WO2017037259A1

WO2017037259A1 - Coil device with persistent current switch

Info

Publication number: WO2017037259A1
Application number: PCT/EP2016/070764
Authority: WO
Inventors: Tabea Arndt; Marijn Pieter Oomen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2015-09-03
Filing date: 2016-09-02
Publication date: 2017-03-09
Also published as: DE102015216882A1

Abstract

The invention relates to a coil device with at least one electric coil winding with superconductive conductor material. The coil winding is part of a closed current circuit for forming a persistent current. The closed current circuit has a persistent current switch with a switchable conductor portion which can be switched between a superconductive state and a normal conductive state. The switchable conductor portion has a high-temperature superconductive conductor and a resistance of at least 300 ohm in the normal conductive state of the conductor. A decay resistor of at least 50 ohm and/or a load with an effective resistance of at least 50 ohm is connected parallel to the switchable conductor portion. The invention further relates to a persistent current switch for such a coil device and to a method for charging or discharging a persistent current.

Description

description

The present invention relates to a coil device having at least one electrical coil winding with superconducting conductor material, wherein the coil winding is part of a self-contained circuit for forming a continuous current, and wherein the closed circuit has a permanent current switch with a switchable conductor section which between a superconducting state and a normal conducting state is switchable. Furthermore, the invention relates to a continuous current switch for such a coil device and a method for loading or unloading a continuous current in a coil winding of such a coil device.

From the prior art, various applications are ^¬ be known, in which superconductive coils are used to maintain a constant current in a closed superconducting circuit with virtually no loss. This can be used at ^¬ play, for generating magnetic fields and / or for storing energy. In magnetic resonance imaging and magnetic resonance spectroscopy, such superconducting magnet coils are used to generate the strong and temporally constant static magnetic fields required here. In rotating electrical machines shorted superconducting coils can be used to ^¬ to provide a permanent magnetic excitation field are available. Such a short-circuited coil can be arranged in particular on the rotor of such a machine. Another application of short-circuited superconducting magnetic coils is in the field of superconducting magnetic energy storage (SMES), in which the loading and unloading of such a short-circuited coil is used to temporarily store electromagnetic energy in the Mag ^¬ netfeld generated by the coil and then again in an outer Circuit to provide. The description One common application is that one typically

DC current flows permanently through a short-circuited coil while a stationary magnetic field is generated. The present invention is concerned with the specific probing of loading and unloading of the current flowing in such coils.

In order to load such a coil with a current, a superconducting persistent current switch is typi cally ^¬ integrated into the closed circuit. Such permanent current switch comprises a superconducting conductor portion which can be displaced by heating the pitch to a resistive conducting state at ^¬. If the coil is simultaneously connected to a power source in an external circuit, it can be charged with an open permanent-current switch.

Discharging the current flowing in the closed circuit through the coil winding current can be triggered intentionally or unintentionally. An intentional unloading can be done by a

Opening the persistent current switch are triggered, and the Spu ^¬ le can be connected to an external circuit, in which the previously flowing through the closed circuit current can at least partially discharge. This can be used, for example, to retrieve the energy stored in an SMES. On the other hand, when the coil is not connected to an external circuit during discharge, the electromagnetic energy stored in the coil is completely dissipated as heat in the area of the persistent current switch. This heat could destroy the switch in large magnet systems. Such an opening of the switch without an external circuit is therefore to be avoided there.

Discharging the coil can also be triggered in other ways than by controlled opening of the permanent-current switch: Thus, a local temperature increase in the coil winding can lead to the superconducting properties of the entire coil winding starting from this region. menbrechen. As a result of this heat development, the superconducting properties of the entire coil winding can break down, which is referred to as "quench." Such a quench can spread rapidly due to the thermal coupling of the various regions Typically, all of the helium will evaporate in such a quench, resulting in relatively high costs and failure in the useful life of the system In order to avoid damage to the superconducting conductor elements by locally overheating the conductors, the rapid propagation of such quench may even be promoted . A local overheating can be detected, and other preparation ^¬ che the coil winding can then also be intentionally brought to quenching, so that the current flow collapses as soon as possible and no damage to the first locally heated semiconductor region occurs. D This ti method is used üb ^¬ SHORT- in magnetic coils to protect the conductors from permanent overheating.

It may also be expedient to trigger such a quench via an emergency stop switch in order to enable a rapid shutdown of the magnetic field generated by the coil in the event of a fault of the coil device. Over such emergency stop one of the coils can be heated intentional ^¬ Lich example, to trigger a collapse of the superconductivity in the entire coil winding in the sequence.

A disadvantage of the described prior art is that in the discharge and quenching processes, a high part of the energy stored in the coil winding is dissipated as heat in the region of the coil winding. This can lead to unnecessary loss of expensive coolant, loss of energy and / or thermal stress on the sensitive superconducting conductor materials. Particularly in the case of magnetic resonance coils, the loss of the liquid helium in such quenching processes is a high cost factor. With SMES storage reels, the loss of stored ones is the most important Energy disadvantageous when a part of it is lost by quenching or controlled discharge as heat in the coil winding. Another disadvantage of the known persistent current switch is that the switching time for the opening of the switch is relatively slow and thus discharging the energy into an external circuit can be done only slowly. This, too, can lead to higher losses and higher heat development in the coil winding than would be the case with a faster discharge.

Object of the present invention is therefore to provide a coil device which avoids the disadvantages mentioned. In particular, a continuous current switch is to be specified with which a reduction in the dissipation of heat in the region of the electrical coil winding can be achieved. Another object is to provide such a continuous current switch for such a coil device and a method for loading or unloading a continuous current. These objects are achieved by the coil device described in claim 1, the persistent current switch described in claim 14 and the method described in claim 15. The coil device according to the invention comprises at least one electric coil with superconducting conductor material, wherein the coil winding is part of a CLOSED ^¬ Senen in itself circuit for forming a continuous current. The closed circuit has a persistent current switch with a switchable conductor section which is switchable between a superconducting state and a normal conducting state. The switchable conductor section has a high-temperature superconducting conductor and has a resistance of at least 300 ohms in the normal conducting state of the conductor. The switchable conductor section is a Abklingwiderstand of at least 50 ohms and / or a consumer with an effective resistance of at least 50 ohms parallelge ^¬ switches. Under a high-temperature superconductor or high-T _c - superconductor (HTS) is here generally a superconducting material with a transition temperature above 25 K to be understood. In some classes of materials, such as the cuprate superconductors, the critical temperature of these superconductors is even above 77 K, so that the operating ^{tempera ¬} ture can be achieved by cooling with other cryogenic materials as liquid helium. An advantage of high-temperature superconductors compared with many metallic low-temperature superconductors for use in said persistent current switch is that they often have a relatively high resistance in the normal conducting state and thus that the continuous current switch in the open state can also be made relatively resistant to breakdown.

In the coil device according to the invention, the continuous-current switch has a decay resistance of at least 50 ohms or a corresponding load connected in parallel with it. An essential advantage of this parallel current path is that, when the permanent current switch is opened, a large part of the electrical energy is diverted into this parallel current path and thus this part is not dissipated as heat in the coil winding or in the permanent current switch. The Abing resistance or the effective resistance of the consumer is at least 50 ohms large enough to avoid Abflie ^¬ Shen the continuous current in this parallel-connected current path in the closed state of the persistent current switch, because then the current in the almost resistance-free closed superconducting Current path of the coil winding and the continuous current switch flows.

The resistance of the persistent current switch of at least 300 ohms in the normal, that is opened, causes a state that flows in the open state of the persistent current switch, the current to the RESIZE ^¬ ßeren part about the Abklingwiderstand or the consumer, and only to a lesser extent on the normal conducting conductor portion of the permanent current switch. This advantageously achieves that when discharging the coil winding a smaller part of the energy previously stored in the coil winding is dissipated as heat in the coil winding and a larger part is either dissipated via the Abklingwiderstand or vice versa ^¬ sets. Thus, an energy loss within the closed circuit ^¬ ge of the coil winding and the continuous current switch is advantageously reduced. Especially beneficial ^¬ way the dissipation of thermal energy in the coil winding can be reduced so that the superconducting properties can be maintained in the coil winding, so do not quench the coil winding. In a cooling of the superconducting components with helium loss is then avoided at liquid helium or at least reduced because the surrounding cooling the superconductor ^¬ medium is not completely vaporized at the same time. In this way, the duration can be advantageously reduced to a possible re-loading of the coil winding. The persistent current switch according to the invention is designed for a coil device according to the invention. It has a switchable conductor section, wherein the latter comprises a high-temperature superconducting conductor and has a resistance of at least 300 ohms in the normal conducting state of the conductor. The advantages of the persistent current scarf ^¬ ters invention arise in conjunction with the other elements of the coil means and correspond to the advantages described above in connection with the coil means. The inventive method is used for loading or unloading a continuous current in a coil device according to the invention. In this case, the switchable conductor section of the permanent ^¬ current switch is switched from a superconducting state to a normal conducting state. The advantages of this method are analogous to the advantages of the coil device described above. Advantageous embodiments and further developments of the invention will become apparent from the dependent claims of claim 1 and the following description. In this case, the described embodiments of the coil device, the Dauerstrom- switch and the method can be combined miteinan ^¬ generally advantageous.

The coil means may comprise a cryostat for cooling the superconducting conductor material, wherein the superconductors tend coil winding and the switchable conductor portion are disposed in ^¬ nerhalb of the cryostat. The Abklingwiderstand and / or the consumer is then advantageously arranged outside the cryostat. With the help of the cryostat, the superconducting conductor materials of the coil winding and the switchable conductor section can be cooled to a temperature below the transition temperature of the respective superconductor, so that a continuous superconducting closed circuit can be obtained. The cryostat can be, for example, an open bath cryostat from which the coolant used can optionally evaporate. Alternatively, it may also be a cryostat with a closed coolant circuit, in which a coolant is either liquefied or can change between a liquid and a gaseous (or supercritical) state. The arrangement of the Abklingwiderstands or consumer outside the cryostat advantageously has the effect that the transferred during a discharge of the coil winding in the Abklingwiderstand or the consumer energy does not contribute to a heating of the interior of the Kryosta- th. A maintenance of the cooling and the superconducting operating state for the components arranged within the cryostat is thereby also made possible during the unloading of the coil. The switchable conductor portion may have a resistance which is larger of the Abklingwiderstand and / or the consumer advantageous normallei ^¬ conducting condition of the conductor. The main advantage of this embodiment is that after an opening of the persistent current switch, a greater part of the energy previously stored in the coil winding is dissipated via the Abklingwiderstand and / or the consumer and only a comparatively smaller part is dissipated in the region of the persistent current switch. Even a majority of the energy in the area of decay resistance and / or consumers is particularly advantageously dissipated. For this purpose, in particular the resistance of the switchable conductor section in its normal conducting state can be greater than a total resistance of the parallel current path having the decay resistance and / or the load. The resistance of the switchable conductor section may be, for example, at least a factor of 5, in particular by at least a factor of 20 higher than the total resistance of the parallel current path in the normally-conductive state.

The switchable conductor portion may have in the normal conducting state of the conductor to ^¬ a resistivity of at least 1000 ohms, particularly at least 5000 ohms. Such high resistances are particularly advantageous in order to implement a particularly high, in particular a majority, part of the energy previously stored in the coil winding in the area of the decay resistance and / or of the load and only a small dissipation of energy in the region of the coil winding and / or or the permanent current switch to verursa ^¬ chen. The higher resistance values of at least 5000 ohms are particularly advantageous in connection with the application in SMES systems, since there only a particularly small proportion is to be dissipated in the region of the coil winding. The essential part of the energy stored in an SMES system should rather be able to reach a load connected in parallel to the constant-current switch when discharging. But for other systems, a particularly high resistance ^¬ stand of the open persistent current switch is generally advantageous: For example, when a voltage of about 20 kV is applied during the decay time, a leakage current of at least 1 MOhm in the open ^¬ th state only about 0.02 A come about. This will be done during the a short-term power of only 400 W is dissipated in the continuous current switch, which the permanent-current switch can advantageously endure for the duration of the switching. Thus, the switchable conductor portion in the normal stand to ^¬ of the conductor may have a generally advantageous Durchschlagfes ^¬ ACTION for voltages of at least 20 kV. This can achieve that does not occur even during scarf ^¬ least, so especially during the transition from superconductivity Tenden in the normal state of the switchable conductor section to a flashover and the shorted continuous current can be switched off controlled. A dielectric strength of at least 20 kV is appropriate to ^¬ particular for solenoid coils for magnetic resonance imaging, since very high local stresses at the persistent current switch can come about by the very high magnetic fields and very high continuous current during switching. In order to avoid a burn-through of the switch, for example, the resistance of the switchable conductor portion in the normal conducting state and its thermal coupling to the other components can be chosen so that the remaining leakage current, the continuous current switch at the maximum voltage occurring at a temperature in the range below 320 K. heated. The distance of the switchable conductor section should generally be long enough to achieve the required resistance in the normal conducting state. On the other hand, the cross section of the conductor section should be large enough to reach the current carrying capacity required for the respective continuous current.

The switchable conductor section may comprise a ceramic high-temperature superconductor. With a ceramic material has a high dielectric strength can it be enough ^¬ particularly well. In particular, in comparison to metallic low-temperature superconductors with such a ceramic material also a high resistance in the open state of the switch can be easily achieved. In the normal conducting state, a high resistance and / or a high dielectric strength To achieve the entire switchable conductor section, it is particularly advantageous if this conductor section has no continuous metallic conductive elements. In embodiments in which the ceramic superconducting material is deposited as a layer on a carrier, it is therefore advantageous if this carrier is not metallic, but is formed from poorly conductive or non-conductive materials such as glass, ceramic and / or composite materials. Alternatively, however, the conductor section can also have a ceramic superconducting conductor element present in bulk, that is to say in a solid form. If the superconducting ceramics are too high or too undefined resistance to the demands of continuous current scarf ^¬ ters, then a relatively poorly conducting paralleling stand parallel. Such a resistance can, for example, values in the range between 0.3 kOhm and

1000 kOhm.

Particularly advantageously, the switchable conductor section may comprise a material of the BaKBiO type. Under this type of a material to be understood, which is present as the compound of these four elements, in particular the compound of the composition Ba _x to ^¬ K _y Bi03, wherein, for example, x is about 0.6 and y may be about 0.4. This is a ceramic superconducting material, which is characterized by one for a

HTS material is ^¬ rich in comparatively low transition temperature in the loading of about 30 K and a relatively low upper critical magnetic field of approximately 60 mT.

In general, the upper critical magnetic field strength B _C 2 for the superconducting material of the switchable conductor section may be below or at 100 mT. Such a low kriti ^¬ specific magnetic field strength B _C 2 causes the shiftable LEI terabschnitt can be easily switched by a change of a locally we ^¬ kenden magnetic field. For example, the upper critical magnetic field strength B in the range _C 2 Zvi ^¬ rule 40 mT and 80 mT may be. Advantageously, the transition temperature for the superconducting material of the switchable conductor section is at most 50 K, for example between 25 K and 35 K. Such a relatively low transition temperature for a high-temperature superconductor causes the switchable conductor section to be easily switched by local heating. Alterna ^¬ tively to a real high-temperature superconductor, a superconducting material with a jump can in principle also similarly be temperature used below 25 K for the switchable conductor region, provided they are in this material is a ceramic material which is therefore not metal ^¬ cally conductive , An operating temperature for the superconducting state of the switchable conductor section can advantageously be between 4 K and 40 K. With such an operating temperature can be achieved that the conductor section can be brought into the normal ^¬ conductive state by a relatively small increase in temperature and / or a relatively small increase in a locally acting magnetic field. Particularly advantageously, the operating temperature of the superconducting state of the switchable conductor section between 10 K and 25 K. The switching time for switching the switchable Leiterab ^¬ section from the superconducting to the normally conducting state can advantageously be at most 0.5 s, in particular at Hoechsmann ^¬ least 0 , 1 s lie. Such a short opening time has the advantage that, for a discharge of the superconducting coil, a high proportion of data stored in the coil electrical energy to the Abklingwiderstand or Ver ^¬ consumers is transmitted and is thus not dissipated at constant current scarf ^¬ ter or the coil winding. This applies in particular ^¬ sondere for an incident in which the discharge of the coil winding is to be carried out as quickly as possible. Through such a rapid discharge in particular can be ^¬ it enough that it does not necessarily lead to completeness, ^¬ ended quenching. In other words, the electric Coil winding are discharged and still remain essentially in the superconducting state, for example, after a local heating, the opening of the persistent current switch takes place fast enough that only a small proportion of the stored energy is dissipated in the coil winding and thus remain the remaining portions of the coil winding supra ^¬ conductive , Also, the locally heated area can quickly reach its operating temperature after such a rapid unloading. For example, very quickly return back to its original operating state ^¬ a magnetic coil of a magnetic resonance apparatus according to such a local heating and a subsequent discharge of the coil when there is no quenching of the magnet coil and thus no complete evaporation of the surrounding liquid helium around takes place. This reduces downtime and coolant consumption. In particular, after such an incident, the system can be remotely restarted, and after a complete quench usually required visit of a service technician to refill the helium can be omitted.

By such a rapid switching the risk of local overheating of the conductor material of the coil can be further reduced at a (full or local) quench: Especially with coil windings with ceramic high-temperature superconductors or magnesium diboride, the risk of local overheating is particularly high, since these materials have a low thermal conductivity and such overheated ^{zones will} propagate correspondingly slowly. Rapid opening of the persistent current switch in the detection of a local quench can therefore effectively prevent material damage to these poorly thermally conductive superconductors.

By contrast, in embodiments in which the persistent current switch need not be designed for sudden discharge upon local heating of the coil winding, it is sufficient if the switch opens fast enough to allow controlled discharge of the current to the decay resistance. and / or to the consumer. So if in a magnetic resonance coil no sudden quench must be prevented, but only a controlled discharge or shutdown of the system is to be made possible, a switch opening time of up to 10 s may be sufficient. This is the case even in SMES systems or excitation coils of electric machines, which typically do not ge with such sudden quenching processes ^¬ expects to be and when unloading not as large amounts of energy must be dissipated as Magnetreso ^¬ nanzsystemen.

The coil device may have a further magnetic coil for generating a local magnetic field B _ext for switching the switchable conductor section. For example, an opening of the permanent current switch may be effected by a turning of such a magnetic coil by _ext by the Mag ^¬ netfeld B exceeding the upper critical magnetic field strength B ^¬ _C 2 of the superconductive material of the permanent current switch is effected. The opening of the persistent current switch can in principle be effected solely by a change in the lo ^¬ cal magnetic field or by a combination of magnetic and thermal switching. The magnetic field of the further magnet coil can also be an already superimposed pre handenen magnetic field thereby to generate a magnetic field B _ext with which the magnetic field strength exceeded B _C 2 who can ^¬.

The coil means may comprise a switchable arranged around the conductor portion with a shielding shorted ^¬ closed in itself current path, the short-circuited current path can be opened by a switchable portion of the conductor from ^¬ screen coil. In other words, the closed current path of the shielding coil can be opened via this further switchable conductor section, which considerably reduces the magnetically shielding effect. In this way, a magnetic background field, which was previously largely shielded by the shielding, on the switchable conductor area of the persistent current switch act and this brin ^¬ gene by exceeding its upper critical magnetic field strength B _C 2 in its normal conducting state, so open the persistent current switch.

As already described in the introductory part, may be copy in the coil means, for example, a Magnetspu ^¬ leneinrichtung for generating a magnetic field in a magnetic resonance imaging apparatus or Magnetresonanzspektros-. Alternatively, it can be an excitation coil device for generating an electromagnetic exciter field in a rotating electrical machine. Or it may, for example, be a magnetic coil device for storing energy in a superconducting magnetic energy store (SMES). In principle, the basic idea of the present invention is suitable for all systems in which a continuous current flows in a short-circuited superconducting coil system.

The superconducting conductor material of the coil winding may in principle be a different material than the superconducting material of the switchable conductor section. In particular, the material of the coil winding can also magnesium diboride aufwei ^¬ sen or it may be a metallic superconductor, so for example, a system based on NbTi or Nb3Sn material. Alternatively, the superconducting material of the coil winding and the persistent current switch may also be identical or at least have the same components. The SPU ^¬ lenwicklung may also have another ceramic HTS material than the persistent current switch, for example a material of the type REBa ₂ Cu ₃ O _x (short REBCO), where RE stands for a Ele ^¬ element of the rare earths or a mixture of such elements. In cases in which different superconducting materials are used for coil winding and permanent-current switch, these materials for the closed circuit must be superconducting or with a minimum of gene connection resistance are interconnected. Superconducting connections between a ceramic superconductor and an NbTi-based conductor are already known from the prior art. Due to the large coherence length of NbTi, such superconducting compounds are relatively easy to produce. For example, a solid ceramic superconductor can be provided with holes that are filled for contacting with NbTi filaments and superconducting solder. Alternatively, a contact can be created via a press sintering.

In the method for loading or unloading a continuous current, a magnetic field B _ex t acting at the location of the switchable conductor section can be changed for switching over. This change can be effected, for example, by switching a magnetic coil on or off or by breaking or joining a magnetic shielding coil. In this case, causes a higher local magnetic field B _ex t opening the switch and a lower local magnetic field closing the switch, provided that the relevant for the respective temperature upper critical magnetic field B _C 2 is exceeded or fallen below. Alternatively or additionally, opening of the switch can be effected by heating the switchable region, or closure of the switch can be effected by removal of the heating. In other words, the persistent current switch can be switched either magnetically or thermally or by a combination of both methods. In this case, the continuous current switch is generally opened for loading or unloading the coil winding and closed for operation of the coil winding in the continuous current mode.

The discharging of the continuous current can for example be selectively eliminated from ^¬ if a local heating is detected in the coil winding. A fast and especially automatic ^¬ diagram unloading in such an event, the coil winding before a complete collapse of the super- conducting protect the features and system from loss of coolant.

Alternatively, the discharge can also be triggered manually or otherwise controlled by a control unit, in ^¬ example, in a controlled shutdown of the system, in the removal of stored energy in an SMES system or even when pressing an emergency stop switch.

In the following, the invention will be described by means of some preferred embodiments with reference to the appended drawings, in which:

1 shows a schematic equivalent circuit diagram of a Spulenein ^¬ direction according to the prior art,

Figure 2 shows a schematic equivalent circuit diagram of a Spulenein ^¬ device according to a first embodiment,

Figure 3 shows a schematic equivalent circuit diagram of a Spulenein ^¬ direction according to a second embodiment,

FIG. 4 shows a schematic representation of the dependency of the upper critical magnetic field strength on the temperature for a persistent current switch according to a third exemplary embodiment,

FIG. 5 shows a persistent current switch according to a fourth exemplary embodiment,

Figure 6 shows a persistent current switch according to a fifth embodiment and

Figure 7 shows a persistent current switch according to a sixth embodiment.

1 shows a schematic equivalent circuit diagram of an SPU ^¬ leneinrichtung 1 according to the prior art is shown. Shown is a superconducting coil winding 3, which is arranged together with a persistent current switch 6 within a cryostat 11. By the cryostat, the superconducting conductor elements of the coil winding 3 and the Dauerstromschal ^¬ ters 6 to a temperature below their respective jump temperature to be cooled. About the coil winding 3 and the persistent current switch 6, a closed circuit 5 is formed in which a continuous current I i can flow almost lossless due to the supra ^¬ conductive properties and thus does not decay or only extremely slowly over time. In the coil device 1 may be, for example, punching han ^¬ a magnet coil means of a magnetic resonance apparatus. To charge the continuous current I i for the first time in the coil winding 3, the hitherto described part of the closed circuit to an external power source 13 may be connected ^¬ the in such a way that this current source is connected in parallel with the continuous current ^¬ switch 6. 13 The current source 13 is in this case arranged outside the cryostat 11. It can be electrically connected via a switch 10 with the other components. During operation of the coil device 1, it can either remain connected to the other components via a line as shown in FIG. 1, or it can also be disconnected from the coil device 1 after a loading operation. For loading, the continuous current switch is opened, that is, it is set from its superconducting state to a normal conducting state, whereby its line resistance increases greatly. In the open state thus flows only a small leakage current through the persistent current switch 6, and the majority of the power source 13, he testified ^¬ charging current I ₂ is fed as a current in the coil winding. 3 Now, if the persistent current switch closed by a change in its superconducting state, and then shut down the charging current I ₂ , the current I i remains as a ring-shaped continuous current in the coil winding. The switching of the persistent current switch is typically effected by turning on and off a heating element in the prior art.

A discharging of the coil device 1 shown in FIG. 1 can be triggered, for example, by a Lei ^¬ terabschnitt of the coil winding 3 is locally heated and there- through normal conducting becomes. According to the state of the art, such a region spreads rapidly and leads to a quenching of the entire coil, whereby the coil winding 3 is strongly heated. Controlled discharge into the parallel loading circuit external to the cryostat, similar to loading, would also be theoretically possible, but the known persistent current switches 6 are generally too slow to prevent complete quenching after initial local heating of a portion of the superconducting conductor ,

Figure 2 shows a similar schematic equivalent circuit diagram of a coil device 1 according to a first embodiment of the invention. Shown is an analogous to Figure 1 arrangement of coil winding 3, persistent current switch 6, cryostat 11 and external current source 13. In addition to these components, the persistent current switch 6 is a decay resistor 9a arranged outside the cryostat 11 is connected in parallel. The ^¬ ser Abklingwiderstand 9a has a resistance of 50 ohms WE nigstens. The loading of the coil device 1 by means of the current source 13 is analogous as for Figure 1 ^{¬ written} . Again, the power source after loading can either be disconnected or remain connected to the rest of the system. During charging, only an extremely small proportion of the charging current I _{2 flows} through the Abklingwiderstand 9a, since this resistance is significantly higher than the total resistance of the coil winding 3 in the superconducting state.

When discharging the current flowing in the coil winding 3 continuous current I i, in the embodiment of the coil device according to the invention by opening the persistent current switch 6, a significant portion of the flow through the parallel Abklingwiderstand 9a be effected. When the permanent current switch 6 is opened, a switchable conductor section of the closed circuit 5 is switched from a superconducting state to a normal conducting state, and the resistance increases accordingly. The resistance of the conductor section in the normal conducting state should here amounting to at least 300 ohms, so that when discharging only a small part of the current as leakage current I _{4 flows} through this open permanent current switch 6. The ratio between the current flowing through the discharge Abklingwiderstand 9a Ström I3 and the current flowing through the switch 6 open leakage current I ₄ is provided over give the ratio of the resistances of the Abklingwiderstands 9a and the opened switch ^¬. Therefore, a highest possible resistance of the geöffne ^¬ th permanent current switch 6 is advantageous in order to flow on unloading a very high proportion of the current through the Abklingwiderstand 9a and to avoid in particular an undesirable heating of the elements arranged in the cryostat. A controlled discharge can be triggered by switching the persistent current switch 6 in its normal conducting state. At a favorable resistance ratio may be dependent on voltage applied in the circuit 5, current and stored energy as well as the operating points of the superconducting conductor elements advantageously a quench the

Superconductivity in the coil winding 3 can be avoided. Under the operating point here in particular the Betriebstem ^¬ temperature and the locally acting in the region of the conductor magnetic field ^¬ is to be understood.

An uncontrolled, ie spontaneously triggered discharge, can be triggered as described by a local heating of a conductor region of the coil winding 3. Advantageously, such a local quench can be detected by a sensor, and then an opening of the persistent current switch 6 can be triggered, which as described above subsequently causes a discharge of a large part of the current as discharge current I3 via the Abklingwiderstand. Again, with a sufficiently high resistance ratio and in turn dependent on voltage, current, energy and operating points due to the rapid discharge quenching of the entire coil winding 3 can be advantageously avoided. Advantageous for a successful avoidance of such a complete constant quench is a sufficiently fast opening time of the persistent current switch 6, which may advantageously be less than 0.5 s. Such rapid switching may in particular be possible when switching between the superconducting state and the normal conducting state is caused at least in part of a locally acting Magnetfel ^¬ by the change of, since such a magnetic field can be switched much faster typically as the temperature of the switchable conductor portion can be changed. Due to the heat capacities of the elements typically thermally coupled to such a conductor section, purely thermal switching is normally slower than switching based at least in part on the change of electromagnetic fields. Fast switching is thus advantageous, above all, for avoiding quenching in the event of spontaneous discharge. If such a spontaneous He ^¬ eignis however, largely ruled by the choice of operating conditions of the coil winding 3 and just have a controlled unloading are made possible, then your thumb can also be switched erstromschalter 6 slower, so, for example, by means of heat-triggered switching.

Figure 3 shows a schematic equivalent circuit diagram of an SPU ^¬ leneinrichtung 1 according to a second embodiment of the invention. The coil device 1 is similarly constructed as in the example of Figure 2. In contrast to this, in the ^¬ Abklingwiderstandes 9a place a consumer 9b parallel to the constant current circuit 5 is arranged. The example of FIG. 3 may be, in particular, an SMES system, in which excess electrical energy of a superordinate energy source is used

Circuit cached in the coil winding 3 who ^¬ can. In order to make this energy usable for the consumer 9b, a controlled discharging process can again be triggered by opening the persistent current switch 6. Analogously, as described above, when the switch 6 is open, a discharge current I _{5 flows} through the load 9b, so that the electrical energy previously stored in the coil winding can be used by the consumer 9b. To a high To ensure utilization efficiency for this energy, the relationship between the resistance of the open persistent current switch 6 and the effective resistance of the Ver ^¬ brauchers 9b should therefor be very high, for example at least 10: 1, especially at least 100: 1. Thus, a current flowing through the open permanent current switch leakage current I _{4 are kept} as low as possible and the associated energy consumption is reduced. An additional, optional switch 10a can be arranged in the example of FIG. 3 between the consumer and the coil winding 3 in order to connect the consumer to the energy storage system only when required.

FIG. 4 shows a plot of the locally acting magnetic field B _ex t in the region of a continuous current switch 6 against the temperature T. As a curve, the dependence of the upper critical magnetic field strength B _C 2 of the superconducting material of the switchable conductor section on the operating temperature T, ie B, is in this coordinate system _C 2 (T) shown. This curve B _C 2 (T) is a relatively shallowly decreasing function of temperature in the low temperature range and decreases steeper and steeper towards higher temperatures. T _c indicates the critical temperature of the material for a local magnetic field B _ext going to zero. Above this temperature no superconducting state is possible. Shown is a schematic exemplary course for a ceramic superconductor material, wherein the exact values are highly dependent on material. For operating points P - ie value pairs of operating temperature T _P and local magnetic field B _P - which are left below the curve shown, the switchable conductor material is superconducting, for operating points right above the curve, it is normally conducting. By a shift of the shown, initially superconducting operating point P on the curve B _C 2 (T) addition, thus opening the persistent current switch is possible.

As shown in Figure 4, such a opening Dau ^¬ erstromschalters can be ^¬ acts in different ways in principle because either the temperature dependence of the sup- raleitenden properties or the magnetic field dependence or both can be exploited simultaneously. The arrow marked with the reference numeral 14a shows a change of the operating point P, in which only the temperature is changed. Such a purely thermal switching in the normallei ^¬ border operating range can therefore be triggered by a local heating of the switchable conductor section. In ^{contrast to} this, the arrow marked with the reference symbol 14b shows a change of the operating point P, in which only the locally acting magnetic field B _ex t is changed. In such a purely magnetic switching, for example, by switching on a magnetic coil or by interrupting a magnetic shield, a collapse of the superconductivity can be effected. Finally, the arrow indicated by the reference numeral 14c shows a combined thermal-magnetic switching in which the material is brought into the normal conducting state by simultaneous change of temperature and magnetic field. In this case, the proportion of the change of these two operating parameters can also be chosen differently. It is essential that such a change can be effected particularly effectively by a combination of both changes. For the switching variants 14b and 14c, in which the opening is effected at least in part by the change ^¬ tion of the magnetic field B _ex t, the switching can generally generally be faster than in the purely thermal switching 14a. Especially in ceramic high-temperature superconductors, which are preferred for the present invention due to their poor conductivity after collapse of the superconductivity, a purely thermal switching by the poor thermal conductivity is typically slower than an at least magnetically supported Schal ^¬ th.

In order to enable the fastest possible switching, it is favorable when the operating point P indicated schematically ^¬ table as shown in Figure 4, rather in the vicinity of the flat portion of the curve B _C 2 (T). Then even a slight change in the local magnetic field B _ex t can trigger an opening of the switch. while the risk of accidental opening due to thermal fluctuations is low.

Advantageously, a distance of the operating point P from the curve B _C 2 (T) with respect to the magnetic field coordinate at Höch ^¬ least ΔΒ = 100 mT, in particular between 10 and 50 mT. The distance with respect to the temperature coordinate can be advantageous ^¬ at least 3 K, in particular between 10 K and 40 K.

For example, the switchable conductor section in the permanent ^¬ current switch of the third embodiment based on a Ma ^¬ material of the type BaKBiO. This switchable Leiterab can ^¬ cut advantageous see at an operating point be- 10 and 25 K and between 0 and 50 mT are operated. As a result, a fast switching, which is at least partially triggered magnetically, facilitated. When using a low-temperature superconducting material or magnesium diboride for the coil winding 3 so the operating temperature of the persistent current switch is also relatively close to Be ^¬ operating temperature of the coil winding, so that no excessively high temperature gradient within the cryostat 11 or via the conductor loop of the circuit. 5 must keep away upright ^¬.

Figure 5 shows a persistent current switch 6 according to a fourth embodiment of the invention. Shown is a supralei ^¬ tender conductor 23 which is connected in the further course not shown here with a coil winding 3 to a closed circuit 5, similar to the figures 2 and 3.

The superconducting conductor 23 has a switchable Leiterab ^{¬ section} 7, which is arranged in this example within a Ab ^¬ screen coil 15. This shielding coil 15 serves to shield an existing external magnetic field in the region of the switched conductor section 7, wherein the Mag ^¬ netfeld is without shielding above the given at the operating temperature Tempe ^¬ B _C 2 (T). In this existing external magnetic field, it may be at least partially that of the Coil winding 3 field generated act. In particular, it may be the comparatively strong background field of Mag ^¬ netresonanzgeräts. The arranged around the switchable Leiterab ^{¬ section} shielding coil 15 reduces this external magnetic field in its interior considerably, so that the section 7 is largely shielded in normal operation of the magnetic field. Thus, according to the figure, an operating point P can be set below the B _C 2 (T) curve. The shielding effect of the coil 15 can in turn be canceled out or at least reduced by switching over the coil properties. For this purpose can be geöff within the shielding 15 ^¬ net connect.

For example, as shown in FIG. 5, the shielding coil 15 may be a cylindrical coil. It can in turn also have a superconducting material, in particular a zy ^¬ lindrisches superconducting element. To open the switch, the superconductivity is interrupted at least in a portion of the cylinder, whereby the shielding effect is largely eliminated. Then, also acts in the interior of the shielding coil a local magnetic field B above _C 2 (T), and the switchable conductor portion 7 is put in a normal direct ^¬ the state of the persistent current switch 6 is so ge ^¬ opens. For example, a hollow cylinder made of solid (bulk) superconductor material can be used as the shielding ^coil . Alternatively, a hollow cylinder coated with a cylindrical superconducting layer may be used. Suitable superconducting materials for Abschirmspu ^¬ le 15 are for example magnesium diboride or a material of the type REBCO. To interrupt the shield, a peripheral segment 15a of the cylinder can be heated with a heating element 17 so far that the superconductivity breaks down in this section 15a. The magnetic switching shown in Figure 5, in which a superconducting shielding coil 15 is in turn thermally switched, can be realized much faster than if the switchable conductor section would be directly thermally switched. A major reason for this is that the shielding must be dimensioned as a second switch for much lower withstand voltages and / or current carrying capacities than the continuous current Turn 6 in the main circuit 5. In particular, the conductor cross-section and / or circuit ^¬ mass can be lower. Thus, the shielding coil can be designed so that even with purely thermal switching a rapid change in their superconducting properties is possible. May alternatively be arranged to that shown in Figure 5 arrangement also so 15a, the heating element used for switching the shielding coil 15, that the inner switchable Leiterab ^¬ section 7 is heated with. And / or it can be arranged on the inside, an additional heating element to heat the conductor section 7 separately. In this way, a combined thermal-magnetic switching according to arrow 14c of Figure 4 can be realized.

FIG. 6 shows a schematic representation of another continuous-current circuit breaker according to a fifth exemplary embodiment of the invention. Shown again is a switchable conductor section 7, around which a shielding coil 15 is arranged. In contrast to the example of Figure 5 but is not a flat cylindrical conductor, but a coil winding with multiple windings w ± from a superconducting conductor material. The conductors of the outermost windings are in this case connected via a superconducting contact 19 to a closed shielding circuit. A switchable conductor section 15a of this shielding circuit is in turn thermally gekop- with a heating element 17 pelt over which the conductor portion can be brought into a conducting condition normallei ^¬ 15a. Here, too, a secondary thermal switch exists, via which a superconducting shielding can be switched off, so that a switchable conductor section 7 of the persistent current switch 6 is switched indirectly magnetically into a normally conducting state. Again, the thermal switching of Abschirmspu ^¬ le 15 can be done faster than would be possible with a purely thermal switching of the conductor portion 7, since the conductor the coil 15 does not have to be dimensioned for the high voltage strengths and current carrying capacities of the circuit 5 of the coil winding 3. Again, a switching of the switchable conductor portion may additionally through another optional and therefore not shown here heating element Be ^¬ rich of the conductor portion are supported 7, or ge ^¬ showed heating element 17 may alternatively be arranged so that this conductor portion 7 is with heated. The head of the shield coil 15 may for example be formed of similarity ^¬ Lichem superconducting wire as the coil 3. In particular, a Tieftemperatursupra- conductor or a magnesium diboride-based conductor can be used here. And technologies are known for such materials to the required superconducting contact 19 herzustel ^¬ len. Advantageously, the thermal conductivity of the material of the shielding winding supra ^¬ conductive 15 may be higher than in the superconducting material of the switchable conductor section 7, since no resistor to a high electric Wi possible in the normal state must be taken into consideration. When choosing a ceramic material for the schaltba ^¬ ren conductor section 7 and a metallic conductor material for the shield 15 can therefore be achieved in the secondary switching area 15a with thermal switching, a higher switching speed than with a purely ther ^¬ mixing switching of the conductor section. 7 it is possible. Supported by the magnetic switch with a thermally ge ^¬ switched secondary switch 15a thus opening the switching time of the permanent current switch 6 can be advantageously shortened.

In order to achieve an even shorter opening time of the persistent current switch, alternatively, the coil winding 15 with a fast magnetically switchable conductor material such

BaKBiO be trained. This can be switched, for example, with a magnetically coupled thereto magnetic coil. In other words, such a fast switching via a cascade of two superconducting magnetically switchable conductor regions.

In all the variants in which for switching a magnetic shield is removed, it is advantageous if the shielded from ^¬ volume is comparatively small. In particular, in magnetic resonance applications, the shielding should be chosen small in order to avoid magnetic field distortions in the imaged or measured volume. Even with the other variants of the magnetic, thermal or thermal-magnetic switching, it is advantageous to choose a pos ^¬ lichst small volume for the persistent current switch, since then the switching times can be kept very small. Advantageously, the volume of the continuous current switch is generally not more than 100 cm ³ .

In the embodiments in which a magnetic shielding is canceled for switching, it is advantageous if in series with the switchable conductor section 7, a second, not shown in the figures, is provided with a heating element thermally switchable conductor section. Such a serial second switch can be advantageously used to load the coil winding 3 with a charging current. For this charging process, the second switch should be opened, because at an initial charging of the coil system 1, the background field generated by the coil winding 3 is not yet large enough to enable a magnetic switching by canceling a shield. The same applies to a field winding which, as described below, interacts with a background field to exceed the B _C 2 (T) curve. In such cases, an additional thermal switch is useful to allow for initial charging and possibly complete discharge without the nominal background field. In this case, however, complete discharge is less critical, since a leakage current I ₄ flowing in the persistent current switch generally leads to a thermal load of the switchable conductor discharge during discharge. Section 7 and thus leads to a prolonged leaving the superconducting work area.

Figure 7 shows a schematic representation of another continuous current switch according to a sixth embodiment of the invention. In this embodiment, simplified two different variants of the switching are shown in a figure, which can either be used separately or optionally can be combined with each other.

Shown in turn is a switchable conductor section 7 of a continuous current switch 6, which is connected in this example via two sup ^¬ raleitende contacts 19 with a superconducting conductor 23 which forms a closed circuit 5 together with a coil winding 3, not shown here, similar to the figures 2 and 3. In this example, therefore, the switchable conductor portion 7 is formed of a different superconducting material than the remaining superconducting conductor 23. Such a choice of another material and the introduction of additional superconducting contacts 19 may optionally also in the embodiments of Figures 5 and 6 are used, so for each of the described switching variants. Alternatively, however, in principle a uniform superconducting material for switchable conductor section 7 and the remaining conductor 23 as well as the coil winding 3 can also be used for the respective variants.

In the example of FIG. 7, a magnetic field winding 21 is arranged around the switchable conductor section 7 or at least a part thereof. This magnetic field winding 21 is vorteilhat small compared to the coil winding 3, but they should be sufficient in the area of the conductor portion 7 a local Mag ^¬ netfeld B _ex t to reach above the respective B _C 2 (T). It advantageously has a comparatively low inductance, so that the magnetic field can be switched on quickly to ermögli ^¬ chen a rapid opening of the persistent current switch 6. The magnetic field winding 21 can be a superconducting conductor. However, they can in principle also be normally conductive.

The persistent current switch 6 is advantageous in this Schaltme- Thode in a region within the cryostat 11 angeord ^¬ net, in which the magnetic field of the coil winding 3 ^¬ comparison example is low. This is particularly important for magnetic ^¬ systems with high background magnetic fields, so B 2 (T) is not already exceeded the background field _C, but 21 only when switching on the magnetic field coil, the magnetic field of the magnetic coil 21 can then interact favorably with the background magnetic field B _C 2 (T), so that the magnetic field generated by the additional winding 21 need not be very large.

Particularly advantageous in the embodiment of Figure 7 for the switchable line section 7, a material with anisotropic, ie direction-dependent B _C 2 (T) can be used. For example, a crystalline material having a high B _C 2 (T) in crystallographic ab direction and a low B _C 2 (T) in crystallographic c direction can be used. The persistent current switch can then be aligned so that the background field is aligned in the down direction of the mate rials ^¬ and thus the superconducting portion of the curve according to Figure 4 is not left. Only by switching on the magnetic field winding 21 in the c-direction, a sufficiently high magnetic field B _ex t is generated to leave the supraleiten ^¬ the area below the B _C 2 (T) curve. In a further advantageous variant of the sixth embodiment, the Benö for the magnetic switching ^¬ preferential magnetic field strength can be reduced by forming a conductor geometry is chosen for the switchable semiconductor region 7, which promotes the formation of local field enhancements. For example, a flat, band-shaped conductor can be used and the magnetic field of the field winding 21 can impinge substantially perpendicular to such a strip conductor. Shielding currents in the conductor cause a field increase in the conductor Range of edges. Once these are 2 by exceeding the _C B (T) curve of normal-conductive, the field enhancement penetrates further into the interior before until all switchable Leiterab ^¬ section 7 becomes normally conductive. Thus, with a relatively small additional magnetic field of the field winding 21, the conductor portion 7 can be effectively and rapidly switched.

The embodiments described with a magnetic switch according to arrow 14b of Figure 4 represent in itself is completely permanent solutions for which the optio ^¬ dimensional heating element 17 shown in Figure 7 is not required. However, such a Heizele ^¬ element 17 may additionally be provided to assist the shifting operation and / or to accelerate in the manner of a thermo-magnetic switching according to arrow 14c of Figure 4. In Figure 7 the heating element sake of clarity with respect to the field winding 21 axially offset. However, it may advantageously be arranged to surround also on the same part ^¬ portion of the conductor 7 in the field winding and / or these, so that enhance the thermal and magnetic effects on the superconductive properties of the conductor material on a very short section ge ^¬ genseitig.

Alternatively to the embodiment shown in Figure 7, the field winding 21 may be omitted, and the switchable conductor portion 7 can in principle only by the heating ^¬ element 17 according to variant 14a of Figure 4 can be switched between its superconductive state and its normally conducting state. In comparison with the purely thermal switching of metallic superconductors, the thermal switching of ceramic superconductive conductor portions 7 can take place quickly, since a smaller mass of ceramic conductor material is Benö ^¬ Untitled for the expedient to be achieved resistors.

Claims

claims

1. coil device (1) with at least one electrical coil winding (3) with superconducting conductor material,

- wherein the coil winding (3) is part of a self-contained ^¬ nen circuit (5) for forming a continuous current (I i),

- Wherein the closed circuit (5) has a persistent current ^¬ switch (6) with a switchable conductor section (7) up, which is switchable between a superconducting state and a normal conducting state,

- wherein the switchable conductor section (7) has a high-temperature superconducting conductor,

- Wherein the switchable conductor section (7) has a resistance of at least 300 ohms in the normal conducting state of the conductor

- And wherein the switchable conductor section (7) a Abklingwiderstand (9a) of at least 50 ohms and / or a consumer ^¬ cher (9b) is connected in parallel with an effective resistance of at least 50 ohms.

2. Coil device (1) according to claim 1, which comprises a cryostat (11) for cooling the superconducting conductor material,

- Wherein the superconducting coil winding (3) and the switching ^¬ ble conductor section (7) are angeord ^¬ net within the cryostat

- And wherein the Abklingwiderstand (9a) and / or the consumer ^¬ cher (9b) is arranged outside of the cryostat.

3. coil device (1) according to any one of claims 1 or 2, wherein the switchable conductor portion (7) in the normal conducting state of the conductor has a resistance which is greater than the Abklingwiderstand (9a) and / or the effective resistance of the consumer (9b).

4. coil device (1) according to any one of the preceding claims, wherein the switchable conductor section (7) in nor- malleitenden state of the conductor has a resistance of wenigs ^¬ th 1000 ohms, in particular at least 5000 ohms.

5. coil means (1) according to one of the preceding arrival sayings, wherein the switchable conductor section (7) nor ^¬ malleitenden state of the conductor has a dielectric strength of tension of at least 20 kV.

6. coil device (1) according to one of the preceding claims, in which the switchable conductor section (7) has a Ke ^¬ ramischen high-temperature superconductor.

7. coil device (1) according to claim 6, wherein the switchable conductor section (7) comprises a material of the type BaKBiO up.

8. coil device (1) according to any one of the preceding claims, wherein the upper critical magnetic field strength (B _C 2) for the superconducting material of the switchable Leiterab- section (7) is at most 100 mT.

9. coil device (1) according to one of the preceding claims, wherein an operating temperature for the superconducting state of the switchable conductor portion (7) is between 10 K and 40 K.

10. coil device (1) according to any one of the preceding claims, wherein the switching time for the switching of the switchable conductor portion (7) from the superconducting to the normal conducting state is at most 0.5 seconds.

11. coil device (1) according to one of the preceding claims, which has a further magnetic coil (15) for generating a magnetic field (B _ex t) for switching the switchable conductor section (7).

12. coil device (1) according to one of the preceding claims, which is a switchable to the conductor section arranged shielding coil (15) with a short-circuited current path (16),

wherein the short-circuited current path (16) through a switching ^¬ cash conductor portion (15a) of the shielding (15) can be opened.

13. coil device (1) according to one of the preceding claims, which

- Is designed as a magnetic coil device for generating a magnetic field in a device for magnetic resonance imaging or magnetic resonance spectroscopy or

- Is formed as an excitation coil means for generating an electromagnetic excitation field in a rotating electric machine, or

- Is designed as a magnetic coil device for storing energy in a superconducting magnetic energy storage (SMES).

14. persistent current switch (6) for a coil device (1) according to one of the preceding claims with a switchable conductor section (7),

- Wherein the switchable conductor section (7) has a high-temperature superconducting conductor

- And wherein the switchable conductor section (7) in the normallei- state of the conductor resistance of at least

300 ohms.

15. A method for loading or unloading a continuous current (I i) in a coil winding (3) of a coil device (1) according to one of claims 1 to 13, wherein the switchable conductor ^¬ section (7) of the continuous current switch (6) of a Supralei ^¬ border state is switched to a normal conducting state.