Method of producing brazeless accelerating structures

Abstract

A resonant apparatus such as a resonant waveguide module in an RF particle accelerator includes an unbrazed joint that provides a reliable vacuum seal and RF contact between resonators with precisely controlled internal geometry. The joint can be disassembled and reassembled without degradation. Hard, stainless steel end faces include knife edges pressed into a copper central component, such as a gasket. The knife edges extend the waveguide interiors without gaps or interruptions. The central component serves as a coupling iris or other functional component of the resonant apparatus, thereby allowing the central component to have substantial dimensions that inhibit mechanical distortions thereof. The waveguides and knife edges can be copper plated. Embodiments include embedded passages and/or recesses used for cooling, radiation shielding, magnetic focusing coils, and/or electron optics element formed by permanent magnets.

Claims

1. A resonant apparatus comprising: a first waveguide having therein a first internal channel bounded by first internal walls, said first internal channel extending to and penetrating through a first distal end face of the first waveguide; a first knife edge having flat first inner sides terminating at a distal leading edge, said first inner sides being coincident with and parallel to said first internal walls so as to functionally extend said first internal walls without substantial interruption thereof; a second waveguide having therein a second internal channel bounded by second internal walls, said second internal channel extending to and penetrating through a flat proximal end face of the second waveguide; a second knife edge having flat second inner sides terminating at a proximal leading edge, said second inner sides being coincident with and parallel to said second internal walls so as to functionally extend said second internal walls without substantial interruption thereof; and a central component having a central opening, said central component being made from a metal that is softer than metals from which said knife edges are made; said first and second waveguides being assembled with said central component being sandwiched in between, such that said central opening extends between said first and second internal channels, and such that said first and second knife edges are pressed into opposing proximal and distal faces of said central component respectively, thereby simultaneously forming vacuum and RF seals between said first and second waveguides and said central component, said central component being an element that is functionally necessary to said resonant apparatus.

2. The apparatus of claim 1, wherein the first and second knife edges are made from stainless steel, and the central element is made from copper.

3. The apparatus of claim 1, wherein the first and second internal walls and the first and second knife edges are plated with copper, and the central element is made from copper.

4. The apparatus of claim 3, wherein the resonant apparatus can be tuned by selective etching of the copper plated internal walls of the waveguides.

5. The apparatus of claim 1, wherein the central opening is smaller in cross sectional area than cross sectional areas of said first and second channels.

6. The apparatus of claim 5, wherein the central opening functions as an iris separating the first and second central channels.

7. The apparatus of claim 1, wherein the central element is a gasket.

8. The apparatus of claim 1, wherein the first waveguide includes a plurality of separated passages or recesses.

9. The apparatus of claim 8, further comprising a coil wound in one or more of the passages and/or recesses of the first waveguide.

10. The apparatus of claim 8, wherein the first waveguide includes an electron optics element formed by permanent magnets placed in the passages or recesses.

11. The apparatus of claim 10, wherein the electron optics element is a Halbach array.

12. The apparatus of claim 10, wherein the electron optics element is a quadrupole.

13. The apparatus of claim 12, wherein the quadrupole includes iron inserts.

14. The apparatus of claim 1, wherein the resonant apparatus is an RF-driven particle accelerating waveguide.

15. The apparatus of claim 1, wherein the first waveguide further comprises a cooling channel.

16. The apparatus of claim 1, wherein the first waveguide further comprises magnetic beam optics embedded therein.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is side view of a particle accelerator waveguide that includes joints formed according to an embodiment of the present invention;

(2) FIG. 2 is an enlarged sectional side view of the particle accelerator waveguide of FIG. 1;

(3) FIG. 3 is an exploded view of a joint included in the embodiment of FIG. 1;

(4) FIG. 4A is a front view of a flange-cell in an embodiment of the invention that includes embedded cooling channels of complicated geometry;

(5) FIG. 4B is a front view of a flange-cell in an embodiment of the invention that includes embedded Halbach array magnetic quadrupole focusing;

(6) FIG. 4C is a front view of a flange-cell in an embodiment of the invention that includes embedded permanent magnet quadrupole focusing;

(7) FIG. 5 is an exploded view of a particle waveguide accelerator similar to FIG. 1 that incorporates joints according to embodiments of the present invention;

(8) FIG. 6 is a sectional view of a test assembly comprising a conflat joint of the prior art, as well as joints according to embodiments of the present invention that join cells made of unplated stainless steel, stainless steel plated with copper, and stainless steel plated with copper and burn-tested; and

(9) FIG. 7 is a plot comparing resonant curves for a resonant waveguide incorporating embodiments of the present invention obtained before and after plating of the waveguide flange-cells with copper.

DETAILED DESCRIPTION

(10) The present invention is an unbrazed joint structure that is suitable for joining together resonant waveguide modules, whereby the joint structure provides a precisely controlled internal geometry suitable for resonant structures, combined with a reliable vacuum seal and high quality RF shielding. The joint structure can be produced at a much lower cost as compared with typical brazed structures, and can be readily disassembled and reassembled with substantially no degradation.

(11) The disclosed joint structure adopts some features of the conflat design, in that two hard flanges, typically made from stainless steel, are assembled with a soft copper gasket sandwiched in between, and also in that each of the hard flanges includes a knife edge that cuts into the copper gasket to form a vacuum seal as well as a reliable RF connection. Unlike typical conflat flanges, however, the hard flanges of the present design are plated with copper. In embodiments entire modular cells, including the central bodies and terminating flanges, are constructed from stainless steel and plated with copper, so that the interiors present a uniformly copper environment for RF shielding. In other embodiments, the flanges themselves function as the resonant cells, and are referred to herein as flange-cells.

(12) Furthermore, the interior surfaces of the knife edges are constructed so as to functionally extend the internal structure of the cell, so that the internal cell geometry is unbroken and unmodified until it encounters the gasket.

(13) Also, the copper gaskets in the disclosed joint structure are not simply added components necessary to the formation of vacuum seals. Instead, they are incorporated as functional RF components of the resonator or other device being constructed, thereby allowing them to be thicker more rigid than the gaskets used in typical conflat joints.

(14) Referring to FIG. 1, an overall assembly design of a particle accelerating structure 100 in an embodiment of the present invention includes a mode launcher 108 and a coupling cell 102 at each end of a regular corrugation of resonant amplifying cells 104. A copper gasket 106 that also serves as a coupling iris is inserted between each pair of cells 102, 104.

(15) With reference to the sectional view of FIG. 2, due to the short lengths of the cells 102, 104 in this embodiment, separate joining flanges are not required, and instead the cells 102, 104 themselves function as the flanges, whereby each flange-cell 102, 104 includes four bolts 200 inserted through counter-sunk holes 202 and threaded into threaded holes 204 in the next adjoining flange-cell 102, 104.

(16) This structure of the flange-cells and joints can be seen more clearly in the expanded view of two adjacent flange-cells 104 in FIG. 2. Essentially, each accelerating structure cell 102, 104 is a flange having a resonant interior 206 bounded by knife edges 208. The flange-cells 102, 104 are bolted one to another with a copper gasket 106 in between each pair. The gaskets have central holes 210 of reduced diameter, and thereby function as irises (gasket-irises) of the accelerating waveguide assembly 100. The threaded holes 204 in each cell are offset by 45 degrees from the countersunk holes 202.

(17) Any number of cells 104 can be strung together in this fashion, depending on the requirements of the embodiment. Flange-cells 102, 104 and gasket-irises 106 can be chosen with appropriate dimensions so as to accommodate a variety of accelerating waveguide designs in terms of phase advance, a necessity for coupling cells 102, irises 106, and mode launchers 108. For example, a low energy accelerating structure that requires a sequential increase of the cell length along the structure can be made in the same brazeless fashion. To be able to crush a copper gasket-iris 106 without distortion, the flange-cells 102, 104 are made of a hard material, such as stainless steel. To maintain the required RF properties, the flange-cells 102, 104 are copper plated.

(18) A standard conflat flange joint introduces gaps in the interior walls of the flanges because the knife edges are offset from the central channel of the flange and thereby space the flanges apart and create gaps between the gaskets and the adjoining flange surfaces. The present invention overcomes this problem by forming the knife edges 208 as extensions of the inner walls of the cavities 206, so that the knife edges 208 effectively represent continuations of the cavities 206. This geometry can be seen in the expanded section of FIG. 2. The interior geometry of the cell cavity 206 is thereby smoothly extended until the gasket-iris 106 is encountered by the knife edge 208.

(19) Brazeless assemblies in embodiments of the present invention can be used for ultra-relativistic accelerating structures with identical cells, as shown in FIGS. 1-3 as well as in low energy accelerating structures with irregular cell lengths which accommodate the increase in particle speed as it gains energy. In various embodiments, as shown in FIG. 3, a flange-cell assembly 100 is constructed by successively bolting the flange-cells 102, 104 to each other. In other embodiments, larger groups of cells or even the entire assembly may be assembled in a single step.

(20) While the flange-cells 102, 104 and copper gaskets 106 in the embodiment of FIGS. 1-3 have relatively simple geometries, the flanges and flange-cells in other embodiments have more sophisticated configurations. With reference to FIGS. 4A-4C, in some embodiments the flange-cells include additional passages or recesses that provide, for example, water cooling channels of complicated geometry (FIG. 4A). Magnetic focusing configurations can be provided by placing permanent magnets in the recessed volumes or passages so as to form permanent magnet based electron optics elements such as Halbach arrays (FIG. 4B) and/or quadrupoles with or without iron inserts (FIG. 4C). In various embodiments, coils are wound in the recessed volumes or passages of the flange-cells 102, 104. Excess material can also be removed in this manner for weight management. And in some embodiments, effective gamma ray shielding such as lead plates is embedded within recesses or passages provided within the flange-cells, rather than being wrapped around the outer diameter of the structure.

(21) Combinations of cooling, focusing, and/or shielding are provided in various embodiments with much lower costs of manufacture as compared to conventional milling by creating voids and channels in the resonant cells of the accelerating structure.

(22) As is mentioned supra, mode launchers 108 used to deliver RF power into an accelerating waveguide can be made with the same brazeless approach as is used to interconnect the resonant cells 102, 104. This is illustrated in FIG. 5, which is an exploded view of an embodiment similar to FIGS. 1-3. In this embodiment, a mode launcher 108 is machined out of a stainless steel block, and includes an RF flange 500 on the RF side and a flange-cell 502 with a knife edge 208 on the accelerating structure side. The launcher 108 is connected to the accelerating waveguide 100 with a copper gasket-iris 106.

(23) FIG. 6 is a photograph of a test assembly of cells that include joints according to the present invention as well as a traditional conflat joint at the lower end. The assembly was prepared, cut in half, and photographed so as to provide a visual comparison between the brazeless assembly principle of the present invention and a standard conflat vacuum assembly. As can be seen in the figure, a standard conflat flange 600 and gasket 602 can provide a vacuum seal, but there is a gap 604 left between them that will cause breakdown and arcing if RF is introduced. A flange-cell 104 of the present invention together with a gasket-iris 106 seals vacuum in the same way the conflat does, but without creating a gap 606. FIG. 6 includes a stainless steel flange-cell that has not been plated 608, a stainless steel cell that has been freshly plated with copper 610, and a flange-cell that has been copper plated and hydrogen burn tested 612. No bubbles or copper delamination is observed on the burn-tested cell, even though it was cycled to a temperature of 500 C in a hydrogen furnace.

(24) FIG. 7 is a graph showing experimental results from tests performed on a 5-cell accelerating structure in an embodiment of the present invention. A set of 5 stainless steel flange-cells was produced along with a set of 5 copper gasket-irises. The structure was bolted together and measured on a network analyzer prior to (700) and following (702) copper plating of the flange-cells. In the zero-transmission measurement, 5 resonances were observed in each case, with quality factors (Q's) as indicated in the figure. After copper plating, the quality factors of the resonances were found to be identical to those of a brazed solid copper structure of similar dimensions.

(25) The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application.

(26) The invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein and is not inherently necessary. However, this specification is not intended to be exhaustive. Although the present application is shown in a limited number of forms, the scope of the invention is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof. One of ordinary skill in the art should appreciate after learning the teachings related to the claimed subject matter contained in the foregoing description that many modifications and variations are possible in light of this disclosure. Accordingly, the claimed subject matter includes any combination of the above-described elements in all possible variations thereof, unless otherwise indicated herein or otherwise clearly contradicted by context. In particular, the limitations presented in dependent claims below can be combined with their corresponding independent claims in any number and in any order without departing from the scope of this disclosure, unless the dependent claims are logically incompatible with each other.