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US HL-LHC Accelerator Upgrade Project

Technical Specification

Supply of RFD Crab Cavities

Prepared by:

Leonardo Ristori, US HL-LHC AUP 302.3 L2 Manager, FNAL

Paolo Berrutti, US HL-LHC AUP 302.3.02 L3 Manager, FNAL

Reviewed by:

Ruben Carcagno, US HL-LHC AUP Deputy Project Manager, FNAL

Approved by:

Giorgio Apollinari, US HL-LHC AUP Project Manager, FNAL

Revision History

Revision

Date

Section No.

Revision Description

v0

6/9/17

All

Initial Release

Contents1INTRODUCTION51.1Description of the Superconducting Radio Frequency Crab Cavities52SCOPE OF THE SUPPLY52.1Activities at the Contractor’s Premises62.2Materials provided by Fermilab63TECHNICAL REQUIREMENTS FOR THE BARE CAVITIES63.1General Description of the BCs63.2General Requirements of the BCs73.3Materials73.4Dimensions and tolerances83.5RF frequency83.6Technical documentation prior to manufacturing83.7Manufacturing83.7.1General requirements83.7.2Shaping93.7.3Machining93.7.4Vacuum brazing93.7.5Electron-beam welding93.7.6Permanent joints samples103.7.7Pre-weld etching103.8Verification requirements of the BCs103.8.1Metrology controls103.8.2Non-destructive tests of welded joints103.8.3BC RF frequency check133.8.4Helium leak tightness tests134INFORMATION AND DOCUMENTATION134.1Documentation prior to manufacturing134.2Documentation to be supplied with the shipment of cavities134.3Documentation Handling, Quality Control and Quality Assurance134.3.1Technical Documents prior to starting the manufacturing of BCs144.4Manufacturing and Inspection Plan144.5Manufacturing Records144.6Acceptance Tests154.6.1Tests Carried Out at the Contractor’s Premises154.7Contract Follow-Up and Progress Monitoring154.8Packing and Shipping154.9Acceptance and Warranty165ANNEXES165.1Normative References165.2Other applicable documents16

INTRODUCTION

This specification document is based on CERN EDMS No. 1803555 and adjusted to align with the procurement strategy of RFD crab cavities by the US HL-LHC AUP project.

Description of the Superconducting Radio Frequency Crab Cavities

Superconducting Radio-Frequency (RF) Crab Cavities are one of the key devices for HL-LHC. The crab cavities are RF cavities whose geometry is designed in such a way that the electromagnetic force imparted is perpendicular to the motion of the charged particle going through them. The choice of the correct RF phase allows for the rotation of the colliding bunches, thus maximizing the luminosity. To sustain the high electric and magnetic fields, RF cavities are made of superconducting materials, typically high purity niobium (Nb) sheets, and operated at 2 K. Two crab cavity concepts have been developed: The Double Quarter Wave (DQW) and the RF Dipole (RFD). This Technical Specification concerns the RFD cavity type. The cavity with flanges and all the niobium-titanium (Nb55Ti) interfaces to other objects is called a bare cavity (BC), Figure 2.

Figure 2: 3D view of bare cavity

SCOPE OF THE SUPPLY

Seller shall supply bare cavities manufactured and assembled in compliance with this technical specification and the documents and drawings attached to it.

The supply is divided in 2 prototype units and an option for 12 production units after the prototypes are completed successfully.

Bare cavities shall be delivered without performing any chemical processing or heat treatment. These activities will be carried out at Fermilab after delivery and incoming inspection is completed.

Seller must also supply documentation as described in §4.

Activities at the Contractor’s Premises

The contractor shall perform the following activities:

• Design and fabricate tooling for shaping, machining and welding;

• Produce trial pieces to verify tooling and fabrication processes;

• Produce fabrication drawings for all sub-components;

• Forming, electron-beam welding (including pre-weld chemical etching) and machining of parts according to §3.7

• Verification tests according to §3.8;

• Compile MIP throughout fabrication §4.4;

• Issue NC reports as needed;

• Pack, and ship according to §4.8;

• Utilize dedicated storage space at contractor’s premises for Fermilab supplied material, forBCs and all sub-components.

Materials provided by Fermilab

Fermilab will make available the following materials:

· Raw ultrahigh-purity niobium (Nb) sheets and niobium-titanium (Nb55Ti) plates;

· Stainless Steel (SST) EN 1.4429 (equivalent to AISI 316LN) blanks for the BC flanges;

· Nb-SS Brazed joints for all cavity flanges, in the stock state.

The material provided by Fermilab shall be clearly marked as Fermilab property.

TECHNICAL REQUIREMENTS FOR THE BARE CAVITIESGeneral Description of the BCs

Each BC is made of 4 mm and 6.35 mm thick niobium sheets properly shaped and machined and joined by electron beam welding.

For information, the expected performance of the cavities at 2 K are:

1. Deflecting voltage of 4.1 MV or above;

2. Dynamic heat load of 10 W or less:

3. Nominal operating frequency of 400.79 MHz.

While these parameters depend also on the processing performed at Fermilab, surface quality and geometrical dimensions are key parameters for obtaining the desired performance.

Bare cavities in their final configuration, integrated in liquid helium containment vessels, are pressure vessels belonging to the Category I of the European Pressure Equipment Directive.

The mechanical design has been performed in compliance with ASME BPVC (Section VIII, div. 2) for the load cases indicated in Table 1.

Table 1: Load cases

* data are indicated for reference (don’t affect directly the BC)

General Requirements of the BCs

The overall requirements for the BC are listed below:

• Dimensions in compliance with specification drawing and 3D file;

• Resonance frequency at 300 K in air in a range ±100 kHz with respect to the nominal valuecommunicated by Fermilab (see § 3.5);

• Manufacturing process and inspection tests in compliance with harmonized standard EN 13445 or ASME BPVC (§ 5.1) and the standards referred to therein, unless stated otherwise in this specification. This includes, in particular, all the relevant qualification of welds and welding procedures;

• Leak tightness for the volume inside each BC;

• Internal surface quality.

Detailed description and quantitative values are provided in the following sections.

Materials

The materials for the BC are provided by Fermilab. The specifications for them are listed in Table 2 and are provided in the annexes for information.

Table 2: Materials specifications

Components

Material

Applicable documents

BC – Flanges

Stainless Steel

Technical Specification N°1002, Annex 5

Niobium-Titanium

Material Specification N°4055, Annex 4

BC - Body

Niobium (RRR > 300)

Material Specification N°3300, Annex 2Material Specification N°3301, Annex 3

The use of any non-listed materials is excluded by the present specification. Under exceptional conditions Fermilab may approve other materials upon a written request.

Dimensions and tolerances

The dimensions of the BC are described in the functional drawings provided by Fermilab that refers to the BC before the processing step. Deviations from such requirements must be approved by Fermilab in written form.

RF frequency

The RF frequency of the BC depends on the shape and size of the internal volume of the cavity as well as on the electrical properties of the dielectric material contained. The RF frequency is therefore a parameter evolving throughout the manufacturing sequence. Fermilab will provide a table with a step-by-step indication of the expected RF frequency value once the contractor’s MIP is approved.

Technical documentation prior to manufacturing

The documentation specified in §4.1, shall be submitted to Fermilab for written approval prior to starting the manufacturing.

ManufacturingGeneral requirements

The following general requirements are applicable throughout the complete manufacturing process:

• The use of clean gloves is mandatory for manipulating finished components after any

degreasing and chemical polishing;

• Full traceability of BC subcomponents shall be ensured throughout the entire manufacturing process by using un-erasable marks on the outer surfaces, or another identification system whenever this is not possible;

• All parts shall be properly protected against damage and contamination with foreign materials;

• The inner surface of the BC shall be handled properly, as to avoid any scratches;

• Shaping tools must be used exclusively for the niobium of the supply and cleaned of any prior contamination (via cloth) before any use;

• Material for tools must be agreed with Fermilab;

• All traces of lubricants shall be completely removed by ensuring cleaning operations;

• The lubricants used for niobium machining, shall be halogen-free, silicone-free and sulfur free;

• Surface abrasion processes shall be performed only after approval from Fermilab.

The internal surface quality is of uppermost importance. Any defect on the BC internal RF surface (such as inclusions of foreign materials or scratches) must be avoided as potential quench initiators during operation.

Shaping

The BC shall be shaped, by deep drawing or other techniques, from plates in niobium (RRR > 300).

The inner surface of the BC shall be handled with greatest care to avoid any contamination and damage during shaping. Possible seizing marks or other damage on the inner resonator surface must be strictly avoided. The surfaces of the tooling and the niobium plates must be carefully cleaned prior to each shaping operation, such that no dirt, metal particles or other material gets embedded in the niobium surface.

Local grinding of the internal surfaces shall be performed only after written approval from Fermilab.

Machining

The protecting niobium oxide layer is damaged at temperatures above 150 °C. Oxygen and other gases will diffuse in this case into the niobium and hinder the superconducting properties.

Therefore, during the machining of niobium, it is essential to keep the temperature near the tool as low as possible. This can be achieved with adequate lubrication as indicated already in §3.7.1. Fermilab reserves the right to analyze the cutting fluid and supply mode before starting of the machining of the final BC components.

In terms of machining features, the following guidelines are proposed, for information:

• Use of carbide tools (sharpest tool available for finishing operations);

• Use of high stiffness tool holders to reduce vibrations, such as hydraulic chuck;

• Tool wear shall be kept under a value of 0.15 mm on the clearance face;

• Use of ‘flood’ cooling.

During niobium-titanium machining, the contractor shall limit the formation of burrs and account for the accelerated tool wear. The contractor shall send to Fermilab for written approval the method used for machining the threads.

Vacuum brazing

No vacuum brazing is requested from the contractor. All Nb-SS transitions present in the bare cavity will be provided by Fermilab in a stock stage. Machining of knife edges, bolt holes and all other features will be responsibility of the contractor.

Electron-beam welding

Prior to the electron beam welding sequence, all parts shall undergo the pre-weld etching procedure described in 3.7.7. Before welding, the chamber shall also be cleaned from the metallization of other materials that are not niobium.

All niobium — niobium welds shall be performed with 100% penetration, and all welds shall retain a smooth inner surface. Whenever it is possible welding from inside is recommended. Pressure of the electron-beam welding chamber shall be maintained below 5×10-5 mbar, and niobium vapour from welding shall be evacuated. The welding chamber shall be vented with normal air only after the temperature of the niobium part has dropped to 100 °C at the hottest spot.

The welds shall be smooth and uniform. No repair of defective welds is allowed without prior approval from Fermilab.

The electron-beam welding, and operator, qualifications shall be in agreement with the standards specified in Table 3.

Table 3: Standards applicable to electron-beam welding qualifications

Permanent joints samples

In addition to the test samples required by the standards, one or more welded samples shall be performed and supplied to Fermilab to check the capability to perform electron-beam welding with the Fermilab requirements specified in §3.8.2, and to verify that the RRR degradation on the welds is not higher than 10% of the initial value of RRR of niobium.

These samples shall be delivered before starting welding. Test samples dimensions shall be defined in agreement with Fermilab, based on the contractor’s welding strategy.

Pre-weld etching

The BC will be subjected to chemical polishing also called Buffer Chemical Polishing (BCP) prior to the qualification tests at 2K at Fermilab. The contractor is requested to only perform light local “pre-weld” etch on the surfaces next to the edges to be welded, less than 8 h before each EBW step. The chemical process typically consists of HF, HNO3 and H3PO4 in volume ratio of 1:1:2 with the phosphoric acid as the buffer to stabilize the reaction rate.

Verification requirements of the BCsMetrology controls

Metrology controls shall be performed along the manufacturing process. These checks consist of the verification of dimensional and geometrical tolerances with respect to the functional drawings approved by Fermilab. The results of 3D dimensional controls performed at the steps agreed in the MIP shall be reported to Fermilab for approval.

Non-destructive tests of welded joints

3.8.2.1 Niobium welds

Concerning the NDT of welded joints, Fermilab requires:

• Visual Testing (VT): a 100 % visual inspection of welds is required (external surfaces and internal surfaces wherever possible) according to ISO 17637. The visual inspection shall be performed:

· Before welding: surface inspection is to detect any possible defects, ensuring that the plates do not have burrs or are unevenly cut, thus interfering with the welding process, verification of the tack welds, checking that the joint design complies with the applicable drawing and specifications.

· After welding: The visual inspection shall be carried out prior to any other nondestructive test and any defect found will be repaired in compliance with the specified acceptance criteria.

• Radiographic Testing (RT): a 25 % X-ray test according to ISO 17636 of the total circumferential seams and 100% of the total longitudinal seams. The extent of the X-ray test in case of 25% required, shall be in accordance with the criteria specified in EN 13445-5 (§5.1). Moreover, corner joints and areas of high bending stress shall be treated as longitudinal seams.

Due to the lack of any specific standard for niobium welds as part of a pressure equipment, the standard ISO 13919-2 shall be used to assess the quality level of imperfections. The required quality level is level B.

Furthermore, a high-quality smooth inner surface without any contamination, scratch, weld spatters or inclusion shall be ensured in compliance with the RF requirements defined in Table 4, where t is the thickness. These requirements are based on Fermilab and CERN experience with 3 mm and 4 mm welds.

Table 4: Acceptance levels of niobium inner welded joints imperfections

3.8.2.2 Other welded or brazed joints

For reference, the acceptance criteria regarding other joints are specified in Table 5.

Table 5: Acceptance levels of other welded or brazed joints imperfections

BC RF frequency check

The BC RF frequency at the moment of the delivery shall be in a ±100 kHz range with respect to the value indicated in the abovementioned frequency table provided by Fermilab. This RF frequency shall be measured in air at ambient temperature. Exact temperature and humidity shall be agreed with Fermilab.

Helium leak tightness tests

The helium leak tightness (from helium to insulation vacuum) of individual joints and BC shall be performed according to the tracer gas method (EN 13185) and the maximum allowable leak rate shall be lower than 2×10-11 Pa m3/s (2×10-10 mbar l/s) at room temperature. The helium mass spectrometer shall be calibrated according to ISO 3530. The personnel performing leak tightness tests shall be qualified according to ISO 9712 (minimum level 2). The helium mass spectrometer shall have a sensitivity for helium of at least 1×10-11 Pa m3/s. The helium leak tightness test shall be performed at the manufacturing steps indicated in Annex 1. Helium leak rate data charts shall be recorded and annexed to the test reports. Additional information and a test report template are available in Annex 6.

INFORMATION AND DOCUMENTATIONDocumentation prior to manufacturing

• Manufacturing drawings for all sub-components;

• Manufacturing and Inspection plan (MIP);

• Welding qualification samples;

• Any Certification required by the applicable codes and standards;

• Cleaning procedures (§3.7.1);

Documentation to be supplied with the shipment of cavities

• For each cavity, identified with a serial number: filled MIP (see §4.4) and all the applicable manufacturing and testing procedures, such as but not limited to metrology, EB welding, leak checks.

• Traceability information from raw materials to finished cavities;

• Nonconformance reports.

Documentation Handling, Quality Control and Quality Assurance

The contractor shall plan, establish, implement and adhere to a documented quality assurance

program that fulfils all the requirements described in this technical specification.

In addition to the requirements of this technical specification, the contractor may propose any internationally recognized design standard, subject to prior written approval by Fermilab. The contractor shall state his intended method of design including applicable codes as part of his bid. Fermilab reserves the right to veto the use of certain codes or norms if it is considered that their application will not ensure compliance with this technical specification. The contractor shall submit all documents produced in electronic format:

• 2D drawings in PDF format;

• 3D models in STEP format;

• Text documents in Microsoft Word® and/or PDF® format;

• Cost breakdowns and equipment lists in Microsoft Excel® format;

• Schedule in Microsoft Project® format.

Technical Documents prior to starting the manufacturing of BCs

At least one month before the start of manufacturing of the BC, the following documentation and samples shall be submitted to Fermilab for written approval:

• Functional and manufacturing drawings (with tolerances) of both BC and relevant tools;

• Welding plan including:

· Welding maps;

· Welding procedure qualification record (WPQR), §3.8.2;

· Welding procedure specification (WPS);

· Welding Operators Performance Qualifications (WOPQ, electron-beam welding)

• Electron Beam welded samples according to the requirements specified in §3.8.2;

• Nondestructive Test personnel qualifications.

Manufacturing and Inspection Plan

The contractor shall establish and make available to Fermilab a Manufacturing and Inspection Plan (MIP) describing the complete manufacturing process and all tooling, machines and equipment intended to be used, including a flow chart, diagram and narrative description. The production of the supply cannot start until Fermilab has given written approval to the MIP. The MIP shall also include a detailed description of the inspection and test procedures and the model test certificates that the contractor intends to use.

The implementation of any changes to the manufacturing plan after the start of the manufacturing is subject to prior written approval by Fermilab. At the submission date, the final MIP shall be made of all the production procedures & qualifications.

An example of MIP is attached in Annex 1.

Manufacturing Records

All the manufacturing records obtained during the quality control activities of the supply shall be sent to Fermilab. Among others, the reports must include the following:

• All metrology and dimensional reports;

• The leak test reports as described in Annex 6;

• Report of any non-destructive tests on the welds;

• Report of any non-destructive tests on the cavity internal surface;

• RF measurements;

• All non-conformity reports as soon as and if they occur.

At the beginning of the contract the contractor shall submit for Fermilab’s written approval a detailed schedule defining the processes and methods which he intends to implement. At Fermilab’s request, he shall provide for information, in writing, a detailed account of the arrangements that he intends to make and the equipment and installations to be provided.Fermilab and/or its representatives shall have free access during normal working hours to the manufacturing or assembly sites, including any subcontractor’s premises, during the contract period. The place of manufacture may only be changed after written approval by Fermilab.

Acceptance TestsTests Carried Out at the Contractor’s Premises

Fermilab reserves the right to be present, or to be represented by an organization of its choice, to witness any tests carried out at the contractor's or his subcontractors' premises. The contractor shall give at least ten working days’ notice of the proposed date of any such tests.

The contractor shall perform the abovementioned tests, here summarized:

• 3D dimensional controls;

• Leak test of BC, before delivery to Fermilab;

• Non-destructive tests of BCs welds;

• RF frequency measurement at warm.

Contract Follow-Up and Progress Monitoring

The contractor shall assign a person responsible for the technical execution of the contract and its follow-up, as well as a person responsible for the commercial follow-up, throughout the duration of the contract. They shall be able to communicate in English.

The contractor shall send a written progress report to Fermilab every month until completion of the contract. All communications and documents shall be in English.

This report shall include all the necessary information and, in particular, the actual progress in comparison to the scheduled progress;

Packing and Shipping

The contractor is responsible for the packing and, where specified by Fermilab for the transport to Fermilab of each BC. In all cases, he shall ensure that the equipment is delivered to Fermilab without damage and any possible deterioration in performance due to transport conditions. The contractor shall comply with professional regulations in matter of packing and shipping.

At each delivery, the BCs shall be sealed with Conflat flanges and corresponding gaskets. On top of that they shall contain clean air (equivalent to an ISO 5 clean room or cleaner) or nitrogen atmosphere, be enclosed by a clean polyethylene foil, be mounted in a transport box, and be secured against displacement. A specific frame shall be designed to avoid de-tuning of the BCs during transport.

Acceptance and Warranty

Acceptance of the supply shall be given by Fermilab only after the delivered supply is deemed to be in conformity with the contract including documentation referred to in this technical specification, all tests specified have been successfully completed and all tests or other certificates have been submitted to Fermilab.

The warranty shall be as defined in the tender form.

ANNEXESNormative References

This specification incorporates provisions from European, international or national standards. They are cited in this document, to be used as a whole or in part, and shall be considered part of this specification, for application in the scope for which they are referred. For undated references, the latest edition applies, including amendments.

EN 15614 -11

Specification and qualification of welding procedures for metallic materials – Welding procedure test- Part 11: Electron and laser beam welding

EN 15609-3

Specification and qualification of welding procedures for metallic materials – Welding procedure specification – Part 3: Electron beam welding

BPVC VIII

Rules for construction of Pressure Vessel

EN 13445

Construction of unfired pressure vessels

EN 13185

Non-destructive testing. Leak testing. Tracer gas method

ISO 14732

Welding personnel. Qualification testing of welding operators and weld setters for mechanized and automatic welding metallic materials.

ISO 9712

Non-destructive testing – Qualification and certification of NDT personnel

ISO 17637

Non-destructive testing of welds – Visual testing of fusion-welded joints

ISO 17636

Non-destructive testing of welds – Radiographic testing

ISO 13919-2

Welding – Electron and laser beam welded joints- Guidance on quality levels for imperfections. Part2: Aluminum and its weldable alloys

ISO 3530

Vacuum technology – Mass -spectrometer-type leak-detector calibration

Other applicable documents

Annex 1

Example of the Manufacturing Inspection Plan (MIP) for the DQW Crab Cavity, version 1.0

Annex 2

CERN material specification Nº 3300 Ed. 4 - Pure niobium sheets for superconducting applications, EDMS 1095252

Annex 3

CERN material specification Nº 3301 Ed. 3 - Pure niobium bars and plates for superconducting applications, EDMS 1476934

Annex 4

CERN material specification Nº 4055 Ed. 3 – Nb-55Ti wrought products for superconducting applications, EDMS 1485727

Annex 5

CERN technical specification Nº 1002 Ed. 5 – Stainless steel sheets/plates for ultra-high vacuum applications, 1.4429 / X2CrNiMoN17-13-3 / AISI 316 LN, EDMS 790774

Annex 6

Leak test report - procedure and template, EDMS 1318157