Passive runaway electron mitigation coil

Abstract

Concepts, structures, and techniques are described for passively mitigating relativistic electrons generated in a tokamak plasma. These electrons are sometimes referred to herein as "runaway" electrons (REs). In an embodiment, the passive runaway electron mitigation coil (REMC) includes an electrical conductor having a non-axisymmetric loop shape including multiple sections, which are arranged along a toroidal direction and along a path defined by the surface of the torus. During operation, the REMC is energized by a collapse-induced voltage, and the resulting magnetic field stochasticity causes electrons to be lost more rapidly than the RE beam can generate them. The REMC is configured for external mounting within a vacuum vessel.

Description

[Background technology]

[0001] Actively driven coils have been successfully used for runaway electron mitigation. Actively driven coils can be located on the outer or inner walls of a tokamak. However, active coils are impractical for high-field and high-current devices where it is desirable to generate megajoules of magnetic energy in a few milliseconds. Summary of the Invention [Problem to be solved by the invention]

[0002]

[0002] Described herein are concepts, structures, and techniques for passively mitigating relativistic electrons generated in tokamak plasmas, sometimes referred to herein as "runaway" electrons (RE). [Means for solving the problem]

[0003] In embodiments, a conductive coil having a three-dimensional (3D) shape (referred to herein as a runaway electron mitigation coil (REMC)) is energized with a voltage that induces collapse, and the resulting magnetic field stochasticity causes the RE beam to lose electrons more rapidly than they can be formed. The REMC is provided with a non-axisymmetric shape and configured for external attachment to the vacuum vessel. In some embodiments, the REMC may be formed from a single continuous loop of conductive material.

[0004] In an embodiment, REMCs eject REs from the tokamak plasma that occurs during collapse, after which such electrons accelerate to high energies and multiply. REMCs cause runaway electron losses by opening tearing mode regions (or "islands") in the plasma, which, when overlapping, generate stochastic magnetic fields, thereby causing stochastic migration of electrons out of the plasma. In addition to the vacuum magnetic field generated by REMCs, the plasma further enhances the magnetic field. Runaway electrons follow perturbing magnetic field lines exiting the plasma (i.e., travel along paths defined by the perturbing magnetic field lines) and collide with walls or other surfaces at random locations, thereby dissipating the RE energy in a manner that reduces (ideally minimizes) damage to the walls. This process is diffusive, and the loss rate characteristic can, for example, scale with the square of the perturbing magnetic field. Thus, the REMC is configured to generate perturbing magnetic fields (ideally, to generate the maximum perturbing magnetic fields) within engineering constraints to overcome avalanches, Compton scattering, and tritium beta decay growth periods. In embodiments, the REMC is driven by exploiting mutual inductance with the plasma during a current quench, and the non-axisymmetric geometry of the coil generates a resonant magnetic field that opens up magnetic islands across a short radius of the plasma.

[0005] The systems, structures, and techniques described herein may include one or more of the following features, alone or in combination with any subset of the listed features, including, but not limited to, external mounting, vertical legs in each half-cycle going between ports, and flexibility in the number of vertical coil legs. Also, the characteristic decay time (i.e., L / R time) may be adjusted to increase (ideally maximize) the coupled current while decreasing (ideally minimize) the total force.

[0006] External mounting allows the coil to be spaced a distance from the vacuum vessel wall, resulting in a higher drive current at the desired level.

[0007]

[0007] The vertical legs are positioned in the vacuum vessel so that the REMC avoids ports in the vacuum vessel, thereby not obstructing plasma access. The upper and lower toroidal legs can have the same length, so that the REMC has net-zero coupling with the tokamak's vertical stability coils. External mounting with the vertical stability coils reduces the number of structural mounts required.

[0008] In an embodiment, the coil L / R time can be long relative to the current quench period to ensure an increased, ideally maximum, coupled current. In an embodiment, the coil L / R time can be shorter than or compared to the vessel resistance diffusion time to ensure that a large (ideally maximum) coil current is achieved at the end of the current quench and that this magnetic field does not persist long after the plasma has terminated. This reduces unwanted forces on the REMC.

[0009] Furthermore, with the passive REMC approach described herein, mutual inductance with the plasma does not require a power source: only the REMC current (ideally a very large current) flows during collapse, which is the only time current is required.

[0010]

[0010] According to one aspect of the concepts described in this specification, a nuclear fusion reactor includes an electrical conductor, which is a non-axisymmetric loop including multiple portions, which are arranged along a path defined by the surface of a torus and aligned along the toroidal direction of the torus.

[0011]

[0011] In an embodiment, the non-axisymmetric loop of conductor may include a first portion arranged along the toroidal direction of the torus at a first poloidal angle and a second portion arranged along the toroidal direction of the torus at a second poloidal angle different from the first poloidal angle.

[0012]

[0012] In an embodiment, the non-axisymmetric loop of conductor includes one or more legs arranged along the poloidal direction of the torus and coupled to a first portion and / or a second portion of the non-axisymmetric loop of conductor.

[0013]

[0013] In an embodiment, the non-axisymmetric loop of conductor includes a plurality of upper portions, each positioned along the toroidal direction of the torus at a first poloidal angle, and a plurality of lower portions, each positioned along the toroidal direction of the torus at a second poloidal angle different from the first poloidal angle.

[0014]

[0014] In an embodiment, the non-axisymmetric loop of conductor includes a plurality of legs, each of which is coupled to one of a plurality of upper portions and one of a plurality of lower portions.

[0015]

[0015] In an embodiment, the non-axially symmetric loop of conductor includes a first portion, the first portion including a first upper portion of a plurality of upper portions, a first leg of a plurality of legs coupled to the first upper portion, a first lower portion of a plurality of lower portions coupled to the first leg, and a second leg of the plurality of legs coupled to the first lower portion.

[0016] In an embodiment, the non-axisymmetric loop of the conductor includes multiple instances of the first portion coupled together to produce the non-axisymmetric loop.

[0017] In an embodiment, the plurality of legs are arranged along a path defined by the surface of the torus along a poloidal direction.

[0018]

[0018] In an embodiment, the fusion reactor may further include a vacuum vessel, the conductor being disposed along a path defined by the inner surface of the torus, the conductor being attached to an inner wall of the vacuum vessel.

[0019]

[0019] In an embodiment, the fusion reactor may further include a vacuum vessel, the conductor being disposed along a path defined by the outer surface of the torus, the conductor being attached to an outer wall of the vacuum vessel.

[0020] In an embodiment, each of the plurality of upper portions and each of the plurality of lower portions have the same length.

[0021] In an embodiment, the fusion reactor may further include a switching element coupled to the non-axisymmetric loop of conductor.

[0022] In an embodiment, a fusion reactor includes a vacuum vessel having a conductor mounted therein, and a switching element coupled to a non-axisymmetric loop of the conductor and positioned outside the vacuum vessel.

[0023] In embodiments, the fusion reactor may further include a switch coupled to the non-axisymmetric loop of conductor, the switch including one or more varistors arranged as a non-conductive open circuit along the non-axisymmetric loop of conductor.

[0023]

[0024] In an embodiment, the conductor is an electrically closed conductor.

[0024]

[0025] According to further aspects of the concepts described herein, a runaway electron mitigation coil (REMC) includes an upper horizontal leg, a lower horizontal leg, and at least one vertical leg coupled between the upper and lower horizontal legs, wherein the upper and lower horizontal legs are configured such that the REMC functions as a passive REMC.

[0025]

[0026] In an embodiment, the REMC is used in a Tokamak fusion reactor.

[0026]

[0027] In an embodiment, the REMC is configured for external mounting in the vacuum vessel of a tokamak.

[0027]

[0028] In an embodiment, the REMC includes a vertical leg in each half period of the upper horizontal leg and the lower horizontal leg. In an embodiment, the REMC is configured to avoid ports in the vacuum vessel of the tokamak. Thus, the upper horizontal leg and the lower horizontal leg are positioned in the vacuum vessel of the tokamak while avoiding the ports in the vacuum vessel.

[0028]

[0029] In an embodiment, the REMC further includes a switching element disposed on one of the upper horizontal leg, the lower horizontal leg, and at least one of the at least one vertical leg.

[0029]

[0030] The methods and processes for making and using the disclosed embodiments can be understood by reference to the accompanying drawings. It should be understood that the components and structures shown are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts described herein. Like reference numerals designate corresponding parts throughout the different drawings. Furthermore, the embodiments are shown by way of example, and not limitation, in the drawings. [Brief explanation of the drawings]

[0030] [Figure 1A]

[0031] FIG. 1 is a partial cross-sectional isometric view of a tokamak fusion reactor incorporating runaway electron mitigation coils (REMC). [Figure 1B]

[0032] FIG. 1B is a perspective view of an outer REMC that may be the same as or similar to the REMC used in the tokamak fusion reactor of FIG. 1A. [Figure 1C]

[0033] FIG. 1C is a top view of the REMC of FIG. 1B. [Figure 2A]

[0034] FIG. 10 is a perspective view of an alternative outer REMC having switching elements on its legs. [Figure 2B]

[0035] FIG. 10 is a perspective view of an outer REMC coupled to an external switching element. [Figure 3]

[0036] FIG. 10 is a perspective view of another alternative outer REMC. [Figure 4A]

[0037] FIG. 10 is a perspective view of another alternative outer REMC. [Figure 4B]

[0038] FIG. 1 is a partial cross-sectional isometric view of a tokamak fusion reactor incorporating runaway electron mitigation coils (REMC). [Figure 5A]

[0039] FIG. 1 is a perspective view of a net-free REMC. [Figure 5B]

[0040] FIG. 5B is another perspective view of the net-free REMC of FIG. 5A. [Figure 5C]

[0041] FIG. 5C is a top view of the net-free REMC of FIGS. 5A and 5B. [Figure 5D]

[0042] FIG. 1 is a partial cross-sectional view of a vacuum vessel with a net-free REMC disposed therein. [Figure 5E]

[0043] FIG. [Figure 5F]

[0044] FIG. 10 is an explanatory wiring diagram of a series connection. [Figure 6]

[0045] FIG. 10 is a perspective view of another alternative outer REMC design in which the switching element is located on the horizontal leg. DETAILED DESCRIPTION OF THE INVENTION

[0031]

[0046] Described herein are concepts, structures, and techniques for passively mitigating relativistic electrons generated in a tokamak plasma. These electrons are sometimes referred to herein as "runaway" electrons (RE). As described herein, such passive mitigation is achieved via runaway electron mitigation coils (REMCs). The REMCs are sometimes referred to herein as "passive," meaning that no external voltage or current source needs to be coupled to the REMC to achieve RE mitigation. Rather, current can flow in the REMC only during a disruption event as a result of mutual inductance between the REMC and the plasma.

[0032]

[0047] 1A-1C, in which like elements are designated with like reference numerals, a tokamak fusion reactor 10 includes a vacuum vessel 12 defined by a wall 13 (sometimes referred to herein as outer wall 13) having an inner surface 13a (sometimes referred to herein as outer surface 13a). In embodiments, the vacuum vessel 12 may be provided as a double-walled structure, with a first wall (or inner wall) surrounded by a second wall. Runaway electron mitigation coils (REMC) 14 are integrated into or otherwise disposed within the vacuum vessel 12. The outer wall 13 may be constructed from a number of panels or components.

[0033]

[0048] The REMC includes an electrical conductor, the conductor being a non-axisymmetric loop including multiple portions disposed along a path defined by a surface of a torus and aligned along a toroidal direction of the torus. In an embodiment, the non-axisymmetric loop of conductor includes a first portion disposed along the toroidal direction of the torus at a first poloidal angle and a second portion disposed along the toroidal direction of the torus at a second poloidal angle different from the first poloidal angle.

[0034]

[0049] The size and shape of the REMC are selected according to the size and shape of the plasma in the tokamak vacuum vessel. Generally, the diameter of the REMC is selected so that the toroidal (or horizontal) leg is as close as possible to the outer plasma separatrix, and the two horizontal legs are spaced so as not to cross, cover, or otherwise obstruct or impede the ports 18, 19, and 20. It is desirable for the REMC to have a relatively large cross-section relative to the cross-sectional area of ​​the plasma. The REMC is provided with a shape that allows it to be energized by a voltage induced in the collapse, and the resulting magnetic field stochasticity causes electrons to be lost more rapidly than the RE beam can generate them. Thus, the REMC ejects relativistic electrons from the tokamak plasma generated during the collapse before such electrons can be accelerated to high energies and multiplied.

[0035]

[0050] One or more electrically isolated mounting structures may be coupled to the wall of the vacuum vessel or other structures. For example, the mounting structures may include mounting studs, mounting brackets, or any mounting means provided on or coupled to the vacuum vessel or any structure within the vacuum vessel, and the REMC may be coupled to such mounting structures. In general, the REMC may be coupled to the vacuum vessel by any permanent or semi-permanent attachment technique, including, but not limited to, welding.

[0036]

[0051] As shown in FIG. 1A, the REMC is coupled to the outer portion of the vacuum vessel. The outer portion has a larger semi-major axis than the plasma and is complemented by the inner portion to represent all of the space in which the plasma resides. Any technique may be used to secure the REMC within the vacuum vessel. In an embodiment, the REMC may be positioned within the vacuum vessel via a bracket and an alumina bushing.

[0037]

[0052] As can be seen more clearly in FIG. 1B , the REMC is provided with a non-axisymmetric shape and is configured for external mounting within a vacuum vessel. The REMC has a shape selected to generally follow the shape of the plasma and is simultaneously configured for external mounting. In this exemplary embodiment, the REMC 14 includes a pair of toroidal (or horizontal) legs 14 a, 14 b and a pair of vertical legs 14 c, 14 d (or legs arranged along the poloidal direction of the torus). The vertical legs may be coupled to the toroidal legs, for example, as shown in FIG. 1B , with legs 14 c, 14 d coupled to and between toroidal legs 14 a, 14 b. This toroidal and vertical leg configuration is sometimes referred to as an n=1 configuration, since it is formed from a single upper toroidal leg and a single lower toroidal leg. In this exemplary embodiment, vertical legs 14c, 14d have a curved shape (i.e., the vertical legs are arcuate) between toroidal legs 14a, 14b. In other embodiments, vertical legs 14a, 14b may be straight. The shape of vertical legs 14c, 14d may not be critical to the operation of REMC 14 and may be selected to suit the needs of a particular application and to accommodate loading forces experienced during operation.

[0038]

[0053] Thus, the REMC may include an upper portion 14a arranged along the toroidal direction of the torus at a first poloidal angle of the torus that defines the shape of at least a portion of the REMC, a lower portion 14b arranged along the toroidal direction of the torus at a second poloidal angle of the torus that is different from the first poloidal angle, and one or more legs (including two legs 14c, 14d shown in FIG. 1B) arranged along the poloidal direction of the torus, each of the one or more legs being coupled to at least one of the plurality of upper portions and one of the plurality of lower portions.

[0039]

[0054] The REMC is provided with a height (i.e., the distance between the toroidal legs) that is smaller than the height of the tokamak plasma, and a diameter D (FIG. 1C) that is selected so that the REMC is large enough to intercept the plasma such that the coil resistance is not dominant and the time constant (characteristic decay time) of the REMC is long compared to the decay time.

[0040]

[0055] Referring again to FIG. 1A, the vertical legs are configured to allow REMC 14 to avoid the vacuum vessel ports (e.g., midplane port 18 as well as upper and lower midplane ports 19 and 20) so that REMC 14 does not obstruct plasma access. The equal extent of the upper and lower toroidal legs ensures net-zero coupling with the vertical stability coils. Vertical legs 14c, 14d are arranged in half-periods that run between the ports (i.e., the legs are spaced 180° apart, as seen most clearly in FIG. 1C).

[0041]

[0056] In embodiments, the REMC can have a ribbon shape. In embodiments, the REMC can have a poloidal length of about 10 cm and a radial width of about 1 cm. Generally, it is desirable to maximize the coil-plasma mutual inductance while reducing the resistivity and coil self-inductance (i.e., coil impedance). All dimensions correspond to the linear size of the plasma.

[0042]

[0057] The REMC is positioned outside the plasma in the vessel. The outside mounting approach allows the REMC to be spaced a distance from the vacuum vessel wall, resulting in a desired level of current. That is, the outside mounting approach allows for greater coil spacing from the vacuum vessel wall, and therefore a higher drive current. In the exemplary embodiment of FIG. 1A, the REMC is positioned above or around the vertical stability coil, but is positioned so as not to interfere with the vertical stability coil. It is desirable to position the REMC in a location that will modify the plasma in a desired manner to prevent RE accumulation in the plasma. In an embodiment, the toroidal legs 14a, 14b are spaced a distance of approximately 4 cm from the outer surface.

[0043]

[0058] In addition to coupling current to the REMC, it is important that the REMC current generates a magnetic field that subsequently drives the stochastic field in the plasma. For maximum excitation of the core tearing modes that drive stochasticity, the coil should be optimized to generate a maximum radial magnetic field (i.e., perpendicular to the plasma surface) in the outer midplane, and the poloidal decay length of this field should be several tens of percent of the plasma's semi-minor radius.

[0044]

[0059] In embodiments, the REMC may be provided as a single loop conductor that reduces the terminal voltage. This allows for the use of a mounting structure provided from an electrically insulating material (e.g., a ceramic-based material). In embodiments, the mounting structure may be provided as a rod and tube structure. In embodiments, the mounting structure may include plasma spray / detonation spray coated insulators. The ratio of plasma inductance, coil inductance, wall inductance, and mutual coupling are factors in current generation. The size, shape, and mounting location of the REMC are selected to increase (ideally maximize) the coil-plasma mutual inductance while reducing (ideally minimize) the self-inductance of the REMC and the mutual inductance with the wall.

[0045]

[0060] During operation of the fusion reactor 10, the REMC 14 is subjected to various electromechanical stresses and forces. The n=1 configuration of Figures 1A-1C introduces a net lateral force, F=2ILBφ<18MN, due to opposing currents I in the two vertical legs, each with a length L=1.5 m.

[0046]

[0061] In embodiments, the REMC may be secured to the upper vertical stability coil 21 a and the lower vertical stability coil 21 b within the vacuum vessel. More specifically, in embodiments, the vertical stability coil may be secured or otherwise coupled to the vacuum vessel via a bracket (e.g., a U-shaped clamp or bracket), with the REMC coupled to the plasma side of the clamp. This approach allows the REMC to withstand net lateral forces and forces caused by vertical displacement events. Note, however, that in embodiments, forces due to vertical displacement are initially negligible. Thus, in some embodiments, the REMC may be directly coupled to the vacuum vessel wall 13 a, and in some embodiments, the REMC may be directly coupled to the vacuum vessel wall 13 a via another structure (e.g., a vertical stability coil or a vertical stability coil bracket). In still other embodiments, a combination of a mounting structure and coupling the REMC to one or more vertical stability coils may be used. In such embodiments, this can reduce the number of structural mounts 14 required for external mounting.

[0047]

[0062] During operation, REMCs create runaway electron (RE) losses by opening tearing mode regions (or "islands") in the plasma, which, when overlapping, generate stochastic magnetic fields, thereby creating stochastic migration of electrons out of the plasma. In addition to the vacuum magnetic field generated by the REMC, the plasma further enhances the magnetic field. Runaway electrons follow the perturbed magnetic field lines exiting the plasma (i.e., travel the path defined by the perturbed magnetic field lines) and collide with random locations on the vacuum vessel wall, dissipating their energy in a manner that reduces (ideally minimizes) first wall damage.

[0048]

[0063] This process is diffusive, with a loss rate characteristic that scales with the square of the perturbation field. Thus, the REMC is configured to generate a perturbation field (ideally, to generate the maximum perturbation field) within engineering constraints to overcome avalanches, Compton scattering, and tritium beta decay growth periods. In embodiments, the REMC may be driven by exploiting mutual inductance with the plasma during a current quench, and the non-axisymmetric geometry of the coil generates a resonant magnetic field that opens up magnetic islands across a short radius of the plasma.

[0049]

[0064] As will become apparent from the description herein below, in general, a REMC can include a vertical leg for each half-cycle traveling between ports; in the embodiment of FIG. 1A, the REMC is provided with a pair of vertical legs, but in other embodiments, the REMC can include four or more vertical legs. Thus, there is flexibility in the number of vertical legs a REMC can include. Flexibility in the number of vertical coil legs allows for coupling to multiple plasma toroidal modes and also allows for high toroidal harmonic content and non-plasma resonant loss mechanisms, while reducing inductive coupling due to the asymmetry of the vertical stability coils, which cancels the net mutual inductance.

[0050]

[0065] Additionally, the characteristic decay time (i.e., L / R time) may be adjusted to increase (ideally maximize) the coupled current while decreasing (ideally minimize) the total force. In embodiments, as described below in conjunction with FIG. 2B , a resistive element (e.g., a fixed or variable resistance resistor) may optionally be electrically coupled to the REMC to adjust the L / R time and peak current (thus reducing the force experienced by the REMC). Such a resistive element may be located inside the container (e.g., as in the exemplary embodiment of FIG. 2A ) or outside the container (as described in the exemplary embodiment of FIG. 2B ). Furthermore, by changing the cross-sectional shape of the REMC, the characteristic decay time (L / R time) may also be adjusted, since changing the cross-sectional shape of the REMC changes the resistance R of the REMC.

[0051]

[0066] In embodiments, the coil L / R time is long relative to the current quench period (e.g., the coil L / R time may be at least about 200 percent longer than the CQ period (TCQ), ideally more than 200 percent longer) to ensure increased, ideally maximum, coupled current, and the L / R time is short compared to or less than the vessel resistance diffusion time to ensure that a large (ideally maximum) coil current (i.e., a coil current of about 5-10 percent of the pre-collapse plasma current) is achieved at the end of the current quench rather than after. This reduces undesirable forces on the REMC (e.g., electromechanical forces after the plasma is extinguished).

[0052]

[0067] Furthermore, with the passive REMC approach described herein, mutual inductance with the plasma does not require a power source: only the REMC current (ideally a very large current) flows during collapse, which is the only time current is required.

[0053]

[0068] 2A , REMC 20 includes a pair of toroidal legs 14 a, 14 b and a pair of vertical legs 14 b, 14 c. A switching element 22 is disposed on one of the vertical legs (here, leg 14 c). When switching element 22 is closed, a low-impedance signal path (ideally, a closed-circuit impedance path) exists between switching element ports 22 a, 22 b, such that REMC 22 exhibits an electrically continuous conductive path. Conversely, when switching element 22 is open, a high-impedance signal path (ideally, an open-circuit impedance path) exists between switching element ports 22 a, 22 b, such that REMC 22 is electrically discontinuous.

[0054]

[0069] In embodiments, the switching element 22 has fast switching speed characteristics (e.g., switching speeds on the order of microseconds or hundreds of microseconds or faster) and is passively triggered by the collapse of the voltage across the coil. That is, the switch is desirably passive and automatically responsive to rapidly occurring high current events that occur without warning. Rapidly occurring high current events can occur without warning and begin within very short time scales (e.g., milliseconds), and in embodiments, the switching element can include a collapse predictor.

[0055]

[0070] In embodiments, the switching element 22 may be provided as an active high-speed switch that is triggered by other means. In embodiments, the switching element 22 may include one or more Shockley diodes (e.g., high-voltage Shockley diodes). In embodiments, the switching element 22 may include a varistor. In embodiments, the switching element 22 may include an I 2t (i.e., the switching element should not be substantially damaged by a current of such magnitude). Of course, switching elements other than those specifically mentioned above may be used. For example, in embodiments, the switching elements may be provided as mechanical switches, metal oxide varistors, or solid state thyristors, which may be any suitable switching element suitable for use in applications where the closed circuit REMC is non-perturbative to the plasma during normal operation, i.e., produces a sufficiently small error magnetic field. p To make the system completely passive, the switch may be provided as a spark gap with a threshold voltage higher than the voltage driving the plasma current (ideally much higher (<10V) than the voltage driving the plasma current V-loop, but lower than the voltage expected during collapse (approximately 1 kV)).

[0056]

[0071] Referring now to FIG. 2B, the REMC 23 includes a pair of toroidal legs 114a, 114b and a pair of vertical legs 14c, 14d. A switching element 24 is coupled to the open ends 26a, 26b of the REMC via signal paths (or legs) 28a, 28b. The signal paths 28a, 28b are configured to reduce the inductance of the paths as much as possible. For example, the signal paths 28a, 28b are preferably spaced as close to each other as practical. The signal paths 28a, 28b are also preferably provided with lengths as short as practical (this can be achieved, for example, by physically locating the switching element 24 close to the REMC ends 26a, 26b). In this embodiment, the switching element 24 is external to the vacuum vessel in which the REMC is disposed. The switching element 24 may be of any of the types described above in conjunction with FIG. 2A.

[0057]

[0072] In this embodiment, the switching element 24 is located outside the vessel for ease of access and radiation protection. In embodiments, an external switching element may be preferred for simplicity and maintainability. Furthermore, the external switching element is exposed to a less neutron environment than the internal switching element (e.g., as shown in FIG. 2A ). Another tradeoff between using an internal switch (e.g., switching element 22 shown in FIG. 2A ) and an external switch (e.g., switching element 24 shown in FIG. 2B ) is that the external switch requires the use of a feedthrough structure (e.g., including signal paths 28 a, 28 b, which may be part of a bus) that is disposed through a port in the vessel (e.g., through one or more of vacuum vessel ports 18, 19, 20 in FIG. 1 ). Thus, the external switching element requires the use of additional mechanical structures (and associated electrical routing). Furthermore, the signal paths (e.g., 28 a, 28 b) required to couple the external switch to the REMC increase inductance to the switch (e.g., the inherent inductance associated with signal paths 28 a, 28 b).

[0058]

[0073] To make the system completely passive, the switch may be provided as a spark gap with a threshold voltage higher than the voltage driving the plasma current (ideally much higher (<10V) than the voltage driving the plasma current V-loop, but lower than the voltage expected during collapse (approximately 1 kV)).

[0059]

[0074] In embodiments, the switching elements may be provided as mechanical switches, metal oxide varistors, or solid state thyristors, which may be used as long as the closed circuit REMC is non-perturbative to the plasma during normal operation, i.e., produces a sufficiently small error magnetic field. p It is configured to close near the end of ramp-up.

[0060]

[0075] Analysis of an n=1 REMC in a SPARC fusion reactor suggests that, in embodiments, a coil current I of only 3 kA is required to seed the locked mode in the SPARC L-mode reference discharge, so an order of magnitude smaller current is targeted. Therefore, a coil resistance of at least about 33 mΩ is required.

[0061]

[0076] However, this minimum resistance is required for the "starting" RE (low density I) since a coil current I > 1 kA may be required to counter the avalanching seed. p Note that this may interfere with the REMC's ability to suppress lower-I n More complete studies must be performed to evaluate the effect of REMC on the operation and plasma formation.

[0062]

[0077] In this exemplary embodiment, the REMC 23 includes a resistive element 27 (e.g., a fixed, selectable, or variable resistance resistor), which is optionally coupled to the REMC to adjust or tune its characteristic decay time (i.e., L / R time) and / or peak current. Such adjustment can reduce forces experienced by the REMC. In the exemplary embodiment of FIG. 2B, the resistive element 27 is external to the container in which the REMC is disposed. In embodiments in which the resistive element 27 includes a resistor having fixed resistance characteristics (i.e., a fixed resistance value), resistors having different resistance values ​​may be used. That is, the resistance value is selectable. For example, the resistance provided by the resistive element 27 can be changed by changing the resistor from a first resistor having a first resistance characteristic to a second resistor having a second, different resistance characteristic. In this manner, the characteristic decay time (i.e., L / R time) and / or peak current of the REMC can be adjusted.

[0063]

[0078] As will become apparent from the following description, the REMC can have one of many possible periodicities (i.e., REMC configurations where n>1, in which the period of the pattern of the upper and lower toroidal legs of the REMC is given by (2π / n) radians). Three exemplary outer REMC designs are shown and described in conjunction with Figures 3-6, namely, REMCs with periods of 2πR (n=1), πR (n=2), and 2πR / 3 (n=3), where R is in radians, shown in Figures 3-6, respectively. Of course, it should be understood that other designs are possible according to the concepts described herein.

[0064]

[0079] It should be understood that any of the REMCs described herein in conjunction with Figures 1-6 may include one or more switching elements in the vertical or horizontal legs. Such switching elements may include any of the switches or switching structures described above in conjunction with Figures 2A and 2B. It should also be understood that any of the REMCs described herein may include resistive elements electrically coupled to adjust the characteristic decay time (i.e., L / R time) and / or peak current of the REMC.

[0065]

[0080] Referring to FIG. 3, REMC 30 includes four toroidal legs 30a-30d and four vertical legs 30e-30h coupled between the toroidal legs (referred to as an n=2 configuration).

[0066]

[0081] Referring now to FIG. 4A, REMC 40 includes six toroidal legs 40a-40f and six vertical legs 40g-40l coupled between the toroidal legs (referred to as an n=3 configuration).

[0067]

[0082] Vertical legs 40g-40l of REMC 40 are generally non-axisymmetric to allow current to traverse the vertical steps each half-cycle. For REMCs described in conjunction with Figures 1A-6, the vertical legs can be positioned or otherwise aligned or positioned between vessel ports (e.g., ports 18, 19, 20 in Figure 1A) to allow for coil attachment without interfering with plasma access.

[0068]

[0083] 4B, a tokamak fusion reactor 42 includes a REMC 40' having an n=3 configuration integrated into or otherwise disposed in a vacuum vessel. REMC 40' may be the same as or similar to REMC 40 of FIG. 4A.

[0069]

[0084] For a tokamak with 16 toroidal field coils, this allows for symmetry periods of 2π radians (360 degrees), π radians (180 degrees), π / 2 radians (90 degrees), and π / 4 radians (45 degrees). For a tokamak with 18 toroidal field coils, symmetries of 2π, 2π / 3, and 2π / 9 radians are available. However, other non-periodic options are also available, and such options may be effective in coupling with multiple toroidal mode numbers. Although not required for REMC operation, the coils are placed inside the vertical stability coils, as shown in Figure 1. This allows the REMC coils to share a structural mount with the vertical stability (VS) coils. This is possible because the REMC has no mutual inductance when the VS coils are connected anti-series.

[0070]

[0085] 5A-5C, in which like elements are designated by like reference numerals, a net-free (n=1) REMC 60 includes a pair of horizontal legs 61a, 61b and a pair of vertical current path connectors 66, 67, with a vertical current path connector 66 including two current paths 66a, 66b and a vertical current path connector 66 including two current paths 67a, 67b. Importantly, current paths 66a, 66b provide both source and sink current leads to the upper leg. Similarly, paths 67a, 67b provide both source and sink current leads to the lower leg. This arrangement allows opposite currents to flow through paths 66a, 66b and opposite currents to flow through paths 67a, 67b. These opposite currents experience opposing forces that cancel each other out.

[0071]

[0086] The horizontal leg 61a is also referred to as the upper main winding 61a, and the horizontal leg 61b is referred to as the lower main winding 61b. The REMC further includes a plurality of upper return paths 62a, 62b, and 62c and connector paths 63a, 63b, and 63c that couple each of the paths 62a, 62b, and 62c to the upper main winding 61a. The REMC further includes a plurality of lower return paths 64a, 64b, and 62c and connector paths 65a, 65b, and 65c that couple each of the paths 64a, 64b, and 64c to the lower main winding 61b. The REMC 60 further includes a vertical current path connector 66 composed of two conductors 66a, 66b, including a conductor 66a referred to as the upper vertical current path conductor and a conductor 66b referred to as the lower vertical current path conductor. Thus, a single vertical current path connector is composed of two conductors that conduct currents in opposite directions to null the force.

[0072]

[0087] The upper and lower vertical current path conductors 66a and 66b lead to signal paths 70 and 72, respectively. The signal paths 70 and 72 are configured to be coupled to switching elements (e.g., switching element 24 of FIG. 2B) that source and sink current throughout the coil and control when the coil is active. Therefore, the signal paths 70 and 72 must be configured to carry high currents. As noted above, the signal paths 70 and 72 are configured to be coupled to switching elements (e.g., external switching elements) that may be the same as or similar to any of the switching elements described above in conjunction with FIGS. 2A and 2B.

[0073]

[0088] 5D, a portion of a vacuum vessel 80 includes a first or inner wall 81 and a second or outer wall 82. Thus, in this exemplary embodiment, the vacuum vessel 80 is provided as a double-walled structure, with a first wall (or inner wall) surrounded by a second wall.

[0074]

[0089] A net-free REMC 83 is disposed in the vacuum vessel. The REMC may be the same as or similar to the net-free REMC described above in conjunction with FIGS. 5A-5C. One or more return current paths, shown here as three return current paths 86, 88, and 90, are disposed along the surface of the vacuum vessel wall 81. The return current paths 86, 88, and 90 may be the same as or similar to the return current paths 62a, 62b, and 62c described above in FIG. 5A. The return current paths 86, 88, and 90 carry a current approximately equal to TotalCurrent / N, where N represents the number of return current paths (thus, in this example, N=3). The return current paths are distributed to resemble natural eddy currents within the vessel that would occur in the absence of these return paths.

[0075]

[0090] It should be noted that the main current windings 61 a, 61 b ​​can have two embodiments (or variations): In a first embodiment, the main current windings 61 a, 61 b ​​can be further divided into N insulated conductors in series (not shown); In a second embodiment, the main current windings 61 a, 61 b ​​are provided as single conductors, and the switching element is arranged to interrupt the main winding rather than one of the return legs.

[0076]

[0091] It should be understood that the short connector between the main windings 61a, 61b and the return path is still subject to normal and lateral forces. The lateral forces are of most concern, but by adjusting the vertical position of the main windings relative to the return windings, the lateral forces can be made net zero.

[0077]

[0092] Also shown in FIG. 5D are upper and lower stabilization coils 92, 94.

[0078]

[0093] 5E and 5F are illustrative wiring diagrams of the REMC, with FIG. 5D including connections 63a-63c, 65a, 65c that electrically connect the REMC loops, and FIG. 5F showing the illustrated series connections.

[0079]

[0094] Referring now to FIG. 6, REMC 110 includes an upper horizontal leg and a lower horizontal leg. A switching element is coupled to one of the upper horizontal leg and the lower horizontal leg. As discussed above, REMC 110 may include one or more switching elements (not explicitly shown in FIG. 6) coupled to the horizontal legs. Such switching elements may include any of the switches or switching structures described above in conjunction with FIGS. 1A-5D. It should also be appreciated that REMC 110 may include a resistive element electrically coupled to adjust the characteristic decay time (i.e., L / R time) and / or peak current of the REMC, as discussed above.

[0080]

[0095] It should be understood that the non-axisymmetric magnetic field, possibly generated with the aid of the plasma response, opens magnetic islands in the plasma, the size of which corresponds to the square root of the perturbation resonance field. With the perturbation field large enough and the spectrum selected to open islands in many flux planes, the islands overlap, generating a fully stochastic magnetic field. The transport of runaway electrons is then governed, to a good approximation, by the Richester-Rosenbluth stochastic diffusion coefficient, including a correction on the order of 50% introduced by finite orbital width effects. The induced current in the REMC becomes high enough to initiate runaway electron loss very early in current quench (CQ), effectively preventing RE accumulation throughout the remainder of the CQ. After CQ, when the high loop voltage is no longer present, the current in the REMC remains relatively high for approximately L / R time.

[0081]

[0096] A REMC is a toroidal conductor, and with the coil electrically closed, its toroidal electrical resistance is still significantly higher than that of a fully developed plasma. During normal operation (i.e., not during a collapse current quench), the B-field perturbations due to the REMC's relatively small induced currents can be compensated for by error field correction coils, if necessary, even at the expense of a larger high-mode number error field. Also, small REMC B-field perturbations can sometimes be a problem during plasma discharge initiation (i.e., failure and premature current ramp-up). This disclosure encompasses both concepts of a fully closed (i.e., toroidally conductive) REMC and a REMC with a non-conductive open circuit, or an active mechanical switch, or an active or passive solid-state switch, or a passive varistor switch (e.g., a metal oxide varistor).

[0082]

[0097] Examples of REMCs having non-conductive opens or active mechanical or solid-state switches or passive varistor switches are shown in Figures 5-7. Of course, embodiments other than those shown in the examples of Figures 5-7 are possible. Regardless of the particular implementation, a structure or circuit (e.g., an open, switch, varistor, diode, or equivalent) is configured to prevent current from flowing through the REMC during start-up and possibly during discharge flat-top, but may be actively shorted or closed after discharge is established or before collapse begins, or may be passively closed (e.g., by a high voltage generated at the beginning of collapse).

[0083]

[0098] In some applications, an n=1 REMC configuration (see, e.g., FIGS. 1A-2B) may be the optimal coil configuration for driving tearing modes. For the reasons stated above, the resonant field in each resonant plane is desirable. As the toroidal harmonics of the coil increase, the resonant field in a given plane increases by approximately 1.5 for an n=1 coil for equal current.

number

[0084]

[0099] The outer REMC design is expected to carry more current than the inner design due to the greater separation from the vessel provided by the larger plasma-vessel gap that can be achieved with the REMC outer mounting approach. To a good approximation, on short timescales such as current quenches, the REMC maintains a constant poloidal magnetic flux trapped between the REMC and the vessel. Increasing (ideally maximizing) the REMC current requires increasing (ideally maximizing) the coil-plasma coupling while decreasing (ideally minimizing) the coil's self-inductance and the coil-vacuum vessel mutual inductance (i.e., maximizing the ratio of plasma-coil mutual inductance to coil self-inductance while minimizing coil-vessel mutual inductance). The outer coil has a larger semimajor axis and therefore a higher self-inductance, but the increase in trapped magnetic flux is greater due to the plasma-vessel geometry.

[0085]

[0100] The coil L / R time is preferably adjusted to be longer than the current quench but shorter than or compared to the vessel resistance diffusion time: the former ensures maximum coil current slope and earliest application of the perturbation field during the current quench (assuming the vessel resistance time is always longer than the current quench period), while the latter ensures that the REMC current stops increasing once the plasma is extinguished.

[0086]

[0101] Other nearby conductors that have significant mutual inductance with the REMC will reduce the drive current. If possible, it is important to lower such mutual inductance or increase the resistivity of the opposing components.

[0087]

[0102] Finally, while the desired operation of REMCs relies at least in part on the coupling of REMCs to enhance lower-order plasma modes, it should be noted that higher-order non-resonant magnetic fields can also cause energetic particle losses. Thus, in embodiments, non-resonant effects that do not rely on plasma interactions (produced by such non-resonant magnetic fields) can provide a sufficient and reliable means of energetic electron loss. In this case, selecting a maximum period for the vertical legs can be advantageous.

[0088]

[0103] While an n=1 REMC configuration is described hereinabove, it should be understood that n=2 and n=3 designs are also possible. It should be understood that simulations indicate that the respective effects of n=2 and n=3 coils on RE formation are small or ineffective because inductive transport does not extend to the plasma core where most REs are generated. Because the engineering requirements of an n=1 coil are feasible, an n=1 coil may be preferable over n=2 and n=3 designs.

[0089]

[0104] The coil may be located on the inner wall, but the space inside is fairly small, making the wall separation very small. As a first approximation, for a fixed self-inductance, the current driven in the coil varies linearly with the wall separation, so a larger wall separation is desirable.

[0090]

[0105] If the coil L / R time is taken too large rather than adjusted appropriately, the force on the coil can be three times longer after the current quench without an increase in the perturbing magnetic field during the current quench. The force on the vertical leg of the coil is on the order of meganewtons, so tripling can greatly complicate the coil engineering.

[0091]

[0106] Various embodiments of the concepts, systems, devices, structures, and techniques for which protection is sought are described above with reference to the associated drawings. Alternative embodiments may be devised without departing from the scope of the described concepts, systems, devices, structures, and techniques. It should be noted that various connections and relationships (e.g., above, below, adjacent, etc.) may be used to describe elements in the description and drawings. These connections and / or relationships may be direct or indirect unless otherwise specified, and the described concepts, systems, devices, structures, and techniques are not intended to be limiting in this regard. Thus, coupling of entities may refer to either direct or indirect coupling, and relationships between entities may be direct or indirect relationships.

[0092]

[0107] As an example of an indirect positional relationship, positioning element "A" over element "B" may include a situation where there are one or more intermediate elements (e.g., element "C") between element "A" and element "B," so long as the relevant features and functions of element "A" and element "B" are not substantially changed by the one or more intermediate elements.

[0093]

[0108] Additionally, the following definitions and abbreviations are to be used for interpreting the claims and this specification. The terms "comprise," "comprises," "comprising," "include," "includes," "including," "has," "having," "contains," or any other variation thereof are intended to cover a non-exclusive inclusion. For example, a device, method, composition, mixture, or article that includes a list of elements is not necessarily limited to only those elements and can include other elements not expressly listed or inherent in such device, method, composition, mixture, or article.

[0094]

[0109] Additionally, the term "exemplary" means "serving as an example, instance, or illustration." Any embodiment or design described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "one or more" and "at least one" refer to any integer greater than or equal to one, i.e., 1, 2, 3, 4, etc. The term "plurality" refers to any integer greater than or equal to two. The term "connected" can include indirect and direct "connections."

[0095]

[0110] References herein to "embodiments," "one embodiment," "embodiment," "exemplary embodiment," "example," "case," "aspect," and the like indicate that the described embodiment may include a particular feature, structure, or feature, but that not all embodiments may include the particular feature, structure, or feature. Moreover, such phrases do not necessarily refer to the same embodiment. Furthermore, when particular features, structures, or features are described in connection with an embodiment, they may affect such features, structures, or features in other embodiments, whether or not explicitly stated.

[0096]

[0111] Relative or positional terms, including but not limited to "above," "below," "right," "left," "vertical," "horizontal," "top," "bottom," and derivatives thereof, refer to the described structures and methods as oriented in the drawings. The terms "above," "on," "upper," "positioned above," or "positioned above" mean that a first element, such as a first structure, is above a second element, such as a second structure, and there may be intervening elements, such as interface structures, between the first and second elements. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediate elements.

[0097]

[0112] The use of ordinal terms such as "first," "second," "third," etc. in the claims to modify claim elements does not, by itself, imply any priority, precedence, or ordering of one claim element relative to another element, or the chronological order in which acts of a method are performed; the ordinal terms are used solely as markers to distinguish one claim element having a certain name from another element having the same name (but using ordinal terms) to distinguish between claim elements.

[0098]

[0113] The terms "approximately" and "about" can be used in some embodiments to mean within ±20% of a target value, in some embodiments within ±10% of a target value, in some embodiments within ±5% of a target value, and in some embodiments even within ±2% of a target value. The terms "approximately" and "about" can include the target value. The term "approximately equal" can be used to refer to values ​​that are within ±20% of each other in some embodiments, within ±10% of each other in some embodiments, within ±5% of each other, and in some embodiments even within ±2% of each other.

[0099]

[0114] The term "approximately" may be used to indicate a value that is within ±20% of a reference point in some embodiments, within ±10%, within ±5%, and even within ±2% in some embodiments. For example, a first direction that is "approximately" perpendicular to a second direction may refer to a first direction that is within ±20% of a 90° angle with the second direction in some embodiments, within ±10% of a 90° angle with the second direction in some embodiments, within ±5% of a 90° angle with the second direction in some embodiments, and even within ±2% of a 90° angle with the second direction in some embodiments.

Claims

1. A tokamak fusion reactor (10) including passive runaway electron mitigation coils (14, 30, 40), i.e., REMCs, and a vacuum vessel (12), the REMC includes an electrical conductor attached to an inner or outer wall of the vacuum vessel; the electrical conductor is a complete single non-axisymmetric loop surrounding the toroidal surface of the vacuum vessel (12), the electrical conductor including a plurality of portions (14a-14d, 30a-30h, 40a-40l), the plurality of portions being arranged along a path defined by the toroidal surface of the vacuum vessel (12) and aligned along a toroidal direction of the toroidal surface of the vacuum vessel (12); Tokamak fusion reactor (10).

2. The complete single non-axisymmetric loop of electrical conductor is one or more upper portions (14b; 30c; 30d; 40d-40f), each disposed along the toroidal direction at a first poloidal angle and disposed above a midplane passing through the vacuum vessel (12) along the toroidal direction; one or more lower portions (14a; 30a; 30b; 40a-40c), each disposed along the toroidal direction at a second poloidal angle different from the first poloidal angle and disposed below the midplane; 10. The tokamak fusion reactor of claim 1, comprising:

3. A tokamak fusion reactor as described in claim 2, wherein the complete single non-axisymmetric loop of the electrical conductor includes a plurality of legs (14c-14d; 30e-30h; 40g-40l), each leg of the plurality of legs being coupled to a respective upper and lower portion of the one or more lower portions and one or more upper portions and extending between the upper and lower portions.

4. The complete single non-axisymmetric loop of the electrical conductor includes a first portion, the first portion comprising: a first upper portion (14b; 30c; 40d) of said one or more upper portions; a first leg (14c; 30h; 40l) of the plurality of legs coupled to the first upper portion (14b; 30c; 40d); and a first lower portion (14a; 30b; 40c) of the one or more lower portions coupled to the first leg (14c; 30h; 40l); and a second leg (14d; 30g; 40k) of the plurality of legs coupled to the first lower portion (14a; 30b; 40c); and 4. The tokamak fusion reactor of claim 3, comprising:

5. 5. The tokamak fusion reactor of claim 4, wherein the first leg (14c; 30h; 40l) has a first end coupled to the first end of the first upper portion (14b; 30c, 40d) and a second end coupled to the first end of the first lower portion (14a; 30b; 40c), and the second leg (14d; 30g; 40k) has a first end coupled to the second end of the first lower portion (14a; 30b; 40c).

6. A tokamak fusion reactor as described in claim 4 or 5, wherein the complete single non-axisymmetric loop of the electrical conductor includes multiple portions, each corresponding to the first portion, that are coupled to each other to create the complete single non-axisymmetric loop.

7. 4. The tokamak fusion reactor of claim 3, wherein the plurality of legs are arranged along a poloidal direction along a path defined by the toroidal surface of the vacuum vessel (12).

8. 6. The tokamak fusion reactor of claim 5, wherein the second leg (14d) has a second end coupled to a second end of the first upper portion (14b).

9. A tokamak fusion reactor as described in claim 1, wherein the electrical conductor is attached to the outer wall (13) of the vacuum vessel (12) and arranged so as to have a larger semi-major axis than the plasma within the vacuum vessel (12).

10. A tokamak fusion reactor as described in any one of claims 2 to 5 and 7, wherein the complete single non-axisymmetric loop of the electrical conductor includes a plurality of upper portions (30c, 30d; 40d-40f) and a plurality of lower portions (30a, 30b; 40a-40c), and each of the plurality of upper portions and each of the plurality of lower portions has the same length.

11. A tokamak fusion reactor as described in claim 1, wherein the complete single non-axisymmetric loop of electrical conductor is coupled to a switch (22).

12. The electrical conductor (14) is mounted within the vacuum vessel (12), 12. The tokamak fusion reactor of claim 11, wherein the switch (22) is located outside the vacuum vessel.

13. 12. The tokamak fusion reactor of claim 11, wherein the switch includes one or more varistors arranged as a non-conducting open circuit along the complete single non-axisymmetric loop of the electrical conductor.

14. A tokamak fusion reactor as described in claim 1, wherein the electrical conductor is an electrically completely closed conductor.

15. The tokamak fusion reactor according to any one of claims 1 to 5, 7 to 9 and 11 to 14, wherein the electrical conductor is attached to an inner surface of the inner wall or the outer wall of the vacuum vessel (12).

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