Tube comprising at least one end with an oblique plane section

Abstract

The invention relates to a microwave power transmission window assembly comprising: - a microwave power transmission window comprising: - two tubes each comprising two parallel oblique plane sections, an oblique plane section not perpendicular to the central axis of the tube and having constant thickness in the oblique plane section; and - an optical blade assembled between two respective ends of the two tubes arranged opposite each other; - a tubular extension element of the microwave power transmission window; - two centering rings of the microwave power transmission window in the tubular extension element; and an external housing provided with two transparent portions arranged at the ends of the tubular extension element of the microwave power transmission window.

Description

[0001] The invention relates to a tube comprising at least one end with an oblique plane section.

[0002] When a tube 1, of constant thickness, is cut obliquely, i.e., whose obliquely cut end has an oblique plane section not perpendicular to the central axis 2, its thickness is not constant, as shown in the [ Fig.1 ].

[0003] US document 3 555 450 A and GB 857 331 A also illustrate a microwave power transmission window assembly comprising a tube having an oblique plane section of non-constant thickness.

[0004] Indeed, since the cut is oblique, the thickness of the cut end 3 is not constant, as shown on the [ Fig.1 ], on which is represented the variation of the thickness, which takes for example several values, the extreme values ​​of which are represented e 1 and e 2.

[0005] The assembly of such an end 3 of tube 1 on a flat surface of a different material, or on another tube with a corresponding oblique cut (cutting angles relative to the axis of complementary tubes), leads to an asymmetry with the consequence that from a diameter greater than 30 mm the stresses linked to the difference in expansions and the large thicknesses of the collars or brazing in places create a catastrophic break of the assembly.

[0006] One aim of the invention is to overcome the problems mentioned above.

[0007] According to one aspect of the invention, a microwave power transmission window assembly is proposed, comprising: a microwave power transmission window comprising: two tubes each comprising two parallel oblique plane sections, one oblique plane section not perpendicular to the central axis of the tube and of constant thickness in the oblique plane section; and an optical blade assembled between two respective ends of the two tubes arranged opposite each other; a tubular extension element of the microwave power transmission window; two centering rings of the microwave power transmission window in the tubular extension element; and an external housing provided with two transparent portions arranged at the ends of the tubular extension element of the microwave power transmission window.

[0008] According to one embodiment, the optical blade is made of diamond, or quartz, or sapphire, or glass.

[0009] In one embodiment, the microwave power transmission window is a so-called Brewster window in which the oblique plane section is such that the angle between the central axis of the tube and a normal to an oblique plane section is 67.22°.

[0010] The invention will be better understood upon examination of some embodiments described by way of non-limiting examples and illustrated by the accompanying drawings, in which: [ Fig.1 ] schematically illustrates a tube of constant thickness, cut obliquely, according to the prior art; [ Fig.2 ] schematically illustrates a tube having a flat-section end and constant thickness, according to one aspect of the invention; [ Fig.3 ] schematically illustrates a microwave power transmission window, according to one aspect of the invention; [ Fig.4 ] schematically illustrates a microwave power transmission window of the [ Fig.3 ] in the case of a so-called Brewster window, according to another aspect of the invention; and [ Fig.5 ] schematically illustrates a microwave power transmission window assembly, according to another aspect of the invention.

[0011] Across all figures, elements with identical references are similar.

[0012] There [ Fig.2 ] schematically illustrates a tube 4 having a flat cross-section end 3, and constant thickness e, according to one aspect of the invention.

[0013] The constant thickness e can be obtained by machining 5a.

[0014] Because of this angle, in the absence of such machining, the oblique ends do not have a constant dimension and in particular have an oblong shape and a non-constant wall thickness which thickens from the center towards the end of each side of the largest dimension.

[0015] Oblique is understood to mean a plane cutting angle that makes a non-perpendicular angle with axis 2 of tube 4.

[0016] This asymmetry means that, from a diameter greater than 30 mm, the stresses linked to the difference in expansion and the large thicknesses of the oblique ends in places create a break in an assembly with a plate or tube of another material.

[0017] The object of the present invention is to mechanically achieve a machining process that creates a constant thickness e throughout the circumference of the oblique cut, regardless of the angle of the oblique cut, over a height large enough to minimize the forces due to thermo-mechanical stresses.

[0018] The assemblies can be made by brazing, welding, gluing... The [ Fig.3 [This schematically represents a microwave power transmission window comprising an assembly including:] two tubes 4a, 4b, each having two ends of constant thickness and parallel oblique plane sections; and an optical plate 5 assembled between two respective ends of the two tubes 4a, 4b, arranged opposite each other.

[0019] Indeed, the present invention is particularly well-suited to microwave power transmission windows for electron tubes. These power windows must be able to transmit the energy supplied by the microwave tube while minimizing losses due to the intrinsic properties of the material and microwave matching, all while ensuring the maintenance of ultra-high vacuum sealing. Microwave matching is performed at a specific frequency or over a frequency band.

[0020] In some cases, near-perfect matching is required not just across a single frequency band, but across two or more specific frequencies. This is particularly true for the use of dual-frequency gyrotron tubes, which deliver very high power levels on the order of megawatts at frequencies exceeding 100 GHz. In such cases, a frequency window designed to be compatible with all frequencies must be used.

[0021] This is a window called a Brewster window, as illustrated on the [ Fig.4 The main characteristic of this type of window is the use of a blade, for example a diamond blade, inclined at the Brewster angle, which is exactly 67.22° when using a diamond blade. To create such a window, a tube must be made and placed on either side of the blade positioned at the appropriate angle to create a sealed assembly that fully meets the operating conditions of the power window on the electronic tube, thus guaranteeing its airtightness.

[0022] Large windows of this type designed for tube mounting do not exist. There are numerous ways to assemble ceramics, for example, on copper skirts, to guarantee microwave and sealing properties.

[0023] Due to Brewster's angle of 67.22°, in state-of-the-art designs, the ends of the oblique plane section, not perpendicular to the tube's central axis, do not have a constant dimension and, in particular, are oblong in shape. The resulting wall thickness is not constant and increases from the center of the collar towards the end on each side of the longest dimension. This asymmetry means that, for diameters greater than 30 mm, the stresses related to the difference in thermal expansion and the significant thicknesses of the ends in certain areas can lead to catastrophic failure of the assembly.

[0024] The aim is to create a sealed assembly that is resistant to various thermal cycles. The basic concept is to assemble, for example by brazing, a wall made of a dielectric material such as diamond onto copper ends placed on either side of the microwave transmission wall, and to ensure that the assembly is sealed.

[0025] The present invention makes it possible to mechanically perform machining which creates a constant thickness throughout the brazed length regardless of the angle over a height which is large enough to create flexibility and thus minimize the stresses due to thermo-mechanical stresses during assembly and curing operations.

[0026] In order to be able to carry out this assembly under the best conditions, taking into account the Brewster angle, as illustrated on the [ Fig.4 The wall is brazed flat, as with conventional cylindrical windows, and the necessary tooling is created to perform this operation without requiring complex tooling to ensure the positioning of the transmission blade relative to the angled copper ends. A second brazing step joins this first stage with the rest of the assembly to create a window assembly that can be mounted onto the tube in question.

[0027] A window assembly is schematically represented on the [ Fig.5 ], including: a microwave power transmission window 6 according to the [ Fig.2] ; a tubular element 7 extending the microwave power transmission window; two rings 8a, 8b for centering the microwave power transmission window 6 in the tubular element 7 extending; and an external housing 9 with two transparent portions 10a, 10b arranged at the ends of the tubular element 7 extending the microwave power transmission window.

[0028] For example, given the ratio between the dimensions of the actual diameter and the apparent dimensions due to the Brewster angle in a ratio of 2.5, it is necessary to carry out machining which reduces the brazing area to a ring of 1 mm width while allowing flexibility at the level of the tubes 4a, 4b without reducing the thickness of the tubes 4a, 4b to values ​​too low to avoid the phenomena of permeation, deformations and more generally sealing defects.

[0029] The aim is to create flexibility at the end of assembly 6 related to the material allowing the transmission of microwave energy, in order to reduce the stresses due to differential expansion between the different materials and also related to the Brewster angle which leads to a ratio of 2.5 between the wall thickness at the diameter perpendicular to the cut which corresponds to the actual diameter of the tube and the wall thickness located at the cutting plane located on the diameter of the long side of the ellipse.

[0030] Furthermore, the wall thickness of assembly 6 is subjected to the same ratio, resulting in a thickness that does not allow assembly 6 to adapt to the stresses due to differential expansion. This machining depends on the actual diameter of the tube and its thickness.

[0031] To overcome this drawback, this width is reduced by machining around the perimeter of the tubes in places where the thickness becomes greater than the desired thickness.

Claims

1. Microwave-frequency power-transmission window assembly comprising: - a microwave-frequency power-transmission window (6) comprising: - two tubes (4a, 4b) each comprising two parallel oblique planar cross sections, one oblique planar cross section being non-perpendicular to the central axis of the tube and being of constant thickness in the oblique planar cross section; and - an optical plate (5) assembled between the two respective ends of the two tubes positioned facing one another; - a tubular extension element (7) extending the microwave-frequency power-transmission window (6); - two centering rings (8a, 8b) that center the microwave-frequency power-transmission window (6) in the tubular extension element (7); and - an external housing (9) equipped with two transparent portions (10a, 10b) positioned at the ends of the tubular extension element (7) extending the microwave-frequency power-transmission window (6).

2. Microwave-frequency power-transmission window assembly according to claim 1, wherein the optical plate (5) is made of diamond, or quartz, or sapphire, or glass.

3. Microwave-frequency power-transmission window assembly according to one of the preceding claims, wherein the microwave-frequency power-transmission window (6) is a so-called Brewster window wherein the oblique planar cross section is such that the angle between the central axis of the tube and a normal to an oblique planar cross section is 67.22°.

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