Double Warm Window

1
Double Warm Window

• M. Bevins

2
CONTENTS

• Objective
• Requirements Constraints
• Design Description
• Window Improvements
• Window RD Effort
• Design Status Where We Go From Here

3
OBJECTIVE
Incorporate a second warm window to establish a
UHV waveguide guard vacuum space employing
knife-edge sealing technology in the C100
cryomodule.
4
REQUIREMENTS

• Cavity string must be hermetically sealed prior
  to leaving clean room and installation into the
  vacuum vessel
• Design must avoid RF breakdown and excessive
  heating
• Diagnostics to include
• Arc detector and vacuum monitor in guard vacuum
  region
• IR sensor for each window
• Waveguide guard vacuum design goal lt10-8 torr
• RF Interlock set at 10-7 torr

5
DESIGN CONSTRAINTS

• Limited space allows only the inner window to be
  installed on the cavity string in the clean room
• Requires inner window to have an in-line
  double-sided knife-edge to attach guard vacuum
  waveguide section and outer window

Vacuum vessel
Space frame
Double-sealing inner window flange required
Cavity string
6
DESIGN CONSTRAINTS
Current Window Flange

• Current window flange is not wide enough to
  accommodate 2nd knife edge.
• Requires change in width of ceramic window OR
  change in width of the flange.
• Strong desire to avoid changes to the RF design
  drove decision to increase the width of the
  flange

Single knife-edge seal to cavity string flange
Ceramic windoweyelet
7
DESIGN CONSTRAINTS
The width of the window flange is constrained by
the spacing between fundamental RF power couplers
(FPC) 4 5 at the center top hat.

• Increased FPC 4 5 spacing by trading drift
  length from one end to the other
• Allows window flange width to increase to
  accommodate 2nd knife-edge
• Forces mod to mating FPC warm flange

Renascence FPC 4 5 Spacing
NEW 12GeV FPC 4 5 Spacing
FPC 8

Center Top Hat FPC 4 5
Increased drift here
Decreased drift here
Maintained 39.37inch FPC to FPC spacing
FPC 1
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DESIGN DESCRIPTION NEW Spacing at Center Top Hat
FPC 4
FPC warm flange
FPC 5
Inner window flange
Center top hat
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DESIGN DESCRIPTION Double-Sided Knife-Edge
Flange

• Flange design requirements were presented to
  three leading industry flange makers
• Allowed industry to define the number, size and
  spacing for the bolts and the knife-edge geometry
• Approach minimizes cost through competition
• Responses from vendors
• Vendor 1 has developed a detail design
• Vendor 2 is developing a design
• Vendor 3 No Bid
• Plan to down-select to one design based on sample
  testing at JLab

Outside Dimensions 3.78in x 7.62in x 1.36in
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DESIGN DESCRIPTION Center Top Hat Configuration
Renascence Top Hat
NEW 12GeV Top Hat
Instrumentation ports moved off top hat to
dedicated feed through flange
Explosion bonded AL to stainless instrumentation
ports
22.25 OD
18.65 OD
Single-sided knife edge sealed window flange
Double-sided knife edge sealed window flange
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DESIGN DESCRIPTION UHV Guard Waveguide Section
Flange to 1st (inner) window flange
Flange to 2nd (outer) window flange
1-1/3 mini Conflat inst. port (IR)
Cu plated SS tube (inside dimensions match FPC)
2-3/4 Conflat vacuum port
1-1/3 mini Conflat inst. port (arc)
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DESIGN DESCRIPTION RF Shielded Pump Port

• Holes bored into wall of waveguide
• Radius inside edge of holes

2.5 OD tube
RF shield holes
Inside weld
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DESIGN DESCRIPTION Center Top Hat Configuration
Inner window IR sensor
1st (inner) window flange
Vacuum pump port
Air side waveguide (same position in tunnel as
existing modules)
2nd (outer) window flange
Port for outer window IR sensor
Arc detector
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DESIGN DESCRIPTION Vacuum System Design
Roughing valve

• Vacuum design goal lt10-8 torr (RF interlock 10-7
  torr)
• Assumed 2.510-11 torr-liter/s/cm2 outgassing
• Guidance for conductance calculations from J.M.
  Lafferty, Vacuum Science text
• Net pumping speed provides margin of 5 based on
  expected gas load

30L/s ion pump
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DESIGN DESCRIPTION Vacuum System Design
Elevation View
Top View
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DESIGN DESCRIPTION - Overall Layout
Plan View
Elevation View
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DESIGN DESCRIPTION - Waveguide Support Brackets
Simple - Robust Adjustable

• Stainless steel construction
• Simplified design minimizes features that must be
  controlled
• Provides adequate translation and rotation in all
  six d-o-f to support as-built waveguide
  position

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DESIGN DESCRIPTION - Waveguide Support Brackets
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DESIGN DESCRIPTION - Cryomodule Tunnel
Installation

• Complete double window waveguide assembly can be
  installed prior to installation in tunnel
• Module is narrower than original CEBAF design

C100 module in aisle
Original CEBAF module installed in beamline
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WINDOW IMPROVEMENTS Weld-in Window Adapter

• Several 304 stainless steel window flange seals
  have failed as a result of softening of the
  knife-edge during brazing
• Recent tests using 316LN stainless have resulted
  in successful post braze seals
• An alternative to the use of 316LN is to braze
  the ceramic and eyelet into 304/304L stainless
  steel adapter
• Brazed assembly is then welded into the flange
  (flange never sees braze cycle)
• Design separates braze and flange sealing
  challenges
• Allows use of 304/304L stainless steel for both
  the flange and the adapter

Ceramic
Eyelet
Adapter
Double-sided flange
21
WINDOW IMPROVEMENTS Copper vs Kovar Eyelet

• High power RF testing of our Renascence windows
  shows significant heating in the Kovar eyelet
• An effort underway to support refurbishment of
  the original CEBAF cryomodules warm window is
  investigating use of a copper eyelet to reduce RF
  heating
• Several windows were successfully brazed using a
  copper eyelet at an outside braze house and
  tested in our RF test stand

Copper eyelet
CEBAF Replacement Window with Copper Eyelet
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WINDOW IMPROVEMENTS Copper vs Kovar Eyelet

• Tests demonstrate a significant reduction in RF
  heating using the Cu eyelet
• Thermal cycle testing underway to study fatigue
  limit of Cu eyelet

Tmax 85C
Tmax 321C
Renascence Window (RF Power 8kW) (Kovar eyelet)
CEBAF Replacement Window (RF Power 8kW) (Copper
eyelet)
Temp C
Large temp gradient in ceramic ?T160 C
Nearly uniform ceramic temp
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WINDOW RD EFFORT Thermally Matched Window
Flange

• The difference in thermal expansion of the
  alumina ceramic window and the stainless steel
  flange presents a significant mechanical design
  challenge
• Conventional window design uses a eyelet
  structure to provide strain relief to the ceramic
  to accommodate the braze cycle and operational
  thermal loading
• Eyelet compliance must be balanced against
  ability to remove heat generated in ceramic from
  RF losses
• A window flange fabricated from a pseudo-alloy of
  tungsten and copper may offer significant
  improvements in the design of RF windows
• Idea is to tune the CTE of a WCu flange to
  closely match the alumina window by adjusting Cu
  fraction
• These methods have been used for many years in
  the semiconductor industry

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WINDOW RD EFFORT Thermally Matched Window
Flange

• Offers opportunity to eliminate complex eyelet
  structure
• WCu CTE matches that of alumina
• 304 SST CTE gt 2x that of alumina
• As-sintered hardness 170 BHN for 20 Cu
  fraction
• Critical for good knife-edge seal
• Additional advantages include
• High thermal conductivity (gt170 W/m/K) Improves
  thermal management of RF losses in window
• Low electrical resistivity Reduces RF heating in
  flange
• Readily machined
• Reasonable cost
• Testing
• Fabricated four 2.75 Conflat style blank flanges
  for vacuum testing from 80 and 85W
• Multiple seal/re-seal tests bake to 150?C
• Results successful ? material is suitable for
  UHV Conflat flange
• Additional testing is scheduled to investigate
  post braze vacuum sealing properties

WCu Conflat Flange
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DESIGN STATUS WHERE WE GO FROM HERE

• Detail design of the UHV waveguide section and
  weld-in adapter is complete
• Procurement of flanges and waveguide sections has
  been initiated
• Plan in place to evaluate flanges from both
  vendors then down-select to one design and
  fabricate two complete double window waveguide
  assemblies for use in ¼ Cryomodule Test
• Complete thermally-matched flange RD effort