Method for forming metal-to-metal seal

Abstract

A metallic seal ring (1) for forming a metal-to-metal seal between two opposing metal surfaces. The metallic seal ring (1) includes a tubular metal body (3) and an inlet tube (7) extending from the body (3) for introducing internal pressure into the body (3). The body is configured to deform under the internal pressure against each of the opposing metal surfaces to form the seal (1).

Description

[Technical field]

[0001] The present invention relates to metallic seal rings and methods of forming metal-to-metal seals, particularly, but not exclusively, to metallic seal rings used to seal vacuum chambers, such as the vacuum chambers in Tokamak fusion reactors, or piston engines. [Background technology]

[0002] Metal seal rings are often used to provide an air-tight or liquid-tight seal between two metal surfaces, such as between the flanged ports of two vacuum chambers that are joined together. In some applications, the metal seal ring is a flat, circular metal gasket made of a relatively soft metal, such as copper or aluminum, that is crushed between metal surfaces made of a harder metal, such as stainless steel. Each metal surface or "conflat flange" is provided with a circular ridge or "knife edge" that bites into the respective face of the gasket, causing the metal of the gasket to extrude around the knife edge, thereby forming a seal between the two metal surfaces.

[0003] Conflat flanges and metal gaskets can be used to form very good seals, for example in ultra-high vacuum systems, but they have many drawbacks, including the need for careful alignment ("mating") of the flange and metal gasket and high clamping forces, and if the compressive load on the gasket is uneven or too high, the quality of the seal can be significantly degraded.

[0004] Another type of metal seal ring is the so-called Wills ring, which is an O-ring formed from a metal tube. In use, the Wills ring is compressed between two flanges so that its cross section deforms against the surface of the flange to form a seal. Some versions of the Wills ring are pressurized to increase elasticity. Another type of seal ring, available commercially under the name Helicoflex®, includes a tubular metal ring with a C-shaped cross section and a helical spring inserted inside the metal ring to increase its elasticity. However, these types of metal seal rings require relatively precise alignment and careful control of the clamping force to obtain a uniform seal and to avoid damage to the seal ring. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide a metallic seal ring which addresses or at least mitigates the above problems. [Means for solving the problem]

[0006] According to a first aspect of the present invention, there is provided a metallic seal ring for forming a metal-to-metal seal between two opposing metal surfaces. The metallic seal ring includes a tubular metal body and an introduction tube extending from the body for introducing an internal pressure into the body. The body is configured to deform under the internal pressure against each of the opposing metal surfaces to form a seal.

[0007] The body can have a cross-section (eg, a radial cross-section) that includes two or more sections made of different respective metals, each metal having a different ductility and / or yield strength.

[0008] The body can have a cross-section (eg, a radial cross-section) that includes two or more sections having different respective thicknesses.

[0009] The two or more sections may be arranged such that introduction of internal pressure into the body causes a cross-section of the body to expand preferentially along an axial direction.

[0010] The body may include one or more ridges extending around the ring to form a knife-edge seal with one or more of the metal surfaces upon introduction of internal pressure to the body.

[0011] The body may include an outer layer of a ductile metal, such as indium.

[0012] The body may be wholly or partially filled with a hydraulic medium, which may be silicone rubber.

[0013] The body may include a wall having a thickness of 0.1 mm to 10 mm, preferably 0.2 mm to 2 mm.

[0014] The body may be configured to increase in volume by at least 5% upon introduction of an internal pressure above ambient pressure by no more than 300 MPa, preferably no more than 150 MPa.

[0015] The body may be configured to increase in volume by plastically deforming upon the introduction of internal pressure, the plastic deformation allowing the internal pressure of the body to be released without rupturing the seal.

[0016] The inlet tube can be sealed such that the body and the inlet tube together form a closed system, whereby internal pressure is introduced into the body by reducing the internal volume of the inlet tube. The metal seal ring can include a piston surface movable within the internal volume of the inlet tube to introduce internal pressure into the body. The piston surface can be provided by or movable with a screw.

[0017] The metal seal ring can include a piston chamber for maintaining an internal pressure in the body, the piston chamber being in fluid communication with the body and / or the inlet conduit and including a piston configured to compress a hydraulic medium within the body.

[0018] The tubular metal body may be toroidal.

[0019] The interior of the body can be divided into first and second chambers by a partition configured to move toward the second chamber and expand the body against respective opposing metal surfaces in response to internal pressure introduced into the first chamber using the introduction tube. The second chamber can include struts configured to resist movement of the partition, and preferably the struts are resiliently compressible to provide an elastic restoring force to the partition.

[0020] The inlet tube can extend from the outer peripheral wall of the tubular metal body (i.e., the wall that defines the outer periphery of the ring formed by the tubular metal body). For example, if the tubular metal body has an axis of rotation (e.g., if the tubular metal body is toroidal), the inlet tube can extend from the outer peripheral wall of the tubular body such that the tubular body is closer to the axis than the inlet tube. In particular, the inlet tube can extend outwardly from the tubular body, away from the axis, along a radial direction (i.e., a direction perpendicular to the axis and perpendicular to the outer peripheral wall of the tubular body).

[0021] According to a second aspect of the invention, a seal is provided between two opposing metal surfaces, the seal including a metallic seal ring as described above, the metallic seal ring being at least partially disposed within a channel formed in at least one of the metal surfaces.

[0022] According to a third aspect of the invention there is provided a vacuum chamber comprising two opposing metal surfaces sealed to each other with a metal seal ring as described above (or a seal as described above in the second aspect), wherein an inlet tube of the metal seal ring may extend outside the vacuum chamber through a channel in at least one of the opposing metal surfaces.

[0023] According to a fourth aspect of the present invention, there is provided a piston engine comprising an engine block and a cylinder head sealed to the engine block by a head gasket including the metal seal ring described above (the seal described above in the second aspect).

[0024] According to a fifth aspect of the present invention, there is provided a kit including the metal seal ring as described above, a hydraulic pump, preferably a hydraulic hand pump, and a connector for connecting an inlet tube of the metal seal ring to the hydraulic pump.

[0025] According to a sixth aspect of the invention, there is provided a tokamak comprising a vacuum chamber having a toroidal internal volume. The vacuum chamber comprises a plurality of segments, each segment providing a sector of the toroidal internal volume and comprising one or more toroidal field coils wound around the segment to generate a toroidal magnetic field within the sector. The vacuum chamber further comprises a seal formed between at least two of the segments using the metal seal ring as described above (or the seal as described above in the second aspect).

[0026] Each segment is individually removable from the vacuum chamber, i.e., each segment can be removed from the vacuum chamber without requiring removal or movement of the other segments. The plurality of segments can include 12 or more segments, preferably 16 segments.

[0027] According to a seventh aspect of the invention there is provided a vacuum system comprising an outer vacuum chamber surrounding the tokamak as described above, the outer vacuum chamber being connected to another vacuum chamber capable of moving one or more segments of the vacuum chamber of the tokamak.

[0028] According to an eighth aspect of the present invention, there is provided a method of forming a metal-to-metal seal between two opposing metal surfaces using the metallic seal ring described above, the method comprising: placing a body of the metallic seal ring between the metal surfaces and injecting an internal pressure into the body using an inlet tube to deform the body against the metal surfaces to form a seal.

[0029] The internal pressure can be introduced into the body by forcing a fluid, such as hydraulic fluid, through the inlet conduit into the body. Forcing the fluid through the inlet conduit into the body can include crimping the inlet conduit. The body can be plastically deformed such that the internal pressure in the body can be released without breaking the seal.

[0030] According to a further aspect of the present invention, there is provided a piston including a metal seal ring according to any of the above aspects.

[0031] According to yet another aspect of the present invention there is provided a plasma compression device comprising a chamber and one or more pistons according to the further aspect above, the piston being in fluid communication with the chamber, the plasma compression device being configurable to enable compression of the plasma in the chamber with the piston. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic perspective cross-sectional view of a metal seal ring used to provide a seal between two flanges. [Diagram 2] 2 is a schematic perspective cross-sectional view of the metallic seal ring of FIG. 1 prior to forming a seal; [Diagram 3] 3A and 3B are schematic cross-sectional views of the body of a metal seal ring before and after expansion. [Figure 4] 4A and 4B are schematic cross-sectional views of the body of a metal seal ring before and after expansion. [Diagram 5] 5A and 5B are schematic cross-sectional views of the body of a metal seal ring before and after expansion. [Figure 6] 6A and 6B are schematic cross-sectional views of the body of a metal seal ring before and after expansion. [Figure 7] 1 is a schematic cross-sectional view of a vacuum system including a Tokamak nuclear fusion reactor. [Figure 8] 1 is a schematic cross-sectional view of a vacuum system including a Tokamak nuclear fusion reactor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] 1 shows a cross-section of a metallic seal ring 1 including a body 3 formed from a hollow metal tube having a cross-section 5. Although only a portion of the ring 1 is shown in the figure, the body 3 extends around in a circle to form a torus. The metallic seal ring 1 also includes an inlet tube 7 that extends radially outward from the outer wall of the body 5 and is joined to the body by a "T" joint 7. In this example, an end 11 of the inlet tube 7 is not sealed, but as will be described below, in some cases, it may be sealed to maintain internal pressure within the metallic seal ring 1.

[0034] The metal seal ring 1 is disposed between a pair of mated circular metal flanges 13A,B. In this example, each of the flanges 13A-B has one of a pair of complementary circumferential grooves or channels 15A-B that together house the body 3 of the metal seal ring 1. As described below, the cross section 5 of the body 3 of the metal seal ring 1 is configured to generally match the cross section 17 formed by the grooves 15A-B to form a seal between adjacent inner surfaces of the flanges 13A-B. In this example, the channel cross section 17 and the cross section 5 of the body 3 are square or rectangular, although other shapes can be used. In some applications, it is beneficial to provide the grooves or channels 15A-B in only one of the two metal flanges, which allows the flanges to slide into position relative to one another (while the seal ring is disposed in the channel). Such an approach is particularly useful when there are geometric constraints that prevent or make it impossible for the flanges to be brought together axially (i.e., along the axis of the seal ring). Examples of such constraints are described below in connection with Figures 6 and 7.

[0035] The inlet tube 7 of the metal seal ring 1 is received by a pair of complementary channels that extend radially from the circumferential channels 13A,B through the flanges 13A-B, allowing the end 11 of the inlet tube 7 to protrude through the radially outermost edge of the flanges 13A-B. The cross section of the radial channels 19A-B can be any shape, but preferably its shape matches the inlet tube 11 to securely hold the inlet tube 11 in place, which helps to avoid stressing the joint 9 and prevents the inlet tube 7 from deforming.

[0036] FIG. 2 shows a portion of the metal seal ring 1 prior to forming a seal between the flanges 13A-B. The cross section 5 of the body 3 of the metal seal ring 1 is initially circular as shown in FIG. 2 and is smaller than the channel cross section 17, allowing the body 3 to be easily inserted into one of the channels 15A, 15B before the flanges 13A, 13B are brought together. The seal is formed by introducing internal pressure into the body 3 of the metal seal ring 1 using an introduction tube 7, which causes the cross section 5 of the body 3 to deform (e.g., expand) against the walls of the grooves 15A-B, i.e., the outer surface of the body 3 is forced into contact with the walls of the grooves 15A-B around the entire circumference of the seal ring 1.

[0037] Depending on the properties of the metals and alloys used to form the body 3 and the degree of deformation, the body 3 can be plastically deformed, i.e., the deformation is essentially irreversible once the internal pressure of the body 3 is released. This process shares some similarities with a manufacturing method known as hydroforming, in which a tube is inserted between a pair of dies and expanded with high pressure water to produce a shape that conforms to the opposing faces of the dies. In this case, it may not be necessary to maintain the internal pressure of the body 3. However, in many cases it may be preferable to keep the body 3 in an "expanded" state, at least to some extent, as this improves seal strength and prevents mechanical forces such as vibration from further deforming the body 3. Advantageously, the metal seal ring 1, unlike some conventional seal rings, can be manufactured with relatively wide manufacturing tolerances because it can conform to the shape of the channels 15A-B during expansion, i.e., it does not need to precisely match the channels 15A-B before sealing.

[0038] Alternatively, the body 3 can be elastically deformed such that the metal seal ring 1 substantially regains its original shape when the internal pressure of the body 3 is released, potentially allowing the metal seal ring 1 to be reused and / or allowing the leakage rate of the seal to be adjusted, for example to allow for the controlled introduction of gas into the vacuum chamber (e.g., as occurs during venting).

[0039] The metal seal ring 1 is preferably made of a ductile metal such as copper or aluminum, which reduces the internal pressure required to deform the cross section 5 of the body 3. Also, for the same reason, it is preferable that the walls of the body 3 are relatively thin. However, the thickness of the walls will generally depend on the size of the seal. For example, in some applications, such as large tokamaks (see below) requiring large seal rings, the thickness of the walls of the body 3 may be 1 mm to 10 mm, or 2 mm to 5 mm. In other applications, such as those involving relatively small vacuum chambers, the walls of the body 3 may be 0.1 mm to 1 mm, or 0.2 mm to 0.5 mm. Part or all of the outer surface of the metal seal ring 1 may be coated with a layer of a softer metal, such as indium, to form a sealing surface of the metal seal ring 1 that better conforms to the surfaces of the flanges 13A-B.

[0040] The internal pressure can be introduced into the body 3 in various ways. For example, an air pump can be used to force compressed gas through the inlet tube 7 into the body 3. Alternatively, a hydraulic press or pump, such as a hydraulic hand pump, can be used to force a hydraulic medium, such as water, oil or silicone rubber, into the body 3. The end 11 of the inlet tube 7 can be configured to connect to the pump and / or press, for example by providing a thread on its outer or inner surface. The inlet tube 7 can also be fitted with a piston that can be used to compress the fluid in the metal seal ring 1. In one example, the piston is formed by a screw, such as a grub screw, screwed into the end 11 of the inlet tube 7, such that advancing the screw into the inlet tube 7 increases the internal pressure in the ring 1.

[0041] Alternatively or additionally, the internal pressure may be generated by sealing the end 11 of the inlet tube 7 and compressing at least a portion of the inlet tube 7, for example by crimping the inlet tube 7, to force the fluid (e.g., air) into the body 3. The internal pressure may also be generated by introducing a liquid or solid, such as liquid nitrogen or solid carbon dioxide, into the inlet tube 7, sealing the inlet tube 7, and then allowing or causing the liquid or solid to vaporize (or sublime).

[0042] In some examples, a sealed auxiliary chamber may be provided that is in fluid communication with the sealing ring 1 and / or the inlet tube 7 and acts as a hydraulic accumulator to maintain internal pressure within the ring 1. For example, the auxiliary chamber may be a piston chamber that houses a piston configured to compress a fluid (hydraulic medium) within the body 3, the piston being biased using a resilient member such as a spring.

[0043] Generally, the seal formed by expanding the body 3 can prevent fluids (such as gas or liquid) from passing radially between the flanges 15A,B, although other geometries can be used. For example, a seal can be formed between a pair of nested cylinders or tubes using a sealing ring similar to the metal sealing ring 1. In this case, the metal sealing ring is provided in a channel formed in the end of one cylinder and expands against the other cylinder after the cylinders are nested, i.e. the sealing ring expands radially. This geometric shape can, for example, join two pipes to hermetically seal.

[0044] In the above examples, a circular cross-section seal ring is used for ease of explanation. In some circumstances, other cross-sections may be of further benefit to the integrity of the resulting seal. FIG. 3A shows a cross-section 19 of the body of a metal seal ring 21 before expansion. The vertical arrow (labeled "z") in the figure indicates the direction of the axis of the metal seal ring 21. The cross-section 19 includes two sharp (i.e., pointed) ridges 23A-B located on opposite axial faces of the ring 21. As shown in FIGS. 1 and 2, the body of the metal seal ring 21 is confined within a cavity 25 (shown in dashed lines in FIGS. 3A and 3B) formed by channels in the metal surface to be sealed. FIG. 3B is the same as FIG. 3A, except that the body of the metal seal ring 21 has been expanded and deformed by introducing an internal pressure into the body using an inlet tube of the metal seal ring 21. The cross-section 25 is deformed to fit the cavity 25, and the tops of each of the ridges 23A-B are driven into the opposing metal surfaces of the cavity to form a knife-edge seal.

[0045] In another example (not shown), each of the metal surfaces (flanges) to be sealed includes one or more sharp knife edges. When the metal seal ring expands, the knife edges bite into the outer surface of the metal seal ring to form a seal. In some cases, the outer surface of the metal seal ring includes one or more notches to receive the knife edges to provide a stronger seal. In some examples, the characteristic dimension of the knife edges is much smaller than the thickness (i.e., minor radius) of the ring, providing a textured (i.e., rough) surface to bite into the outer surface of the ring.

[0046] 4A and 4B are similar to FIGS. 3A and 3B, except that the metal seal ring 21 is replaced by a metal seal ring 27 having a body cross-section made of sections 29A-B, 31A-B that are generally circular or elliptical and made of different metals (or alloys). In this example, one pair of sections 29A-B are made of a relatively ductile metal such as copper and are arranged along a radius of the seal ring 27, while the other pair of sections 31A-B are made of a relatively less ductile metal such as steel and are arranged axially relative to the seal ring 27. The sections 29A-B, 31A-B are joined together, for example by welding, although other methods of joining the sections together, such as brazing or soldering, can also be used. After expansion, the less ductile sections 31A-B remain substantially the same shape, while the more ductile sections 29A-B are stretched along the axial direction, bringing the less ductile sections 31A-B into contact with the metal surfaces of the cavity 25, thereby forming a seal between the metal surfaces. The internal pressure required to expand sealing ring 27 can be controlled by varying the thickness of the less ductile sections 29A-B, with thinner sections being used for applications requiring relatively lower internal pressures, for example when sealing ring 27 has a larger diameter or is only capable of generating lower internal pressures.

[0047] 5A and 5B are again similar to FIGS. 3A and 3B, except that the body of the metal seal ring 33 has a hollow circular cross section 34 with a nib 35 forming a pointed ridge that extends around one face of the ring 33. In this example, the nib 35 is made of steel (although other relatively hard metals can be used) and the remainder of the body 34 is made of copper (although other relatively soft metals can be used). The nib 35 is typically attached to the body by welding, although other attachment methods can be used such as brazing, soldering, or mechanically attaching the nib in place, for example by co-extrusion or drawing. The cavity 36 surrounding the metal ring 33 in this example has a different shape than that of FIGS. 3A and 3B, and the cavity 36 has a smaller section to accommodate the nib 35 after the metal seal ring 33 expands / expands. The nib 35 “bites” into the adjacent metal surfaces, forming a “knife-edge” seal, while the circular cross section 34 also forms a seal by expanding to fit the larger section of the cavity 36 .

[0048] 6A and 6B are again similar to FIGS. 3A and 3B, except that the metal seal ring 37 includes an inner wall 38 that divides the interior of the body into two chambers 39A, 39B. The partition 38 is initially buckled (bent) toward the first chamber 39A. Upon introduction of internal pressure into the first chamber 39A using the inlet tube 7, the partition 38 moves and straightens toward the second chamber 39B. This movement forces the outer walls of the body of the seal ring 37 apart, causing the body to deform against the metal surfaces 40A, 40B and form a seal (see FIG. 6B). In this example, the second chamber 39B includes struts 41 that resist further movement of the partition 38 after it straightens, to prevent it from buckling (bending) in the opposite direction (i.e., into the second chamber 39B).

[0049] The struts 38 may be resiliently compressible to maintain the internal pressure of the first chamber 39A and thus the sealing pressure exerted by the outer wall of the body on the metal surfaces 40A, 40B. The second chamber 39B may also be pressurized to increase the pressure that must be introduced into the first chamber 39A to move the bulkhead 38 and thereby increase the sealing pressure.

[0050] Alternatively or additionally, the septum 38 can be displaced by reducing the pressure in the second chamber 39B (e.g., using a vacuum pump) to create a pressure differential between the chambers 39A, 39B. Conversely, the movement of the septum 38 into the second chamber 39B can be reversed by introducing internal pressure into the second chamber 39B to create a pressure differential in the opposite direction, thereby causing the metal seal ring 37 to "shrink" and thereby release the seal.

[0051] Another way in which the seal can be released is by dissolving or chemically reacting part (or all) of the metal seal ring 1, 21, 27, 33, 37. For example, the body of the metal seal ring can be made of copper plated with gold (on the outside). The copper can be dissolved using a solvent (e.g., ferric chloride) introduced to the seal ring through an introduction tube 7 (for example) to leave a layer of gold, which allows the seal to be easily removed and the mating parts to be separated from each other. Of course, other combinations of materials and / or solvents can also be used.

[0052] The above metal seal rings 1, 21, 27, 33, 37 can be used in a variety of applications. For example, one or more of the above metal seal rings can be used in a head gasket to seal a cylinder head to an engine block of a piston engine. As another example, one or more of the above metal seal rings can be included in a piston device including a piston head that slides in a cylinder against (or in response to) fluid pressure acting on the piston head. In this case, the metal seal ring can be used to form a seal between the piston head and the cylinder, or between the cylinder and a connecting rod attached to or integral with the piston head. One or more such pistons can be used in a plasma compression device. The plasma compression device can be, for example, a fusion reactor including a chamber containing a liquid metal vortex into which the plasma is injected. The piston is configured to drive the liquid metal toward the center of the chamber, thereby collapsing the vortex and compressing the plasma to initiate a fusion reaction.

[0053] 7 and 8 show a vacuum system 42 including an outer vacuum chamber 43, a tokamak 45 (i.e., a toroidal fusion reactor for controlling fusion reactions in a magnetically confined high temperature plasma), and a maintenance vacuum chamber 47. The outer vacuum chamber 43 surrounds the tokamak 45 and is connected to the maintenance vacuum chamber 47 as described below. In one particular embodiment, the tokamak 45 has a height of about 5 to 15 m and the outer vacuum chamber has a height of about 20 to 30 m, although typically the height of the outer vacuum is about 2 to 2.5 times the height of the tokamak 45. The outer vacuum chamber 43 and the maintenance vacuum chamber 45 together surround the components of the tokamak 45 to prevent tritium and other radioisotopes from escaping.

[0054] The tokamak 45 includes an inner vacuum chamber 49 having an annular internal volume 51 for containing the plasma. As seen most clearly in FIG. 8, the inner vacuum chamber 49 is formed from a number of independently removable segments 53, with each segment 53 providing a sector (i.e., a tapered, angular portion) of the inner vacuum chamber 49. For example, each segment may span an angle of 22.5 degrees such that the inner vacuum chamber 49 is formed from 16 segments (although the segments need not each span the same sized angle, and any number of segments may be used). Each segment 53 includes a toroidal field (TF) coil 55 that surrounds the segment's internal volume such that a toroidal magnetic field is generated within the inner vacuum chamber 49 when the inner vacuum chamber is fully assembled and current is supplied to the coil 55. In this case, the toroidal field coil 55 is attached to the inner wall of the segment 53 and follows the generally elliptical cross section of the segment 53.

[0055] Each segment 53 houses a segment 57 of the "first wall" of the tokamak 45, i.e. the wall directly adjacent to the plasma when the tokamak 45 is in use. The majority of the first wall segment 57 is located towards the radially outermost wall of the inner vacuum chamber segment 53, but there is an inner portion 59 of the first wall segment 57 located at the radially innermost wall of the inner vacuum chamber segment 53. A pair of diverters 61, 63 are provided between the radially outer and inner portions of the first wall segment 57 to capture plasma escaping axially from the magnetic field of the tokamak 45 during operation of the tokamak 45. One diverter 61 is provided on the bottom wall of the segment 53 and the other diverter 63 is provided on the top wall of the segment 53 (upper and lower are used here with reference to FIG. 7 where the axis of the segment 53, i.e. the axis of the toroidal internal volume, is vertical). The first wall segment 57 and divertors 61 , 63 are surrounded within segment 53 by shielding 65 to limit the neutron flux exiting the tokamak 45 .

[0056] Each segment 53 is mounted within an in-plane support structure 67 (or "carrier") that supports the segments 53 when they are assembled to form the inner vacuum chamber 49. The frame includes a central support 69 that supports an underside of the in-plane support structure 67 near the axis of the tokamak 45, and support columns 71 arranged around the outside of the tokamak 45 to support each in-plane support structure 67 along its radial edge. The in-plane support structure 67 includes couplings 73 at its base for supplying cryogenic coolant (typically at a temperature of about 20 to 30 K) to the segments 53, supplying electrical current to the TF coils 55, supplying coolant to the shield 65, and providing cooling to the first wall segments 57. The couplings are connected to complementary feedthroughs 75 at the base of the outer vacuum chamber 43 so that coolant and electrical power are provided to each segment 53 when the tokamak 45 is assembled.

[0057] In FIG. 8, one of the segments 53 has been moved (as shown by the fainter line to the right of the tokamak 45) from the outer vacuum chamber 42 to the maintenance chamber 47, e.g., using a robotic handling system (not shown) located within the outer vacuum chamber 43. In this example, the dimensions of the maintenance chamber 47 are selected to be able to accommodate a single segment 53, thereby allowing access to the surface of the segment 53 for inspection and / or maintenance, e.g., using another robotic system. In some examples, an isolation valve, such as a gate valve (not shown), is provided to allow the maintenance chamber 47 and the outer vacuum chamber 43 to be isolated from each other, e.g., to allow the maintenance chamber 47 to be brought to atmospheric pressure so that a portion of the segment 53 (or the entire segment 53) can be removed and replaced.

[0058] In order to reassemble the inner vacuum chamber 49, for example after the segment 53 has been repaired, it is necessary to form a vacuum seal between the segment 53 and the adjacent segments on either side of the segment 53. However, the segments 53 must fit closely together to form the inner vacuum chamber 49, and are typically clamped tightly in place by frames 69, 70, which means that seals that rely on compression of a seal ring (e.g., conflat seals) may not be suitable. A solution to this problem is provided by the above-mentioned metal seal rings 1, 21, 27, 33, which are placed between the segments 53 and can expand to form the required seal. The use of metal-to-metal seals between the segments 53 is particularly important to prevent tritium from escaping from the tokamak 45.

[0059] Each segment may include a groove or channel that seats the seal ring 1, 21, 27, 33 such that the seal ring 1, 21, 27, 33 is flush with (or embedded in) the face of the segment 53 prior to expansion. Such a configuration allows the segments 53 to fit closely together (e.g., less than 5 mm apart) when assembled, thereby minimizing the size of gaps between the respective first wall segments 57, diverters 61, 63, and shields 65 contained within each segment 53.

[0060] Additionally or alternatively, the shield 65 may be secured to a compatible mounting (not shown) that provides the shield with some freedom of movement as the segments 53 are moved radially into the vacuum chamber 53 during assembly. This freedom allows the shield 65 to snap securely into place without interfering with the insertion of the segments 53.

[0061] Alternatively, the metal seal rings 1, 21, 27, 33 can be mounted on removable carriers (not shown) that are inserted between adjacent segments 53 and removed after the seal rings have expanded to form a seal. The advantage of this approach is that none of the segments 53 require grooves, which means that the seal rings and segments 53 can each be slid into place, e.g., slid vertically (axially) into place from above the tokamak 45, before forming a seal. This configuration therefore allows segments 53 to be removed and replaced individually without having to move adjacent segments 53.

[0062] Poloidal field (PF) coils (not shown) are provided above and below the inner vacuum chamber 49 to provide a poloidal magnetic field within the inner vacuum chamber 49 when the tokamak 45 is operating. Unlike the TF coils 55, the PF coils do not need to be segmented because the upper PF coil can be lifted out of the tokamak 45 to allow removal of the segments 53, while the lower PF coil can remain in place below the inner vacuum chamber 49 between the in-plane support structure 67 and the central support 69.

[0063] When the inner vacuum chamber 49 is assembled (see FIG. 7), the in-plane support structure 67 is clamped in place by a capping structure 77. The capping structure 77 is on the axis (central column) of the tokamak 45 and can be lifted to the top of the outer vacuum chamber 43 to allow the segments 53 to be removed or replaced.

Claims

1. 1. A method of forming a metal-to-metal seal between two opposing metal surfaces using a metallic seal ring including a tubular metal body and an introduction tube extending from the body for introducing an internal pressure into the body, the method comprising: placing the body of the metallic seal ring between the metal surfaces; introducing an internal pressure into the body using the introduction tube and deforming the body against the metal surfaces to form the metal-to-metal seal, the body being plastically deformed such that the internal pressure in the body can be released without destroying the metal-to-metal seal.

2. The method of claim 1 , wherein the internal pressure is introduced into the body by forcing a fluid, such as a hydraulic fluid, through the inlet conduit and into the body.

3. The method of claim 2 , wherein forcing the fluid from the inlet tube into the body includes crimping the inlet tube.

4. 4. The method of claim 1, wherein the internal pressure is generated by introducing a liquid or solid into the inlet tube, sealing the inlet tube, and then allowing or causing the liquid or solid to vaporize or sublimate.

5. 5. The method of claim 1, further comprising releasing the metal-to-metal seal by dissolving or chemically reacting a portion or all of the metallic seal ring.

6. 5. The method of claim 1, wherein the body of the metal seal ring is made of copper that is plated on the outside with gold, the method further comprising dissolving the copper with a solvent to leave a layer of gold.

7. 7. The method of claim 1, wherein the internal pressure is introduced into the metal seal ring by moving a piston surface within the internal volume of the inlet tube.

8. The method of claim 7 , wherein the piston surface is provided by or is movable with a screw.

9. 9. The method of claim 1, wherein the interior of the body is divided into first and second chambers by a partition, the partition moving toward the second chamber in response to internal pressure introduced into the first chamber using the introduction tube, thereby causing the body to expand against each of the opposing metal surfaces.

10. The method of claim 9 , wherein the second chamber includes a support that resists movement of the septum.

11. The method of claim 10 , wherein the struts are elastically compressed to provide an elastic restoring force to the septum.

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