EP0958585B1 - Current supply device for a cooled electrical device - Google Patents

Description

The invention relates to a power supply device with at least one between a higher temperature level and a lower temperature level electrical Pipe at its low-temperature end connected to a cooled electrical device and thermally coupled to a cold head of a pulse tube cooler which has a regenerator and a pulse tube. Such a power supply device is e.g. from "Advances in Cryogenic Engineering ", Vol. 41, 1996, pages 1443 until 1447.

One of the main problems in the design of cryogenic systems is the efficient introduction of relatively large currents into superconducting or semiconducting devices, such as are provided, for example, for magnetic field generation or for short-circuit current limitation or for voltage transformation or for current transmission. The greatest thermal leak in an insulated cryocontainer is often caused by the at least one electrical conductor of the power supply device, which is between a higher temperature level, in particular at room temperature of about 300 K, and a lower temperature level of, for example, 77 K, the temperature of the liquid nitrogen LN ₂ . runs on which the electrical device can be located. If the electrical line of the power supply device running between these temperature levels cannot be constructed with little loss and the resulting heat loss is not effectively dissipated, the cooling effort alone can question the technical or economic meaning of the entire system.

When designing known power supply devices, a distinction is made in particular between line-cooled and exhaust-cooled designs. Line cooled power supplies are generally cooled only by conduction from a cold end. If you optimize the dimensions so that the sum of the Joule losses of the metal of the line with a specific resistance ρ (T) and due to the heat transport determined by the temperature-dependent thermal conductivity λ (T) is minimal, then the specific loss is, that is Heat input per unit current, for copper about 43 W / kA when considering a single electrical line (see the magazine "IEEE Transactions on Magnetics", Vol. MAG-13, No. 1, 1977, pages 690 to 693).

In the case of exhaust gas-cooled power supply devices, the enthalpy of a vaporized coolant, for example of LN ₂ at 77 K or of liquid helium LHe of 4.2 K, is used to dissipate the heat loss introduced in countercurrent. This enables the specific loss between 300 K and 77 K to be reduced to approximately 25 W / kA, with approximately 0.56 liters of LN ₂ evaporating per hour, kiloampere and power supply line.

The amount of heat introduced into a cryostat dictates given a coolant supply, the service life of the cryogenic System that requires replenishment, or the size of one Cooling unit if no cooling liquids are used. It is also important for a user how high the necessary power at room temperature is provided for cooling must become. This service is e.g. in one Compressor of a cooling unit or in the manufacture of the liquid coolant consumed.

Depending on the specific application, a large number of embodiments for current supply devices are known (cf. the reference "Cryogenics", Vol. 25, 1985, pages 94 to 110 ). As a rule, copper or brass is used as the material for the electrical cable running between the different temperature levels. In the case of line-cooled power supply devices, the cold end is also often connected with good heat conduction, but in an electrically insulating manner, to the cold side of a refrigerator which operates in particular according to the Gifford-McMahon principle. In the case of exhaust gas-cooled power supply devices, at least a large part of the evaporated coolant is guided along the electrical line, which should have the largest possible surface so that an effective heat exchange takes place.

From the mentioned publication "Advances in Cryogenic Engineering" is a power supply device with the input characteristics mentioned. An efficient one Cooling their electrical lines is a cold head of one Pulse tube cooler in the upper, warmer area of a cryostat arranged between the electrical lines. The pulse tube cooler is with the power lines over a copper bridge well connected to heat, with the required insulation produced between the lines by the cold head itself becomes. Such a structure is correspondingly complex.

The object of the present invention is based on this State of the art an improved power supply device with reduced heat loss, reduced space requirements and to provide a simpler structure.

This object is achieved with those specified in claim 1 Measures solved. Accordingly, in a power supply device with the features mentioned at the beginning a portion of the electrical line of at least be part of the cold head.

So in the power supply device according to the invention a pulse tube cooler integral part of the device. It takes advantage of the fact that the cold head of such a pulse tube cooler compared to cold heads of conventional cryocoolers, e.g. work according to the Gifford-McMahon principle, is a simple component with no mechanically moving parts is advantageously inexpensive to manufacture and that due to the lack of further electrical drives against high voltages is isolable. The power supply device according to the invention thus represents an intermediate form in terms of heat technology between a line and exhaust-cooled power supply that does not require a flowing liquid coolant and one in relation to a line-cooled power supply causes a comparatively lower heat input. It thus combines the advantages of the two conventional ones Types of power supply.

Advantageous embodiments of the power supply device according to the invention emerge from the dependent claims.

deren Figur 1

eine erste Ausführungsform einer erfindungsgemäßen Stromzuführungsvorrichtung,

deren Figur 2

eine weitere Ausführungsform einer solchen Stromzuführungsvorrichtung

und

deren Figuren 3 bis 7

verschiedene Ausführungsformen bekannter Pulsröhrenkühler.

To further explain the invention and its developments, reference is made below to the drawing. Each shows schematically as a longitudinal section

whose figure 1

a first embodiment of a power supply device according to the invention,

whose figure 2

a further embodiment of such a power supply device

and

whose figures 3 to 7

different embodiments of known pulse tube coolers.

Corresponding parts are the same in the figures Provide reference numerals.

In the embodiment of a power supply device according to the invention shown in FIG. 1, generally designated 2, parts of a cold head 3 of a pulse tube cooler are used to conduct the electrical power between a warmer side, in particular at room temperature RT, and a colder side, for example at low temperature TT of 77 K LN ₂ side. The cold head 3 projects at least with its colder part into the vacuum space V of a vacuum vessel 4 or a cryostat. Instead of the vacuum space of a vacuum vessel, the interior of a (bath) cryostat can also be provided with the cold head or cold head part. The cold head has a regenerator 6 and a pulse tube 7, which are connected to one another at their low-temperature ends via an overflow line 15. The power line forms the cladding tube 6a of the regenerator 6 and / or the cladding tube 7a of the pulse tube 7 in a coaxial or parallel design. In this case, either the regenerator and the pulse tube can be electrically insulated from one another and form two electrical lines which are at different potential, as is assumed in the exemplary embodiment shown. Or these parts can also be connected in parallel. In the figure, 8a and 8b also denote the power connections at the warmer temperature level RT, 9a and 9b the corresponding power connections at the lower temperature level TT, with 10 an installation opening for the cold head 3 in the vacuum or cryostat vessel 4, with 11 the cold head 3 on its warmer side, insulating mounting flange, which ensures a vacuum or gas-tight seal of the installation opening 10, with 13 a gas inlet and / or outlet on the regenerator, with 14 a gas inlet and / or outlet on the pulse tube , with 15 the, for example, electrically insulating overflow line between the regenerator and the pulse tube, and with 16 a connection for a thermal busbar. An external power supply unit located at room temperature RT, for example, is to be connected to the power connections 8a and 8b, while a cooled electrical device, which is generally to be kept at the low temperature TT, is connected to the power connections 9a and 9b. The electrical device can be, in particular, a cable, a current limiter, a magnetic field winding or parts of electronics, each with superconducting material. LHe cooling technology can generally be used for classic superconductor materials such as Nb ₃ Sn or NbTi and for metal oxide superconductor materials with a high transition temperature such as Y-Ba-Cu-O or (Bi, Pb) -Sr-Ca-Cu-O- Typically an LN ₂ cooling technology can be provided. However, the electrical device can also have normal-conducting or semiconducting parts to be cooled and need not necessarily be at exactly the temperature level TT.

The embodiment shown in Figure 2 of a designated 22 Power supply device differs from that Embodiment according to Figure 1 in that its cold head 23 one Pulse tube cooler only by means of its regenerator 26 Power supply is used. The regenerator contains as current-carrying part in the form of a metallic body e.g. a tightly rolled metal net packed in its cladding tube 26a 26b. Instead of the metal mesh, a porous one can also be used Sintered metal granule body or a bundle of thinner Wires or at least a thin, rolled or folded one Serve metal strips or a number of profile sheets. This metallic bodies are on the warm and cold end e.g. electrically contacted by soldering, welding or pressing. A bundle of thin wires is particularly suitable for an introduction of alternating current, since the wire thickness is the skin depth can be adjusted. In the embodiment according to the figure However, 2 is compared to a stack of fine wire nets the heat conduction in the regenerator is greatly increased, so that this Embodiment preferably only for comparatively large Currents is considered.

In the power supply devices according to the invention, such as they emerge from Figures 1 and 2, an electrical Isolation advantageous by dielectric, e.g. plastics and / or ceramics. On the low temperature side Sapphire, BeO or aluminum nitride are also preferred to use, which advantageously have a high thermal conductivity. This means that other components to be cooled, e.g. Radiation shields or electrical or magnetic apparatus be thermally coupled. A separation of potentials between a compressor with possibly electrical Valve train and the power supply device can e.g. through an insulating connecting pipe, for example made of plastic, fiber-reinforced plastic or ceramic can be reached.

The pulse tube coolers used for a power supply device according to the invention are based on embodiments known per se (cf., for example, "Cryocoolers 8 ", Plenum Press, New York, 1994, pages 345 to 410; or "Advances in Cryogenic Engineering", vol. 35, plenum Press, New York, 1990, pages 1191 to 1205; or "INFO PHYS TECH" of the VDI Technology Center, No. 6 / February 1996, with the title: "Pulse tube cooler: New refrigeration machines for superconductivity and cryoelectronics", 4 pages; or US 5,335,505 A ). Such a pulse tube cooler has, according to FIG. 3, a cold head 33 which is generally surrounded by an insulating vacuum, at least with its colder part. This cold head has two tubes connected to each other. A tube is designed as a so-called regenerator 36 and contains in its interior a body which stores the gas heat periodically, for example in the form of stacked metal meshes 36a with a small mesh size. In the embodiment of a power supply device 22 according to the invention according to FIG. 2, this body is used for power conduction. In contrast, the other tube represents a so-called pulse tube 37, which only has heat exchangers 38 or 39 formed at each of its warm and cold ends, for example formed by fine copper networks, and is otherwise hollow. The two not necessarily tubular parts 36 and 37 are connected at their ends lying at low temperature TT by means of an overflow channel 40 for a coolant. A first supply line 41 serves to supply the regenerator 36 with a generally uncooled, in particular at room temperature RT working gas, for example He gas, under high pressure via the valve train 42a pulsating at a frequency, for example between 2 Hz and 50 Hz. During a low-pressure phase of the pulse tube cooler, working gas is also discharged again via the supply line 41 by means of a valve drive 42b. The pulse tube 37 can be connected at its room temperature end via a connecting channel (not shown in the figure) to a second supply line which, depending on the design of the pulse tube cooler, leads to a further valve train (not shown in the figure) or to a buffer volume of the working gas, for example a few liters in size leads (see Figures 5 to 7). FIG. 3 also shows a compressor 43 which is connected to the first connecting line 41 by means of an outgoing line 41a with a (high-pressure) valve 42a for the working gas under high pressure and a return line 41b with a (low-pressure) valve 42b for the working gas is connected under low pressure.

While in the embodiment shown in Figure 3 Cold head 33 of a known pulse tube cooler regenerator 36 and pulse tube 37 spatially parallel or possibly are also arranged spatially one behind the other in the in Figure 4 shown embodiment of the cold head 45 a another known pulse tube cooler a concentric (Coaxial) arrangement of pulse tube 47 and surrounding it Regenerator 46 provided. In this embodiment is the working gas by means of a pump device 48 with a working piston 48a funded.

In all of these embodiments of known pulse tube coolers periodically one through the working piston 48a or pressure wave generated by the compressor 43 with valve train let in, which is pre-cooled in the regenerator 36 or 46 and in the pulse tube 37 or 47 is relaxed so that a usable cooling capacity arises. The relaxed, cold gas then cools the regenerator as it flows out of the pulse tube.

Embodiments of corresponding phase shifters on the warm 5 to 7 show the end of the pulse tube, with a Cold head 33 according to FIG. 3 is used as a basis. According to Figure 5 a buffer volume 51 with throttle 52 is provided for this purpose. In addition, as shown in Figure 6, a second inlet from the warmer Regenerator side forth via a line 53 with nozzle 54 respectively. According to FIG. 7, a corresponding phase shifter can be used also be formed with four valves 42a, 42b, 55a and 55b.

In addition, current supply devices according to the invention can also be based on two-stage and multi-stage variants of pulse tube coolers (cf., for example, magazine "Cryogenics", vol. 34, 1994, pages 259 to 262 ).

Of course, other embodiments of the invention are also Power supply devices than those in the Figures 1 and 2 conceivable: For example, design features the power supply device 2 according to FIG. 1 and the power supply device 22 according to FIG. 2 combined be, so that then the electrical current both within of the regenerator and also flows through its cladding tube. All Variants can also be carried out coaxially and in parallel be one, two or more power lines with different Potentials in a cold head are conceivable. It can also have multiple power supply devices on one Compressor are operated. Provided a cooling level for one Certain application is not sufficient, two or multilevel versions can be built by at the cold end the warmer stage the warmer end of another, colder one Stage is connected. A corresponding arrangement can as a thermal series connection of several cold heads be considered.

1. Die Wärmeverluste sind im Vergleich zu einer leitungsgekühlten Stromzuführungsvorrichtung deutlich reduziert. Die Stromzuführungsvorrichtung 2 nach Figur 1 nutzt nämlich die elektrische Leitfähigkeit der Hüllrohre 6a und 7a von Regenerator 6 und Pulsröhre 7, die ohnehin vergleichsweise massiv sind, um einem Arbeitsdruck von typischerweise 20 bar Heliumgas standzuhalten. Beispielsweise kann ein Edelstahlrohr von 1 mm Wandstärke, 20 mm Durchmesser und 200 mm Länge einen Strom von 32 A optimal übertragen, wobei die Verluste gegenüber einer mit einem Pulsröhrenkühler nur indirekt gekühlten Stromzuführungsvorrichtung bei Belastung mit dem Nennstrom auf ein Drittel reduziert sind. Im stromlosen Zustand ergibt sich überhaupt kein zusätzliches Wärmeleck. Bei großen Strömen werden vorteilhaft größere Wandstärken bzw. Materialien höherer spezifischer Leitfähigkeit wie z.B. Messing oder Bronze oder Kupfer eingesetzt. Eine weitere Verlustreduktion ergibt sich durch den Gegenstromkühleffekt in Regenerator 6 und Pulsröhre 7, der durch das kalte Arbeitsgas erreicht wird. Um diesen Effekt noch zu erhöhen, können gegebenenfalls weitere Verbesserungen angebracht werden, die z.B. in Rohren mit variablem Querschnitt oder zusätzlichen Wärmetauschern auf verschiedenen Höhen in der Pulsröhre bestehen. Auch können Maßnahmen zur Vergrößerung der Oberfläche, beispielsweise durch besondere Rippen oder durch eine Aufrauhung oder eine Besinterung der Innenflächen mit einem porösen Metall vorgesehen werden. Bei der Stromzuführungsvorrichtung 22 nach Figur 2 ist die Ersparnis besonders groß, da ein optimierter Regenerator 26 ohnehin eine große Oberfläche aufweist, so daß die Kühlung durch das kalte Arbeitsgas thermodynamisch besonders effektiv ist.

2. Da bei der Stromzuführungsvorrichtung der Kaltkopf kein separates Bauteil darstellt, ergeben sich entsprechende Kosteneinsparungen. Die integriert gekühlte Stromzuführungsvorrichtung arbeitet zudem kryotechnisch gutmütig, da sie kein warmes Endstück in ein Kryostatsystem einzubringen braucht, das erst mit beträchtlichem konstruktiven Aufwand an ein Kältereservoir angekoppelt werden muß.

3. Durch gemeinsame Auslegung der Stromzuführungsvorrichtung und des Pulsröhrenkühlers kann die Kühlleistung des Pulsröhrenkühlers optimal an die Verluste der Stromzuführungsvorrichtung angepaßt werden. Dadurch lassen sich Verluste einsparen, die häufig durch die erforderliche Überdimensionierung des Kühlers auftreten.

4. Sofern die Kühlleistung am kalten Ende auf z.B. 77 K groß genug gewählt wird, können weitere Kryostatverluste z.B. aufgrund einer Wärmeeinstrahlung ohne weitere Kühleinheit oder Nachschub von Kryoflüssigkeiten ausgeglichen werden.

5. Durch den einfachen Aufbau ist eine ökonomische Anpassung an den Strombedarf eines gegebenen Kryosystems auch durch eine modulare Bauweise möglich, bei der mehrere Stromzuführungsvorrichtungen an einen gemeinsamen Kompressor mit Ventiltrieb angeschlossen werden.

6. Herkömmliche Stromzuführungsvorrichtungen, die für einen bestimmten Nennstrom optimiert sind, können am warmen Ende betauen oder sogar vereisen, wenn bei einem Unterstrom die abzuführende Joule'sche Wärme reduziert ist. Dabei besteht für Hochspannungs-Stromzuführungen die Gefahr, daß sich die Überschlagsfestigkeit verringert. Bei der integriert gekühlten Stromzuführungsvorrichtung nach der Erfindung kann diesem Effekt durch eine entsprechende Reduktion der Kühlleistung auf einfache Weise entgegengewirkt werden. Dazu wird z.B. die Betriebsfrequenz des Ventiltriebs oder des Kolbens, der eine periodische Heliumdruckwelle erzeugt, gesenkt.

With the inventive integration of at least one cold head of a pulse tube cooler into a power supply device, a number of significant advantages are achieved compared to known embodiments:

1. The heat losses are significantly reduced compared to a line-cooled power supply device. The power supply device 2 according to FIG. 1 uses the electrical conductivity of the cladding tubes 6a and 7a of the regenerator 6 and pulse tube 7, which are comparatively massive anyway in order to withstand a working pressure of typically 20 bar helium gas. For example, a stainless steel tube with a wall thickness of 1 mm, a diameter of 20 mm and a length of 200 mm can optimally transmit a current of 32 A, the losses being reduced to a third compared to a power supply device that is only indirectly cooled with a pulse tube cooler when loaded with the rated current. In the de-energized state there is no additional heat leak at all. For large currents, larger wall thicknesses or materials with higher specific conductivity, such as brass or bronze or copper, are advantageously used. A further reduction in losses results from the countercurrent cooling effect in the regenerator 6 and pulse tube 7, which is achieved by the cold working gas. In order to increase this effect, further improvements can be made, if necessary, for example in tubes with a variable cross-section or additional heat exchangers at different heights in the pulse tube. Measures can also be provided to enlarge the surface, for example by means of special ribs or by roughening or sintering the inner surfaces with a porous metal. In the case of the power supply device 22 according to FIG. 2, the savings are particularly large, since an optimized regenerator 26 has a large surface area anyway, so that the cooling by the cold working gas is particularly thermodynamically effective.

2. Since the cold head is not a separate component in the power supply device, there are corresponding cost savings. The integrated cooled power supply device also works cryotechnically good-naturedly, since it does not need to introduce a warm end piece into a cryostat system, which only has to be coupled to a cold reservoir with considerable design effort.

3. By jointly designing the power supply device and the pulse tube cooler, the cooling capacity of the pulse tube cooler can be optimally adapted to the losses of the power supply device. This makes it possible to save losses that often occur due to the over-dimensioning of the cooler.

4. If the cooling capacity at the cold end is selected to be sufficiently high, for example 77 K, further cryostat losses, for example due to heat radiation, can be compensated for without any further cooling unit or replenishment of cryogenic liquids.

5. Due to the simple structure, an economic adaptation to the power requirements of a given cryosystem is also possible through a modular design, in which several power supply devices are connected to a common compressor with a valve train.

6. Conventional power supply devices that are optimized for a certain nominal current can condense or even freeze at the warm end if the Joule heat to be dissipated is reduced in the case of an undercurrent. There is a risk for high-voltage power supplies that the flashover resistance is reduced. In the integrated cooled power supply device according to the invention, this effect can be counteracted in a simple manner by a corresponding reduction in the cooling capacity. For this purpose, for example, the operating frequency of the valve train or the piston, which generates a periodic helium pressure wave, is reduced.

Claims (11)

1. Power supply apparatus (2,22) having at least one electrical line which runs between a higher temperature level (RT) and a lower temperature level (TT) and is connected at its end on the low-temperature side to a cooled electrical device and thermally coupled to a cold head (3,23) of a pulse tube cooler, which cold head has a regenerator (6,26) and a pulse tube (7,27), characterized in that at least one portion of the electrical line is formed by at least one part (6a, 7a, 26b) of the cold head (3, 23).
2. Power supply apparatus according to Claim 1, characterized in that an encasing tube (6a) of the regenerator (6) and/or an encasing tube (7a) of the pulse tube (7) is provided as a line portion.
3. Power supply apparatus according to Claim 1 or 2, characterized in that a metallic body (26b) is provided in the interior of an encasing tube (26a) of the regenerator (26), as a line portion.
4. Power supply apparatus according to Claim 3, characterized in that the metallic body (26b) is a metal mesh, a sintered body, a wire bundle or at least one sheet-metal strip.
5. Power supply apparatus according to one of Claims 1 to 4, characterized in that two different, mutually insulated, line portions are formed by the regenerator (6) and the pulse tube (7).
6. Power supply apparatus according to one of Claims 1 to 4, characterized in that two electrically parallel-connected line portions are formed by the regenerator (6) and the pulse tube (7).
7. Power supply apparatus according to one of Claims 1 to 6, characterized by the regenerator (6) and the pulse tube (7) being arranged physically parallel.
8. Power supply apparatus according to one of Claims 1 to 6, characterized by the regenerator and the pulse tube being arranged physically concentrically.
9. Power supply apparatus according to one of Claims 1 to 8, characterized in that the cold head is designed with a plurality of stages.
10. Power supply apparatus according to one of Claims 1 to 9, characterized in that at least the colder part of the cold head (3, 23) projects into the vacuum area (V) of a vacuum vessel (4), or into the interior of a cryostat.
11. Power supply apparatus according to one of Claims 1 to 10, characterized by an electrical connection to a superconducting device.

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