FNAL Specification of Welded 325 MHz Superconducting SPOKE Resonators
USED for FNAL Proton DrivER

Table of Contents

1 Introduction [3](#introduction)

2 Deliverables [3](#deliverables)

2.1 manufacturing plan [3](#manufacturing-plan)

2.2 quality assurance plan [4](#quality-assurance-plan)

2.3 schedule [4](#schedule)

2.4 Nb-to-SS Braze Sample [4](#nb-to-ss-braze-sample)

2.5 Endwall to Cylindrical Cavity Weld Sample
[4](#endwall-to-cylindrical-cavity-weld-sample)

2.6 Progress Report [5](#progress-report)

2.7 Superconducting CaVITIES [5](#superconducting-cavities)

2.8 Final reports and documentation (Traveler)
[5](#final-reports-and-documentation-traveler)

2.9 excess material and spare parts
[5](#excess-material-and-spare-parts)

3 Fabrication drawings [6](#fabrication-drawings)

4 Supply of Material [6](#supply-of-material)

4.1 Nb Quantity [6](#nb-quantity)

4.2 Incoming inspection [6](#incoming-inspection)

4.3 Sheet material for Spokes [7](#sheet-material-for-spokes)

5 Production of parts [7](#production-of-parts)

5.1 Cavity assembly [7](#cavity-assembly)

5.2 Cavity and subassembly manufacturing
[7](#cavity-and-subassembly-manufacturing)

5.3 Identification Marking [7](#identification-marking)

6 Production of subgroups [8](#production-of-subgroups)

6.1 SPOKES [8](#spokes)

6.2 spoke Beamline tubes and flange connections
[8](#spoke-beamline-tubes-and-flange-connections)

6.3 Cylinder body and pull-out Holes
[8](#cylinder-body-and-pull-out-holes)

6.4 endwalls [9](#endwalls)

6.5 Cavity tuning [9](#cavity-tuning)

7 Welding of elements [9](#welding-of-elements)

7.1 niobium to niobium joints [9](#niobium-to-niobium-joints)

7.2 weld quality [9](#weld-quality)

7.3 Niobium to Stainless Steel Joints
[10](#niobium-to-stainless-steel-joints)

7.4 Flange-Nb Tube Subassemblies [10](#flange-nb-tube-subassemblies)

7.5 Rework [10](#rework)

8 Final test of cavity [11](#final-test-of-cavity)

8.1 Leak check [11](#leak-check)

8.2 Mechanical measurement [11](#mechanical-measurement)

8.3 visual inspection of the final product
[11](#visual-inspection-of-the-final-product)

9 Acceptance, Packing and shipping
[12](#acceptance-packing-and-shipping)

9.1 Certification and Authorization to Ship
[12](#certification-and-authorization-to-ship)

9.2 Identification and Marking [12](#identification-and-marking)

9.3 Packaging [12](#packaging)

9.4 Shipping [12](#shipping)

10 Time schedule [13](#time-schedule)

11 Progress report [13](#progress-report-1)

12 Quality Assurance Documentation
[13](#quality-assurance-documentation)

12.1 Responsibility for testing and inspection
[13](#responsibility-for-testing-and-inspection)

12.2 hold points [13](#hold-points)

12.3 purchaser right to inspection [14](#purchaser-right-to-inspection)

12.4 corrective action [14](#corrective-action)

13 Appendix [15](#appendix)

13.1 Degreasing, ultrasonic cleaning, drying
[15](#degreasing-ultrasonic-cleaning-drying)

13.2 Chemical cleaning, Rinsing, Drying
[15](#chemical-cleaning-rinsing-drying)

13.3 Handling and storage conditions
[15](#handling-and-storage-conditions)

13.4 Welding preparation [16](#welding-preparation)

13.5 general electron beam Welding conditions
[16](#general-electron-beam-welding-conditions)

13.6 Grinding [16](#grinding)

13.7 Cavity contour, frequency and length
[17](#cavity-contour-frequency-and-length)

13.8 List of drawings [17](#list-of-drawings)

# Introduction

This specification describes fabrication details of the double spoke
resonators for the initial acceleration of protons and electrons in the
FNAL Proton Driver. The double spokes cavity described in this Scope of
Work is designed for a geometrical beta of β=0.4 and is operated at a
frequency of 325 MHz.

The resonator is assembled from spokes and a cavity cylinder entirely by
forming and electron beam welding. Correct spoke shape is important to
reach the desired resonant frequencies (accelerating mode) at specified
cavity and resonator lengths.

This specification is a first version for the production of two
prototype double-spoke cavities and is based on specifications from the
Los Alamos National Laboratory (2 Gap Single Spoke Resonator for
AAA/Leda) and from DESY (1.3 GHz Superconducting Resonators for TESLA
Test Facility TTF). Changes to these specifications based on the
experience are to be expected.

# Deliverables

Except for the Nb material specifically furnished by the Purchaser as
listed in Section 4.1, the Contractor shall provide all supervision,
labor, necessary materials, tooling fixtures, consumable supplies,
engineering, inspection, testing equipment, and all other services
needed to meet the requirements of this Scope of Work. All necessary
facilities, e.g., buildings, clean room, chemical treatment facilities,
chemical waste system, high purity water system, and testing devices for
cavity mechanical inspection, and vacuum leak detection shall be the
responsibility of the Contractor.

## manufacturing plan

The contractor shall submit a manufacturing plan to the purchaser for
acceptance by the date specified in the contract. The plan shall
identify and describe all aspects of work to be executed from the point
of initial inspection of supplied Nb material through delivery of the
cavities. The Manufacturing Plan shall include the following:

-   Manufacturing drawings for the various parts conforming to the FNAL
    engineering drawings.

-   Procedure for identification marking of Nb blanks as described in
    Section 5.3.

-   Method for weld preparation machining on tubes, nipples, spokes,
    endwalls, and outer body.

-   Procedure for inspection and chemical treatment of raw parts before
    EB welding.

-   Procedure for brazing stainless steel flanges to Nb tubes.

-   Procedure for chemical polishing (BCP) of parts including a
    description of the method for determining the amount of material
    removed.

-   Procedure for EB welding of Flange-Nb tube subassemblies to the beam
    tube extensions.

-   Procedure for EB welding of tubes, spokes, and outer body to form
    the cavity including the weld sequence.

-   Procedure for visual inspection of the final product.

-   Design of shipping container and packaging procedure.

The Purchaser must accept the Manufacturing Plan prior to use. Sections
of the Manufacturing Plan may be submitted earlier for acceptance. These
sections must be independent of sections submitted later. This will
allow the Contractor to commence some fabrication tasks earlier.

## quality assurance plan

The Contractor shall submit a Quality Assurance (QA) Plan to the
Purchaser for acceptance by the date specified in the contract. The plan
shall ensure that each item offered for acceptance conforms to the
requirements herein. The requirements of IS0 9002/ANSI Q9002 shall be
considered as a guideline for the QA Plan. The Purchaser must accept the
Quality Assurance Plan prior to use. As a minimum requirement the QA
plan shall include:

-   Description of manufacturing traceability.

-   Proposed layout of Travelers.

-   Methods for inspection and dimensional control of mechanical parts
    and subassemblies including description of the measuring equipment,
    sequence and frequency of inspection, methods for defect/flaw
    determination, criteria for rejection of parts including corrective
    action and plan for record keeping

-   Description of EB welding equipment including information on
    achievable vacuum and pumping system.

-   Qualifying procedure for each weld joint.

-   Description of brazing equipment.

-   Description of chemical treatment facility

-   Description of Quality Control (QC) process of chemicals including
    purity and history of previous use, if any.

-   Plan for Non-Conformance reporting. Discrepancies shall be reported
    in the Contractor\'s Non-Conformance Reports and submitted to the
    Purchaser for acceptance. Work shall be placed on hold until the
    corrective action has been accepted by the Purchaser.

## schedule

The Contractor shall submit a Preliminary Schedule to the Purchaser with
the Proposal. The Contractor shall submit to the Purchaser a Final
Schedule for acceptance by the date specified in the contract. Updates
to the Final Schedule shall be included in the Progress Reports required
under Section 2.6.

## Nb-to-SS Braze Sample

The Contractor shall manufacture one sample Nb-to-SS weld joint and
submit the sample to the Purchaser for approval as discussed in Section
7.3.

## Endwall to Cylindrical Cavity Weld Sample

The Contractor shall prepare a sample of the endwall to cylindrical
cavity body EB weld. The purpose of this sample is to determine weld
shrinkage during the final weld. As described in Section 12.2, the
Purchaser requires a hold point before these final welds are performed
on the cavities in order ascertain the cavities RF performance and
determine if a need exists for corrective machining. The information
obtained from welding of the sample will be used in this determination.
The contractor shall use the same weld preparations and weld parameters,
including joint pressure, for the final cavity endwall to outer body
weld as are used in the manufacture of the sample.

## Progress Report

The Contractor shall submit a monthly progress report to the Purchaser
documenting full details concerning the Contractor\'s progress during
the previous month. The progress report shall include a copy of the
schedule that reflects the Contractors progress during the month. The
progress report shall include any identified deviations and their
disposition. The progress report shall be submitted by the 15th day of
the month following the month on which progress is being reported.

## Superconducting CaVITIES

The Contractor shall deliver to the Purchaser two (2) low beta (β=0.4),
325 MHz superconducting Niobium (Nb) cavities complete with beam tubes,
RF ports and flanges fabricated in accordance with FNAL engineering
drawings as listed in Appendix A.

## Final reports and documentation (Traveler)

Prior to shipment, the Contractor shall furnish the Purchaser one copy
of the Traveler documenting the results of inspections, analyses and
tests performed by the Contractor, or his Designated Test Agency, to
determine conformance of the product to the requirements of this Scope
of Work. The proposed layout of the traveler shall be submitted to the
Purchaser with the Quality Assurance Plan for acceptance. This report
shall include the following:

-   The Testing Agency (if other than Contractor) name and address,
    including the date that the inspection, analysis, or test was
    performed.

-   Copies of all applicable manufacturing drawings both in paper and
    electronic format. Acceptable formats of the electronic form are
    IGES, STEP, Unigraphics part files, AutoCad files, SolidWorks files,
    or DXF.

-   Nb Receipt Certificate, as required by Section 4.2.

-   Information from visual inspection of each Nb sheet per Section 4.2.

-   The results of inspections performed to determine conformance of the
    RF surface profile to FNAL drawings.

-   Information on rework performed (if any), as required by Section
    7.5.

-   Sign-off sheet (\"Traveler Entry\") certifying that weld
    preparations were chemically polished (BCP) as required by Section
    6.1.

-   The welding parameters for each Nb-to-Nb EB joint and vacuum level
    in the welding chamber during EB welding, as required by Section
    7.1.

-   Results of weld inspection, as required by Section 7.2.

-   Results of vacuum integrity tests on parts, subassemblies and
    assembled cavity, as required by Section 8.1.

-   Results of final visual inspection of cavity, as required by Section
    8.3.

-   Copies of all Non-Conformance Reports, and their resolutions
    (corrective action), and other information specified in the Contract
    and agreed upon in advance by the Purchaser and the Contractor.

## excess material and spare parts

Nb material cutouts from raw part formation, Nb scrap, and material not
needed for cavity fabrication shall be identified as to heat, lot, and
Purchase Order Number, and returned to the Purchaser.

# Fabrication drawings

The marked-up drawings are listed in Appendix A. A Bill Of Material with
all the necessary parts to complete a full assembly is given in Appendix
B.

On the basis of the furnished drawings the contractor will produce his
own fabrication drawings for the resonator. The dimensions in these
drawings must allow for the material removal by etching and weld
shrinkage such that after etching and welding the tolerances specified
by the FNAL drawings are achieved. He will also prepare prescriptions
for chemical treatment and controls of drawings of tools and fixtures
for production. For the content of the documents he prepares the
contractor is responsible exclusively.

FNAL is furnished with a full set of the above mentioned fabrication
documents at least 2 weeks prior to their use for production. FNAL will
check if the specified characteristics of the resonator may be achieved
with these documents. Possible comments from FNAL pertaining to these
documents are without any liability. FNAL finally receives a set of the
documents actually used for production. In view of the still ongoing
development work, FNAL may wish to modify details of the current design
of the resonator. Such modifications will be carried out by the
contractor.

# Supply of Material

## Nb Quantity

FNAL will furnish the Nb material as Government Furnished Material
(GFM). This GFM material will be RRR grade 250 (or better) Nb sheets of
appropriate dimensions (approximately 50 cm x 50 cm). When FNAL delivers
the raw material, it will deliver the amount needed for one resonator
plus a reserve of ca. 10 %. All stock for the resonator is eddy current
scanned by FNAL to detect and sort out material with inclusions of
foreign materials or other defects. Any left over niobium stock and
scrap pieces of more than 20 grams will be returned to FNAL with the
last resonator shipment.

## Incoming inspection

The contractor will accept accountability for the GFM Nb sheets. Upon
receipt, the contractor will inspect the niobium stock for conformity
with specification. In case of nonconformity FNAL will inspect the
material at the contractor\'s plant and replace the material. As a
minimum, inspection shall be performed with the naked eye with
correction, if necessary, to 20/20 vision, at a distance of no more than
10 inches, and with the aid of a 100-watt light source. Magnifying aids
may be used to confirm the presence of visually observed defects and
deposits that would be detrimental to the fabrication of cavities for
the intended application. The annealed Nb sheet shall exhibit a clean
\"metallic\" surface condition and at least one side of each annealed Nb
sheet, thereafter called the \"RF\" side, shall be free from
imperfections (scratches, etched grain boundaries, etc.) deeper than
0.004 inch. The Contractor shall remove all visible surface
imperfections, scratches, indentations, and inclusions using Scotch
BriteTM (3-M Company). In the event that the Nb sheet contains defects,
imperfections, inclusions, etc. that can not be removed by this method,
the Contractor shall issue a Non-Conformance Report and submit it to the
Purchaser, who will replace the nonconforming Nb material at the
Purchaser's expense.

## Sheet material for Spokes

All sheet material for spokes will be eddy current scanned at FNAL. The
\"outer\" surface is marked by FNAL by methods to be agreed on by the
contractor. This mark should be visible after deep drawing, welding and
chemical cleaning. The opposite sheet surface is the \"inner\" surface
which carries the superconducting surface current. This surface shall
not be contaminated by any handling procedure (see Section 13.3).

# Production of parts

## Cavity assembly

The major components of a double spoke cavity assembly are the
following:

-   Spokes.

-   Spokes Beamline Tube and Weld Collars.

-   Endwalls.

-   Beamline Half Nipple.

-   Cavity Cylinder.

-   Stainless Steel Enclosure.

## Cavity and subassembly manufacturing

The Contractor shall choose the most appropriate method for cavity and
subassembly manufacture subject to the following conditions:

-   The welds that join the end walls to the cavity must be the final
    welds performed. As described in Section 12.2, the Purchaser
    requires a hold point before these final welds are performed in
    order ascertain the cavity RF performance and determine if a need
    exists for corrective machining.

-   The resulting final product (cavity) shall conform to the drawings
    listed in Appendix A.

-   Forming of the Nb material shall not reduce the wall thickness of
    any portion of the cavity, including weld zones, to less than 0.100
    inches.

-   Forming of the Nb Material shall not reduce the wall thickness of
    any portion of the spoke, including weld zones, to less than 0.115
    inches.

-   The Contractor shall use sufficient care to provide parts and
    cavities that are clean and free of internal and external
    imperfections, cuts, cracks, laminations, and tears, or other
    defects. In the event that such defects exist on the 'RF surface' of
    the part or cavity and are deeper than 0.004 inches, the part or
    cavity shall be reworked per Section 7.5 of this Statement of Work.

##  {#section .unnumbered}

## Identification Marking

The Contractor shall transfer identification information from each Nb
sheet to the corresponding Nb raw part according to the method of
manufacturing traceability and labeling developed by the Contractor and
accepted by the Purchaser. The identification marking shall be at least
3/8 inch in height, clearly legible, and shall be applied by stamping or
engraving on the \"non-RF\" side of the part. The marking shall have no
deleterious effect upon the cavity\'s intended performance. The
characters shall be sufficiently stable to withstand chemical polishing
of the exterior surface of the cavity. The marking procedure shall be
supplied to the Purchaser in the Manufacturing Plan for acceptance prior
to use.

# Production of subgroups

## SPOKES

In previous applications, spoke shapes have been hydroformed in two
separate halves and Electron Beam Welded (EBW) together. The parts are
formed from a 3.4 mm thick RRR 250 or better Nb sheet. Cutting the Nb
material should not deteriorate the bulk properties. Water cutting or
spark erosion can be used for this purpose. Before welding the spoke
halves, both parts must be cleaned by removing 20 μm by the standard
chemistry for Nb (see Section 13.2). Cleaning with ultrapure water,
drying and storage shall be done according to conditions described in
Sections 13.2 and 13.3. If welding cannot be carried out within 8 hours
after the chemical cleaning, another flash of 3 μm chemical etching is
necessary immediately before welding. Shrinkage of material during
welding must be accounted for in order to obtain the proper final shape.
The center pass-through hole for the beamline tubes is machined after
the EB welding.

## spoke Beamline tubes and flange connections

Tubes are cut from seamless Nb tube of RRR 250 or better provided by the
purchaser. In previous applications collars have been hydroformed.
Collars and beamline tube are EB welded together. Orientation markings
are allowed as long as the marking is placed in a position that will be
covered by the welding poodle. Before welding the collars to the beam
tube, all parts must be cleaned by removing 20 μm by the standard
chemistry for Nb (see Section 13.2).

SS flanges are connected to Nb parts by Nb-to-SS brazing. In the past
pure copper brazing at 1100C has proven adequate. Before brazing the Nb
parts need to be cleaned by removing 20 μm by the standard chemistry for
Nb (see Section 13.2). The finished sealing surfaces of the above
mentioned flanges shall be protected by plastic caps (soft polyvinyl
chloride is acceptable) at all times, except for flange dimensions
measurements and inspection of finish of sealing surfaces.

## Cylinder body and pull-out Holes

The cylindrical body is made by rolling and seam-welding together
rectangular pieces of Nb RRR 250 or better. The rolling of the Nb must
be performed with appropriate protective paper or plastic to avoid any
inclusion of extraneous particulates in the Nb sheets. The length of the
cylindrical body is kept longer by \~10 mm to allow proper start and
stoppage of the seam weld and tuning of the cavity frequency. Holes for
spokes and coupling ports are then machined and formed with a pull-out
technique. Finally the spoke are aligned and maintained concentrical by
use of a round bas passing throiugh the beam holes and the spokes are EB
welded to the cylindrical cavity. Before welding the spoke to the
cylindrical cavity, all parts must be cleaned by removing 20 μm by the
standard chemistry for Nb (see Section 13.2).

## endwalls

The endwalls can be hydroformed. The edge of the endwall that will
connect to the cylindrical body is left longer by \~5 mm to allow for
tuning of the cavity frequency. Stiffeners of Nb RRR 50 are then welded
on the outside surface of the endwalls in a single vacuum cycle.

## Cavity tuning

Before the final weld of the endwalls to the cylindrical body, the
cavity is measured at FNAL for tuning of the frequency. Final machining
of the cylindrical body and endwalls is a responsibility of the vendor.
Final standard chemistry for Nb (see Section 13.2) or Electron Beam
polishing, if available, is performed on the internal surface of the
cavity before the final welding of the endwalls to the cylindrical body
and of all connection flanges.

# Welding of elements

## niobium to niobium joints

The Contractor shall develop a joint design (weld procedure) for every
Nb-to-Nb interface. All Nb-to-Nb welds shall be high-vacuum, full
penetration, cosmetic under-bead electron-beam (EB) welds. The
Contractor shall specify required dimensional inspection and weld
examination after each weld in the Traveler. The EB welder vacuum
chamber shall be wiped free from tramp particulate material from other
welding tasks prior to use for Nb welding. The vacuum level in the
welding chamber, and inside the cavity, shall be \< 5 x 10^-5^ Torr
during welding and at any time Nb parts are at a temperature \>80°C. The
vacuum level in the chamber during EB welding as well as all EB welding
parameters shall be reported in the Traveler. Once a weld design and
parameters have been accepted by the Purchaser, they shall not be
revised without written permission of the Purchaser.

The Contractor shall prepare fabrication drawings for all weld
preparation machining. These drawings shall be included in the
Manufacturing Plan and accepted by the Purchaser prior to beginning the
work.

The Contractor shall thoroughly inspect each raw part and remove any
defects. Particular emphasis has to be exercised to detect any surface
irregularities, embedded particles, loose Nb shavings, or scratches.
These imperfections shall be removed by mechanical grinding, as required
by Section 7.5. Prior to welding, each machined part shall be
solvent-degreased and chemically cleaned by buffered chemical polish to
remove 20 μm (unless otherwise noted) by the standard chemistry for Nb
(see Section 13.2). The parts then shall be rinsed in high purity water
(electronic grade E-1, as per ASTM Standard D5127-90 (Ref 2)), dried in
air, and put in new, clean nylon bags for protection. This operation
shall be performed in a clean area. The Contractor shall establish
optimum EB welding parameters and fixtures. The Purchaser recommends the
use of a low energy density beam accomplished by defocusing and/or
\"rhombic raster\" patterns. No vapor column is permitted when making
welds that are exposed to the cavity interior. The welding parameters
and fixture design shall be documented in the Traveler.

## weld quality

The weld quality will satisfy the following conditions:

-   No cracks visible with a 10X magnifier shall be permitted on the
    surface at any weld joint in the cavity.

-   Full penetration of all welds is required. The interior bead shall
    be smooth and free of visible (with 10X magnifier) weld splatter.

-   No obvious EB start or stop marks (craters) on the interior bead
    shall be allowed. Overlap of weld and tapering out at the overlap
    are required.

-   Finished welds shall be free of voids and foreign particles or
    material inclusions. No cracks at the edge of melted zones shall be
    present as determined by a visual inspection with a 10X magnifier.

-   After completion of EB welding, the part shall be allowed to
    cooldown in the welding chamber until the part temperature is below
    80°C. The part may either be left under vacuum or the welding
    chamber may be vented with dry nitrogen from liquid nitrogen
    boiloff, or ultra-pure nitrogen (99.999% pure), or ultra-pure argon
    (99.999%pure). The welding chamber shall not be vented to air until
    the Nb temperature is below 80°C and a minimum of 30 minutes has
    passed since the welding operation was completed. In case of a
    defect in a weld (voids, cracks, etc.), a maximum of three (3)
    repair cycles (RI or R2 or R3) as applicable, using the same welding
    process/procedure, may be accomplished in the same area of the weld
    defect. If after the third attempt the repair is not successful, a
    Non-Conforming Report shall be initiated and submitted to the
    Purchaser for disposition.

## Niobium to Stainless Steel Joints

The Contractor shall develop a brazed joint design for every
Niobium-to-Stainless steel interface. The brazing alloy shall be either
Nioro (AWS specification AWSA 5.8-76, BAu-4 - 82% Au and 18% Ni) or
Copper. The brazing temperature shall be kept below 1100°C.

The Contractor shall build a minimum of one prototype of each joint type
used on the double spoke cavity. The prototypes shall be tested and the
results supplied to the Purchaser for acceptance prior to commencing
with tube-vacuum flange subassembly fabrication. During test the minimum
joint shear stress shall be 4000 psi. The joint shall be leak tight at
operational temperature. The prototype testing procedure shall be:

-   Vacuum leak test assembly after brazing.

-   Tensile test each prototype assembly at 3000 lbs.

-   Cycle between room temperature and liquid nitrogen temperature a
    minimum of 10 times.

-   Vacuum leak test assembly.

## Flange-Nb Tube Subassemblies

All sealing surfaces of the cavity (beam pipe flanges, power coupler
flanges, and test port flanges) shall be stainless steel CONFLATTM
flanges as specified in the FNAL engineering drawings. The Contractor
shall braze the stainless steel CONFLATTM flanges to Nb tubes in
accordance with the braze joints developed under Section 7.3. The
Contractor shall exercise extreme care to avoid any scratches on the
sealing surface. New polyethylene covers shall be used to protect the
flanges. No adhesive material shall be applied to the sealing surfaces.

## Rework

Rework of a part in the form of reshaping, grinding, and mechanical
straightening is permitted. Each part that needs to be reworked shall be
considered as a Non-Conforming item. The Contractor shall document the
need for the rework and nature of corrective action in the Non
Conformance Report and submit it to the Purchaser for acceptance, as
required by Section 12.4. The Contractor shall use aluminum oxide
abrasive embedded in fibrous material grinding wheels (General Purpose
Unitized Wheel GPW-U type 7A MED, 3M-Company or similar). Cutting,
grinding and abrasive tools shall be Nb dedicated and shall not be, or
have been, used on other materials. A tracking program of the use of the
tools shall be a part of the QA Plan and shall be reported in the
Traveler. BCP Chemical polishing shall follow any rework (Section 13.2).

# Final test of cavity

## Leak check

Before lowering the internal pressure, the resonator must be constrained
against becoming shorter and thus being permanently deformed, by fixing
its connecting flanges to external braces. Silicon grease must be
strictly avoided.. The finished resonator is subjected to a leak test.
The prescribed leak-tightness of

$1 \times \text{10}^{- 6}$ cc/s

must be determined with the sensitivity of the helium leak tester such
that full range of its instrument corresponds to

$1 \times \text{10}^{- 9}$ cc/s

A plot of the indication of the leak tester as function of time shall be
made over ca. 5 min before and ca. 5 min after application of ca. 1 bar
helium, with time of application of He marked in the plot. This plot
shall be included in the quality control documentation.

The Helium leak check shall be performed according to the ASTM Standard
E1603 -99 or equivalent. The leak check procedure shall be submitted to
the Purchaser in the Manufacturing Plan for acceptance. All vacuum lines
to the tested part or cavity shall have a liquid nitrogen cold trap
installed between the cavity and the pumping systems.

Repair of leaks requires in all cases prior approval of FNAL as to the
method, and possible risks.

## Mechanical measurement

Dimensions, inner surface, welds and other features of the resonator are
inspected as per Section 12.1.

The Contractor shall perform measurements of cavity straightness. Each
cavity shall be simply supported at cavity beam tube joints. A measure
of straightness shall be determined by the concentricity of the spoke
bore tube and end wall bore tubes as measured relative to a straight
line. The testing procedure shall be supplied to the Purchaser in the
Manufacturing Plan for acceptance. Care should be exercised to avoid
scratches on the bore tube surfaces. The results of this test shall be
reported in the Traveler. The total length of the cavity as measured
between end flanges, shall be reported in the Traveler.

All results of measurements and inspections are recorded in a traveler
and sent to FNAL **prior** to shipment of resonator.

## visual inspection of the final product

The Contractor shall visually inspect the exterior and interior finish
of each cavity. The interior examination shall be performed using an
endoscope. All findings shall be described in the Traveler.

# Acceptance, Packing and shipping

## Certification and Authorization to Ship

The Contractor shall furnish a certificate of compliance to the
Purchaser that the superconducting cavity was manufactured and inspected
in accordance with the requirements of this Scope of Work and that the
cavity and has been found to meet the requirements (except as documented
in Purchaser-accepted Non-Conformance Reports). Shipment of the
completed cavity shall not occur until all inspections identified in the
Contract have been completed and the Traveler has been received and
accepted by the Purchaser. Authorization to ship the cavity shall be
communicated in writing by the Purchaser\'s authorized representative
within 10 calendar days.

The Purchaser will perform any tests deemed necessary to ensure that
superconducting cavities conform to the requirements of this Scope of
Work. As a minimum, this would be a frequency measurement in air at room
temperature.

## Identification and Marking

Each cavity shall be marked with the Contractor\'s identification,
marked on the beam tube extensions. Characters shall be at least 3/8
inch in height, clearly legible, and shall be applied by stamping or
engraving. The marking shall have no deleterious effect upon the
cavity\'s intended performance. The characters shall be sufficiently
stable to withstand ordinary handling. The marking procedure shall be
supplied to the Purchaser in the Manufacturing Plan for acceptance prior
to use.

## Packaging

The finished cavity shall be prepared for shipment in accordance with
commercial practice and in compliance with applicable rules and
regulations pertaining to the handling, packaging, and transportation of
the product to ensure carrier acceptance and safe delivery. Each
finished cavity shall be individually sealed inside a new, clear
polyethylene or nylon bag, with inner wooden container packaging using
\"Foam-in-Place\" Technology or equivalent as approved by the Purchaser
to support the cavity weight, stabilize against movement, and prevent
any mechanical or chemical damage during transportation. All flanges
shall be sealed with CONFLATTM blanks with gaskets. Part numbers shall
be visible without having to open the bag seal. Wooden containers that
prevent impact damage and bending shall be used. The containers shall be
constructed such that they can be handled by forklift, and no palletized
load shall exceed 1,000 pounds. Two, five, and 20 g accelerometers or
equivalent as approved by the Purchaser in vertical and horizontal
orientation shall be installed in the container. Two TIP (N) TELL
indicators shall be attached to the exterior of the wooden container, on
opposing sides of the container. The Purchaser shall accept the design
of containers prior to fabrication. The containers shall be so marked as
to indicate the nature of the best method of handling.

## Shipping

The shipment shall be by air. Ground transportation to and from airports
both at point of origin and destination shall be by air-ride vehicle,
most direct route, with minimum handling. Maximum acceleration in
vertical and horizontal orientations shall not exceed 5g. In the event
that the Contractor is a foreign entity, arrangement shall be made prior
to shipment with the shipping agency to preclear with U.S. Customs the
import of cavities. The Contractor shall place the following warning
message at the exterior of the container: \"Open Only in Presence of the
U.S. Department of Energy Authorized Representative\"

# Time schedule

A reliable time schedule has to be provided by the contractor when
signing the contract. It must contain reasonable details to follow
closely the production as well as state milestones, e.g. frequency
measurement of half cells and dumb-bells, start of welding the cavity
body and delivery of individual resonators.

# Progress report

The contractor shall submit a monthly progress report to the FNAL
technical representative. The progress report shall provide full details
concerning the contractor\'s progress during the previous month. The
progress report shall be submitted within the 15^th^ day of the month
following the one for which progress is reported.

# Quality Assurance Documentation

## Responsibility for testing and inspection

The Contractor shall be responsible for performing all required
inspections, analyses, and tests designated herein. The Contractor shall
provide space, personnel, and test equipment to meet all inspection
requirements. All testing and inspection shall be performed at the
Contractor\'s facilities, or at the facilities of a mutually acceptable
Designated Test Agency. The Contractor shall notify the Purchaser 15
calendar days in advance of scheduled commencement of any tests and
inspections required by this Scope of Work to allow for the Purchaser to
arrange for witnessing the inspection, if elected. Results of
inspections, analyses, and tests performed by the Contractor shall be
reported in the Traveler, as required by Section 2.8. Inspections
specified herein are not intended to supplant any controls,
examinations, inspections, or tests that the Contractor shall perform to
assure the quality of the final product.

## hold points

The Purchaser may specify in the contract the hold points in the
processing and fabrication of the finished product covered by this Scope
of Work. The purpose of all hold points shall be to determine
conformance of products to the requirements of this Scope of Work before
continuation of further processing and/or fabrication. The following
hold points are Purchaser defined, minimum engineering holdpoints which
shall be identified in the Traveler in addition to any hold points
identified by the Contractor in the normal course of QC, Test, or
Fabrication operations. The Purchaser may elect to witness and sign off
any mandatory hold points but in any case, as a minimum, the Contractor
QA/QC representative/inspector signature is required for each one.

-   Material receipt inspection.

-   BCP of weld joint preparation.

-   Leak rate test/inspection.

-   Frequency measurement immediately prior to the final EB welding of
    the endwalls to the cavity.

-   Cavity geometry measurements.

-   Final visual inspection of the cavity.

In the event of a Non-Conforming condition further processing of the
Non-Conforming item shall be put on hold until the corrective action has
been accepted by the Purchaser.

## purchaser right to inspection

The Purchaser reserves the right to have its designated representative
witness, at the place of manufacture, processing/fabrication operations
agreed upon by the Purchaser and Contractor and specified in the
Contract including metal forming, inspection of weld preparations,
electron beam welding parameters and vacuum recording charts, etc. The
Purchaser reserves the right to have its designated representative
witness, at the place of manufacture, the inspections, analyses, and
tests established under the Contractor\'s QA Program to demonstrate
compliance with the Scope of Work. The intent of the Purchaser in
witnessing inspections, tests, and/or processing/fabrication operations
is to gain confidence that production operations will produce
superconducting cavities conforming to this Scope of Work.

## corrective action

In the event that the cavity or any portion thereof is rejected by the
Purchaser as a result of poor workmanship or nonconformance to this
Scope of Work, the Contractor shall take corrective action on the
material or process, or both as necessary, on all items or portions
thereof which were similarly manufactured which are subject to the same
cause for rejection. Acceptance shall be withheld until inspections and
tests have shown that the corrective action was successfully implemented
and the cavity or any portion thereof conforms to the requirements of
this Scope of Work.

# Appendix

## Degreasing, ultrasonic cleaning, drying

Degreasing and ultrasonic cleaning with \"Ticopur\" or equivalent,
followed by rinsing in de-ionized, filtered (0.2 μm particle size)
water, precedes all etching operations. Rinsing is done until a
resistivity of 10 MΩcm is reached. Hot water (temperature about 60 ^0^C)
is preferred for more intense cleaning action. For selection of baths
for degreasing and ultrasonic cleaning the contractor will contact FNAL.
Drying is carried out in laminar airflow in a clean room of class 1000
or better. The parts must be supported in places well away from the weld
preparations and the RF surfaces to avoid drying stains there.

## Chemical cleaning, Rinsing, Drying

Generally, all etching operations are carried out with the niobium part
immersed in the acid mixture, i.e. over the entire surface. The acid
mixture consists of HF (48 % conc.), HNO~3~ (65 %) and H~3~PO~4~ (85
conc.) in the volume ratio 1 : 1 : 2, respectively. All acids are p.a.
grade. The removal rate is roughly 1 μm/min for fresh acid at 15 ^0^C,
but depends on agitation as well as niobium content and temperature of
acid mixture. Before etching resonator parts, a test etching must be
made. After etching, the parts are quickly (within max. 15 sec) immersed
in a rinsing bath. At no time during etching and transfer to the rinsing
bath may the acid temperature be permitted to exceed 20^0^C. The acid
mixture is replaced when its niobium content reaches 10 g/l,
corresponding to an etch rate of about 0.5 μm/min. Removal of thickness
always is understood to refer to one surface only.

For all etching operations the following should be recorded in the
travelers: Part type and serial number, bath temperature, duration and
thickness removed (determined by weighing of at least one sample out of
each batch).

The etched parts are rinsed with de-ionized, to 0.2\~μm particle size
filtered water, of Electronic Grade Type E-1 conformed to the ASTM
Standard D 5127 -- 90, until a resistivity of 10 MΩcm is achieved.

Drying is carried out in laminar airflow in a clean room of class 1000
or better. The parts must be supported in places well away from the weld
preparations and the RF surfaces to avoid drying stains there.

## Handling and storage conditions

Contact of the niobium surfaces with substances that the cleaning and
etching processes described in "13.1, 13.2" will not completely remove
must be prevented. Such forbidden materials include silicone products,
chemically stable plastics such as Teflon, fingerprints and others. They
can disturb etching processes and limit RF performance. General
precautions against contamination of the Nb parts include use of
suitable lint free gloves, keeping work areas and tools used in clean
condition, and protection against dust during storage and assembly of
cavity components. Moreover the \"inner\" surface of the cavity and
spokes must be free of the following surface contaminations:

-   Scratches deeper than 15μm

-   Mechanical damage larger 15 μm

-   Imprints of foreign material

## Welding preparation

Before welding, all parts must be cleaned by 3 μm chemical etching at
the welding area. Welds at the equator and iris of cells and at the HOM
coupler parts will be exposed to high magnetic or electric fields.
Therefore absolutely clean conditions must be assured during welding.
These parts must undergo a chemical cleaning of 20 μm after the last
mechanical treatment. Another 3 μm chemical cleaning is necessary if the
time between last chemical cleaning and welding exceeds 8 hours.
Touching the weld preparation area after the last cleaning must be
strictly avoided. Especially storing the half cells or dumb-bells with
the equator/iris weld preparation area touching the storage table is not
allowed. Also wiping the welding step with some alcohol soaked \"dust
free\" cloth must be avoided. A last cleaning of the welding step from
dust by blowing with clean and dry nitrogen gas is recommended. Ionized
gas may be helpful to remove dust.

## general electron beam Welding conditions

To prevent oxidation and other contamination of weld preparations,
welding shall generally commence within the same work shift in which the
parts were cleaned, etched, rinsed and dried.

The pressure in the welding chamber has to be less than 5 x 10^-5^ mbar
during welding. The welding chamber shall be vented with clean gas (see
Section 7.2) only after the temperature of the niobium part has dropped
to 80 ^o^C at the hottest spot.

All welds must have full penetration, be smooth and of uniformly wide
root on the inside surface of resonator and must neither protrude nor
stay back by more than 0.1 mm with respect to the neighboring surface.
Welding from the inside (RF-side) is recommended, wherever possible.
Wiggling the electron beam according to a suitable pattern has been
found to be very useful in producing uniformly wide and flat roots and
to reduce risk of burning holes. Niobium vapor from welding must be
prevented from contaminating weld preparations elsewhere by the use of
suitable shields.

The contractor shall, after optimization of welding parameters,
demonstrate by test welds to FNAL that the RRR in the welds and weld
overlaps is not degraded by more than 10 % over that of the unwelded
niobium. No cracks, pores, inclusions of foreign materials or other
defects are allowed in welds. FNAL will check that these requirements
are met on test- and production welds by eddy current- and other
methods. During the weld tests the welding-chamber gas is analyzed with
a mass spectrometer (FNAL can assist with equipment and personnel). The
final welding parameters for production are subject to approval by FNAL.

The welds connecting the spokes to the cylindrical cavity (spoke weld
collars) will experience the highest fields during operation of the
cavity. As such it is expected that no appropriate procedure exist to
repair a hole in a spoke weld collar. Although the visual appearance of
a repaired weld may look good, the RF performance of such a cavity is
degraded. Therefore a repaired collar weld cannot be accepted. In such a
case the contractor has to inform FNAL and propose a procedure to cut
the damaged collar and replace it in a way that is free of welding
defects. The repair procedure has to be agreed on by FNAL but will be
carried out at the contractor\'s risk and cost.

Any repair of a weld contemplated by the contractor requires in each
instance prior approval of the methods by FNAL.

## Grinding

Grinding of defects at the \"inner\" cavity surface has proven to avoid
performance limitations of superconducting resonators. Grinding should
be restricted to the defect area and produce a smooth surface. The
pressure and velocity of the grinding wheel should be chosen so that no
heating of the ground Nb area occurs, no deep scratches are produced at
the ground area and a smooth transition is gained at the border from the
ground to the untreated surface area.

Two different types of grinding tools have been successfully applied:
rubberized abrasives of various shapes (cylinders, cones, thin wheels,
..) and flapped wheel (fan shaped rotating grinding paper). Two types of
abrasives are commonly in use: silicon carbide and aluminum oxide
(Korund). Both materials are only slowly dissolved by the Nb-chemistry
(\"13.2\"). Therefore the size of the abrasive particles should be not
larger than 50 μm. In this case any imbedded abrasive particle will be
removed from the bulk Nb when etching a layer of 150 μm during final
preparation of the resonator.

Recommended abrasive wheel: CRATEX, No. 545097, rubberized abrasive 120
No 83C

Recommended flapped wheel: \"Pferd\", abrasive size 320 or higher.

## Cavity contour, frequency and length

In the accelerator the cavity has to operate at the frequency of
325.000+/-0.030 MHz. The frequency sensitivity of the cavity is
determined by the all dimensions of the cavity itself, with major
emphasis on the diameter of the cylindrical body, the shape of spokes,
the length of the gap between spokes and between spoke and endwall, and
by the contour of the spokes around the beam opening. Major parameters
to control are the following:

-   Diameter of the cylindrical cavity

-   Diameter of the spoke base

-   Diameter of spoke beam opening

-   Curvature radius for the spoke contour shape around the beam opening

-   Gap between spokes

-   Gap between spoke and endwall

The change of the resonance frequency by changing mechanical dimensions
is given in the following list.

-   Change in the diameter of the cylindrical body by 0.1 mm changes
    frequency by 0.1 MHz

-   Change in the diameter of the spoke base by 0.1 mm changes frequency
    by 0.02 MHz

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-   Change in the diameter of the central part of one spoke by 0.1 mm
    changes frequency by 0.05 MHz.

-   Change in the distance from Enwall to spoke by 0.1 mm changes
    frequency by 0.02 MHz.

The delivered cavity is tuned at FNAL to establish the right resonance
frequency. This is accomplished by slightly changing the gap between
endwalls and spokes. Any deviation of the ideal cavity contour will be
compensated hereby but with the consequence of changing the total cavity
length and field distribution. At this time, it is believed that
acceptable tolerances are

-   ±0.1 mm for welding shrinkage

-   ±0.2 mm for contour change of the spokes

## List of drawings

The list of drawings is attached separately.