ED0041324 Rev - Manufacturing Specs 0221825.pdf

Rectangular 3cell Cavity Manufacturing Specification

Author: O. Pronitchev

Document Number: ED0041324

SQMS

Document Title: Rectangular 3Cell Cavity Manufacturing Specification

Document Number: ED0041324 Rev -

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Document Approval Date Approved Originator O. Pronitchev As in Teamcenter Reviewer tbd As in Teamcenter Approver tbd As in Teamcenter

Revision History Author Revision Date Description of Change

O. Pronitchev 18 February 2025 Initial release

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Table of Contents 1 Introduction 4

2 Scope of Work 5

2.1 Fabrication Plan 5

2.2 Quality Assurance Plan 6

2.3 Schedule 6

3 Fabrication Drawings 7

4 Supply of Materials 8

5 Production of Component Parts 9

6 Welding of the Cavity 10

7 Quality Control, Mechanical Measurements, and Inspection 11

8 Serial Numbers 12

9 Cleaning, Packaging, and Shipping 13

10 Appendix 14

10.1 Visual inspection of components 14

10.2 Ultrasonic Cleaning of Components 14

10.3 Electron-Beam Welding Preparation 14

10.4 Electron-Beam Welding Conditions 15

10.5 Handling and Storage of Components 15

10.6 Polishing 16

10.7 Development of Electron-Beam Welding Parameters 16

11 Design Model 18

11.1 PROVIDED BY FNAL: 18

11.2 REVIEW OF THE DESIGN: 18

12 Acceptance of bare cavities 19

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1 Introduction

This document describes the required specifications and conditions for the fabrication of Rectangular 3Cell superconducting RF (SRF) cavities (Figure 1).

SRF cavities are fabricated by joining machined niobium components via the method of electron-beam (EB) welding. The shape of the cavity components inner surface is designed so that the welded cells will electrically resonate at a precise frequency.

Mechanical tolerances are strict. Adherence to established procedures is essential to avoid contamination during fabrication.

Throughout this document, Fermi National Accelerator Laboratory shall be referred to as “FNAL” and cavity manufacturing companies or collaborator will be referred to as “the fabricator”. FNAL drawing numbers start with letter F.

Figure 1. Rectangular 3Cell SRF Cavity

In addition to the specifications provided in this document, the notes and specifications mentioned in the cavity drawing, F10239301 apply to this procurement. In case of discrepancy between this document and the drawing, the drawing will apply.

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2 Scope of Work

The fabricator shall:

1. Develop their own fabrication drawings from the attached FNAL cavity drawing,

2. Design and fabricate all required dies, tooling, and welding fixtures,

3. Develop the required EB welding parameters,

4. Perform testing at their facility in accordance with this specification,

5. Fabricate and deliver [number specified on PO] 3cell SRF cavities in accordance with the requirements detailed in this document,

6. Supply all documentation required in this specification.

The fabricator shall provide all supervision, engineering, necessary materials (Niobium will be provided to the fabricator depending on the PO terms), labor, QC inspections, and other services necessary to fabricate the cavities. All necessary facilities (e.g., buildings, machine shop, clean room, ultra-pure water system, ultrasonic cleaning, chemical etching, devices for mechanical inspection) shall be the responsibility of the fabricator unless otherwise specified. All tooling and welding fixtures shall become the property of FNAL or collaborating institute upon completion of the fabrication.

A Traveler for each cavity containing records of all fabrication, measurements and inspections shall be submitted to FNAL with the completed cavities. FNAL approval of the proposed Traveler format is required prior to the start of work.

FNAL reserves the right to observe all processes, and to invite the advice and collaboration of established experts in the field.

2.1 Fabrication Plan

The fabricator shall submit a Fabrication Plan to FNAL for acceptance by the date specified in the Purchase Order (contract). The Plan shall identify and describe all aspects of the work to be executed from the point of initial inspection of the niobium material through delivery of the cavities. The Fabrication Plan shall include the following:

• General overview of planned work process flow.

• Description of the forming and machining process for each part.

• Proposed geometry of weld preparations for each joint.

• Procedures for cleaning and chemical etching of components to prepare for welding.

• General procedures for electron beam (EB) welding (e.g., vacuum level, cool down process, etc.).

• Procedures and design of proposed vessels for storage of parts and for transportation of parts to the welding site.

• Design of shipping container and procedure for final packaging of each cavity.

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FNAL approval of the Fabrication Plan is required prior to the start of work.

2.2 Quality Assurance Plan

The fabricator shall submit a Quality Assurance (QA) Plan to FNAL for acceptance by the date specified or as agreed in fabrication plan. The QA Plan shall insure that each device offered for acceptance conforms to the requirements listed in this document. The requirements of ISO 9001:2008 shall be considered as a guideline for the QA Plan. The QA Plan shall include the following:

• Description of fabrication traceability and proposed layout of the Traveler.

Each part of the cavity shall be traced to a raw material ID and such information should be provided to FNAL by the fabricator.

• Description of equipment and general procedures for inspection and dimensional control of components.

• Description of the pre-weld chemical treatment facility.

• Description of EB welding equipment and its performance.

• Procedures for verifying sufficient weld integrity for each joint (e.g., micrographs).

• Procedure for final inspection of each completed cavity.

FNAL approval of the Quality Assurance Plan is required prior to the start of work.

2.3 Schedule

The fabricator shall submit a detailed schedule including milestones with the initial proposal. FNAL approval of the proposed schedule is required prior to the start of work.

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3 Fabrication Drawings

The FNAL drawing and step file are attached. Based on the FNAL drawing and step file, the fabricator shall develop its own set of drawings for the cavities. The dimensions in these drawings must account for the material to be removed by chemical etching and weld shrinkage, so that after welding the dimensions and tolerances specified in the FNAL drawings are achieved.

The fabricator shall supply FNAL with a complete set of manufacturing drawings before the start of fabrication. FNAL approval of the drawings is required prior to the start of work.

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4 Supply of Materials

The Fabricator shall provide the required raw Nb and NbTi materials.

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5 Production of Component Parts

The cavity body will be fabricated out of 4 parts. The inner radius will be machined to

3.2 mm by milling. The flanges will be machined to final geometry and EB welded onto the cavity.

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6 Welding of the Cavity

Requirements for cleaning and BCP etching of the parts to be welded are described in

Appendix 12.2 and Appendix 12.3.

Flanges holes orientation is critical and should be controlled. A ConFlat flange weld joint should be located at proper distance away from the knife edge to avoid compromising its sealing integrity, to ensures the weld process doesn't distort the critical knife-edge geometry, which is essential for achieving a proper vacuum seal.

Four parts of the cavity are EB welded together. Preparation of the iris joints for EB welding will be by the method of choice of the contractor: i.e., butt joint or step joint. The welds must be full penetration or dual pass with full overlap. If dual pass, micrographs must be provided to verify full overlap.

Consult Appendix 10.4 and Appendix 12.7 for EB welding requirements.

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7 Quality Control, Mechanical Measurements, and Inspection

Each component and the finished cavity must be measured and inspected as specified by the Quality Control Assurance Document submitted by the fabricator. All required dimensions, weld quality assessments, frequency measurements, and observations must be included in the Traveler for each cavity.

Micrographs of sample welds performed using the finalized, production EB weld parameters must be provided for all keyhole welds.

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8 Serial Numbers

A serial number is inscribed on the side wall of beam pipe flange of each cavity. The general form shall be agreed. Suggested from is: R3C-XXX-nnn. The second set of characters (XXX) indicates the FNAL code for the specific fabricator. The last three characters is the unique ID number for the cavity. The fabricator code and the ID number will be assigned by FNAL.

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9 Cleaning, Packaging, and Shipping

Each completed cavity is ultrasonically cleaned and degreased. The cavity is sealed in a clean polyethylene bag and mounted in a padded box for shipment to FNAL.

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10 Appendix

10.1 Visual inspection of components

Parts are inspected using an illuminated magnifying glass. Scratches, pits or nicks deeper than 15 microns are prohibited on any RF surface. Unsatisfactory components may be polished as specified in Appendix 12.6 and then re-inspected.

10.2 Ultrasonic Cleaning of Components

Parts are ultrasonically cleaned using Micro90, Citranox or equivalent as the cleaning agent, rinsed with ultrapure water filtered to 0.05 micron particle size until the resistivity of 18 MΩ cm or better is achieved, and dried with filtered nitrogen. Ultrasonic cleaning, rinsing and drying operations must take place in a clean room of ISO 6 or better.

Parts are stored in ultrasonically cleaned vessels under vacuum or backfilled with nitrogen or argon. All parts must be handled as specified in Appendix 10.5.

10.3 Electron-Beam Welding Preparation

All niobium parts must undergo a 20 µm BCP etch after the final machining operation and before welding. The parts are etched with a mixture of nitric acid (65%), hydrofluoric acid (48%), and phosphoric acid (85%) in the volume ratio of 1 : 1 : 2. Parts to be etched are completely immersed in the acid mixture and supported in a manner such that nothing touches any surfaces to be welded. The niobium rate of removal is approximately 1 µm per minute for non-contaminated acid at a temperature of 15 oC. During the etching process the acid temperature must be maintained at a temperature below 18 oC. Acid temperature regulation is dependent upon:

(1) Volume of acid the parts are immersed in,

(2) Rate of acid agitation,

(3) Method for cooling the acid.

It is thus recommended that a sufficient volume of acid is used to minimize temperature fluctuations, the acid is continuously agitated, and the method used for cooling the acid is adequate for the task.

After the parts are etched they are immediately rinsed with ultrapure water filtered to 0.05 µm until the resistivity of 18 MΩ cm or better is achieved, and dried with filtered nitrogen in a ISO 6 clean room or better. During and after rinsing, the drying parts are supported in a fixture designed to ensure that nothing will touch any surface to be welded. After the parts are dried, if more than eight hours (and less than 5 days) is expected to elapse between the 20 µm etch and welding, the parts must be stored in a vacuum vessel evacuated to less than 0.05 atm or in a vessel backfilled with nitrogen or argon. Once exposed to air welding must occur within two hours. It is mandatory that surfaces to be welded do not come in contact with any foreign body before welding.

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If parts which have undergone the primary 20 µm BCP etch have exceeded the eight hour requirement, or have been stored under vacuum for five or more days, the edges to be welded must undergo a secondary 3 µm BCP etch before welding. If practical, this is best accomplished by submerging the entire part in acid. After the parts are etched they are rinsed, dried and stored for transportation to the welding facility following the procedure described above. When etching end groups special care must be taken to protect niobium-titanium components from the acid.

All niobium-titanium parts undergo a 10 µm BCP acid etch. The material removal rate for niobium-titanium is approximately twice that for niobium. After etching the parts are subjected to the same procedure as above.

The BCP mixture is replaced with fresh acid when its niobium content reaches 10 gm/L.

This can be determined by weighing the fresh acid mixture before etching, then checking the weight of acid at periodic intervals.

All parts must be handled as specified in Appendix 10.5.

10.4 Electron-Beam Welding Conditions

Pressure in the welding chamber must be less than 5 x 10-5 mbar [3.75 x 10-5 Torr] during all welding operations. After the temperature of the part has fallen below 100 degrees C at the hottest point, the welding chamber is vented with filtered nitrogen or argon until a pressure of at least 15 mbar is achieved. The parts are allowed to cool under nitrogen for an additional period of time before venting the welding chamber with air to atmospheric pressure.

For equator welds, where it is possible that the threaded rod in the welding fixture could be exposed to e-beam “shine” through the equator joint, the threaded rod must be shielded by a niobium tube.

10.5 Handling and Storage of Components

It is imperative that niobium surfaces are protected at all times from contact with any substance (e.g., Teflon, silicon, etc.) that will not be completely removed by the cleaning and chemical etching processes outlined in Appendix 10.2 and Appendix 10.3. Niobium components must be handled with gloves rated for clean room semi-conductor component assembly (e.g., CR100 nitrile gloves or MicroGrip Ambi PolyShield nitrile gloves). Welding fixtures must be ultrasonically cleaned, rinsed and dried as specified in Appendix 10.2 before each welding operation. Cleaned and etched parts must be protected during storage and transport by enclosure within properly designed vessels

Fermi National Accelerator Laboratory 16 under vacuum, or backfilled with nitrogen or argon. Parts should never be supported on areas to be welded, except when mounted in welding fixtures with those areas in contact with niobium inserts.

10.6 Polishing

Niobium components with unacceptable pits or scratches may be polished using a Dremel tool with 400 grit aluminum oxide paste (abrasive particles < 50 µm) on a felt bob, then ultrasonically cleaned, chemically etched, rinsed and dried as specified in Appendix 10.2 and Appendix 10.3. The fabricator shall describe the intended type of polishing media, polishing sequence, verification of defect removal or compliance with surface roughness specification, photographical record of parts before and after defect removal. If the damage is not repairable by polishing, the components must be rejected.

10.7 Development of Electron-Beam Welding Parameters

Electron-beam (EB) welding parameters must be selected to provide structurally rigid cavities. All EB welds within the pressure boundary of the cavity must be qualified by ASME Boiler and Pressure Vessel Code Section IX. The welds must also insure that all joints that will be exposed to acid during cavity post-processing are completely sealed so that acid will not be trapped.

Parameters to be selected include EB gun voltage, EB gun-to-work distance, EB current, EB focal points, and material feed rates during welding. Weld samples are prepared to determine the proper combination of the parameters listed above for each type of weld involved in the fabrication of the cavities. The samples also yield data on expected weld shrinkage for each type of weld. Components must be machined with extra material to compensate for expected shrinkage.

Full penetration welds require a defocused, oscillating electron-beam as the weld proceeds. The effect is a uniformly distributed deposition of electron-beam energy along the joint, resulting in a smooth weld underbead with minimal protrusion (not to exceed 200 µm) above the surrounding material.

Parameters for non-full penetration (keyhole) welds are developed based on scanning electron microscope or metallographic analysis of cut, etched and polished weld samples.

Micrographs of sample welds performed using the finalized production EB weld parameters must be provided to FNAL for all keyhole welds prior to the start of fabrication.

To satisfy mandates from FNAL’s Environment, Safety and Health Manual, weld documentations are required per BPVC Section IX. A typical documentation includes, but not limited to the following.

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• Weld map

• Weld procedure specifications (WPS)

• Performance qualification records including mechanical test reports (PQR)

• Welder performance qualifications (WPQR)

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11 Design Model

11.1 PROVIDED BY FNAL:

A 3-D STEP file of the cavity will be provided by FNAL. The STEP file will contain all parts associated with the design to assist in the quotation. The fabricator should verify that the STEP file is accurate to the drawings.

11.2 REVIEW OF THE DESIGN:

The fabricator will review the FNAL design for manufacturability and will provide a cost for the design based on Engineering, Materials, Fabrication, Assembly, Shipping, etc.

Prior to manufacturing start-up, the fabricator and FNAL representatives will meet to discuss design features and processes to help ensure quality, optimize delivery schedule, and/or to reduce cost.

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12 Acceptance of bare cavities

Upon receipt of the cavities, FNAL will perform an optical inspection of the inner surface of the cavity, including welds. If large defects, greater than 50 µm, are found, FNAL reserves the right to reject the cavity until the defects are repaired by the fabricator following a procedure to be agreed upon with FNAL. Cavities may also be rejected if they are found not to be compliant with the mechanical parameters specified in this document and attached drawings.

12 Acceptance of bare cavities