Waveguides and associated methods

Abstract

A microwave waveguide (100, 200, 300, 800) of unitary construction having integrated reinforcing ribs (124, 224, 324, 824) and cooling pipes (122, 222, 822) is disclosed. The reinforcing ribs and cooling pipes extend along an outer surface (114, 214, 314, 814) of a tube (110, 210, 310, 810) for guiding microwaves. The waveguide can be formed by extruding metal or by pultruding carbon fibre composite. Also disclosed is a method (600) of transmitting microwaves and a method (700) of geothermal drilling.

Description

[0001] WAVEGUIDES AND ASSOCIATED METHODS

[0002] Technical Field

[0003] The present disclosure relates to microwave waveguides and is particularly, although not exclusively, concerned with microwave waveguides of unitary construction having reinforcing protrusions.

[0004] Background

[0005] A microwave waveguide is a device used to guide microwaves from a source to a destination. Microwave waveguides may be used in a variety of applications, ranging from microwave ovens to nuclear fusion devices.

[0006] In a nuclear fusion device, high power microwave beams of around 1 MW are generated by a gyrotron, pass along a waveguide and are injected into the vessel to heat the plasma to fusion temperatures of around 150 million °C. In order to reduce energy transmission losses from the microwave beams, it is desirable that the waveguide has a high degree of straightness.

[0007] Fusion applications typically use evacuated circular waveguides having a corrugated interior surface. These waveguides may be made from metal bar stock that is gun drilled, then corrugated, and then externally machined to attach cooling clamps. However, this manufacturing process is labour-intensive and materials-wasteful.

[0008] Improvements are therefore desired in the art of microwave waveguides.

[0009] Statements of Invention

[0010] During the gun drilling and corrugation processes, a waveguide may develop a degree of curvature, potentially due to the interior of the waveguide gripping the drill bit differentially. Accordingly, in addition to being labour intensive and materials-wasteful, these processes may reduce the degree of straightness of existing waveguides. A straightness tolerance of less than 0.1 mm / metre is particularly desirable. According to a first aspect of the present disclosure there is provided a waveguide. The waveguide may be configured to guide (e.g., propagate or transmit) microwaves (e.g., electromagnetic radiation having a frequency between 1 GHz and 1 THz). The waveguide may comprise a microwave waveguide. The waveguide may be configured to guide high power microwaves (e.g., microwave beams of at least 10 kW, such as at least 0.5 MW, such as at least 1 MW, such as up to 5 MW). The waveguide may be configured to guide microwaves over long transmission distances (e.g., greater than 1 m, such as at least 5 m, such as at least 10 m). The waveguide may be for a nuclear fusion device.

[0011] The waveguide may comprise a tube (e.g., an inner tube). The tube may be a tube for guiding energy (e.g., microwave energy). The tube may comprise an aperture for guiding microwaves. For example, the tube (e.g., an inner surface) may define an aperture for guiding microwaves. For example, the tube may have an internal diameter of 10 mm to 130 mm, such as 45 mm to 55 mm (e.g., about 50 mm).

[0012] The tube may be cylindrical. The tube may comprise walls of uniform thickness (e.g., between 2 and 5 mm, such as about 2 mm, such as about 5 mm). The tube may define a cylindrical inner surface. The tube may define a cylindrical outer surface. The tube may define a longitudinal axis. A length of the long axis of the tube may be greater than (e.g., significantly exceed) a diameter of the tube. The tube may be linear (e.g., may not comprise bends). The tube may be an inner tube.

[0013] The waveguide may comprise a first end and a second end. The first end may be configured to be attached to a second end of a corresponding waveguide. The second end may be configured to be attached to a first end of a corresponding waveguide.

[0014] The waveguide may comprise a protrusion, e.g., a plurality of protrusions. The or each protrusion may be provided on an outer surface of the tube. The or each protrusion may protrude or extend away from the tube, e.g., extend perpendicularly, radially and / or at any angle, away from an outer surface of the tube. For example, the or each protrusion may extend at least partially in the radial direction (e.g., have a component of its geometry extending in the radial direction).

[0015] The or each protrusion may extend longitudinally, such as in parallel with a longitudinal axis of the tube. The protrusion may extend along the tube with a substantially uniform (e.g., a uniform) transverse cross section. The or each protrusion may extend (e.g., extend continuously) from the first end to the second end. The or each protrusion and the tube may be coextensive. Alternatively, one or more protrusions (e.g., the or each protrusion) may be longitudinally discontinuous (e.g., may not extend continuously from a first end to a second end of the tube). For example, at one or more longitudinal co-ordinates, one or more protrusions may comprise a cutaway portion extending in the longitudinal direction.

[0016] The plurality of protrusions may be provided in parallel with one another and the long axis of the tube. The plurality of protrusions may be discrete from one another (e.g., angularly discrete). The plurality of protrusions may be spaced apart from one another about the tube. The plurality of protrusions may be spaced apart equiangularly about a longitudinal axis of the tube. The waveguide may comprise at least one, such as at least two, such as at least three, such as at least four, such as at least five, such as at least six protrusions. For example, the waveguide may comprise 1 , 2, 3, 4, 5 or 6 protrusions.

[0017] The protrusions may be spaced apart by at least 30 degrees, such as at least 45 degrees, such as at least 60 degrees, such as at least 90 degrees, such as at least 120 degrees, such as 180 degrees. For example, the protrusions may be spaced apart by about 30 degrees, about 45 degrees, about 60 degrees, about 90 degrees, about 120 degrees, or about 180 degrees. Alternatively, the protrusions may not be spaced apart equiangularly.

[0018] The or each protrusion may extend away from the tube, such as the inner tube, (e.g., perpendicularly away, such as radially away) by a distance similar to (e.g., equal to) a radius of the tube.

[0019] The or each protrusion may comprise a reinforcing structure, such as a rib or a fin. The ribs may be identical. The or each rib may extend longitudinally and away from the outer surface of the tube. The or each rib may comprise a uniform circumferential thickness along its length in the radial direction. For example, the or each rib may be generally or substantially obloid. The dimensions of the or each rib may be determined according to the space restrictions of the application and also the internal diameter of the microwave tube. A circumferential thickness dimension of the or each rib may be similar to (e.g., equal to) a radial thickness dimension of the walls of the tube. The or each protrusion may have a radial dimension of between 5 and 50 mm, such as about 25 mm, and / or a circumferential dimension of at least 2 mm (e.g., 2 to 3 mm), such as about 5 mm. The or each rib may not transport a cooling fluid.

[0020] The or each protrusion may comprise a pipe or cooling channel (e.g., a cooling pipe, such as for transmitting coolant along the waveguide). The or each pipe may be substantially cylindrical or alternatively comprise another geometry such as triangular or sector-shaped geometry. The or each pipe may define a long axis in parallel with a long axis of the tube. A wall thickness of the tube may be greater than (e.g., significantly greater than) a wall thickness of the or each pipe. A diameter of the or each pipe may be greater than (e.g., about twice) a wall thickness of the tube. The or each pipe may be discrete or discontinuous from the tube. For example, their internal volumes may not communicate.

[0021] The pipe of one or more protrusions (e.g., the pipe of the or each protrusion) may comprise a discontinuity in its perimeter (e.g., circumferential) wall. The discontinuity may extend through the thickness of the wall. The discontinuity may extend longitudinally (e.g., throughout the length of the pipe, such as from a first end of the tube to the second end of the tube). The discontinuity may increase a deformability of the pipe in the circumferential direction. For example, the discontinuity may improve a circumferential extendibility of the pipe to allow a cylindrical channel to be inserted along the length of the pipe. The discontinuity may comprise an opening formed by the removal or omission of an acute sector of cylindrical wall. Alternatively, the discontinuity may comprise a break within the wall of the pipe.

[0022] The protrusions may or may not be identical. A first set (e.g., a subset) of the plurality of protrusions may comprise (e.g., consist of) a rib. A second set (e.g., a subset) of the plurality of protrusions may comprise (e.g., consist of) a pipe.

[0023] The or each protrusion may taper (e.g., in circumferential dimensions) with distance (e.g., radial distance) away from tube. The or each protrusion may comprise a pipe and a rib. Within the or each protrusion, the pipe may be provided nearer to the tube than is the rib. Within the or each protrusion, the pipe may be provided at a proximal end of the protrusion (e.g., an end of the protrusion nearest to the tube). Within the or each protrusion, the rib may be provided at a distal end of the protrusion (e.g., an end of the protrusion furthest from the tube). Additionally or alternatively, the or each protrusion may comprise a hollow triangular transverse cross section, the triangular cross section tapering with distance away from the tube. The walls of the triangular cross section may be provided at about 45 degrees to the radial.

[0024] The waveguide may further comprise an outer tube, e.g., provided coaxially with the inner tube. The outer tube may be cylindrical. The outer tube may be coextensive with the inner tube and / or the or each protrusion. The outer tube may have greater radius than (e.g., twice the radius of) the inner tube. The outer tube may be radially spaced apart from the inner tube. A wall thickness of the outer tube may be similar to (e.g., equal to) a wall thickness of the inner tube.

[0025] The or each protrusion may extend from an internal surface of the outer tube. The or each protrusion may extend between an outer surface of the inner tube and an inner surface of the outer tube. The or each rib may attach to an internal surface of the outer tube. The waveguide may comprise a plurality of channels. Adjacent protrusions in combination with coaxial inner and outer tubes may define a longitudinal channel extending between the ends of the waveguide. The or each channel may have a geometry substantially comprising a prismatic annular sector or a sector of a cylindrical shell. The channels may span at least 30 degrees, such as at least 45 degrees, such as at least 60 degrees, such as at least 90 degrees, such as at least 120 degrees, such as 180 degrees. For example, the channels may span about 30 degrees, about 45 degrees, about 60 degrees, about 90 degrees, about 120 degrees, or about 180 degrees.

[0026] A protrusion (e.g., the or each protrusion) may comprise a pipe (e.g., a cooling pipe) and / or may define a channel in combination with an adjacent protrusion (and optionally in combination with an inner tube and an outer tube between which the protrusion extends).

[0027] The waveguide may be unitary (e.g., integrally formed, or formed as a single piece). The waveguide may have unitary construction (e.g., be integrally formed, or formed as a single piece) throughout (e.g., between the first end and the second end). The tube (e.g., the inner tube) and the or each protrusion may be unitary (e.g., integrally formed). The outer tube and the or each protrusion may be unitary (e.g., integrally formed). The inner tube, the outer tube and the or each protrusion may all be unitary (e.g., integrally formed) with one another. For example, the above components may be formed simultaneously by the same process and from the same material.

[0028] The waveguide may be formed of metal (e.g., consist of metal, such as a metal). The tube (e.g., inner tube) and the or each protrusion may be formed of metal (e.g., consist of metal). The tube (e.g., inner tube), the outer tube and the or each protrusion may be formed of metal (e.g., consist of metal). The metal may comprise aluminium (e.g., an aluminium alloy).

[0029] The waveguide may comprise (e.g., be formed of) a composite material (e.g., consist of a composite). The tube (e.g., inner tube) and the or each protrusion may be formed of a composite material (e.g., consist of a composite). The tube (e.g., inner tube), the outer tube and the or each protrusion may be formed of a composite material (e.g., consist of a composite). The composite may comprise a carbon fibre polymer composite (e.g., consist of a carbon fibre polymer composite).

[0030] An innermost surface of the tube (e.g., the inner tube) may comprise (e.g., be formed of) a layer of conductive material. For example, when the tube comprises a metal, the innermost surface of the tube may comprise the metal or a different metal having a higher conductivity. When the tube comprises a composite (e.g., a carbon fibre polymer composite), a layer of conductive material may be provided to the interior of the tube. The layer of conductive material may be applied as a coating. Alternatively, when the tube comprises a composite, a metal pipe or conduit may be provided to the interior of (e.g., received in) the tube. The metal pipe or conduit may define a cylindrical aperture for guiding microwaves along the waveguide. The layer of conductive material may comprise aluminium, silver, copper and / or gold (e.g., an alloy of one or more of those materials, such as an alloy of copper).

[0031] The innermost surface of the waveguide (e.g., the cylindrical inner surface of the tube) may comprise a series of ridges or corrugations. The ridges or corrugations will have dimensions and spacing dependent upon the frequency of microwaves to be transported and also dependent upon the internal diameter of the tube. For example, the ridges or corrugations may have a height or radial dimension of about 0.5 mm, a longitudinal dimension of about 0.5 mm, and / or a spacing of about 0.5 mm (e.g., a periodicity of about 1.0 mm)

[0032] The tube (e.g., the inner tube) may be hollow. The waveguide may comprise a cylindrical innermost surface. The tube (e.g., the inner tube) may comprise no structures extending radially inwards (e.g., with the exception of the ridges or corrugations). For example, when the waveguide is formed of a composite and comprises a metal conduit within the tube, the substantially cylindrical aperture of the metal conduit may comprise the innermost surface of the waveguide. The tube may be configured to receive a component having an aperture for guiding microwaves.

[0033] According to a second aspect of the present disclosure, there is provided an assembly. The assembly may comprise a microwave source. The assembly may comprise a microwave waveguide according to the first aspect.

[0034] According to a third aspect of the present disclosure, there is provided a microwave waveguide assembly comprising a first waveguide section. The first waveguide section may comprise a waveguide according to the first aspect. The assembly may comprise a second waveguide section. The second waveguide section may comprise a waveguide according to the first aspect. The second waveguide section may be operatively coupled to the first waveguide section. The second waveguide section may be identical to the first waveguide section. The waveguide assembly of the third aspect may be provided in conjunction with and / or be provided as part of the second aspect. For example, the first waveguide section of the third aspect may comprise the microwave waveguide of the second aspect.

[0035] According to a fourth aspect of the present disclosure, there is provided a method of forming a microwave waveguide. The waveguide may be a waveguide according to the first aspect. The method may comprise integrally forming the waveguide according to the first aspect (e.g., integrally forming the tube and protrusions of the first aspect). The method may comprise extruding or pultruding. The method may comprise extruding a metal. The method may comprise pultruding a fibre reinforced polymer composite (e.g., a carbon fibre reinforced polymer composite). The method may comprise providing a conductive layer (e.g., as a coating or as a conductive conduit) on an internal surface of the tube. The method may comprise corrugating an internal surface of the waveguide (e.g., corrugating an internal surface of the tube or corrugating an internal surface of the conductive conduit).

[0036] According to a fifth aspect, there is provided a method of forming a microwave waveguide assembly (e.g., according to the third aspect). The method may comprise providing a first waveguide section (e.g., comprising a waveguide according to the first aspect). The method may comprise providing a second waveguide section (e.g., comprising a waveguide according to the first aspect). The method may comprise operatively coupling the first and second microwave waveguide sections. The fifth aspect may be provided in conjunction with and / or be provided as part of the fourth aspect.

[0037] According to a sixth aspect, there is provided a method (e.g., a method of transmitting microwaves). The method comprise providing the microwave waveguide of the first aspect. The method may comprise injecting microwaves at a first end of the tube.

[0038] The method may be a method of transmitting microwaves in a nuclear fusion device. The method may comprise evacuating the tube; and / or passing a coolant through a cooling pipe of the waveguide.

[0039] The method may be a method of drilling. The method may comprise injecting cooling gas at the first end of the tube. The method may comprise permitting and / or receiving exhaust gas at the first end of the waveguide, e.g., from a channel of the waveguide provided to the exterior of the tube.

[0040] According to a seventh aspect, there is provided an extrusion or pultrusion system (e.g., comprising a die) configured to produce a waveguide according to the first aspect.

[0041] A list of elements with the “and / or” conjunction is used to mean “any combination of” the elements of the list (e.g., any one or more of the elements of the list).

[0042] To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention.

[0043] Brief Description of Drawings

[0044] For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

[0045] Figure 1 A is a perspective view of a microwave waveguide according to the present disclosure;

[0046] Figure 1 B is an end view of the waveguide of Figure 1 A;

[0047] Figure 2A is a perspective view of a microwave waveguide according to the present disclosure;

[0048] Figure 2B is an end view of the waveguide of Figure 2B; and

[0049] Figure 3 is an end view of a microwave waveguide according to the present disclosure;

[0050] Figure 4 is a flowchart showing a method according to the present disclosure;

[0051] Figure 5 is a flowchart showing a method according to the present disclosure;

[0052] Figure 6 is a flowchart showing a method according to the present disclosure;

[0053] Figure 7 is a flowchart showing a method according to the present disclosure;

[0054] Figure 8 is an end view of a microwave waveguide according to the present disclosure.

[0055] Throughout the drawings, like reference numerals will be used to refer to like features.

[0056] Detailed Description

[0057] Waveguide 100

[0058] With reference to Figs. 1A and 1 B (collectively Fig. 1), a microwave waveguide 100 for guiding high power microwave energy (e.g., in the order of 1 MW) is described. The waveguide 100 comprises a tube 110 having an aperture 104 for guiding microwaves from a first end 101 to a second end 102 of the waveguide 100. Microwave energy may be defined as electromagnetic radiation having a frequency between 1GHz and 1 THz. The tube 110 is generally cylindrical, its walls having a circular transverse cross section and extending substantially uniformly and concentrically along a longitudinal axis A-A. The walls of the tube 110 are of uniform radial thickness such that the tube 110 has a substantially cylindrical interior surface 112 and a substantially cylindrical outer surface 114, the surfaces 112, 114 extending along the longitudinal axis A-A of the tube 110.

[0059] The waveguide 100 comprises a plurality of protrusions 120 extending radially away from the outer cylindrical surface 114 of the tube 110. The protrusions 120 additionally extend longitudinally along the tube 110 such that a long axis of each protrusion is parallel with the long axis A-A of the tube 110. Each protrusion 120 comprises a uniform transverse cross section such that a transverse section through the waveguide 100 at any location along its length comprises the same profile as the end view of Fig. 1 B.

[0060] The protrusions 120 are uniformly spaced apart from one another around the outer circumferential surface 114 of the tube 110, such that they are provided equiangularly about the long axis A-A. In the illustrated example of Fig. 1 , there are six protrusions 120 provided at 60-degree intervals.

[0061] Each protrusion 120 comprises a cooling pipe 122, provided (when viewed transversely per Fig. 1 B) at an end radially proximate the tube 110, and a rib 124, provided at an end radially distal to the tube 110. For ease of understanding Fig. 1 B, the cooling pipe 122 and rib 124 have been annotated on just one protrusion 120, but it will be understood that each protrusion 120 of Fig. 1 comprises a cooling pipe 122 and rib 124.

[0062] The cooling pipes 122 are provided in parallel with the long axis A-A of the waveguide 100. In particular, the cooling pipes 122 are substantially cylindrical, defining a central passage of circular geometry. During operation of the waveguide 100, a liquid coolant may be passed along the cooling pipes 122.

[0063] Each rib 124 comprises a generally rectangular transverse cross section such that its circumferential thickness is uniform with radial distance from the tube 110. Accordingly, each rib 124 comprises an obloid geometry.

[0064] As shown in Fig. 1 B, the diameter of each cooling pipe 122 is greater than (e.g., approximately twice) the thickness of the walls of the tube 110. However, the thickness of the walls of the pipes 122 is less (e.g., at least three times less) than the thickness of the walls of the tube 110. The ribs 24 have a thickness dimension in the circumferential direction which is similar to the thickness of the walls of the tube 110. Accordingly, the protrusions 120 generally taper with distance. The protrusions 120 extend in the respective radial direction by a dimension approximately equal to the radial dimension of the tube 110. The waveguide 100 comprises a narrow connection between each cooling pipe 122 and the tube 100. In particular, between each cooling pipe 122 and the tube 100, the waveguide 100 comprises a connection having circumferential dimensions less than a diameter than the pipes 122.

[0065] The cylindrical interior surface 112 of the tube 110 comprises a series ridges or corrugations (not shown) protruding radially inwards from the surface 112 and spaced apart from one another along the longitudinal direction by a fixed distance. Accordingly, the interior surface 112 has a series of longitudinally discrete transverse circular rings. The dimensions and period of the ridges / corrugations are selected in order to encourage particular modes of microwave propagation along the waveguide 100. The tube 110 may comprise no further features to the interior of the ridges or corrugations on the internal surface, such that the tube 110 is essentially hollow.

[0066] In one example, the tube 110 has an aperture 104 (e.g., an interior diameter) of between 10 mm and 130 mm, such as about 50 mm (e.g., 45 mm to 55 mm), the walls of the tube may have a thickness of between 2 and 5 mm, and the ridges have a radial dimension of 0.5 mm, a longitudinal dimension of 0.5 mm and a spacing of 0.5 mm (e.g., a periodicity of 1.0 mm). However, it will be understood that the exact dimensions of the tube, its walls and ridges may be dependent upon the application and the frequency and energy of microwaves being guided.

[0067] The protrusions 120 reinforce the tube 110 such that a bending stiffness of the waveguide 100 is improved. For example, the rigidity of a waveguide can be improved while maintaining the same mass and material volume by reducing the thickness of the walls of the inner tube 110 and providing protrusions 120. Accordingly, a degree of straightness of the tube 110 is improved when compared with an alternative tube having fewer protrusions 120 (e.g., no protrusions). For example, during subsequent drilling of the internal ridges or corrugations, the improved stiffness of the waveguide may reduce (e.g., prevent) the development of curvature within the waveguide 100. In high power microwave applications, a straighter tube 110 reduces energy losses from the microwave beam.

[0068] As will be described later, the waveguide 100 may be formed by extrusion (e.g., of a metal) or pultrusion (e.g., of a carbon fibre reinforced polymer composite), such that the tube 110 and the protrusions 120 may be integrally formed (e.g., have a unitary construction). By providing a waveguide 100 of unitary construction, the conduction of heat from the walls of the tube 100 to the coolant provided within the cooling pipes 122 is improved, meaning that the cooling process is more efficient. Additionally, by providing the cooling pipes 122 at the radially proximal ends of the protrusions 120, the conduction of heat to the coolant within the pipes 122 may be improved when compared with protrusions having pipes 122 provided elsewhere along the protrusions 120 (e.g., pipes 122 at a distal end of the protrusion 120).

[0069] Although the waveguide 100 of Fig. 1 comprises six protrusions provided at 60 degrees to one another, it will be understood by the skilled person that an alternative number of protrusions may be provided. For example, even a single protrusion 120 would reinforce the tube 110. Additionally, the protrusions 120 may not necessarily be provided equiangularly. For example, the protrusions 120 may be provided such that their radial dimension has a significant component in parallel with a direction of gravity during forming and / or in an installed position. For example, the six protrusions 120 could be clustered in groups of three at the top and bottom portions of the tube 110 relative to gravity.

[0070] Similarly, although cooling pipe 122 and ribs 124 are described as being provided as part of the same protrusion 120, cooling pipes 122 and ribs 124 may instead be provided as separate protrusions within the same waveguide 110, or not at all (e.g., only one of cooling pipes 122 and ribs 124 may be provided, such as per Fig. 3). For example, the protrusions 120 may not necessarily be identical.

[0071] Additionally or alternatively, the geometry of the protrusions may differ from the illustrated protrusions 120. For example, the protrusions 120 may comprise a geometry other than the illustrated pipes 122 and ribs 124, such as a triangular transverse cross section (not shown) which may act as a cooling pipe or channel. Similarly, the protrusions 120 may not necessarily extend continuously and / or uniformly from one end of the tube 110 to the other. For example, at one or more locations along its length, one or more protrusions 120 (e.g., one or more ribs 124) may comprise a cutaway or removed section (not shown) extending longitudinally.

[0072] The tube 110 may itself define the aperture 104, for example, by its inner surface 112 which may comprise a conductive coating (e.g., comprising aluminium, silver, copper, and / or gold) on its inner surface 112. Alternatively, a separate component 340 (Fig. 3) may be received in the tube 110 and the separate component may define the aperture 104.

[0073] When a separate component 340 defines the aperture 104, the reinforcement provided by the protrusions 120 may reduce (e.g., prevent) any curvature developing within the waveguide 100 during the drilling of the internal corrugations.

[0074] Waveguide 200

[0075] With reference to Figs. 2A and 2B (collectively Fig. 2), a microwave waveguide 200 is described. The microwave waveguide 200 of Fig. 2 is essentially identical to the waveguide The waveguide 200 additionally comprises an outer tube 230. The outer tube 230 is substantially cylindrical, having a circular cross section that extends uniformly along its length, and is provided concentrically with the inner tube 210 such that their long axes B-B coincide. The outer tube 230 has a radius approximately twice that of the inner tube 210.

[0076] The walls of the outer tube 230 are of uniform radial thickness such that the tube 230 has a substantially cylindrical outer surface 234 extending along the longitudinal axis B-B of the waveguide 200. Accordingly, where the waveguide 100 has a splined outer surface, the waveguide 200 has a cylindrical outer surface. The walls of the outer tube 230 have thickness equal to the thickness of the walls of inner tube 210.

[0077] In the same way as the waveguide 100, the protrusions 220 extend radially away from the outer surface 114 of the tube 210. However, in the waveguide 200, the protrusions 220 extend radially inwards from an internal surface 232 of the tube 230, 230 such that each protrusion 220 extends between the tubes 210, 230. As the protrusions 220 extend radially, the ribs 224 forms a substantially perpendicular contact with the interior surface 232 of the outer tube 230.

[0078] Accordingly, adjacent protrusions 220 in combination with coaxial tubes 210, 230 define a series of longitudinal channels 226 having a geometry that is essentially a prismatic annular sector or a sector of cylindrical shell (e.g., a sector defined between opposing cylindrical arcs of the tubes 210, 230 and between opposing radially extending protrusions 220). Each channel 226 is continuous between the ends 201 , 202 of the waveguide 200 such that the flow of fluids along the waveguide 200 is permitted. For ease of understanding Fig. 2B, only a single channel 226 is annotated. In the example of Fig. 2, the channels 226 span approximately 60 degrees, but it will be understood that channels spanning different angles will be present when a different number of protrusions 220 is provided.

[0079] In the same way as the waveguide 100, each protrusion 220 comprises a cooling pipe 222 and a rib 224, the cooling pipe 222 being provided at a proximal end and the rib 224 being provided at a distal end 224. However, each protrusion 220, specifically the pipes 222, have a broader connection with the inner tube 210 than the between the protrusions 120 and the tube 110 of the waveguide 100. For example, the pipes 222 may be provided closer to the long axis B-B than are the pipes 122 relative to the long axis A-A. In particular, between each cooling pipe 222 and the tube 200, the waveguide 200 comprises a connection having circumferential dimensions greater than a diameter than the pipe 222. In the illustrated example of Fig. 2, the thickness of the ribs 224 may be substantially equal to the wall thicknesses of the tubes 210, 230. By providing an outer tube 230 connected to the inner tube 210 via protrusions 220, the rigidity (e.g., bending stiffness) of the waveguide 200 is improved when compared with a waveguide not having an outer tube 230. For example, the rigidity of a waveguide can be improved while maintaining the same mass and volume by reducing the thickness of the walls of the inner tube 210 and providing an outer tube 230 and protrusions 220 therebetween.

[0080] Waveguide 300

[0081] With reference to Fig. 3, a microwave waveguide 300 extending along the axis C-C is described. The waveguide 300 is essentially identical to the waveguide 200 of Fig. 2 with the following exceptions.

[0082] Each protrusion 320 comprises a rib 324, but no cooling pipe. The protrusions 320 thereby consist of a rib 324, and the channels 326 have a geometry more closely resembling a prismatic annular sector or a sector of cylindrical shell.

[0083] The protrusions 320 therefore have uniform circumferential thickness throughout their radial dimensions, and so the thickness of the protrusions 120 may be substantially equal to the wall thicknesses of the inner tube 310 and the outer tube 320.

[0084] Although the protrusions 320 do not comprise a cooling pipe, as will be described later, the channels 326 defined between the tubes 310, 330 and adjacent protrusions 320 are continuous along their length and so permit the flow of fluids along their length.

[0085] The waveguide 300 additionally comprises a conductive layer 340 to the interior of the tube 310. The conductive layer may comprise a conductive coating applied to the interior surface 312 of the tube 310 or a separate component such as a conductive pipe or conduit (e.g., copper pipe) which engages the interior surface 312 of the tube 310. In the example that the conductive layer 340 comprises a separate component, the component may be received in the tube 310 prior to corrugating the component 340. The inclusion of a conductive layer 340 may be particularly beneficial when a tube 110, 210, 310 is formed from a non-conductive material, but may also be beneficial when a tube 110, 210, 310 is formed from a conductive material (e.g., the layer 340 may comprise a more conductive material).

[0086] Waveguide 800

[0087] With reference to Fig. 8, a microwave waveguide 800 is described. The waveguide 800 is similar to the waveguide 200 of Fig. 2, with the following exceptions. The waveguide 800 has four protrusions 820 distributed equiangularly about the central axis D-D, with each protrusion 820 comprising a cooling pipe 822 and a rib 824. For ease of understanding the drawing, the cooling pipe 822 and rib 824 of only one protrusion 820 are annotated. However, it will be understood that each of the remaining three protrusions 820 also comprises a respective cooling pipe 822 and rib 824.

[0088] The cooling pipe 822 of each protrusion 820 comprises a discontinuity 828 in its circumferential wall. The discontinuity 828 extends in the longitudinal direction throughout the length of the pipe 822 (such as from a first end of the waveguide 800 to the second end of the waveguide 800) and extends in the radial direction (relative to the cooling pipe 822) through the thickness of the circumferential wall, from the interior of the cooling pipe 822 to its exterior. Each discontinuity 828 therefore comprises two substantially opposing faces each extending radially and longitudinally relative to the cooling pipe 822. Although Fig. 8 shows an end view of the waveguide 800, any transverse section through the waveguide 800 may comprise the geometry shown in Fig. 8.

[0089] An additional component (e.g., an aluminium or copper cooling channel for transporting a coolant within the pipe 822) may be inserted into the cooling pipe 822 prior to operation. By providing a discontinuity 828 within the cooling pipe 822, a deformability of the pipe 822 in its circumferential and radial directions may be increased. For example, the discontinuity 828 may improve a circumferential extension of the pipe 822 to allow the additional component to be inserted along the length of the pipe more readily and may allow the pipe 822 to engage or grip the component more securely.

[0090] In Fig. 8, each discontinuity 828 is illustrated as comprising an opening formed by the removal or omission of an acute sector of the cylindrical wall of the cooling pipe 822, such that the substantially opposing faces of the discontinuity 828 are spaced apart from one another by the acute sector of removed or omitted cylindrical wall. Such an opening may be formed during an extrusion process.

[0091] Alternatively, in an example not shown, each discontinuity 828 may instead comprise a break within the wall of the pipe 822 between opposing circumferentially-facing surfaces of the wall. For example, prior to the insertion of an additional component into the cooling pipes 822, the opposing faces of the discontinuity 828 may be in contact with one another. A discontinuity 828 in the form of an opening (illustrated) or a break (not illustrated) will still provide the above advantages for the cooling pipe 822. Composition

[0092] In order to propagate microwaves along the waveguides 100, 200, 300, 800 the apertures 104, 204, 304, 804 of the waveguides 100, 200, 300, 800 are defined by a conductive material. The tubes 110, 210, 310, 810 may be formed from a conductive material (e.g., aluminium or an alloy thereof) and so the inner surfaces 112, 212, 312, 812 may define the apertures 104, 204, 304, 804. Additionally or alternatively, tubes 110, 210, 310, 810 may comprise a layer 340 of conductive material (e.g., a conductive coating) provided on their inner surfaces 112, 212, 312, 812. For example, a tube 110, 210, 310, 810 formed from a conductive material may have a layer of material with a higher conductivity provided on its inner surface 112, 212, 312, 812. Alternatively, when a tube 110, 210, 310, 810 is formed from a non-conductive material, a layer of conductive material may be provided to its interior (e.g., as a separate component, such as a conductive conduit, or as a coating layer), and the layer of conductive material may define the aperture 104, 204, 304, 804. Materials comprising aluminium, silver, copper, and / or gold may be particularly beneficial to define the aperture 104, 204, 304, 804.

[0093] The compositions of the waveguides 100, 200, 300, 800 may be determined by their application. When cooling is a primary consideration for the waveguides 100, 200, 300, 800 (e.g., due to the proximity of other components and / or environmental conditions during operation), it may be desirable to form the tubes 110, 210, 310, 810 and the protrusions 120, 220, 320, 820 (and optionally the outer tubes 230, 330, 830 when present) from a material having a high thermal conductivity and a high electrical conductivity (e.g., aluminium or an alloy thereof). By using such a material, the conduction of heat to the cooling pipes 122, 222, 822 and / or the channels 326, 826 may be improved and so the heat dissipation properties of the waveguides 100, 200, 300, 800 improved. Such a composition may be particularly beneficial in nuclear fusion applications (described later).

[0094] When the waveguides 100, 200, 300, 800 are to have very long length, or be assembled into a waveguide assembly having very long length, it may be desirable to form the tubes 110, 210, 310, 810 and the protrusions 120, 220, 320, 820 (and optionally the outer tubes 230, 330, 830 when present) from a relatively low density but high strength material, such as a carbon fibre reinforced polymer composite. The polymer used may be a high temperature resin, such as a resin which can withstand temperatures of up to 1000 °C. Such a waveguide may comprise a conductive layer on the interior surface 112, 212, 312, 812 of the tube 110, 210, 310, 810. The conductive layer may be applied as a coating or may comprise a separate component such as a conductive pipe or conduit inserted into the tube 110, 210, 310, 810 and the separate component may comprise the corrugations. Such a composition may be particularly beneficial in geothermal drilling applications (described later).

[0095] Forming processes

[0096] With reference to Fig. 4, a method 400 of forming a waveguide 100, 200, 300, 800 is described. The method 400 comprises 402 extruding a metal. The metal may be extruded through a die having geometry closely matching the end views of Figs. 1A, 2A, 3 and 8.

[0097] Alternatively, the method 400 comprises 404 pultruding a carbon fibre reinforced polymer composite. The carbon fibre reinforced polymer composite may be pultruded through a die having geometry closely matching the end views of Figs. 1A, 2A, 3 and 8. The method 400 then comprises 406 providing a conductive layer 340 on an internal surface 112, 212, 312, 812. For example, the conductive layer may comprise a conductive coating, or may comprise a separate component (e.g., a conductive conduit) received in the tube 110, 210, 310, 810.

[0098] The method 400 then comprises 408 corrugating an internal surface 112, 212, 312, 812 of the waveguides 100, 200, 300, 800. For example, when the aperture 104, 204, 304, 804 is defined by a separate component received in the tube 110, 210, 310, 810, the component may be inserted into the tube 110, 210, 310, 810 prior to the drilling of the corrugations in the component.

[0099] When the aperture 104, 204, 304, 804 is defined by the tube 110, 210, 310, 810, the internal surfaces 112, 212, 312, 812 of the tubes 110, 210, 310, 810 may be corrugated. However, application of a conductive coating to the tubes 110, 210, 310, 810 may be performed before or after corrugation.

[0100] The tubes 110, 210, 310, 810 and the protrusions 120, 220, 320, 820 (and optionally the outer tubes 230, 330, 830 when present) are therefore integrally formed and so have unitary construction. For example, the waveguides 100, 200, 300, 800 may be formed by extruding a metal through a die having a geometry corresponding to the end views of Figs. 1 B, 2B, 3, 8. Accordingly, the waveguides 100, 200, 300, 800 may be integrally formed (e.g., from a single material) and so have unitary construction throughout.

[0101] Alternatively, the waveguides 100, 200, 300, 800 may be formed by pultrusion of a carbon fibre composite or a similar material through a die having a geometry corresponding to the end views of Figs. 1 B, 2B, 3, 8. Accordingly, with the exception of an optional conductive coating and an optional conductive conduit provided to the interior of the tubes 110, 210, 310, 810, the waveguides 100, 200, 300, 800 may be integrally formed. Formation of the waveguides 100, 200, 300, 800 by pultrusion or extrusion may provide a higher output of waveguide, reduced materials wastage and may be less labour-intensive.

[0102] Waveguide assembly

[0103] The waveguides 100, 200, 300, 800 may be provided in sections and assembled into waveguide assemblies (not shown). For example, the waveguides 100, 200, 300, 800 may be extruded / pultruded into sections a few metres long, and then attached to one another by flanges provided at either end.

[0104] With reference to Fig. 5, a method 500 of forming a microwave waveguide assembly is described. The method 500 comprises 502 providing a first waveguide section. For example, the method step 502 may comprise performing the method 400 of Fig. 4. The method 500 comprises 504 providing a second waveguide section. For example, the method step 504 may comprise performing the method 400 of Fig. 4. The method 500 then comprises 506 operatively coupling the first waveguide section 100, 200, 300, 800 and the second waveguide section 100, 200, 300, 800 (e.g., such that waveguides may be transmitted from the first waveguide section to the second waveguide section), such as by flanges. The flanges may be attached to the waveguide sections after forming.

[0105] Nuclear fusion

[0106] The waveguides 100, 200, 300, 800 may be used in nuclear fusion applications. Due to their cooling pipes 122, 222, 822, the waveguides 100, 200, 800 may be particularly beneficial in nuclear fusion, especially when formed from a metal such as aluminium (e.g., an aluminium alloy) or another material with high thermal conductivity. By integrally forming the protrusions 120, 220, 820 and the tubes 110, 210, 810, the thermal conduction from the tube 110, 210, 810 to the coolant flowing through the pipes 122, 222, 822 may be improved.

[0107] With reference to Fig. 6, a method 600 is described. The method 600 may be a method of transmitting microwaves from a source, such as a gyrotron, to a destination, such as a nuclear fusion vessel.

[0108] The method 600 comprises 602 providing a microwave waveguide 100, 200, 300, 800 (e.g., as part of a waveguide assembly). For example, the method step 602 may comprise performing the method 400 of Fig. 4. The method 600 then comprises 604 evacuating the tube 110, 210, 310, 810 and 606 passing a coolant through a cooling pipe 122, 222, 322, 822 of the waveguide 100, 200, 300, 800. The method 600 then comprises 608 injecting microwaves at a first end 101 , 201 , 301 , 801 of the tube 110, 210, 310, 810. Geothermal drilling

[0109] The waveguide 300 may be particularly beneficial in geothermal drilling, especially when formed from carbon fibre composite. During geothermal drilling, it may be necessary to drill down into the Earth’s crust up to 20 km. As this is a vertical drill hole, the breaking length and other materials properties of the waveguide may be a critical consideration. For example, typical waveguide materials may not be suitable for being vertically suspended over kilometre-scale lengths.

[0110] However, when formed from a carbon fibre composite (having a breaking length multiple times greater than 20km), the materials limitations may be mitigated (e.g., addressed). For example, in an embodiment in which a waveguide 300 has tubes 310, 320 and protrusions 320 integrally formed of a carbon fibre composite by pultrusion, the breaking length of a conductive conduit received in the tube 310 may be improved by the reinforcement provided by the carbon fibre composite of the waveguide 300. In other words, the weight of copper pipe to the interior to tubes 110, 210, 310, 810 may be partly supported by the carbon fibre composite, and so the breaking length of the copper pipe increased.

[0111] Additionally, a carbon fibre composite comprising a high temperature resistant resin (e.g., a resin able to withstand temperatures of at least 1000 °C, such as at least 2000 °C) is able to withstand the temperature of about 700 °C at its distal end during the drilling process.

[0112] With reference to Fig. 7, a method 700 of drilling (e.g., geothermal drilling) is described. The method 700 comprises 702 providing a microwave waveguide 100, 200, 300, 800 (e.g., as part of a waveguide assembly). For example, the method step 702 may comprise performing the method 400 of Fig. 4. The method 700 then comprises either 704 injecting cooling gas (e.g., inert gases) at a first end 101 , 201 , 301 , 801 of the tube 110, 210, 310, 810. The method 700 then comprises 706 injecting microwaves at a first end 101 , 201 , 301 , 801 of the tube 110, 210, 310, 810. The method 700 then comprises 708 receiving exhaust gas at the first end 101, 201 , 301 , 801 from a channel 226, 326, 826 of the waveguide 200, 300, 800. For example, vaporised earth from the drilling end of the waveguide may pass upwards along channels 226, 326, 826 towards the top end of the waveguide assembly.

[0113] Experimental data

[0114] Finite Element Analysis (FEA) was conducted for waveguides 300 of the type shown in Fig. 3 having different numbers of ribs 324. The waveguides had a 50mm internal diameter of the inner tube 810, a 100mm external diameter of the outer tube 330, and all walls of uniform 3mm thickness. The deflection behaviour of different lengths of waveguide 300 and for waveguides 300 having different numbers of ribs 324 was then determined. For the deflection calculations of Table 1 , the FEA boundary conditions included the waveguides 300 having a fixed support at one end and a frictionless support at the other end. To reduce computation time, the internal corrugations were omitted from the FEA (it was separately determined that the corrugations did not affect the deflection behaviour of the waveguides). The resulting data is shown in Table 1 below.

[0115] Table 1 - Deflection analysis using FEA

[0116] As shown above, it was found that the deflection of the waveguides increases with the number of ribs at both 2m and 4m length. However, the waveguides 300 still had smaller deflections when compared with previously-proposed waveguide structures, and so had improved rigidity and straightness when compared with previously-proposed waveguide structures.

[0117] Thermal analyses were then undertaken for waveguides 200 of the type shown in Fig. 2 and having different numbers of ribs and at different coolant mass flow rates. The results are shown in Table 2.

[0118] It was found that cooling improves with increasing rib number, but there are diminishing returns beyond four ribs.

[0119] Next, a circularity analysis was performed in which the degree of deflection according to orientation was determined. It was found that the deflection of a waveguide having four ribs did not change with orientation when rotated about the central axis. In particular, it was found that the 4m waveguide having four ribs deflected by the same amount when the line of gravity was parallel with a rib 324 and when the line of gravity bisected adjacent ribs 324 (i.e. , deflection did not change with rotation through 45 degrees). The four-rib waveguide 300 may therefore be installable in a rotationally-invariant or an orientationally non-specific manner.

[0120] Table 2 - Thermal analysis using FEA

[0121] In view of the above data, while all of the proposed microwave waveguides provided improvements over previously-proposed waveguides, it was concluded that waveguides having four ribs were most advantageous when deflection behaviour is the primary consideration and according to the specific boundary conditions of the analyses performed.

[0122] It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more exemplary examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

Claims1. A microwave waveguide comprising: a tube comprising an aperture for guiding microwave energy; and a protrusion extending longitudinally along an outer surface of the tube.

2. The waveguide of claim 1 , comprising a plurality of protrusions spaced apart from one another about the tube.

3. The waveguide of claims 1 or 2, wherein the or each protrusion extends in parallel with a longitudinal axis of the tube.

4. The waveguide of any preceding claim, wherein a transverse cross section of the or each protrusion is uniform throughout the length of the waveguide.

5. The waveguide of any preceding claim, wherein the or each protrusion comprises a rib, the rib extending away from the outer surface of the tube.

6. The waveguide of any preceding claim, wherein the or each protrusion comprises a pipe.

7. The waveguide of any preceding claim, wherein the or each protrusion comprises a pipe and a rib, wherein: the pipe is provided at a proximal end of the protrusion; and / or the rib is provided at a distal end.

8. The waveguide of any preceding claim, wherein the or each protrusion is integrally formed with the tube.

9. The waveguide of any of claims 2 to 8, wherein the protrusions are provided equiangularly about a longitudinal axis of the tube.

10. The waveguide of any preceding claim, wherein the tube is an inner tube and the waveguide further comprises an outer tube provided coaxially with the inner tube.

11. The waveguide of claim 10, wherein the or each protrusion extends from an internal surface of the outer tube.

12. The waveguide of any preceding claim, wherein the or each protrusion is unitary with the tube.

13. The waveguide of any preceding claim, wherein the or each protrusion and the tube are formed of metal.

14. The waveguide of any preceding claim, wherein the waveguide comprises a first end and a second end, the waveguide being of unitary construction between the first end and the second end.

15. The waveguide of any of claims 1 to 12, wherein the or each protrusion and the tube are formed of carbon fibre polymer composite.

16. The waveguide of any preceding claim, where in the tube is cylindrical and comprises an internal diameter of between 10 mm and 30 mm.

17. The waveguide of any preceding claim, wherein: the tube defines the aperture; or the aperture is defined by a conductive conduit received in the tube.

18. An assembly comprising: a microwave source; and the waveguide of any preceding claim.

19. A microwave waveguide assembly comprising: a first waveguide section comprising a waveguide according to any of claims 1 to 17; and a second waveguide section comprising the waveguide according to any of claims 1 to 17, the second waveguide section being operatively coupled to the first waveguide section.

20. A method of forming a microwave waveguide according to any of claims 1 to 17, the method comprising: extruding a metal; or pultruding a carbon fibre reinforced polymer composite.

21. The method of claim 20, comprising: corrugating an internal surface of the tube; and / or providing a conductive layer on an internal surface of the tube.

22. A method of forming a microwave waveguide assembly according to claim 19, the method comprising: providing a first waveguide section comprising a waveguide according to any of claims 1 to 17; providing a second waveguide section comprising the waveguide according to any of claims 1 to 17; and operatively coupling the first and second microwave waveguide sections.

23. A method comprising: providing the microwave waveguide of any of claims 1 to 17; injecting microwaves at a first end of the tube.

24. The method of claim 23, comprising: evacuating the tube; and / or passing a coolant through a cooling pipe of the waveguide.

25. The method of claim 23, wherein the method is a method of drilling, comprising: injecting cooling gas at the first end of the tube; and receiving exhaust gas at the first end from a channel of the waveguide provided to the exterior of the tube.

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