Method of manufacturing superconductive and / or normally-conductive particle- accelerating cavities, and accelerating cavities obtained from said method

Abstract

Method of manufacturing a superconductive or normally-conductive particle-accelerating cavity, comprising: a step of wire printing, followed by a step of finishing the inner surface of said cavity.

Description

[0001] TITLE:

[0002] “Method of manufacturing superconductive and / or normally-conductive particleaccelerating cavities, and accelerating cavities obtained from said method”.

[0003] DESCRIPTION

[0004] Field of the invention.

[0005] The present invention relates to a method of manufacturing superconductive and / or normally-conductive particle-accelerating cavities, as well as to accelerating cavities obtained from said method.

[0006] State of the art.

[0007] Superconductive and / or normally conductive particle-accelerating cavities are known in the art.

[0008] One problem that can be observed in the production of said superconductive and / or normally conductive particle-accelerating cavities is that they cannot be created without surface discontinuity.

[0009] Such discontinuity is due to the welded joints between the various sections that make up the final cavity, which in the presence of ultra-high accelerating fields, and may result in the emission of secondary electrons that, as they fall onto the cavity surface, cause localized heating leading to degraded superconductive performance.

[0010] According to a known technique, welded joints are eliminated . More specifically, this is the spinning technique that involves seamless spinning from a sheet or tube, without removing any material, by forming the sheet or tube itself against a mandrel of the desired shape, which is then removed. Furthermore, the internal finish must be brought to specification because the process itself produces surface defects. Such a technique has led to cavities with better performance and a higher quality factor, but nevertheless it can be further improved.

[0011] EP0630172A1 (Application 93830260.1), by the present Applicant, proposes a method of producing accelerating cavities of the jointless type by using a die that can be disassembled into sectors and a spinning forming technique starting from a sheet.

[0012] Another problem suffered by particle-accelerating cavities obtained from known methods lies in the roughness of the inner surface, which requires chemical and electrochemical post-treatments to reduce or eliminate such roughness, resulting in higher costs and longer production times.

[0013] It is preferable that the inner surface of the superconductive and / or normally-conductive accelerating cavity is smooth, so as to prevent any “tip effects” when the cavity is subjected to a strong electric field.

[0014] The publicly available presentation by Mr. Mike Kelly entitled “EM-class Cavity Design, SRF 2013 Tutorial Program “ given on 19-21 September 2013 in Ganil, Caen, provides an overview of the known types of superconductive and normally-conductive accelerating cavities.

[0015] US11202362-B1 describes an electron beam, not laser, wire-printing process. This limits its applicability to vacuum. It also describes a method for creating an Nb3Sn film that involves the interdiffusion of Nb deposited as a thin film on a bronze substrate.

[0016] The publication Mayerhofer et al., “A 3D printed pure copper drift tube linac prototype,” Rev. Scient. Instr., American Instit. of Phisics, vol. 93, no. 2, 22 Feb. 2022, describes the development of a normally conductive drift tube made of pure copper through 3D powder printing on a non-self-supporting bed.

[0017] US9343649-B1 describes a mechanical finishing method using barrel polishing that is not applicable until after the component has been created.

[0018] EP0217127-A2 describes a method for manufacturing superconducting accelerator cavities by forming a hollow aluminium mold with the dimensions and external (not internal) finishes corresponding to those desired for the internal accelerator cavity. Functionalizing thin films are then deposited using PVD technology on the external (not internal) part of the mold. Finally, the aluminium mold is dissolved in concentrated acid solutions.

[0019] The need is felt to propose a technique for manufacturing superconductive and normally- conductive particle-accelerating cavities which represents an improvement over said known techniques and which can solve the above-mentioned problems.

[0020] Summary of the invention.

[0021] It is the object of the present invention to propose a technique for manufacturing superconductive and / or normally-conductive particle-accelerating cavities which represents an improvement over the above-described prior-art techniques.

[0022] The present invention uses the wire printing technique to manufacture superconductive and / or normally-conductive particle-accelerating cavities as an alternative to, and as a future replacement for, the currently known production technique.

[0023] Said technique according to the invention involves forming the accelerating cavity by using the wire printing technique, without requiring the use of a sector die and subsequent finishing of the inner surface during the component fabrication process.

[0024] The invention essentially employs the following production techniques:

[0025] - Forming accelerating cavities and complex accelerator structures by wire printing, using either single-material or multi-material, single-layer or multi-layer wire at atmospheric pressure in inert gas or in a vacuum.

[0026] - Finishing the inner surface of the cavities by using material removal techniques during the fabrication process at atmospheric pressure in inert gas or in a vacuum, as well as chemical or electrochemical processes.

[0027] By combining the component growth step, executed by wire printing, with the finishing step, the invention makes it possible to obtain a cavity with an inner surface having a roughness value as low as a few hundreds of nanometres, thereby reducing to a minimum, unlike the standard procedure, the need for chemical and electrochemical posttreatments.

[0028] Moreover, the elimination of welded joints made possible by the present invention results in cavities having better performance and a higher quality factor.

[0029] The present invention concerns a method of manufacturing a superconductive or normally-conductive particle-accelerating cavity as set out in claim 1.

[0030] Dependent claims 2 to 15 describe some preferred variant embodiments of the method of claim 1.

[0031] The present invention also concerns a superconductive or normally-conductive particle-accelerating cavity obtained from a method according to any one of claims 1 to 15.

[0032] The present invention further concerns the use of the wire printing technique for manufacturing a superconductive or normally-conductive particle-accelerating cavity as set out in claim 17.

[0033] All claims are intended as integral parts of the present description.

[0034] Brief description of the drawings.

[0035] Further objects and advantages of the present invention will become apparent in light of the following detailed description of some exemplary embodiments thereof, provided with reference to the annexed explanatory, but non-limiting, drawings, wherein:

[0036] Figure 1 shows an example of a single-cell elliptic resonant cavity obtained from the method of the present invention;

[0037] Figure 2 shows an example of a multi-cell elliptic resonant cavity obtained from the method of the present invention;

[0038] Figure 3 shows an example of an RFQ (Radio-Frequency Quadrupole) resonant cavity obtained from the method of the present invention;

[0039] Figure 4 shows an example of a QWR (Quarter- Wave Resonator) resonant cavity obtained from the method of the present invention;

[0040] Figure 5 shows a magnified view of the rough surface of the cavity, wherein the higher dashed lines represent the greater roughness prior to surface finishing, the lower dashed lines represent the reduced roughness obtained after material removal, and the continuous profile under the dashed lines represents the roughness further reduced by chemical and electrochemical finishing;

[0041] Figures 6a, 6b and 6c show a further representation of the three steps of Figure 5.

[0042] Detailed description of some embodiments of the invention.

[0043] The invention proposes the introduction of the wire printing technique as an alternative to, and as a future replacement for, the standard technique for manufacturing superconductive and / or normally conductive particle-accelerating cavities.

[0044] Wire printing, when used in combination with material removal and inner surface finishing during the fabrication process by combining a wire printer with a mechanical arm, makes it possible to overcome the surface finishing problems that can be observed when producing jointless cavities by means of the above-described known spinning technique. Furthermore, it also reduces production costs and times.

[0045] In addition, wire printing also makes it possible to re-scale this technique for larger cavities, which is a typical limitation of the jointless spinning production technique. In known cases, spinning a 1.3GHZ cavity requires an initial plate having a 400mm diameter, and spinning a 400MHz cavity requires a plate having a lm diameter, while larger cavities are very difficult, if not impossible at all, to make.

[0046] Within the scope of the present invention, elliptic cavities obtained by spinning (plate turning) range from the smallest one (6GHz) with a cell diameter of approximately 46 mm to the largest one (400 MHz) with a cell diameter of approximately 693 mm. Figures 1, 2, 3 and 4 show some examples of accelerating cavities obtained from the method of the present invention, i.e. a single-cell elliptic resonant cavity, a multi-cell elliptic resonant cavity, an RFQ (Radio-Frequency Quadrupole) resonant cavity, and a QWR (Quarter- Wave Resonator) resonant cavity. The shape and use of said cavities are known.

[0047] One example of a wire printing machine that can be used in the present invention is described in EP3993943 B1, which discloses a multi-mode laser device that configures off-axis, solid-state diode or diode-pumped lasers into an array to perform precision controlled, direct metal deposition printing, cladding, laser welding, laser cutting, laser texturing and laser polishing through a single device. Dual-mode printing, cladding and welding capability using metal wire and powder feedstock sources in the same device is provided with in-line control, precision wire feed driver / controller, adjustable shield gas diffuser, and nozzles tailored to wire feedstock diameter.

[0048] Therefore, this machinery provides wire printing by laser melting in inert environments at atmospheric pressure, and uses a robotic arm to control the growth head and a computerized numerical control machine for material removal.

[0049] According to some variants of the invention, the cavity is manufactured by wire printing from a single material, wherein the wire is made either of pure metal, such as copper, niobium, aluminium, or metal alloy, such as NbsSn, NbTi, with ultra-high purity, in inert environments at atmospheric pressure (like the above-described machinery) or in a vacuum.

[0050] According to other variants of the invention, the cavity is made from multiple materials, including different massive and superficial materials, by wire printing and thin- film deposition.

[0051] Thin-film deposition provides a surface treatment by means of physical vapour deposition processes applying a functionalizing thin film (e.g. Niobium, NbTi, NbsSn, etc.).

[0052] In each one of the above cases, the vacuum chamber is pumped to a vacuum by means of pumping units in order to reach a basic vacuum in molecular regimen of less than 10'6mbar. It is preferable that the vacuum chamber is made of a material with a low degassing rate, e.g. AISI 304 or 316 steel.

[0053] In order to prevent the printed materials from being contaminated, it is preferable that the pumping units are free from lubricating oil (dry pumps).

[0054] More particularly, one of the following examples of creation of particleaccelerating cavities can be implemented.

[0055] When one basic massive material is used for said cavity (single-material cavity):

[0056] - Forming the accelerating cavity, which is a complex-shape component of a particle accelerator, by wire printing using pure or alloy material (e.g. copper, niobium, aluminium, or alloys thereof).

[0057] - Wire printing involves several passes to increase the thickness of the grown wall; the component may be formed either by means of multiple passes of a single material (e.g. Copper, Niobium, Nb3Sn) or by means of multiple passes with a change of material at the n-th pass (n is defined by the thickness reached by wire or multi-layer printing (e.g. n layers of Niobium / n layers of Tin / n layers of Niobium / n layers of Tin).

[0058] Inner finishing by using per se known material removal techniques during the component fabrication process (guided by the robotized arm included in the abovedescribed machine) at atmospheric pressure in inert gas or in a vacuum.

[0059] Inner surface finishing treatment (much less invasive than the one required by the standard process or by powder-based 3D printing) through chemical processes (e.g. SUBU5, BCP) or electrochemical processes (e.g. Electropolishing, PEP).

[0060] The preferred materials for single-material cavities are:

[0061] Copper, Niobium, Aluminium, and alloys thereof, Nb3SN, NbTi.

[0062] When different massive and superficial materials are used for said cavity (wire printing to form a base, plus deposition of a thin film as a functionalizing layer):

[0063] - Forming the accelerating cavity, which is a complex-shape component of a particle accelerator, by wire printing using pure or alloy material (e.g. copper, niobium, aluminium, or alloys thereof).

[0064] Inner finishing by using per se known material removal techniques during the component fabrication process at atmospheric pressure in inert gas or in a vacuum. Inner surface finishing treatment (much less invasive than the one required by the standard process or by powder-based 3D printing) through per se known chemical processes (e.g. SUBU5, BCP) or electrochemical processes (e.g. Electropolishing, Plasma Electrolytic Polishing (PEP)).

[0065] Inner surface treatment by means of per se known physical vapour deposition processes applying a functionalizing thin film layer (e.g. Niobium, NbTi, Nb3Sn, etc.).

[0066] The preferred materials for multi-material cavities are:

[0067] Massive base (wire printing): Copper, Niobium, Aluminium, or alloys thereof.

[0068] Thin film applied by PVD (Physical Vapour Deposition): Nb, NbTi, Nb3Sn, V3Si, etc.

[0069] In the above cases, a finishing treatment may optionally be applied also to the outer surface through the use of techniques similar to those employed for inner finishing.

[0070] Figure 5 shows a magnified view of the rough surface of the cavity, wherein the higher dashed lines represent the greater roughness prior to surface finishing, the lower dashed lines represent the reduced roughness obtained after material removal, and the continuous profile under the dashed lines represents the roughness further reduced by chemical and electrochemical finishing.

[0071] Figures 6a, 6b and 6c show a further representation of the three steps of Figure 5.

[0072] As described above, the forming technique of the invention can be used for both superconductive cavities and normally-conductive cavities (copper or aluminium base) with complex shapes that cannot be obtained in a single piece.

[0073] In conclusion, the invention makes it possible to create a jointless cavity having a complex shape, with an inner surface finishing that reduces the need for chemical and electrochemical post-treatments.

[0074] The above-described non -limiting examples may be subject to further variations without however departing from the protection scope of the present invention, including all equivalent embodiments known to a person skilled in the art.

[0075] The elements and features shown in the various preferred embodiments may be combined together without however departing from the protection scope of the present invention.

[0076] In light of the above description, those skilled in the art will be able to produce the subject of the invention without introducing any further construction details.

Claims

CLAIMS1. Method of manufacturing a superconductive or normally-conductive particle-accelerating cavity, comprising:- a step of wire printing;- a step of finishing the inner surface of said cavity, said step of finishing being performed during said step of wire printing.

2. Method as in claim 1, wherein said step of finishing the inner surface includes:- removal of material at atmospheric pressure in inert gas or in a vacuum;- subsequent inner surface finishing by means of chemical or electrochemical processes.

3. Method as in claim 1 or 2, wherein said cavity is a single-material one, said wire being made of pure-metal or alloy material.

4. Method as in claim 3, wherein said wire printing involves several passes in the form of either multiple passes of a single material or multiple passes with a change of material at the n-th pass.

5. Method as in claim 3, wherein said single material is Copper, or Niobium, or Aluminium, or alloys thereof, or Nb3Sn, or NbTi.

6. Method as in claim 1 or 2, wherein said cavity is a multi-material one, said wire being made of different massive and superficial pure or alloy materials.

7. Method as in claim 6, wherein said multi-material is Copper, or Niobium, or Aluminium, or alloys thereof, or NbTi, or Nb3Sn, or V3Si.

8. Method as in claim 2 and 6, comprising a further step of inner surface treatment through processes of physical vapour deposition, in order to apply a coating layer of functionalizing thin film.

9. Method as in any one of the preceding claims, wherein said cavity is manufactured in an inerting environment at atmospheric pressure, or in a vacuum chamber.

10. Method as in claim 9, wherein said vacuum chamber is made of a material with a low degassing rate.

11. Method as in claim 9, wherein said vacuum chamber is pumped to a vacuum by means of pumping units in order to reach a basic vacuum in molecular regimen of less than 10'6mbar.

12. Method as in claim 11, wherein said pumping units are free from lubricatingoil.

13. Method as in any one of the preceding claims, wherein said accelerating cavity is one of the following types: single-cell elliptic resonant cavity, multi-cell elliptic resonant cavity, RFQ resonant cavity, or QWR resonant cavity.

14. Method as in claim 13, wherein said elliptic cavities have a cell diameter ranging between approximately 46 mm and approximately 693 mm.

15. Method as in any one of the preceding claims, comprising a step of finishing the outer surface of said accelerating cavity.

16. Superconductive or normally-conductive particle-accelerating cavity, obtained by means of a method according to any one of the preceding claims.

17. Use of a wire printing technique for manufacturing a superconductive or normally-conductive particle-accelerating cavity.

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