Superconducting resonant frequency cavities, related components, and fabrication methods thereof

Abstract

This disclosure relates to an apparatus or device commonly referred to as a superconducting resonant cavity or Radio Frequency (SRF) cavity, the related components associated with the SRF Cavity, and various fabrication methods thereof. SRF cavities are used to accelerate charged particles to high energies and high velocities and various fabrication methods of said SRF apparatus. SRF cavities are used in a wide variety of applications ranging from particle accelerators, to light sources for spectroscopy, to linear accelerators for the transmutation of nuclear waste and the advanced production of tritium, to NMR and MRI imaging and spectroscopy, and proton radiation therapy for the treatment of certain types of cancer. This disclosure further describes a wide variety of means and methods for: a) the fabrication of SRF cavity structures, b) at least one or more film deposition means, and c) at least one or more heat treating means using either the Bronze Route or Internal Tin processes to form the superconducting Nb.sub.3Sn phase on the interior surface of an SRF cavity via a solid state diffusion reaction process.

Claims

1. A method of forming a niobium-tin superconducting radio frequency device having a cavity, the method comprising the steps of: forming a unified bulk structure formed of a material including bronze, forming a niobium layer on an interior of the unified bulk structure, and heat treating the unified bulk structure and niobium layer to form a superconducting niobium-tin layer on the interior of the unified bulk structure.

2. The method of claim 1, wherein the unified bulk structure includes a plurality of cavities disposed in a series.

3. The method of claim 1, further comprising cleaning the unified bulk structure prior to forming the niobium layer, using mechanical and chemical polishing.

4. The method of claim 1, wherein the unified bulk structure is formed completely of bronze.

5. The method of claim 1, wherein the superconducting niobium-tin layer is formed with a substantially stoichiometric Nb.sub.3Sn composition.

6. The method of claim 1, wherein the step of forming the unified bulk structure is performed by melt casting.

7. The method of claim 1, wherein the step of forming the unified bulk structure is performed by 3D printing.

8. The method of claim 1, wherein the step of forming the unified bulk structure is performed by melt casting in a 3D printed sand mold.

9. The method of claim 1, wherein the step of forming the niobium layer is performed by sputtering.

10. The method of claim 1, wherein the niobium layer is doped with at least one of titanium, tantalum, or vanadium.

11. A method of forming a niobium-tin superconducting radio frequency device having a cavity, the method comprising the steps of: forming a unified bulk structure formed of a material including copper, forming a tin layer on an interior of the unified bulk structure, forming a copper layer on the tin layer, cleaning the copper layer using mechanical and chemical polishing, forming a niobium layer on the cleaned copper layer, and heat treating the bulk structure, tin layer, copper layer, and niobium layer to form a superconducting niobium-tin layer on the interior of the unified bulk structure.

12. The method of claim 11, wherein the unified bulk structure is formed completely of copper.

13. The method of claim 11, wherein the superconducting niobium-tin layer is formed with a substantially stoichiometric Nb.sub.3Sn composition.

14. The method of claim 11, wherein the step of forming the unified bulk structure is performed by melt casting.

15. The method of claim 11, wherein the step of forming the unified bulk structure is performed by melt casting in a 3D printed sand mold.

16. The method of claim 11, wherein the step of forming the unified bulk structure is performed by 3D printing.

17. The method of claim 11, wherein the steps of forming the tin layer, the copper layer, and the niobium layer are performed by sputtering.

18. The method of claim 11, wherein the niobium layer is doped with at least one of titanium, tantalum, or vanadium.

19. A method of forming a niobium-tin superconducting radio frequency device having a plurality of cavities disposed in a series, the method comprising the steps of: forming a unified bulk structure by, 3D printing a sand mold of the device, and melt casting copper in the mold to form the unified bulk structure, forming a niobium layer on an interior of the unified bulk structure, and heat treating the unified bulk structure and niobium layer to form a superconducting niobium-tin layer on the interior of the unified bulk structure.

20. The method of claim 19, wherein the unified bulk structure is formed completely of copper.

Description

DRAWINGS

(1) Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:

(2) FIG. 1 depicts the operation of a single cell resonant cavity, according to an embodiment of the present disclosure.

(3) FIG. 2 depicts three-dimensional CAD drawing views of a single cell SRF cavity, depicting both interior and exterior views, according to an embodiment of the present disclosure.

(4) FIG. 3 depicts an in-situ bronze route Nb.sub.3Sn fabrication method, according to an embodiment of the present disclosure.

(5) FIG. 4 depicts an ex-situ bronze route Nb.sub.3Sn fabrication method, according to an embodiment of the present disclosure.

(6) FIG. 5 depicts an in-situ internal tin Nb.sub.3Sn fabrication method, according to an embodiment of the present disclosure.

(7) FIG. 6 depicts an ex-situ internal tin Nb.sub.3Sn fabrication method, according to an embodiment of the present disclosure.

(8) FIG. 7 depicts an internal tin Nb.sub.3Sn fabrication method with barrier film, according to an embodiment of the present disclosure.

(9) FIG. 8 depicts a two-dimensional cross-section of bronze route Nb.sub.3Sn layer, according to an embodiment of the present disclosure.

(10) FIG. 9 depicts a two-dimensional cross-section of internal tin Nb.sub.3Sn layer, according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF INVENTION

(11) SRF Cavity Overview

(12) A simple schematic of a typical single cell SRF cavity is shown in FIG. 1. Some common features of an SRF cavity include: cavity equator (10), the magnetic field (20) created by the SRF cavity when in operation, the charged particle beam that traverse along the SRF cavity axis (40), the cavity iris (50) which helps to define the shape or curvature of elliptically shaped cavities and the resulting electric field (60) that is used to accelerate the various types of charge particles. Shown in the upper half of FIG. 2 is 3D CAD drawing of a single cell SRF cavity (70). Shown in the lower half of FIG. 2 is a 3D CAD drawing of a single cell split SRF cavity (80). For a split cavity structure (80), after film deposition on its interior surface, the two halves are joined together to form a single cell SRF cavity structure (70).

(13) Embodiments of the Invention

(14) There are four (4) basic embodiments of this invention that will be described in the detailed description section of this disclosure: 1) A Nb3Sn SRF cavity fabricated via the Bronze Route (BR) using the so-called “in-situ” Nb film deposition process as shown in FIG. 3, 2) a Nb3Sn SRF cavity fabricated via the Bronze Route (BR) using the so-called “ex-situ” Nb film deposition process as shown in FIG. 4, 3) a Nb3Sn SRF cavity fabricated via the Internal-Tin (IT) method using the so-called “in-situ” multi-layer film deposition process as shown in FIG. 5, and finally 4) a Nb3Sn SRF cavity fabricated via the Internal-Tin (IT) method using the so-called “ex-situ” multi-layer film deposition process as shown in FIG. 6. All other embodiments of this invention described in this disclosure are of derivatives of these four basic SRF cavity devices.

(15) Nb3Sn SRF Fabrication Process Steps

(16) Bronze Route Nb3Sn SRF Fabrication Process

(17) Since it is impossible to describe in detail every possible combination and permutation for the Nb3Sn SRF cavity device fabricated via the Bronze Route, the basic fabrication method is comprised of the following high level steps which are shown in FIG. 3 for the in-situ BR method and FIG. 4 for the ex-situ BR fabrication method.

(18) Bulk bronze cavity/scaffold/structure fabricated (90) via low cost process such as AM, melt casting, tube spinning, stamping, punching, forging, etc.

(19) Interior surface preparation, cleaning, and polishing using one or more surface treatments and processes (100).

(20) Deposition of a pure Nb or chemically doped Nb film/coating/layer (approximately 0.05 μm□10 μm thick) on interior surface (110) using one or more film deposition techniques at temperatures ranging from room temperature □˜400° C. for the “ex-situ” process (FIG. 4) or >about 400° C. up to 1000° C. for the “in-situ” process (FIG. 5).

(21) For the ex-situ process, after Nb film deposition at <400° C. an optimized heat treatment (120) at temperature, time, and environment (e g. vacuum, inert gas, reducing gas, etc.) for the solid state diffusion reaction (130) to form the stoichiometric (or near stoichiometric) superconducting Nb3Sn phase

(22) Partially or fully Coat or cover the interior and/or exterior cavity surface (140) with high thermal conductivity material (e.g. Cu, Ag, Au, etc.). This step may be performed prior to the Nb film deposition as well.

(23) Internal-Tin Nb3Sn SRF Fabrication Process

(24) For the Nb3Sn SRF cavity device fabricated via the Internal-Tin fabrication method, a more complex process involving multiple film coatings (i.e. multi-layers) on deposited on the interior surface of the bulk Cu cavity is required. The sequence and thickness of each successive film layer requires optimization depending upon the type of film deposition processing and heat treatment parameters. Since it is impossible to describe in detail every possible combination and permutation for the Nb3Sn SRF device fabrication using the IT method, some basic high level steps are shown in Figure S for the in-situ IT process and FIG. 6 for the ex-situ IT process:

(25) Bulk Cu cavity/cavity/scaffold/structure/structure fabricated (150) via low cost process such as AM, melt casting, tube spinning, stamping, punching, forging, etc.

(26) Interior surface preparation, cleaning, and polishing using one or more surface treatments (100) of bulk Cu cavity structure (150)

(27) Deposition of thin chemical barrier film or coating (e.g. Ta, Nb, V, etc.) on the interior surface (180) of the bulk Cu cavity structure (150) using one or more film deposition techniques.

(28) Deposition of Sn film/coating/layer (160) on interior surface of the bulk Cu cavity (150) (or on top of the (e.g. Ta) barrier layer (180) described above using one or more film deposition techniques.

(29) The thickness of the Sn layer (160) will depend upon many factors including whether a chemical barrier layer (180) was included in the multi-layer film/coating/layer structure.

(30) Deposition of an additional Cu film/coating/layer (170) (about 0.1->20 μm thick) cm top of the underlying Sn layer using one or more film deposition techniques Deposition of Nb film/coating/layer (110) (0.05 μm.fwdarw.10 μm thick) on the top outermost surface of the thin underlying Cu film/coating/layer (170) using one or more film deposition techniques Optimized heat treatment (120) at temperature, time, environment (vacuum, inert gas, reducing environment, etc.) for the solid state diffusion reaction (130) to form the stoichiometric (or near stoichiometric) superconducting Nb3Sn phase

(31) Bulk Cavity, Cavity/Scaffold/Structure

(32) 3D Printing or Additive Manufacturing

(33) Next, we describe the fabrication process of the basic underling physical structure of the Nb3Sn SRF cavity itself. The bulk cavity/scaffold/structure (90) or (150) is the pressure vessel that supports the atmospheric pressure on the outside of the Nb3Sn SRF cavity from its vacuum environment of its interior. Two of the four Nb3Sn SRF cavity embodiments use bronze (90) as the cavity/scaffold/structure material (i.e. Bronze Route), while the remaining two Nb3Sn SRF embodiments that use the IT fabrication process use pure Cu or nearly pure Cu as its bulk cavity/scaffold/structure (150). Please note that the terms bulk cavity, scaffold, and structure are used interchangeably throughout this disclosure for the purposes of clarity and enablement.

(34) As stated previously, whether fabricated from bronze or Cu, there are a plethora of methods that one could implement to fabricate the bulk cavity/scaffold/structure (90) or (150); however, two fabrication methods are described in more detail for the purposes of clarity and enablement: a) 3D Printing (aka AM) and b) Melt Casting, but are not meant to limit the type of fabrication method or methods for the Nb3Sn SRF invention described in this disclosure. The first low cost SRF cavity/scaffold/structure (90) or (150) fabrication method described in this disclosure use the direct printing of metallic particles. Some common types of 3D printers for the direct printing of metals are the wire and granular/powder type include but are not limited to: direct metal laser sintering (DMLS), electron beam melting (EBM), electron beam freeform (EBF), selective laser melting (SLM), and selective laser sintering (SLS), among other types of metal 3D printers.

(35) Another 3D printing technique that is particular advantageous to some of the embodiments described in this disclosure is a technique known as indirect 3D printing, or more commonly referred to as Indirect 3DP. Indirect 3DP is a unique indirect 3D printing process developed by the ExOne Corporation of St. Clairsville, Ohio that is based upon “ink-spray or ink-jet” technology. Indirect-3DP works by utilizing inkjet deposition of “binders” into a powder bed in the forming process. By using Inkjet in the forming process, the layers of the part can be created rapidly and at high resolution. Furthermore, by fusing the powders using a separate well-regulated heating oven, thermal gradients created within the part can be avoided. In this indirect 3D printing method, the material of interest is loaded into the printer in a powder form, combined with a binding material, and 3D printed using an ink-spray technique. The binding material initially “glues” the powders together and the 3D printed piece is then moved to a separate curing oven. The 3D printed piece is then separately cured at a low temperature (˜150-200° C.) to burn off the “binding” material. There are many types of powders that can be printed using the Indirect 3DP process including but not limited to: metals, insulators, plastics, polymers, ceramics, glasses, wood, and sand, among other types of powders. It is particularly advantageous for some of the embodiments described in this disclosure to use either “sand or ceramic” powders to 3D print molds used for bronze or Cu melt casting of the bulk cavity/scaffold/structure (90) or (150) or “metal” powers for the 3D printing of normal or superconducting cavities and their related components. The porosity of the 3D printed object after binder burn off typically varies between about 20 to 40% (i.e. 60-80% part density), although other porosities of the Indirect 3DP printed object are possible. If the 3D printed object is a metal and further densification of the 3D printed metal object is desired (e.g. to improve mechanical strength, enhance thermal conductivity, improve SRF properties, etc), then the 3D printed object can be either: a) sintered a second time at a higher temperature closer to the melting temperature of the metal powder or b) “infiltrated” with another liquid molten metal using an “infiltration” process.

(36) The porosity of the Indirect 3DP printed bronze cavity or cavity component can be reduced, i.e. the SRF apparatus density increased, by sintering the Indirect 3DP cavity or cavity component in a separate curing oven at a temperature close to the melting temperature of the bronze powder.

(37) This will cause the dimensions of the cavity or cavity component to shrink. The amount of dimensional change in the sintered cavity is directly related to its initial starting porosity prior to sintering. The resultant dimensional change in the SRF cavity or cavity component should be considered in the design of the apparatus described in this disclosure.

(38) A second method used to increase the apparatus density (i.e. reduce porosity) is to use a molten metal infiltrate to fill the pores of the Indirect 3D printed structure. Serenedipously, a common molten metal “infiltrate” used in the Indirect 3DP process is bronze (Cu:Sn), which is particularly advantageous to the two embodiments that use bronze as its underlying cavity/scaffold/structure (90).

(39) Melt Casting of the Invention

(40) Another low cost fabrication method for the bulk cavity/scaffold/structure is that of melt casting. Metal casting is one of the oldest and most commonly used metallurgical fabrication processes for a wide variety of devices. For the purposes of enablement in this disclosure, bronze (90) and copper (150) casting is particularly advantageous for the four embodiments described herein for the Nb3Sn SRF device

(41) Both bronze and Cu melt casting for example is a low cost, well understood, metallurgical fabrication techniques which dates back millennia. Using the melt casting technique applied to the apparatus described in this disclosure, bronze with a Cu content typically ranging from 75% to 92% and its corresponding Sn content proportionally ranging from 25% to 8% is casted into the desired shape of the cavity (e.g. 5-cell or 9-cell elliptical cavity, crab cavity, spoke cavity, etc.) or a cavity related component (e.g. RF coupler). Other Cu/Sn ratios are also possible including pure or nearly pure Cu of example in the internal-tin solid state diffusion reaction process.

(42) Split Cavity Fabrication

(43) ASRF cavity is fabricated by depositing/coating a film on the interior surface of a split cavity (80) scaffold/structure and then after film deposition joining the two halves of the cavity together. Once the two halves are joined (70), the SRF cavity can be heat treated to form the correct superconducting phase or simply further enhance its RF properties. The advantages of the split SRF cavity fabrication technique is that depending upon the film deposition technique, it may be easier to coat the interior surface of the scaffold when in its split geometry rather than its closed cavity configuration.

(44) This is not the case for all thin film deposition means such as electroplating, where it is advantageous to fabricate the cavity scaffold/structure as a whole unit, thereby avoiding the subsequent joining of the two halves. When using an electroplating film deposing means, the cleaned and polished interior surface of the cavity scaffold/structure can be electroplated with one or more films and subsequently heat treated via the ex-situ process to form the correct Nb3Sn superconducting phase.

(45) Interior Surface Preparation

(46) Regardless of the fabrication method or material bronze (90) or Cu (150) selected for the bulk cavity/scaffold/structure, the interior surface for all four embodiments of this invention will need some type cleaning and polishing (100) prior to film/coating/layer deposition. The amount and type of surface preparation for the interior surface of the bulk cavity/scaffold/structure will depend on the type of bulk cavity/scaffold/structure fabrication method. The interior surface of the bulk cavity/scaffold/structure and/or cavity component is typically polished (100) using one or more of the surface treatments described in section 8.5 or similar. For some of the embodiments described in this disclosure it is important that the surface roughness (Ra) of the interior wall of the cavity/scaffold/structure is <1-5 nm for optimal Nb film deposition.

(47) Solid State Diffusion Reaction Process

(48) For each of the four Nb3Sn SRF cavity embodiments described in this disclosure, namely a) in-situ BR, b) ex-situ BR, c) in-situ IT, and d) ex-situ IT, four different diffusion reaction processes (130) are utilized to form the stoichiometric or near stoichiometric Nb3Sn superconducting phase with each requiring its own unique optimized heat treatment cycle (120). For the purposes of brevity, clarity, and enablement, an optimized heat treatment cycle is defined as the furnace ramp rate (in ° C./hr), furnace soak temperature (in ° C.) and time, and furnace environment (e.g. vacuum, inert gas species, etc.) to achieve an optimized performance of the SRF device. For the purposes brevity and invention enablement, a high level overview of these diffusion reaction processes are described below; however, it is recognized by one skilled in the art that there may exist a plethora of heat treatment cycles each requiring multiple soak temperatures and multiple dwell times in order to optimize performance.

(49) In-situ Nb3Sn Bronze Route (BR) Fabrication

(50) In one embodiment, the Nb3Sn SRF device is fabricated using the in-situ Bronze Route fabrication method as shown in FIG. 3. For this embodiment, the polished and cleaned interior surface temperature of the bulk bronze cavity (90) is held above about 400° C. during Nb film/coating/layer deposition. A thin Nb film/coating/layer (110) is deposited on the interior surface of the bulk cavity/scaffold/structure or cavity related component at surface temperature ranging anywhere from about 400° C. to 1000° C. Lower temperatures tend to form smaller grains sizes whereas higher temperatures tend to form larger grains sizes. Larger grain sizes may be preferred to improve the RF properties of the SRF cavity. There are many films deposition/coating techniques that can be used to deposit the Nb films including but not limited to: RF/DC sputtering, CVD, MOCVD, laser ablation, ECR, HIPMS, sol-gel, electroplating, among other thin film deposition techniques. When the Nb films are deposited at these high surface temperatures, the superconducting Nb3Sn phase begins to form immediately. Using the in-situ BR process, the resultant Nb3Sn particle size typically varies between ˜20-50 nm. The optimal temperature/time of the bulk bronze cavity/scaffold/structure during Nb film deposition/coating for the in-situ Nb3Sn fabrication method can be determined by the RF property desired. A 2D sketch of the cross section of an SRF cavity surface using the BR fabrication process is shown in FIG. 8.

(51) Ex-Situ Nb3Sn Bronze Route (BR) Fabrication

(52) In a second embodiment, the Nb3Sn SRF device is fabricated using the ex-situ Bronze Route fabrication method as shown in FIG. 4. Using the ex-situ BR fabrication technique, the surface temperature of the bronze interior wall is held below about 400° C. all the way down to room temperature. At these lower surface temperatures, the as deposited Nb film (110) does not immediately “react” with the bronze surface of the bulk cavity/scaffold/structure (90). It is common not to deposit the Nb films on the bronze surface at room temperature because of the CTE mismatch between the brittle Nb3Sn superconducting phase and the underlying bronze cavity/scaffold/structure. This CTE mismatch can be mitigated by depositing/coating the interior wall of the cavity at temperatures higher than room temperature, but lower than the reaction temperature used in the “in-situ” process described above. The Nb film coated bronze cavity is then placed in separate heat treatment oven (120). Common heat treatment temperatures can range from as low as ˜400° C.-up to 1000° C. Heat treatment times can vary from just a few hours to hundreds of hours depending upon the furnace soak temperature. Lower furnace soak temperatures and longer dwell times tend to form smaller Nb3Sn grain sizes while higher furnace soak temperatures and shorter dwell times tend to form larger Nb3Sn grain sizes. Smaller Nb3Sn grain sizes tend to optimize DC superconducting properties in the Vortex state, which has been beneficial to superconducting wire properties, while larger Nb3Sn grain sizes tend to optimize RF properties in the Meissner state of a superconductor, which is beneficial to SRF cavities.

(53) Sometimes multiple furnace soak temperatures and dwell times are required for optimized properties. For example, it is common in Nb3Sn wire fabrication via the BR method to use a two-step diffusion reaction process. The first step in the heat treatment cycle is typically about a 100-200 hour soak at 575° C. and with a slow ramp at 5° C./hr to a second soak at 650° C.-700° C. for 100 hours.

(54) Using this ex-situ technique, the Sn from the high Cu content bronze then slowly diffuses (130) into the thin Nb film forming the stoichiometric (or near stoichiometric) superconducting Nb3Sn phase through a solid state diffusion reaction process known as the Bronze Route (BR). The time and temperature profile as well as the type of environment (e.g. vacuum, inert gas, reducing, etc.) during the heat treatment cycle for this solid state diffusion reaction process (130) can be adjusted as necessary to maximize the RF performance and properties of the bulk cavity/scaffold/structure or cavity related component. Using the ex-situ fabrication method, the resultant Nb3Sn particle size is somewhat larger than the in-situ method typically ranging between ˜50-100 nm. The length scale over which the Sn will diffuse from the underlying bronze cavity/scaffold/structure is typically less than 0.5-5 μm, which is more than adequate for SRF cavities. A 2D sketch of the cross section of an SRF cavity surface using the BR fabrication process is shown in FIG. 8.

(55) In-situ and Ex-Situ Nb3Sn Internal-Tin (IT) Fabrication

(56) In the third and fourth embodiments of the invention described in this disclosure, the Nb3Sn SRF device is fabricated using the either “in-situ” or “ex-situ” Internal-Tin fabrication method as shown in FIGS. 6 and 7, respectively. As stated previously, the IT Nb3Sn fabrication method is far more complex in terms of its multi-layer film deposition processes, more complex phase diagram, and its more involved heat treatment cycle. There are several major differences between the BR and IT Nb3Sn SRF fabrication methods including: a) bulk cavity/scaffold/structure (150), b) multi-layer film deposition process, and c) heat treatment cycle (120). The first major difference between the BR and IT Nb3Sn fabrication methods is the material comprising the bulk cavity/scaffold/structure (150). For the IT Nb3Sn fabrication method, the bulk cavity/scaffold/structure is pure (or nearly pure) Cu (150) and not bronze (Cu—Sn). The Cu cavity/scaffold/structure is advantageous because of its higher thermal conductivity (see also section 8.6), although its mechanical strength is somewhat weaker requiring a thicker wall to compensate for the weaker tensile strength of Cu vs. bronze. Unlike the BR method which involves the deposition/coating of just one type of film (i.e. pure Nb or chemically doped Nb), the IT fabrication method involves the deposition of a series of multiple thin films or coatings on the cleaned and polished (100) interior surface of the bulk Cu cavity/scaffold/structure (150). In these two IT embodiments, multiple films are deposited in series on the interior surface of the surface of the bulk Cu cavity/scaffold/structure (150). The sequence of the deposition/coating/plating of these multiple films is shown in FIGS. 6 and 7. For the IT process, electroplating is a particular simple and straight forward approach to depositing many of the film layers. Each of the multiple films is deposited in succession, with one layer deposited directly on top of the previous layer. There are two different derivatives of these two embodiments: a) a three-layer multiple film structure and b) a four-layer multiple film structure. For clarity and purposes of enablement, the terms layer/film/coating have the same meaning and are used interchangeably thought this disclosure

(57) In the three-layer film derivative of these two IT embodiments, the first layer/film/coating deposited on the interior surface of the bulk Cu cavity/scaffold/structure (150) in a relative thick Sn film ranging in thickness from about 1μ to 100 μm (160). The second layer/film/coating is a thin (0.05-40 μm) Cu film deposited (170) directly on top of the Sn layer/film/coating (160). The third and final layer/film/coating in the three-layer/film/coating derivative is Nb (0.05 μm->10 μm) (110). During the heat treatment (120) a solid state diffusion reaction process (130) occurs, the Sn layer/film/coating (160) diffuses in both directions, i.e. into the thick bulk Cu cavity/scaffold/structure (150) and into the thin Cu layer/film/coating (170) on its top surface.

(58) Eventually the Sn (160) will diffuse (130) into the outermost Nb layer/film/coating (110) forming the desired stoichiometric (or near stoichiometric) Nb3Sn superconducting phase (190).

(59) In the four-layer film derivative of these two IT embodiments, the first layer/film/coating deposited/plated cm the interior surface of the bulk Cu cavity/scaffold/structure (150) in a thin chemical barrier layer/film/coating (180) of either Ta, V, Nb, or some other chemical barrier material. The second layer/film/coating is a relatively thick Sn film (160) on top of the Ta (or equivalent) chemical barrier layer/film/coating (180). The third layer/film/coating is a thin (0.05-20 μm) Cu film (170) deposited/plated directly on top of the Sn layer (160). The fourth and final layer/film/coating in the four-layer film derivative is a thin film of Nb (0.1-10 μm) comprising the outermost layer (110). The advantage of the four-layer derivative versus the three-layer of the two IT embodiments, is that the chemical barrier film/coating/layer (180) on the innermost interior surface of the bulk Cu cavity/scaffold/structure (150) prevents/inhibits the Sn in the second layer/film/coating (160) from diffusing (130) into the bulk Cu cavity/scaffold/structure (150) during heat treatment (120). This preferentially allows the Sn layer/film/coating (160) to diffuse (130) through the Cu layer/film/coating (170) during heat treatment (120) on its surface thereby preferentially promoting the formation of the desired stoichiometric (or near stoichiometric) superconducting Nb3Sn phase (190) on the outermost surface of the multi-layer film coating. The disadvantage of the four-layer approach versus the three-layer is the additional chemical barrier layer/film/coating (180) required on the interior surface of the bulk Cu cavity/scaffold/structure (150), adding unwanted cost and complexity to the IT fabrication process. A 2D sketch of the cross section of an SRF cavity surface using the four-layer IT fabrication process is shown in FIG. 8.

(60) Heat Treatment Means

(61) Two embodiments of the invention described in this disclosure use an “in-situ” heat treatment means (120), where the film or multiple series of films are deposited at elevated temperature greater than about 400° C. directly in the film/coating/layer deposition chamber. At these elevated deposition temperatures, the desired stoichiometric (or near stoichiometric) superconducting Nb3Sn phase (190) can form more rapidly reducing the SRF fabrication time and therefore cost. The other two embodiments of the invention described in this disclosure use an “ex-situ” heat treatment means (120), where the film or multiple series of films are deposited at less than about 400° C. This typically use a separate heat treatment furnace.

(62) The heat treatment means for either the in-situ or ex-situ SRF fabrication method includes but is not limited to: conductive heating, convective heating, radiative heating, non-contact inductive heating, and combinations thereof. During the ex-situ heat treatments it is advantageous to be in an inert, oxygen free, or slightly reducing environment. Typically, the ex-situ heat treatments are performed in either a vacuum furnace or an inert Ar atmosphere.

(63) High Thermal Conductivity Coating of Exterior Surface

(64) An important property for any SRF cavity is to have high thermal conductivity. A high thermal conductivity bulk cavity/scaffold/structure is important in order to aid in the dissipation of heat generated by the BCS losses which are developed by the superconducting material at RF frequencies. Unfortunately, for the two embodiments involving the bulk bronze cavity/scaffold/structure, bronze has a somewhat low thermal conductivity ranging from approximately 10-50 W/m-K depending upon the Cu content at the operating temperatures of interest ˜2 K.fwdarw.4.2K. This low thermal conductivity may be inadequate to remove the heat generated by the BCS losses (or other heat sources) and may need to be improved for stable operation. In order to improve the conductive heat transport properties of the underlying bulk cavity/cavity/scaffold/structure/structure (90), it may be necessary to coat the exterior wall of the bronze casted cavity with a higher thermal conductivity material such as Cu, Sn, or A (140)1. There are many low costs metal coating technologies that could be used to coat the exterior wall of the bronze casted cavity or cavity component including but not limited to: electro-plating, thermal evaporation, RF/DC sputtering, among other types of metal coating techniques.

(65) While the disclosure has been particularly shown and described with reference to various embodiments described herein, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the disclosure. The foregoing has outlined some of the more pertinent objects of the disclosure. These objects should be construed to be merely illustrative of some of the more prominent features and application of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure.

(66) Accordingly, a fuller understanding of the invention may be had by referring to the detailed description of the preferred embodiments in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.