Magnetic coil arrangement, in particular for a nuclear fusion system, and method for operating a magnetic coil arrangement

Abstract

The invention relates to a magnetic coil arrangement (1) having at least one magnetic coil (MS1, MS2, MSN), in particular a stellarator coil or tokamak coil for a nuclear fusion system, wherein: the magnetic coil (MS1, MS2, MSN) comprises a superconducting conductor and one or more annular plate layers which are made of electrically conductive material and in each of which a plurality of windings of the superconducting conductor, which extends along a local longitudinal direction, are accommodated; the windings are arranged in succession in a local transverse direction; and the superconducting conductor of the magnetic coil (MS1, MS2, MSN) is part of a superconducting circuit of the magnetic coil arrangement (1), characterized in that at least one of the plate layers is part of an additional current path (17) which is connected in parallel with respect to at least one portion of the superconducting conductor and, with this, forms a discharge circuit (20), and in that a first switching element (S1) for interrupting the superconducting circuit is present in the superconducting circuit, wherein the switching element (S1) is arranged outside the discharge circuit (20). By means of the magnetic coil arrangement according to the invention, when local heating of the conductor occurs, firstly the magnetic coil can be quickly discharged and secondly the voltage prevailing across the conductor and relative to ground can be limited to an acceptable level.

Description

[0001] Applicant:

[0002] Gauss Fusion GmbH

[0003] Parkring 29

[0004] 85748 Garching near Munich

[0005] Germany

[0006] Representative:

[0007] KOHLER. SCHMID FURNITURE

[0008] patent attorneys

[0009] limited liability partnership

[0010] Gropiusplatz 10

[0011] 70563 Stuttgart

[0012] Germany

[0013] Magnetic coil arrangement, in particular for a nuclear fusion plant, and method for operating a magnetic coil arrangement

[0014] The invention relates to a magnetic coil arrangement with at least one magnetic coil, in particular a stellarator coil or tokamak coil for a nuclear fusion device, wherein the magnetic coil comprises a superconducting conductor and one or more annular plate layers of electrically conductive material, each containing several turns of the superconducting conductor running along a local longitudinal direction, the turns being arranged successively in a local transverse direction, and wherein the superconducting conductor of the magnetic coil is part of a superconducting circuit of the magnetic coil arrangement. The invention also relates to a method for operating the magnetic coil arrangement.

[0015] Gauss Fusion GmbH 04.12.2025 SP14051PCT Background of the invention

[0016] Magnetic fusion devices are operated with magnetic coils containing superconducting conductors. High-temperature superconducting (HTS) materials and / or low-temperature superconducting (LTS) materials can be used.

[0017] One of the most critical problems in the practical application of superconducting coils in magnetic fusion devices is the high-voltage isolation of the magnet coil leads from each other and from ground potential. High critical voltages can arise as a direct consequence of a quench or as a result of a rapid discharge of the magnets to protect them from localized heating, leading to the destruction of the conductor within the magnet. "Quench" refers to the spontaneous transition of the magnet coil from the superconducting to the normal conducting state due to overloading of the current-carrying superconductor. This process can be associated with high electrical voltages, currents, and forces within the superconductor. Since fusion magnets contain many gigajoules of magnetic energy, an uncontrolled discharge can damage the superconducting conductor and other parts of the magnet coil.

[0018] Typically, quench starts locally at one point in the conductor and then spreads across the entire conductor. High-temperature superconductors (HTS) pose a particular challenge because their high critical temperature and slow transition to the normal conducting state result in delayed quenching of the rest of the conductor. This leads to local overheating, which in turn can cause the conductor to burn out. Various quench protection methods for high-temperature superconductors (HTS) [Green_2020] and low-temperature superconductors (LTS) [Marchevsky_2021] are known from the prior art.

[0019] [Duchateau_2023] describes a method for the rapid discharge of energy stored in a superconducting magnet coil, in which the current is conducted through an external resistor. However, the faster the discharge, the higher the voltage across the conductor and to ground. A disadvantage of this method is that an electrical connection to the external resistor is required.

[0020] Gauss Fusion GmbH 04.12.2025 SP14051PCT However, the high electrical voltages across the conductor that occur during a rapid discharge should be avoided.

[0021] From [Duchateau_2023] it is known to provide the superconducting conductor with thermal protection, usually in the form of copper. The copper provides additional heat capacity, thereby reducing local heating and allowing for a longer discharge time, i.e., a lower applied voltage. However, the high energy stored in the magnetic field coils of fusion reactors, typically >1 GJ / magnetic coil for compact devices and up to 5 GJ / magnetic coil for stellarators, means that very large proportions of copper are needed to keep the voltages below a few kV. Such a high copper content, however, leads to impractically low current densities.

[0022] In [LaBombard_2024] it is proposed to provide means by which a quench cascade can be actively triggered in fusion magnets in order to quench the entire magnet.

[0023] [EP3920196] discloses a quench protection method in which the magnet coil is discharged via an external resistor, wherein the magnet coil comprises short-circuited copper induction coils which heat up during the discharge process, thus achieving a quench of the entire magnet. [W02014207130] discloses an AC-induced quench protection system in which alternating current is used to generate heat in the conductor to quench the entire magnet coil, with the heat being distributed over the entire magnet coil.

[0024] In order to accelerate the quenching of the magnetic coil, it is also known to provide internal heating elements along the conductor of the magnetic coil, which, after detection of a local quench, heat the rest of the conductor and thus cause a rapid quench of the entire magnetic coil, as described, for example, in [EP3207549] and [Coull_1993].

[0025] However, the previously described methods for accelerating a quench require additional equipment (induction coils, AC generator, heating elements), which entail additional costs and maintenance.

[0026] Gauss Fusion GmbH 04.12.2025 SP14051PCT Task of the invention

[0027] The object of the invention is to propose a device and a method with which, in the event of local heating of the conductor, the magnetic coil can be discharged as quickly as possible on the one hand, and the voltage across the conductor and to earth can be limited to an acceptable level on the other, without elaborate additional equipment.

[0028] Description of the invention

[0029] This problem is solved according to the invention by a magnetic coil arrangement according to claim 1 and an operating method according to claim 18.

[0030] In the magnetic coil arrangement according to the invention, at least one of the plate layers is part of an additional current path that is connected in parallel to at least a section of the superconducting conductor and forms an internal discharge circuit with it. Furthermore, a first switching element for interrupting the superconducting circuit is provided in the superconducting circuit, wherein the first switching element is arranged outside the internal discharge circuit.

[0031] The magnetic coils store magnetic energy, which, in the event of a loss of superconductivity, is dissipated as heat within the conductor or any other normal conductive material located in the conductor's electrical circuit. According to the invention, the magnetic energy is converted into heat, which warms the plate layers that form the mechanical support structure of the magnetic coil. In this way, the voltage gradients within the coil can be minimized.

[0032] The magnetic coil arrangement according to the invention provides thermal protection for the magnetic coils. The magnetic coils store magnetic energy, which, in the event of a loss of superconductivity, is dissipated as heat within the conductor or any other normal conductive material located in the conductor's electrical circuit. According to the invention, the magnetic energy is converted into heat, which warms the plate layers that form the mechanical support structure of the magnetic coil. In this way, the voltage gradients within the coil can be minimized.

[0033] Gauss Fusion GmbH 04.12.2025 SP14051PCT A "superconducting circuit" is a circuit made of superconducting material that can be brought into a superconducting state. A superconducting circuit can also include ohmic components (e.g., a power supply and connecting wires) provided that the resistance, in addition to the superconducting conductor, is very low. The resistance of a superconducting circuit is typically less than a few milliohms.

[0034] The plate layer(s) connected in parallel with the conductor are not part of the superconducting circuit. The electrical conductor forms a "conductor current path," which is part of the superconducting circuit. The plate layer(s) of the additional current path form an ohmic resistor connected in parallel to the conductor current path.

[0035] In the event of a local quench, the superconducting circuit can be interrupted by actuating the first switching element. When the superconducting circuit is interrupted, the current begins to flow from the conductor current path via the additional current path (the "plate current path"). The conductor current path and the additional current path together form the internal discharge circuit.

[0036] Preferably, a high-resistance resistor is connected in parallel to the first switching element, so that opening the first switching element interrupts the superconducting circuit and the first switching element is "bridged" via the high-resistance resistor. This reduces the voltage across the first switching element.

[0037] The fact that the current flows from the conductor current path via the additional current path means that voltage is present not only at the quenching point of the superconducting conductor, but also in the additional current path, and energy from the magnet coil is absorbed by the plate layers. The plate layers thus act as an energy sink to absorb the energy released during coil quenching (dissipation of the coil current). This enables the absorption of magnetic energy, the discharge of the coil, and the distribution of the resulting heat over a large area. Furthermore, the plate layers are heated. The plate layers therefore form a load resistance for energy dissipation, which (unlike in devices known from the prior art) is integrated into the magnet coil and thus leads to shorter

[0038] Gauss Fusion GmbH 04.12.2025 SP14051PCT conductor paths and low inductances, thus leading to high voltages across the additional current path.

[0039] The discharge of the magnetic coil via the additional current path creates a voltage drop across this path, corresponding to the voltage drop across the conductor current path. A voltage difference then exists between the terminals of the magnetic coil (coil terminal voltage), which can be quite high (well over 1 kV).

[0040] Preferably, the conductor runs in a groove of the plate layer. The conductor running within the plate layer is insulated from the plate layer. Due to their resistance, the electrical voltage across the plate layers corresponds to the inductive voltage across the superconducting conductor. Since the plate layers and the conductor are connected in parallel, the voltage drop across this insulation between the conductor and the plate layer is much lower than the coil connection voltage. This ensures the dielectric strength of the feedthroughs required for charging the magnet coil. The voltage across the insulation between the conductor and the plate layer is preferably a maximum of 5 kV, particularly preferably a maximum of 10 kV.

[0041] The voltage to ground (i.e., between the active parts of the magnet coil (conductor, plate layer) and other, electrically inactive parts in the cryostat) is at least half the coil terminal voltage when the superconducting circuit is interrupted, provided there is a central ground connection in the conductor current path. It is also possible to provide multiple ground connections within the coil current path.

[0042] Preferably, a material with a higher electrical resistance than that of stainless steel is used as the conductive material of the plate layer(s), for example Nitronic® or Inconel®.

[0043] The superconducting conductor should have a sufficient copper content to limit local heating at the quench point to a temperature of less than 250 K, while the magnetic energy is dissipated more evenly across the entire coil via the resistance of the plates. Preferably, the copper content is at least 67 wt%. Due to the high copper content, during quenching-

[0044] Gauss Fusion GmbH 04.12.2025 SP14051PCT When a local quench occurs, the energy is initially absorbed by the copper material, allowing enough time to switch on the additional current path before damage occurs to the coil.

[0045] A power supply can be connected to the superconducting circuit. However, once the current in the superconducting circuit has built up, a power supply is no longer strictly necessary, as the resistance of the superconducting circuit is very low and the magnet would take a very long time (many weeks) to discharge. The superconducting circuit can therefore also be operated in short-circuit mode.

[0046] In a special embodiment, at least one plate layer (preferably all plate layers) is connected in parallel to the complete conductor.

[0047] However, it is also conceivable that not all, but only one of the plate layers (preferably exactly one plate layer) is connected in parallel to a section of the conductor (preferably to the section(s) that is / are included in the plate layer(s)).

[0048] Preferably, at least one section of the conductor and at least one plate layer of the additional current path are electrically interconnected in such a way that they form a series circuit (internal discharge circuit) when the superconducting circuit is interrupted.

[0049] Preferably, the at least one plate layer of the additional current path has end sections that are electrically insulated from each other by means of one or more insulating elements. The electrically conductive material of the plate layer is thus interrupted in the circumferential direction, so that the current cannot circulate completely within a plate layer. The end sections are mechanically connected to each other via the insulating element.

[0050] In a particularly preferred embodiment, each end section has a projection and a recess forming a hook-shaped end, with the projection of one end section hooking into the recess of the other end section. One or more insulating elements are arranged between the hook-shaped ends, covering at least partially the mutually facing surfaces of the end sections. The end-

[0051] Gauss Fusion GmbH 04.12.2025 SP14051 The PCT sections are therefore not spaced apart, but interlocked. The insulating elements can each be designed as an insulating layer on one of the end sections, e.g., as a coating or as a thin-walled insert. Several insulating elements can be present, so that different sections of the hook-shaped end of an end section can be coated with insulating material. The insulating elements are arranged so that the electrically conductive materials of the two end sections do not touch. The insulating elements preferably extend along the local transverse direction over the entire extent of the plate layer.

[0052] An alternative embodiment provides that an insulating element separates the end sections from each other in the local longitudinal direction, and the end sections are mechanically connected to each other by means of bolts, with the insulating element being clamped between the end sections. The end sections are thus kept apart by the insulating element. The bolts preferably protrude through the insulating element and are insulated in such a way that they themselves do not form a short circuit (conductive connection).

[0053] In a particularly preferred embodiment, the magnetic coil comprises several plate layers, wherein several of the plate layers, preferably all plate layers, are interconnected in series within the additional current path. The annular plate layers form an annular plate-layer stack, with successive plate layers abutting each other but insulated from each other in the stacking direction, wherein a local stacking direction LSR is perpendicular to the local longitudinal direction LLR and perpendicular to the local transverse direction LQR.

[0054] To avoid a concentration of the mechanical stress caused by fixing the end sections, a preferred embodiment provides that the position of the insulating elements of the different plate layers is offset from each other in the local longitudinal direction.

[0055] In a particularly preferred embodiment, at least one of the plate layers of the additional current path is divided into an upper sandwich layer and a lower sandwich layer, which are electrically insulated from each other in a local stacking direction that is perpendicular to the local longitudinal direction and perpendicular to the local transverse direction, wherein the upper sandwich layer

[0056] Gauss Fusion GmbH 04.12.2025 SP14051PCT accommodates electrical conductors. The sandwich layers are therefore electrically insulated from each other in the stacking direction and also connected to each other by means of an insulated, force-fit connection, in particular wedged or screwed (e.g. by insulated wedges and / or screws).

[0057] Preferably, the cross-sectional area of ​​the upper sandwich layer is smaller than the cross-sectional area of ​​the lower sandwich layer. The heating rate can be adjusted by appropriately choosing the cross-sectional ratio of the sandwich layers.

[0058] A first embodiment with a sandwich structure provides that the upper sandwich layers and the lower sandwich layers of several plate layers, preferably all plate layers, are connected in series within the additional current path. If the upper sandwich layer has a smaller cross-section and thus higher electrical resistance, it heats up faster. This results in faster dissipation of the magnetic energy and thus reduces local heating.

[0059] A second embodiment with a sandwich structure provides that the upper sandwich layers of several plate layers, preferably all plate layers, are connected in series within the additional current path, and that a further switching element is present which is configured to connect the lower sandwich layers to the additional current path, with the connection being made in series with the upper sandwich layers. The further switching element is an active switching element, e.g., a thyristor or an insulated-electrode bipolar transistor (iGBT). When the further switching element is closed, the lower sandwich layers are integrated into the additional current path such that a series connection of the upper and lower sandwich layers is then present.

[0060] A third embodiment with sandwich partitioning provides that the upper sandwich layers of several plate layers, preferably all plate layers, are interconnected in series within the additional current path, and that at least one additional switching element is provided which is configured to connect at least one of the lower sandwich layers to the additional current path, with the connection being in parallel.

[0061] Gauss Fusion GmbH 04.12.2025 SP14051PCT The series connection of the upper sandwich layers is achieved. This embodiment allows for a particularly rapid, controlled reduction of the magnetic energy and thus a rapid and controlled discharge of the magnetic coil. Preferably, all lower sandwich layers are connected in parallel to each other and can each be switched to the additional current path via an active switch.

[0062] In a particularly preferred embodiment, at least one of the plate layers, preferably all plate layers, of the additional current path has several plate layer rings arranged successively in the local transverse direction, wherein the plate layer rings are electrically insulated from each other in the local transverse direction.

[0063] It is also possible that the plate layer comprises several sub-plates, at least one of which is interrupted in the local transverse direction and thus comprises several plate layer ring parts nested in the local transverse direction. Furthermore, the plate layer may comprise other sub-plates that do not have an interruption in the local transverse direction.

[0064] If the plate layers are to be subdivided into sandwich layers, it is preferred for stability reasons (i.e., regarding the mechanical stability when the sandwich layers are clamped in one direction) that only one of the sandwich layers is subdivided into plate layer rings. It is particularly preferred that the lower sandwich layer is subdivided into plate layer rings, whereas the upper sandwich layer does not have any subdivision into plate layer rings.

[0065] Preferably, the plate-layer rings within the plate layer are interconnected in series. This series connection of the plate-layer rings increases the resistance in the additional current path compared to a series connection of plate layers that are not subdivided into plate-layer rings. In a particularly preferred embodiment, a quench detector is provided for detecting a quench of the superconducting conductor, in particular a fiber-optic quench detector, wherein the switching element is configured to interrupt the superconducting circuit when a quench is detected by the quench detector. Preferably, a plurality of fiber-optic quench detectors are embedded in the plate layer along the conductor.

[0066] Gauss Fusion GmbH 04.12.2025 SP14051PCT Preferably, the superconducting conductor and at least one plate layer of the additional current path are interconnected in such a way that, when the superconducting circuit is interrupted, the current through the plate layers and the current through the superconducting conductor flow in opposite directions. This preferred interconnection allows forces occurring in the magnet coil to be compensated.

[0067] In a particularly preferred embodiment, the magnetic coil arrangement comprises a plurality n of magnetic coils arranged in a cryostat, forming a nuclear fusion magnet, and configured to effect magnetic plasma confinement, particularly in a stellarator or a tokamak. The magnetic coil arrangement according to the invention is preferably suitable for the magnetic confinement of an at least substantially toroidal plasma volume, wherein the magnetic coils are distributed in the toroidal direction of the plasma volume and locally enclose the toroidal plasma volume in a ring-like fashion. Preferably, the internal discharge circuits of the individual magnetic coils are connected in series.

[0068] In one switching variant, the first switching element is located outside the cryostat. In this variant, the first switching element is connected between one of the magnetic coils and a power supply line to a superconducting circuit. This is advantageous because a wide range of switching technologies are available for this purpose.

[0069] In a second switch variant, preferably n-1 first switching elements are provided within the cryostat, with each first switching element being connected between two of the magnetic coils. This is advantageous because the power lines required for the transition to room temperature are avoided.

[0070] The invention also relates to a method for operating a previously described superconducting magnet coil arrangement, wherein a coil current is guided superconductively in the superconducting circuit. According to the invention, quench monitoring of the conductor is carried out by means of a quench detector, and in the event of a quench detection, the superconducting circuit is deactivated by means of the

[0071] Gauss Fusion GmbH 04.12.2025 SP14051PCT The switching element is interrupted, and the coil current then flows via the additional current path and dissipates. After the detection of an incipient quench (local heating of the conductor), the coil current can thus flow through the plate layers, which heat up due to their comparatively high resistance and ensure that the voltage at the coil terminal remains low. The current then flows in the internal discharge circuit, which comprises the superconducting conductor (or at least a section of the superconducting conductor) and the plate layers electrically connected to the superconducting conductor (or at least a section of the superconducting conductor). After interruption of the superconducting circuit, the current begins to flow through the plate layers, preferably in the opposite direction to the current flow in the superconducting conductor.This transfers the magnetic energy as heat energy into the plates, heating the entire magnet coil evenly. If a power supply is connected to the superconducting circuit, the superconducting circuit can be interrupted by disconnecting the power supply from the circuit.

[0072] A preferred method variant provides that at least one of the plate layers of the additional current path is divided into an upper sandwich layer and a lower sandwich layer, which are electrically insulated from each other in the stacking direction, wherein the upper sandwich layer contains the superconducting conductor, that after interruption of the superconducting circuit, initially only the upper sandwich layers are contained in the additional current path, and that the lower sandwich layers are added to the additional current path in series with the series connection of the upper sandwich layers with a time delay, wherein the addition of the lower sandwich layers preferably occurs stepwise. As a result, the upper sandwich layer initially absorbs the magnetic energy, so that the structure around the conductor heats up rapidly and, if necessary, further quenches the conductor.

[0073] A particularly preferred method variant provides that the temperature of the upper sandwich layers is monitored and that the lower sandwich layers are only switched into the additional current path when the temperature of the upper sandwich layers exceeds a predetermined limit. As soon as the temperature of the upper sandwich layers exceeds the limit,

[0074] Gauss Fusion GmbH 04.12.2025 SP14051PCT: The lower sandwich layers are gradually switched on in parallel with the additional current path and thus absorb the majority of the coil current, preventing the upper sandwich layers from overheating. The limit is preferably 150-200 K.

[0075] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those described in more detail below can each be used individually or in any combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention.

[0076] Detailed description of the invention and drawing

[0077] Fig. 1 shows a perspective view of a plate layer of a magnetic coil according to the invention with an interruption of the electrically conductive plate material.

[0078] Fig. 2 shows a perspective view of two interlocking end sections with insulation elements.

[0079] Fig. 3 shows a perspective view of the left end section from Fig.

[0080] 2 with insulating elements.

[0081] Fig. 4 shows a perspective view of the insulation elements from Fig.

[0082] 3.

[0083] Fig. 5 shows a top view of a section of a plate layer subdivided in the transverse and stacking direction, as well as cross-sections of partial plates of the plate layer adjacent to the end sections and of a first embodiment of an insulating element which mechanically connects the end sections to each other by means of bolts.

[0084] Fig. 6 shows a top view of a section of a layer of plates partially subdivided only in the stacking direction and partially in both the transverse and stacking directions, as well as cross-sections of sub-plates adjacent to the end sections.

[0085] Gauss Fusion GmbH 04.12.2025 SP14051PCT of the plate layer and of the first embodiment of the insulating element.

[0086] Fig. 7 shows a top view and a side view of a simplified representation of a magnetic coil according to the invention with several plate layers to illustrate the interconnection of the different plate layers.

[0087] Fig. 8 shows a circuit diagram of a first embodiment of a magnetic coil arrangement according to the invention with several magnetic coils and a single first switching element.

[0088] Fig. 9 shows a circuit diagram of a second embodiment of a magnetic coil arrangement according to the invention, comprising several magnetic coils and several first switching elements and a quench detection system. Fig. 10 shows a circuit diagram of a first embodiment of a discharge circuit of a magnetic coil according to the invention, in which a series connection of several plate layers is connected in parallel to the conductor.

[0089] Fig. 11 shows a circuit diagram of a second embodiment of a discharge circuit of the magnetic coil according to the invention, in which a series connection of several sandwich layers of different plate layers is connected in parallel to the conductor.

[0090] Fig. 12 shows a circuit diagram of a third embodiment of a discharge circuit of the magnetic coil according to the invention, in which a series connection of the upper sandwich layers is connected in parallel to a series connection of the lower sandwich layers and in parallel to the conductor, and a series connection of the lower sandwich layers can be switched on.

[0091] In the following, the structure of the magnetic coil arrangement according to the invention will first be described, followed by the electrical interconnection of the components of the magnetic coil arrangement according to the invention.

[0092] Gauss Fusion GmbH 04.12.2025 SP14051PCT A magnetic coil arrangement 1 according to the invention can comprise several magnetic coils MSI, MS2, MSN. Each magnetic coil MSI, MS2, MSN preferably has several annular plate layers P which form an annular plate layer stack in a local stacking direction LSR.

[0093] Fig. 1 shows a single annular plate layer P of a magnetic coil according to the invention, with slots 2 for receiving a superconducting conductor 10 (see Fig. 5 and Fig. 6). The slots 2 extend in a local longitudinal direction LLR and are arranged successively in a local transverse direction LQR. The local stacking direction LSR (not shown in Fig. 1), in which several such plate layers P can be stacked, extends perpendicular to both the local longitudinal direction LLR and the local transverse direction LQR. The plate layer P comprises several sub-plates 3 made of electrically conductive material. The slots 2 of successive sub-plates 3 of a plate layer P are aligned with each other and abut one another.

[0094] The electrically conductive material of the plate layer P is interrupted at a discontinuity 4 in the local longitudinal direction LLR, such that two end sections 5a, 5b are formed that are separated from each other in the local longitudinal direction LLR. The end sections 5a, 5b are mechanically connected to each other via one or more insulating element(s) 6, so that the plate layer P forms a closed ring on the one hand and has an electrical discontinuity on the other.

[0095] Figures 2 to 4 show a first insulation variant with which this electrical interruption within the plate layer P can be realized. Figure 2 shows end sections 5a, 5b that are interlocked. Several insulating elements 6a, 6b, shown in Figures 3 and 4, are arranged between the hook-shaped end sections 5a, 5b. The insulating elements 6a, 6b cover at least partially the mutually facing surfaces of the end sections 5a, 5b, as shown in Figure 3. The insulating elements 6a, 6b extend over the entire ring width W of the plate layer P in the local transverse direction LQR and are shown in dark in Figure 3. In the illustrated embodiment, the insulating elements 6a, 6b are located in the region of the hook ends of the end sections 5a, 5b. An insert element 7 is provided between the two insulating elements 6a, 6b.

[0096] Gauss Fusion GmbH 04.12.2025 SP14051PCT The wedge-shaped end sections 5a and 5b are dimensioned to allow for some play. This play is eliminated by clamping a preferably insulating wedge element 8.

[0097] Figure 4 shows the two insulating elements 6a and 6b individually. The embodiment shown here consists of angled elements adapted to the shape of the end sections 5a and 5b. However, differently designed insulating elements are also possible, for example, in the form of a coating on the corresponding sections of the end sections 5a and 5b.

[0098] Figures 5 and 6 show a second insulation variant in which an insulation element 6c in the form of a screw-in block made of insulating material is inserted between the end sections 5a, 5b. Bolts 9 are provided for this purpose, which extend through the insulation element 6c and can be screwed to the end sections 5a, 5b, so that the end sections 5a, 5b clamp the insulation element 6c. As indicated in Figure 1, the grooves 2 (in Figures 5 and 6) run

[0099] (6 not shown) of the plate layer P also extends over the insulating element 6c. Thus, the superconducting conductor 10 can be guided from end section 5a via the insulating element 6c to end section 5b, so that at the break point 4 of the plate layer P only the electrically conductive plate structure (the entirety of the sub-plates 3) is electrically interrupted, but not the superconducting conductor 10 itself. In this way, the conductor 10 can form several coils within a plate layer despite the break in the plate structure.

[0100] The electrically conductive part of the plate layer P (in particular comprising sub-plates 3) can be wholly or partially subdivided into sandwich layers PSI, PS2, as shown in cross-sections of the end sections 5a, 5b in Figs. 5 and 6. The sandwich layers PSI, PS2 are electrically insulated from each other in the local stacking direction LSR. The upper sandwich layer PSI contains the slots 2 in which the superconducting conductor 10 is accommodated, the superconducting conductor 10 being electrically insulated from the plate layer P. By subdividing the plate layer P into electrically conductive sandwich layers PSI, PS2 and by appropriately connecting these sandwich layers PSI, PS2 (see below), the magnetic energy can be selectively distributed in the event of a local quench, and the entire conductor 10 can be quenched rapidly.

[0101] Gauss Fusion GmbH 04.12.2025 SP14051PCT Furthermore, it can be provided that the plate layer P is subdivided in the local transverse direction LQR and thereby has several successive plate layer rings 11 in the local transverse direction LQR. Fig. 5 shows an embodiment in which the entire plate layer P (all sub-plates 3 of the plate layer P) is subdivided into plate layer rings 11 in the local transverse direction LQR; Fig. 6 shows an embodiment in which the subdivision in the local transverse direction LQR does not extend to all sub-plates 3 (here only a left sub-plate 3a is subdivided in the local transverse direction LQR, while a right sub-plate 3b is not subdivided), so that here only for the left sub-plate 3a are there several successive plate layer ring parts 11' in the local transverse direction. By subdividing the plate layer P into plate layer rings 11 orBy means of plate layer ring parts 11' and a suitable electrical connection of these plate layer rings 11 or the plate layer ring parts 11' (see below) the electrical resistance of the plate layer P can be increased and thus the energy absorption in the plate layer P can be increased.

[0102] Fig. 7 shows a top view and a side view of a magnetic coil MS of a magnetic coil arrangement 1 according to the invention, comprising several annular plate layers P. The superconducting conductor 10 (not shown in Fig. 7 for clarity) of the magnetic coil MS can be supplied with current via conductor connection points a, b. The superconducting conductor 10 is guided from the uppermost plate layer to the plate layer below it, and so on, so that the superconducting conductor 10 forms several turns of the magnetic coil MS in each plate layer P.

[0103] The plate layers P are electrically connected in series via plate connections 13 and integrated into the magnet arrangement 1 via plate connection points c, d. The plate connections 13 are arranged offset from one another in the local longitudinal direction LLR to concentrate the magnetic field shown in Fig.

[0104] 2, Fig. 5 and Fig. 6 to avoid the mechanical stress occurring during the fixing of the end sections 3a, 3b with the insulating element 6a, 6b, 6c shown.

[0105] Gauss Fusion GmbH 04.12.2025 SP14051PCT Fig. 8 and Fig. 9 show circuit diagrams of two embodiments of a magnetic coil arrangement 1 according to the invention with N magnetic coils MSI, MS2, MSN (here: N = 3), wherein the magnetic coils MSI, MS2, MSN are connected in series via coil connection points A, B and are arranged in a cryogenic area CRYO (in particular in a cryostat).

[0106] The superconducting conductors 10 of the magnet coils MSI, MS2, MSN are part of a superconducting circuit which, in addition to the superconducting conductors 10, includes at least one first switching element SI, S2 connected in series with the magnet coils MSI, MS2, MSN, with which the superconducting circuit can be interrupted. Each superconducting conductor 10 forms a conductor current path 19. Within each magnet coil MSI, MS2, MSN, an additional current path 17 with resistance RP is connected in parallel to the superconducting conductor 10 of the respective magnet coil MSI, MS2, MSN. The additional current path 17 comprises the series connection of the plate layers P realized by the plate connections 13 (see Fig. 7). A power supply 18 supplies the magnet coils MSI, MS2, MSN with current via supply lines 14. To detect a local quench, a quench detection system QDS is provided for each magnetic coil MSI, MS2, MSN (example shown in Fig.9 shown), which receives a temperature signal TS that is significant for the temperature of conductor 10 and triggers the activation of the first switching element SI, S2 upon detection of a quench.

[0107] Within each magnetic coil MSI, MS2, MSN, an earth connection RS is provided. This preferably originates from the center point of the respective magnetic coil MSI, MS2, MSN, i.e., either from the superconducting conductor 10 (as shown in Fig. 8) or from the series connection of the plate layers P (not shown), and is preferably located centrally with respect to the conductor 10 or the series connection of the plate layers P, in order to limit the earth voltage to approximately half the coil terminal voltage.

[0108] Since the resistance of the plate layers P of the additional current path 17 is significantly greater than the resistance of the superconducting circuit, the current initially flows almost exclusively through the superconducting circuit. For this purpose, the first switching element SI, S2 is closed. In normal operation, the power supply 18 only needs to compensate for the current losses due to the resistance of the normal-conducting supply lines 14. In normal operation, due to the high resistance...

[0109] Gauss Fusion GmbH 04.12.2025 SP14051PCTRP of the additional current path 17 compared to the resistance of the superconducting circuit only a negligible current through the additional current path 17.

[0110] In the event of a local quench, the current in the superconducting circuit should be reduced as quickly as possible to discharge the magnet coils MSI, MS2, and MSN and to protect the conductor 10 from damage. According to the invention, in the event of quench detection, the current from the superconducting conductor 10 is diverted across the plate layers P, thus transferring the magnetic energy as heat to the plate layers P. For this purpose, the superconducting circuit is interrupted, so that the current from conductor current path 19 begins to flow via the additional current path 17. Conductor current path 19 and additional current path 17 thus form an internal discharge circuit. The current begins to circulate through the plate layers P in the opposite direction to the current flow in the conductor 10.This causes the magnetic energy to be dissipated as thermal energy in the plate layers, thereby heating the entire magnetic coil MSI, MS2, MSN evenly and rapidly quenching the entire conductor 10.

[0111] In the embodiments shown in Fig. 8 and Fig. 9, each first switching element SI, S2 bridges a high-resistance RI, R2 (RI, R2 >> RP), so that opening at least the first switching element S1 or the first switching elements S2 interrupts the superconducting circuit and instead creates a high-resistance circuit. Since the resistance RI, R2 is chosen to be significantly higher than the resistance RP of the additional current path 17, the current flows through the additional current path 17 when the switch SI, S2 is open, allowing the magnetic energy to be absorbed by the plate layers P.

[0112] The current flowing through the superconducting conductors 10 is therefore discharged via the additional current paths 17. To prevent ground loops from bridging the resistance RP of the series connection of the plate layers P, the resistance RS of the ground connection should be comparable to or greater than the high-resistance RI, R2.

[0113] The conductor current path 19 and the additional current path 17 of each magnetic coil MSI, MS2, MSN together form an internal discharge circuit 20.

[0114] Gauss Fusion GmbH 04.12.2025 SP14051PCT The first switching element(s) SI, S2 is / are connected outside the internal discharge circuit 20.

[0115] In the first switch variant shown in Fig. 8, the first switching element is located outside the cryogenic region CRYO, in which the solenoid coils are arranged, specifically in a room temperature region AIR. The resistor RI, connected in parallel to the switch S1, is also located in the room temperature region AIR in the example shown, but can also be located in the cryogenic region KRYO. In the first circuit variant, all solenoid coils MSI, MS2, and MSN discharge together through the resistor RI. The voltage of all solenoid coils MSI, MS2, and MSN then drops across the resistor RI. In the second switch variant shown in Fig. 9, several first switching elements S2 are provided within the cryogenic region CRYO, with each first switching element S2 being connected between two solenoid coils MSI, MS2, and MSN. Preferably, all first switching elements S2 are opened simultaneously (within a few seconds).In the second circuit variant, each magnetic coil MSI, MS2, MSN discharges separately.

[0116] The quench detection system QDS is shown as an example in the second switching variant depicted in Fig. 9, in which the first switching elements S2 are each controlled by a quench detection system QDS. A corresponding system can also be provided in the first switching variant, in which the quench detection system QDS controls the first switching element S1. The temperature signal TS can be determined, for example, directly by measuring the temperature of the superconducting conductor 10 or indirectly by measuring the voltage behavior of the superconducting conductor 10 using fiber optic methods or from the behavior of the electrical voltages of sections of the electrical conductor 10.

[0117] Figs. 10, 11 and 12 show different embodiments of the electrical interconnection of the plate layers P within the discharge circuit 20', 20", 20'" of a magnetic coil MSI, MS2, MSN between the coil connection points A, B. Only two plate layers Pl, P2 were considered for illustrative purposes.

[0118] Gauss Fusion GmbH 04.12.2025 SP14051PCT In the first embodiment of the discharge circuit 20' shown in Fig. 10, the complete plate layers Pl, P2 are connected in series in the additional current path 17'.

[0119] To increase the resistance of the additional current path 17", in the second embodiment of the discharge circuit 20" shown in Fig. 11, the plate layers Pl, P2 are divided into upper sandwich layers P1S1, P2S1, and lower sandwich layers P1S2, P2S2 (see Fig. 5 and Fig. 6), with all sandwich layers P1S1, P2S1, P1S2, P2S2 being connected in series.

[0120] The third embodiment of the discharge circuit 20'", shown in Fig. 12, is particularly advantageous, as it allows for various circuit configurations. For this purpose, the upper sandwich layers P1S1, P2S1 are connected in series, and the lower sandwich layers P1S2, P2S2 are also connected in series. A changeover switch Ws allows the series connection of the upper sandwich layers P1S1, P2S1 to be connected either in parallel to the conductor current path 19 or in series with the series connection of the lower sandwich layers P1S2, P2S2. The series connection of the lower sandwich layers P1S2, P2S2, in turn, can be connected in parallel to the conductor current path 19 via an additional switching element SP.

[0121] Thus, after interrupting the superconducting circuit, the upper sandwich layers P1S1, P2S1 and / or the lower sandwich layers P1S2, P2S2 can be connected to the additional current path 17'''. This can be achieved by connecting only the upper sandwich layers P1S1, P2S1 in series (changeover switch in the upper position and additional switching element SP open), by connecting the upper sandwich layers P1S1, P2S1 and the lower sandwich layers P1S2, P2S2 in series (changeover switch in the lower position and additional switching element SP open), or by connecting the upper sandwich layers P1S1, P2S1 in series and the lower sandwich layers P1S2, P2S2 in series (changeover switch in the upper position and additional switching element SP closed) in parallel, depending on the desired resistance in the additional current path 17'''.Which of these circuit variants is chosen preferably depends on the voltage applied between the conductor connection points a and the plate connection point c, which is under ei-.

[0122] Gauss Fusion GmbH 04.12.2025 SP14051PCTnen specified limit value should remain, and / or from the temperature of the conductor and / or the temperature of the plate layers, which should remain below a specified temperature limit value.

[0123] For example, the upper sandwich layers P1S1, P2S1 can first be connected in parallel to the conductor current path (changeover switch in the upper position and additional switching element SP open) in order to quickly heat the upper sandwich layers P1S1, P2S1 and thus the conductor 10 contained within them. Once the upper sandwich layers P1S1, P2S1 have reached a predetermined temperature, the lower sandwich layers P1S2, P2S2 can be connected in series to the additional current path 17"' by switching the changeover switch Ws (changeover switch in the lower position and additional switching element SP open) so that the upper sandwich layers P1S1, P2S1 do not heat up further.

[0124] In another variant, the upper sandwich layers P1S1, P2S1 and the lower sandwich layers P1S2, P2S2 can first be connected in parallel (changeover switch in the upper position and additional switching element SP closed). Then, by opening the additional switch SP, the lower sandwich layers P1S2, P2S2 are removed from the additional current path. Finally, by switching the changeover switch WS, the lower sandwich layers P1S2, P2S2 are connected in series with the upper sandwich layers P1S1, P2S1. This gradually increases the resistance in the additional current path 17"'. By gradually increasing the resistance in the additional current path 17"', the discharge time can be shortened.

[0125] Another embodiment is conceivable in which the changeover switch Ws is omitted and the upper sandwich layers P1S1, P2S1 are permanently connected in parallel to the conductor current path. The lower sandwich layers P1S2, P2S2 can then be connected in parallel to the series connection of the upper sandwich layers P1S1, P2S1 by means of the additional switching element SP.

[0126] Gauss Fusion GmbH 04.12.2025 SP14051PCT1 Magnetic coil arrangement

[0127] 2 grooves

[0128] 3, 3a, 3b Sub-plates of the plate layer

[0129] 4. Break point in the plate layer 5a, 5b End sections of the plate layer

[0130] 6, 6a, 6b, 6c insulation elements

[0131] 7 Deployment element

[0132] 8 wedge element

[0133] 9 bolts

[0134] 10 superconducting conductor plate layer rings plate layer ring parts

[0135] 13 plate connections

[0136] 14 supply lines

[0137] 16 superconducting current path circuit

[0138] 17, 17', 17", 17'" additional power path power supply

[0139] Conductor current path

[0140] 20, 20', 20", 20"' Discharge circuit

[0141] A, B coil connection points

[0142] a, b conductor connection points

[0143] c, d plate connection points

[0144] B Ring width of the plate layer

[0145] LLR local longitudinal direction

[0146] LQR local transverse direction

[0147] Gauss Fusion GmbH 04.12.2025 SP14051PCTLSR. Local stacking direction

[0148] MS, MSI, MS2, MSN solenoid coil

[0149] P, Pl, P2 plate layers

[0150] PSI, P1S1, P2S1 upper sandwich layers

[0151] PS2, P1S2, P2S2 lower sandwich layers

[0152] RP Resistance of the additional current path RI, R2 Resistance parallel to the first switching element RS Ground connection

[0153] SI, S2 first switching elements

[0154] SP additional switching element

[0155] WS changeover switch (additional switching element) CRYO cryogenic area

[0156] AIR room temperature range

[0157] QDS Quench Detection System

[0158] TS temperature signal for evaluation in QDS

[0159] Gauss Fusion GmbH 04.12.2025 SP14051PCT Reference List

[0160] [Green_2020] MA Green

[0161] Various Quench Protection Methods for HTS Magnets, Materials Science and Engineering 755 (2020) 012134 doi:10.1088 / 1757-899X / 755 / l / 012134 [Marchevsky_2021] Maxime Marchevsky

[0162] Quench Detection and Protection for High-Temperature Superconductor Accelerator Magnets

[0163] Instruments 2021, 5, 27.

[0164] https: / / doi.org / 10.3390 / instruments5030027 [Duchateau_2023] Jean-Luc Duchateau

[0165] QUENCH DETECTION AND PROTECTION OF FUSION MAGNETS

[0166] Lectures on superconducting magnets test stands, magnet protections and diagnostics https: / / indico.cern.ch / event / 1281454 / contribu- tions / 5383588 / attachments / 2666669 / 4621167 / JLD_pro- tectionoffusionmagnets.pdf

[0167] [EP3920196] EP 3 920 196 Al

[0168] [W02014207130] WO 2014 207 130 Al

[0169] [EP3207549] EP 3 207 549 Bl

[0170] [Coull— 1993] Coull et al.

[0171] LHC Magnet Quench Protection System

[0172] EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN - AT DIVISION

[0173] 13th International Conference on Magnet Technology (MT13), Victoria, Canada 20-24 September 1993 [LaBombard_2024] La Bombard

[0174] Are REBCO NI Magnets Really Self-protected? Commonwealth Fusion Systems

[0175] ASC Salt Lake City September 4, 2024

[0176] Gauss Fusion GmbH 04.12.2025 SP14051PCT

Claims

Patent claims 1. Magnetic coil arrangement (1) comprising at least one magnetic coil (MS; MSI, MS2, MSN), in particular a stellarator coil or tokamak coil for a nuclear fusion device, wherein the magnet coil (MS; MSI, MS2, MSN) comprises a superconducting conductor (10) and one or more annular plate layers (P; Pl, P2) of electrically conductive material, each containing several turns of the superconducting conductor (10) extending along a local longitudinal direction (LLR.), the turns being arranged successively in a local transverse direction (LQR.), wherein the conductor running in the plate layer is insulated from the plate layer, wherein the superconducting conductor (10) of the magnet coil (MS; MSI, MS2, MSN) is part of a superconducting circuit of the magnet coil arrangement (1), characterized in that that at least one of the plate layers (P; Pl, P2) is part of an additional current path (17; 17'; 17"; 17'") which is connected in parallel to at least one section of the superconducting conductor (10) and forms a discharge circuit (20; 20'; 20"; 20"') with it, and that a first switching element (SI; S2) for interrupting the superconducting circuit is present in the superconducting circuit, wherein the switching element (SI; S2) is arranged outside the discharge circuit (20; 20'; 20"; 20"'), that the at least one plate layer (P; Pl, P2) of the additional current path (17; 17'; 17"; 17'') has end sections (5a, 5b) which are electrically insulated from each other by means of one or more insulating elements (6; 6a, 6b; 6c). Gauss Fusion GmbH 04.12.2025 SP14051PCT2. Magnetic coil arrangement (1) according to claim 1, characterized in that at least the partial section of the conductor (10) and the at least one plate layer (P; Pl, P2) of the additional current path (17; 17'; 17"; 17"') are electrically interconnected in such a way that they form a series circuit when the superconducting circuit is interrupted.

3. Magnetic coil arrangement (1) according to one of claims 1 to 2, characterized in that, that at each end section (5a, 5b) a projection and a rebate are formed, which form a hook-shaped end, wherein a projection of each end section is hooked into a rebate of the other end section, and that one or more insulating elements (6a, 6b) are arranged between the hook-shaped ends, covering at least partially mutually facing surfaces of the end sections (5a, 5b).

4. Magnetic coil arrangement (1) according to one of claims 1 to 2, characterized in that the insulating element (6c) separates the end sections from each other in the local longitudinal direction (LLR) and the end sections (5a, 5b) are mechanically connected to each other by means of bolts (9), wherein the insulating element (6c) is clamped between the end sections (5a, 5b).

5. Magnetic coil arrangement (1) according to one of the preceding claims, characterized in that the magnetic coil (MS; MSI, MS2, MSN) comprises several plate layers (Pl, P2), wherein several of the plate layers (P; Pl, P2), preferably all plate layers (P; Pl, P2), are interconnected in series within the additional current path (17; 17'; 17"; 17'").

6. Magnet coil arrangement (1) according to claim 5 in conjunction with claim 3, characterized in that the position of the insulating elements (6) of the Gauss Fusion GmbH 04.12.2025 SP14051PCT different plate layers (P; Pl, P2) are arranged offset from each other in the local longitudinal direction (LLR).

7. Magnet coil arrangement (1) according to one of the preceding claims, characterized in that at least one of the plate layers (P; PI, P2) of the additional current path is divided into an upper sandwich layer (PSI; P1S1, P2S1) and a lower sandwich layer (PS2; P1S2, P2S2), which are electrically insulated from each other in a local stacking direction (LSR.) that is perpendicular to the local longitudinal direction (LLR) and perpendicular to the local transverse direction (LQR), wherein the upper sandwich layer (PSI; P1S1, P2S1) accommodates the electrical conductor (10).

8. Magnet coil arrangement (1) according to claim 7, characterized in that the cross-sectional area of ​​the upper sandwich layer (PSI; P1S1, P2S1) is smaller than the cross-sectional area of ​​the lower sandwich layer (PS2; P1S2, P2S2).

9. Magnet coil arrangement (1) according to claim 7 or 8, characterized in that the upper sandwich layers (P1S1, P2S1) and the lower sandwich layers (P1S2, P2S2) of several plate layers (Pl, P2), preferably all plate layers (Pl, P2), are interconnected in a series circuit within the additional current path (17").

10. Magnetic coil arrangement (1) according to claim 7 or 8, characterized in that, that the upper sandwich layers (P1S1, P2S1) of several plate layers (Pl, P2), preferably all plate layers (Pl, P2), are interconnected in a series circuit within the additional current path (17"'), and that a further switching element, preferably a changeover switch (WS), is present, which is configured to switch the lower sandwich layers Gauss Fusion GmbH 04.12.2025 SP14051PCT(P1S2, P2S2) to add to the additional current path (17"'), the addition being serial to the upper sandwich layers (P1S1, P2S1).

11. Magnetic coil arrangement (1) according to claim 7 or 8, characterized in that, that the upper sandwich layers (PSI; P1S1, P2S1) of several plate layers (P; Pl, P2), preferably all plate layers (P; Pl, P2), are interconnected in a series circuit within the additional current path (17; 17'; 17"; 17"'), and that at least one additional switching element (SP) is provided which is configured to switch at least one of the lower sandwich layers (P1S2, P2S2) to the additional current path (17'"), the switching being carried out in parallel to the series connection of the upper sandwich layers (P1S1, P2S1).

12. Magnet coil arrangement (1) according to one of the preceding claims, characterized in that at least one of the plate layers (P; PI, P2) of the additional current path (17; 17'; 17"; 17'") has several plate layer rings (11) arranged successively in the local transverse direction, wherein the plate layer rings (11) are electrically insulated from each other in the local transverse direction (LQR).

13. Magnet coil arrangement according to claim 12, characterized in that the plate layer rings (11) within the plate layer (P; Pl, P2) are interconnected in a series circuit.

14. Magnetic coil arrangement (1) according to one of the preceding claims, characterized in that a quench detector is provided for detecting a quench of the superconducting conductor, in particular a fiber optic quench detector, wherein the switching element (SI; S2) is configured to interrupt the superconducting circuit when a quench is detected by the quench detector. Gauss Fusion GmbH 04.12.2025 SP14051PCT15. Magnet coil arrangement (1) according to one of the preceding claims, characterized in that the superconducting conductor (10) and the at least one plate layer (P; Pl, P2) of the additional current path (17; 17'; 17"; 17'') are interconnected such that, when the superconducting circuit is interrupted, the current flows through the plate layers (P; Pl, P2) and the superconducting conductor (10) in opposite directions.

16. Magnet coil arrangement according to one of the preceding claims, characterized in that the magnet coil arrangement (1) comprises a plurality N of magnet coils (MS; MSI, MS2, MSN) arranged in a cryostat (CRYO) and forming a nuclear fusion magnet and configured to effect magnetic plasma confinement, in particular in a stellarator or a tokamak.

17. Method for operating a superconducting magnet coil arrangement (1) according to one of the preceding claims, wherein a coil current is guided superconductively in the superconducting circuit, characterized by that quench monitoring of the conductor (10) is carried out by means of a quench detector, and that in the event of a quench detection, the superconducting circuit is interrupted by means of the switching element (SI; S2) and the coil current then flows via the additional current path and is dissipated.

18. Method according to claim 17, characterized in that that at least one of the plate layers (P; Pl, P2) of the additional current path (17; 17'; 17"; 17'') is divided into an upper sandwich layer (PSI; P1S1, P2S1) and a lower sandwich layer (PS2; P1S2, P2S2) which are electrically insulated from each other in the stacking direction, wherein the upper sandwich layer (PSI; P1S1, P2S1) accommodates the superconducting conductor (10), Gauss Fusion GmbH 04.12.2025 SP14051PCT that after interruption of the superconducting circuit, initially only the upper sandwich layers (PSI; P1S1, P2S1) are contained in the additional current path, and that the lower sandwich layers (PS2; P1S2, P2S2) are connected in series to the series connection of the upper sandwich layers (PSI; P1S1, P2S1) with a time delay into the additional current path (17; 17'; 17"; 17'"), wherein the connection of the lower sandwich layers (PS2; P1S2, P2S2) preferably takes place stepwise.

19. Method according to claim 18, characterized in that that the temperature of the upper sandwich layers (PSI; P1S1, P2S1) is monitored, and that the lower sandwich layers (PS2; P1S2, P2S2) are only switched into the additional current path when the temperature of the upper sandwich layers (PSI; P1S1, P2S1) exceeds a predetermined limit. Gauss Fusion GmbH 04.12.2025 SP14051PCT

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