+-----------------------------------+-----------------------------------+
| ![](media/image1.                 | Fermi National Accelerator        |
| png){width="1.8708333333333333in" | Laboratory                        |
| height="0.3548611111111111in"}    |                                   |
|                                   | Technical Division                |
|                                   |                                   |
|                                   | SRF Development Group             |
|                                   |                                   |
|                                   | P.O. Box 500 -- Batavia, Illinois |
|                                   | -- 60510                          |
|                                   |                                   |
|                                   | FAX: (630) 840-8036               |
+-----------------------------------+-----------------------------------+

SPECIFICATION FOR A 325 MHZ ROOM TEMPERATURE POWER COUPLER FOR THE HIGH
INTENSITY NEUTRINO SOURCE AT FERMILAB

[5500-ES-371032]{.underline}

  ---------- ---------- ----------- ----------------- ------------ -----------
  Revision   ER/ECO     Date        Description       Originated   Approved by
                                                      by           

             ER #8407   13-Nov-23   Original Issue                 

                                                                   

                                                                   

                                                                   

                                                                   
  ---------- ---------- ----------- ----------------- ------------ -----------

Table of contents

[1 Introduction 3](#introduction)

[2 Deliverables 3](#deliverables)

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

[2.2 Brazing 3](#brazing)

[2.3 Final reports and documentation
4](#final-reports-and-documentation)

[3 Materials and processing 4](#materials-and-processing)

[3.1 Machining 4](#machining)

[Material 4](#material)

[Roughness and tolerances 4](#roughness-and-tolerances)

[Sharp corners 4](#sharp-corners)

[3.2 Brazing 4](#brazing-1)

[Ceramic feedthrough 4](#ceramic-feedthrough)

[Coupler tip 5](#coupler-tip)

[Cleaning 5](#cleaning)

[Leak tests 5](#leak-tests)

[Virtual leaks 5](#virtual-leaks)

[3.3 Welding 5](#welding)

# Introduction

This specification describes the fabrication details for a room
temperature power coupler used to input radio-frequency (RF) power in
the crossbar h-type cavities (later identified as cavities) used for the
initial acceleration of protons and electrons in the front end section
of the high intensity neutrino source project at Fermilab (Fermi
National Accelerator Laboratory). The front end section consists of 16
room temperature cavities all similar in shape and operated at a
frequency of 325 MHz. The same power coupler will be used in each one of
the 16 cavities.

The power coupler will be fabricated through a series of machining,
brazing and welding cycles.

# Deliverables

## Manufacturing plan

The seller shall submit a manufacturing plan to the buyer for
acceptance. The plan shall identify and describe all aspects of work to
be executed.

The buyer 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 seller to commence some fabrication tasks earlier. The seller
shall also submit a schedule to the buyer, the schedule shall be an
accurate representation of the actual time required to fabricate the
order. Any update to the schedule shall be communicated to the buyer.

## Brazing

Seller is responsible for the performance of all brazed joints
especially regarding leak tests specified on drawings. Fabrication
drawings furnished by buyer include several brazing features (mating
tolerances, alloy wire grooves, counter bores, etc..). These features
are intended to be functional only for brazing purposes and may be
modified or deleted, others may be added if considered necessary. Final
design of all the brazing features shall be discussed with the buyer for
acceptance.

If brazing processes are outsourced by seller, an agreement between the
seller and the outsourced brazing company on the final design of brazing
features shall be submitted to buyer. If seller decides to outsource
brazing to a different company, the same design of brazing features
shall be used and a new agreement between the seller and the new brazing
company shall be submitted to the buyer.

## Final reports and documentation

Prior to shipment, the seller shall furnish the buyer one copy of the
traveler documenting the results of inspections, analyses and tests
performed by the seller, or his designated test agency, to determine
conformance of the product to the requirements of this scope of work.

# Materials and processing

## Machining

### Material {#material .unnumbered}

Only oxygen free electronic copper should be used (UNC C10100). Seller
must provide material certifications for all material used.

### Roughness and tolerances {#roughness-and-tolerances .unnumbered}

A maximum surface roughness of 3.2 µm is requested on surfaces. All
tolerances specified on drawings are functional only for brazing
purposes; a general tolerance of ±0.1mm is requested everywhere else.

### Sharp corners {#sharp-corners .unnumbered}

Sharp corners must be treated with scraping tools, abrasives must never
be used and sandpaper or any other process that may leave inclusions on
inside surfaces[^1] must be avoided.

For this reason, extreme care should be used during fabrication of these
surfaces since any scratch, pit, bevel or groove may not be polished
away with traditional techniques.

## Brazing

Several brazing cycles are required throughout the fabrication process.
More than one brazing alloy is needed to perform subsequent cycles at
different temperatures on the cavity. Most brazed joints are required to
be leak checked for vacuum purposes.

### Ceramic feedthrough {#ceramic-feedthrough .unnumbered}

A ceramic feed-through is used inside the power coupler to separate
vacuum volume from air. The feed-through is composed of two concentric
copper sleeves separated by a ceramic disc. When the feed-through is
brazed in the power coupler's main body, the copper sleeves and the main
body expand considerably compared to the ceramic disc. Air gaps are
provided around the feed-through to avoid damage of the ceramic disc.
Vent holes are machined in the copper sleeves to relieve trapped air.

### Coupler tip {#coupler-tip .unnumbered}

To facilitate correct positioning of tip during brazing cycle, three
stainless steel screws are used (#2-56UNC, #6-32UNF). Brazing alloys in
the form of foil or paste may be used.

### Cleaning {#cleaning .unnumbered}

Surfaces of the metals must be clean for the capillary action to work
properly during the brazing cycle. If contaminations are present (oil
coating, grease, rust, scale or just plain dirt) those have to be
removed or they will form a barrier between the base metal surfaces and
the brazing materials. If the metal surfaces are coated with oxide or
scale, these must be removed either chemically or mechanically. Once the
parts are thoroughly clean, they shall be fluxed and brazed as soon as
possible.

### Leak tests {#leak-tests .unnumbered}

All joints required to be leak tight must be tested by seller as per
Fermilab engineering specification ES-107240.

### Virtual leaks {#virtual-leaks .unnumbered}

Any volume with trapped air should be avoided when brazing the cavity
elements together as this is identified as a virtual leak and might
generate a future leak of air inside the vacuum space. Vent holes should
be used to relieve these trapped volumes.

## Welding

Vacuum flanges must not be baked over 400°C as this may cause warping of
the knife edge feature critical to vacuum performance of the flange. For
this reason, flanges may only be welded on cavity ports after all
brazing cycles on cavity are completed.

Knife edges of all vacuum flanges should be protected at all times,
plastic protection caps shall always be used to protect the flanges
during handling, assembly and transportation.

[^1]: All outer surfaces in contact with air are an exception as their
    quality does not affect the performance of the power coupler.