storage next cold storage (or cold storage set at the same length position on the power supply lines) is thermally coupled. The stated ratios are well within the scope of the invention, and allow the use of active cooling devices (cryocoolers) with low cooling capacity, which is inexpensive, allows compact construction of the magnet assembly and helps to integrate the system into a customer laboratory as simple as possible.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, according to the invention, the above-mentioned features and those which are still further developed can each be used individually for themselves or for a plurality of combinations of any kind. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Detailed description of the invention and drawing

Fig. 1

eine schematische Darstellung einer ersten Ausführungsform einer erfindungsgemäßen Magnetanordnung, mit metallischen Körpern als Kältespeicher;

Fig. 2

eine schematische Darstellung einer zweiten Ausführungsform einer erfindungsgemäßen Magnetanordnung, mit Behältern gefüllt mit verdampfbarer Substanz als Kältespeicher;

Fig. 3

eine schematische Darstellung einer Stromzuführung im normalleitenden Bereich für die Erfindung, mit Teilabschnitten konstanter Querschnittsfläche, mit mittig kontaktierenden Kältespeichern;

Fig. 4

eine schematische Darstellung einer Stromzuführung im normalleitenden Bereich für die Erfindung, mit Teilabschnitten konstanter Querschnittsfläche, mit Kältespeichern am Übergang von Teilabschnitten;

Fig. 5

eine schematische Darstellung einer dritten Ausführungsform einer erfindungsgemäßen Magnetanordnung, mit Hilfskühleinrichtung zur Kühlung des äußeren Strahlungsschilds;

Fig. 6

eine schematische Darstellung einer vierten Ausführungsform einer erfindungsgemäßen Magnetanordnung, mit Hilfskühleinrichtung zur Kühlung des äußeren Strahlungsschilds und einer Temperiervorrichtung einer zu untersuchenden Probe.

The invention is illustrated in the drawing and will be explained in more detail with reference to embodiments. Show it:

Fig. 1

a schematic representation of a first embodiment of a magnet assembly according to the invention, with metallic bodies as a cold storage;

Fig. 2

a schematic representation of a second embodiment of a magnet assembly according to the invention, filled with containers with vaporizable substance as a cold storage;

Fig. 3

a schematic representation of a power supply in the normal conducting area for the invention, with sections of constant cross-sectional area, with centrally contacting cold storage;

Fig. 4

a schematic representation of a power supply in the normal-conducting area for the invention, with sections of constant cross-sectional area, with cold storage at the transition of sections;

Fig. 5

a schematic representation of a third embodiment of a magnet arrangement according to the invention, with auxiliary cooling device for cooling the outer radiation shield;

Fig. 6

a schematic representation of a fourth embodiment of a magnet arrangement according to the invention, with Auxiliary cooling device for cooling the outer radiation shield and a temperature control of a sample to be examined.

The Fig. 1 1 schematically shows a first embodiment of a magnet arrangement 1 according to the invention. It comprises a cryostat 2, a magnet coil system 3, an active cooling device 4 and here two power supply lines 5a, 5b for charging the magnet coil system 3.

The cryostat 3 is here formed with a vacuum container 11, an outer radiation shield 6, a middle radiation shield 7 and an inner radiation shield 8. The vacuum container 11, which simultaneously forms the outer wall of the cryostat 2, is at room temperature (about 20 ° C). The outer radiation shield 6 is at about 213 K (about -60 ° C). The middle radiation shield 7 couples to an upper cooling stage 9 of the active cooling device 4 at about 50 K, and the inner radiation shield 8 couples to a lower cooling stage 10 of the active cooling device at about 3.5 K; the latter also represents the lowest working temperature AT _{mss of} the active cooling device 4.

Inside the inner radiation shield 8, the magnet coil system 3 is arranged in a vacuum, which is superconductingly short-circuitable via a switch 12 of a charging and short circuit 12a. The magnetic field generated by the magnetic coil system 3 can be used in normal operation, for example, for an NMR measurement. The inner radiation shield 8 can also be gas-tight, so that, for example, some gaseous helium can be provided or contained to improve the thermal conductivity, which, however, does not have to be filled during operation (including charging and normal operation) and can not escape ( "cryogenic cryostat"). As an alternative to the cryogenic cryostat, the cryostat 2 can also be designed as a cryogenic cryostat (in US Pat Fig. 1 not shown in detail). In this case, instead of the inner radiation shield 8, a cryocontainer is provided which typically contains liquid cryogen (such as helium) into which the magnet coil system 3 is completely or partially submerged. If necessary, the cryogen in the cryocontainer can be refilled in the cryogenic cryostat during operation, if necessary also during loading.

The power supply lines 5a, 5b lead from terminals 13a, 13b on the vacuum container 11 through the cryostat 3 to terminals 14a, 14b on the charging and short-circuit circuit 12a. The power supply lines 5a, 5b comprise in the embodiment shown in each case a normal conducting region 15a, 15b (between vacuum container 11 and middle radiation shield 7), an HTS region 16a, 16b (between the middle radiation shield 7 and inner radiation shield 8) and an LTS region (within the inner radiation shield 8).

The power supply lines 5a, 5b in the normal-conducting region 15a, 15b here each have a cross-sectional area B, which continuously reduces in size from the cold (near the magnetic coil system) end 18a, 18b to the warm (close to room temperature connection) end 19a, 19b, which can be seen at the top decreasing diameter; By way of example, the cross-sectional area B is approximately in the middle (along the longitudinal direction) of the power supply lines 5a, 5b in the normal-conducting region 15a, 15b located. In the exemplary embodiment shown, the cross-sectional area B decreases by a factor of approximately 3 (note that the diameter enters the cross-sectional area B in a square fashion, the diameter ratio cold-to-warm here being approximately 1.75). The cross-sectional reduction is set up here over the entire (vertical) length of the power supply leads 5a, 5b in the normally-conductive region 15a, 15b. Along the power supply lines 5a, 5b in the normal conducting region 15a, 15b cold storage 20 are coupled to this. The cold storage 20 are formed here as metallic masses 20a. In the example shown, in each case three stages 21, 22, 23 of the thermal coupling are set up, wherein at each of the stages 21, 22, 23 two cold stores 20 (left and right) at the same length position (the length direction runs in Fig. 1 vertical) are coupled. The cold storage 20 of the coldest stage 21 have a total of a heavy mass M1 which is greater than the entire heavy mass M2 of the cold storage 20 of the middle stage 22, and the entire heavy mass M2 of the cold storage 20 of the middle stage 22 is in turn greater than the entire heavy mass M3 of the cold storage 20 of the warmest stage 23. The cold storage 20 of the different stages 21-23, and here also within the stages 21-23, are spaced from each other in the vacuum region 11a of the vacuum vessel 11, to avoid a thermal short circuit.

At the lower, cold end 18a, 18b, the power supply lines 5a, 5b are coupled to the central radiation shield 7, so that a certain cooling capacity of the upper cold stage 9 of the active cooling device 4 can be used. In addition, the outer radiation shield 6 also contacts the power supply leads 5a, 5b in the normally conducting region 15a, 15b, here between the stages 22 and 23; Alternatively, a non-coupling implementation may be provided on the outer radiation shield 6.

When charging (or discharging) of the magnetic coil system 3 via the power supply lines 5a, 5b heat is generated in the power supply lines 5a, 5b in the normal conducting region 15a, 15b, which at least partially compensate for the cold storage 20 by heating the metallic masses 20a, whereby a heat input into the HTS Area 16a, 16b of the power lines 5a, 5b or even in the magnetic coil system 3 is reduced. The geometry of the power supply leads 5a, 5b in the region widening towards the cold end 18a, 18b Normal conducting region 15a, 15b reduces the ohmic heat development near the cold end 18a, 18b, and reduces a heat input from the space temperature warm end 19a, 19b ago. The heat _load (heat flow "down") in the area of the lowest stage 21 when loading WL _load can be limited compared to the heat _load in the equilibrium state during normal operation WL _gg , so that applies WL _load ≤ 2 * WL _gg . The remaining heat _load WL can be compensated by the active cooling device 4, so that the superconducting magnet coil system 3 and not the HTS region 16a, 16b of the power supply lines 5a, 5b inadmissible heated (above the respective transition temperature).

The Fig. 2 shows a second embodiment of a magnet assembly 1 according to the invention, which largely the design of Fig. 1 corresponds; only the essential differences will be explained below.

The cryostat 2 here has only one outer radiation shield 6, which is coupled to the upper cooling stage 9 of the active cooling device 4, and an inner radiation shield 8, which is coupled to the lower cooling stage 10, but not via a central radiation shield.

The power supply lines 5a, 5b in the normal-conducting region 15a, 15b each extend here with two cylindrical sections 25, 26, wherein the colder section 25 has a significantly larger cross-sectional area B ₁ compared to the cross-sectional area B _{2 of} the warmer section 26.

The lower portion 25 extends substantially in a cold storage 20, which is formed with a gas-tight container 27 and an evaporable substance 28 contained therein. The vaporizable substance 28 is liquid; slightly vaporizable substance 28 is already in the container 27th evaporated. The lower end of the container 27 is coupled via a heat-conducting element 29 with the lower cooling stage 10 of the active cooling device 4.

The upper portion 26 extends substantially in a cold storage 20, which is formed with a gas-tight container 30 and an evaporable substance 28 contained therein. The lower end of the container 30 is coupled via a heat-conducting element 29 to the upper cooling stage 9 of the active cooling device 4.

The lower container 27 is significantly larger than the upper container 30, and the lower container 27 contains significantly more (based on the heavy mass) vaporizable substance 28 than the upper container 30th

When charging (or discharging) of the magnetic coil system 3 via the power supply lines 5a, 5b heat is generated in the containers 27, 30, which at least partially compensates by evaporation of vaporizable substance 28 (which increases the gas pressure in the containers 27, 30), whereby a heat input is reduced in the HTS region 16a, 16b of the power supply lines 5a, 5b or even in the magnetic coil system 3 in the inner radiation shield 8. In normal operation, stored heat energy can be gradually released again via the heat-conducting elements 29 to the cooling stages 9, 10, which act as heat sinks, so that the vaporized substance can recondensate again. When designing the containers 27, 30, it should be noted that the evaporation and recondensation are isochoric processes, since no substance is allowed to escape from the containers 27, 30 during operation. The change in the latent heat with increasing pressure and rising temperature in the respective container 27, 30 must be taken into account accordingly.

The Fig. 3 shows a power supply 5a in the normal conducting region 15a for the invention. This here comprises N = 4 successive sections 41, 42, 43, 44, wherein each section 41-44 has its own, uniform cross-sectional area B1-B4. The cross-sectional areas B1-B4 decrease from the cold end 18a to the warm end 19a.

The different sections 41-44 are coupled to different cold storage 20, here in the form of metallic bodies 20a. The two coupled cold storage 20 of a section 41-44 contact each section 41-44 here approximately centrally relative to the vertical longitudinal direction of the power supply 5a by means of a short bridge element 45. The number K of the stages of thermal coupling, here each formed by the contacting of two cold storage 20 at a common length position, here is also 4, so that here K = N = 4. The total heavy mass Mi of the cold storage 20 of the four stages of thermal coupling decreases from the cold end 18a to the warm end 19a out.

Note that for setting a particular heat flux or temperature profile, the ratio Bi / Hi at the various sections 41-44 may also be varied, with Hi: length of the section i, with i = 1 to 4 for the sections 41-44. Typically, the ratio Bi / Hi decreases from the cold end 18a to the warm end 19a.

In the Fig. 4 is a further power supply 5a shown in the normal conducting region 15a, which largely the design of Fig. 3 so that only the main differences are explained.

The cold storage devices 20 are each coupled at the transitions between the sections 41-44 with short bridge elements 45, and in addition a pair of cold storage 20 is coupled at the lower, cold end 18a of the power supply 5a in the normal conducting region 15a via bridge elements 45.

The power supply 5a is hereby made integrally from a single part, e.g. as a metal plate cut into a corresponding shape.

The Fig. 5 shows a third embodiment of a magnet assembly 1 according to the invention, which largely the design of Fig. 1 corresponds; only the essential differences will be explained below.

In addition to the active cooling device 4, an active auxiliary cooling device 50 is also present here, which is coupled to the outer radiation shield 6 via a heat exchanger 51. The outer radiation shield 6 in turn contacts a part (a portion) of the power supply lines 5a, 5b in normal conducting region 15a, 15b, here between the stages 22, 23 of the thermal coupling. The auxiliary cooling device 50 can here a lowest operating temperature AT _help of about -60 ° C to achieve.

About the auxiliary cooling device 50, a part of the heat load occurring during charging from the power supply lines 5a, 5b are derived in the normal conducting region 15a, 15b, so that the active cooling device 4 is relieved. It is also possible to support the cooling in normal operation with the auxiliary cooling device 50.

The Fig. 6 shows a fourth embodiment of a magnet assembly 1 according to the invention, which largely the design of Fig. 5 so that only the main differences are explained below.

The active auxiliary cooling device 50 cools not only the heat exchanger 51 to the outer radiation shield 6, but also a heat exchanger 52, which in turn cools a heat exchanger 53 a temperature control device 54 for a sample 55 to be examined. The sample to be examined 55 is during their measurement by NMR spectroscopy in a non-illustrated held at a constant temperature, wherein the magnetic field generated in the normal operation of the magnetic coil system 3 of the magnet assembly 1 is used.

LIST OF REFERENCES

1

magnet assembly

2

cryostat

3

superconducting magnet coil system

4

active cooling device

5a, 5b

power leads

6

outer radiation shield

7

medium radiation shield

8th

inner radiation shield

9

upper cooling stage (heat sink)

10

lower cooling stage (heat sink)

11

vacuum vessel

11a

vacuum range

12

superconducting switch

12a

Superconducting charge and short circuit

13a, 13b

Connection (to the vacuum tank)

14a, 14b

Connection (on the charging and short-circuit circuit)

15a, 15b

normal conducting area

16a, 16b

HTS range

17a, 17b

LTS area

18a, 18b

cold end

19a, 19b

warm end

20

cold storage

20a

metallic body

21

coldest stage of thermal coupling

22

middle stage of thermal coupling

23

warmest stage of thermal coupling

25, 26

part Of

27

container

28

vaporizable substance

29

thermally conductive element

30

container

41-44

part Of

45

bridge element

50

active auxiliary cooling device

51-53

heat exchangers

54

tempering

55

sample

B

Cross sectional area

B1-B4

Cross-sectional area (subsection)

H1-H4

Length (subsection)

M1-M3

heavy masses

Claims (16)

Magnet arrangement (1), comprising a cryostat (2), a superconducting magnet coil system (3), an active cooling device (4) for the magnet coil system (3) and power supply lines (5a, 5b) for charging the magnet coil system (3) in the cryostat (2). .
wherein the power supply lines (5a, 5b) comprise at least one normally-conductive area (15a, 15b), in particular wherein the power supply lines (5a, 5b) also comprise an HTS area (16a, 16b),
wherein a plurality of cold accumulators (20) are thermally coupled to the power supply leads (5a, 5b) along the normal conducting region (15a, 15b) of the current supply leads (5a, 5b) in order to charge the magnet coil system (3) in the normally conducting region (15a, 15b) to absorb the resulting heat
characterized,
that the supply leads (5a, 5b) in the normal area (15a, 15b) B have a variable cross-sectional area along its extending direction,
wherein the cross-sectional area B decreases from a cold end (18a, 18b) to a warm end (19a, 19b) at least over a predominant portion of the total length of the power supply leads (5a, 5b) in the normally-conducting region (15a, 15b). Magnet arrangement (1) according to claim 1, characterized in that the power supply lines (5a, 5b) in the normal conducting region (15a, 15b) each have N successive sections (25, 26; 41-44), with N≥ 2, in particular 3≤ N≤7,
wherein the subsections (25, 26, 41-44) each one within a 41-44) have a constant cross-sectional area Bi, and that the cross-sectional areas Bi decrease from the cold end (18a, 18b) toward the warm end (19a, 19b). Magnet arrangement (1) according to claim 2, characterized in that different sections (25, 26, 41-44) are thermally coupled to different cold storage (20). Magnet arrangement (1) according to claim 2, characterized in that in each case at a transition of two partial sections (25, 26; 41-44) at least one cold storage (20) is thermally coupled, in particular also at the cold end (18a, 18b) of the Power supply (5a, 5b) in the normal conducting region (15a, 15b) is at least one cold storage (20) is thermally coupled. Magnet arrangement (1) according to one of the preceding claims,
characterized in that K along the power supply lines (5a, 5b) in the normal conducting region (15a, 15b) each K stages of the thermal coupling (21-23) are arranged, wherein at each stage (21-23) at least one cold storage (20) the power supply lines (5a, 5b) is thermally coupled,
with K≥2, in particular 3≤K≤7. Magnet assembly (1) according to claim 5, characterized in that a heavy mass Mi of cold accumulating material in the at least one cold storage (20) of a respective stage of the thermal coupling (21-23) via the steps (21-23) from the cold end ( 18a, 18b) decreases towards the warm end (19a, 19b). Magnet arrangement (1) according to one of the preceding claims,
characterized in that the cryostat (2) is designed as a cryogen-free cryostat (2). Magnet arrangement (1) according to one of the preceding claims,
characterized in that at least a part of the cold storage (20) as a gas-tight container (27, 30) is formed, wherein a part of the volume of the gas-tight container (27, 30) is filled with an evaporable substance (28). Magnet arrangement (1) according to claim 8, characterized in that the power supply lines (5a, 5b) extend in the normally conducting area (15a, 15b) at least partially within the containers (27, 30). Magnet arrangement (1) according to one of the preceding claims,
characterized in that at least a part of the containers (27, 30) with a lower end via a heat conducting element (29) to a heat sink (9, 10) of the active cooling device (4) is thermally coupled, and the boiling point of the container (27 , 30) contained substance (28) is above the temperature of the heat sink (9, 10). Magnet arrangement (1) according to one of the preceding claims,
characterized in that at least a part of the cold storage (20) as a metallic body (20a) are formed. Magnet arrangement (1) according to claim 11, characterized in that a plurality of metallic bodies (20a) formed cold storage (20) spaced from each other in a vacuum region (11a) of the cryostat (2) are arranged. Magnet arrangement (1) according to one of the preceding claims,
characterized in that further active auxiliary cooling means (50) is present, to a part of the current supply leads (5a, 5b) in the normal area (15a, 15b) is thermally coupled, in particular wherein a lowest working temperature AT _help of the auxiliary cooling device (50) is higher is the lowest working temperature AT _{mss of} the active cooling device (4) for the magnet coil system (3). Magnet arrangement (1) according to claim 13, characterized in that the auxiliary cooling device (50) further to a radiation shield (6, 7, 8) of the cryostat (2) and / or a vacuum container (11) of the cryostat (2) and / or a Temperature control device (54) for a sample to be examined (55) is thermally coupled. Magnet arrangement (1) according to one of the preceding claims,
characterized in that the cross-sectional area B changes from the cold end (18a, 18b) towards the warm end (19a, 19b) by at least a factor of 3. Use of a magnet arrangement (1) according to one of the preceding claims,
wherein the magnetic coil system (3) via the power supply lines (5a, 5b) is charged and a charging current is selected and the variable cross-sectional area B and / or the cold storage (20) are arranged so that _load for a heat _load WL, which on a coldest Stage (21) of the power supply lines (5a, 5b) in the normal-conducting region (15a, 15b) during charging maximally acts, and for a heat load WL _gg on this coldest stage (21) in an equilibrium state with charged magnetic coil system (3) applies:
WL _load ≤ 5 * _gg WL, WL particular _load ≤ 2 * WL _gg.

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