Power Couplers

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• Power Couplers
• For ILC and Project X

Nikolay Solyak Fermilab
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Outline

• Coupler designs
• List of Parameters
• Issues for ILC, Project X
• Overview of alternative designs
• Coupler conditioning /assembly at SLAC
• Technical progress infrastructure components
• Plans for coupler industrialization
• The plan for ARRA funds
• Technical Milestones
• Conclusion

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Couplers Parameters for the SC linac
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TTF-3 Coupler Design
Design complicated by need for tunablity (Qext),
dual vacuum windows and bellows for thermal
expansion.
Coaxial Power Coupler
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Design criteria for the TTF-3 Coupler

• coax is easy for - variable coupling
• - fabrication
• - assembly
• two windows for - clean assembly of the cavity
• - save operation
• cold coax - at 70 Ohm, 40 mm diameter
• warm coax - at 50 Ohm, 60 mm diameter
• bias on inner conductor - suppress multipacting
• flexibility - bellows in the warm and cold coax
• ceramics - Al2O3 with TiN coating
• copper plating - 10/30 µm outer/inner coax
• - high thermal conductivity (RRR 30)
• - high purity, Hydrogen free

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Coupler Tests at 35 MV/m

• Long run test of EP cavities in the horizontal
  cryostat
• ILC Meeting 2005 W-D Möller, DESY/Hamburg)
• This test includes all auxiliaries like power
  coupler, HOM coupler, tuner, piezo,
• Gradient 35 MV/m 10 Hz 1.3ms rise-time
  0.5ms Max forward power 600 kW (reflected max
  2.4 MW), N2 -cooling
• RF on time 2400 hrs
• No MP activity or breakdowns in the coupler
• High gradient test with beam (in module ACC1)
• Gradient 35 MV/m
• Gradient calibration with beam

This is good sign that TTF-3 coupler has no peak
power limitation for Project X parameters 500 kW
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TTF-3 coupler CW tests at BESSY
Overheating inner below gt130ºC
J. Knobloch, PAC05

• Average power with air cooled inner conductor 10
  kW
• For the inner conductor cooling the coupler is to
  be redesigned

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MP in 40mm coaxial line
SLAC tests in SS coaxial line
PrX
MP levels found around 150kW, 250kW, 450kW in the
warm coupler part, 150 and 450kW in the cold
coupler part (not in the all tests). Calculations
also show MP near to this power levels. Those
levels are not dangerous
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Power Coupler Issues

• For nominal ILC and PrX parameters TTF-3 coupler
  will work.
• Project X coupler will see 2 MW power during
  the filling time 0.2 ms. SLAC will test coupler
  parameters 2MW _at_ 0.2 ms required for Project X
• Note Standard processing procedure for TTF-3
  coupler is 0.5 MW _at_ 1.5 ms and 1MW _at_ 0.5 ms.
• TTF-3 coupler and few other designs (ILC and ERL)
  already demonstrated 2 MW power even for longer
  pulses.
• Average power up to 4 kW was demonstrated, but
  need more tests to prove reliability.
• For 4 MW Upgrade Project X the average coupler
  power is Pav 15 KW. Needs modification of TTF-3
  coupler or new design.

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Processing of TTF-3 Power Coupler

• Required processing parameters for Project X
  coupler should be (to demonstrate peak power)
• 550 kW at 1.5 ms and (10 overhead)
• 2.2 MW at 0.2ms (10 overhead)
• SLAC will test next pairs of coupler in this
  regime
• RD program at SLAC for coupler should be
  demonstration of processing regime, required for
  Project X.
• Average power requirements for 4 MW Project X
  upgrade can be achieved for TTF-3 coupler with
  the air cooled central conductor (15 kW)

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Other Coupler Developments

• KEK - STF capacitive (40 mm cold port) coupler
  with flat window. Tested 2MW 3Hz 1.5ms 9 kW
  average power
• DESY design for a 62 mm coax diameter is finished
  for the 2 x 9 cell super structure (TTF-5).
  Tested
• LAL design of 60 mm coax diameter and disc
  windows. Tested
• KEK-STF 60mm coupler (TRISTAN-like) designed and
  tested
• ERL coupler based on this design with 20 kW CW
  power.
• Cornell ERL coupler for CW 50 kW based on TTF-3
  design (cold part increased to 60 mm ). Tested at
  61 kW CW
• DESY Coupler design with 80 mm coax diameter
  TTF-4 (foreseen for the 4 x 7 cell
  superstructure). Built and tested at LAL/Orsay.
• In collaboration with AMAC a 80 mm coax coupler
  with disc windows is designed, fabricated and
  tested at DESY

60 mm
80 mm
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KEK capacitive coupler
(S.Kazakov, et al. LINAC06)

• 40mm coupler cold port connection
• Fixed coupling (adjustable design under way)
• Warm window same as in TTF-3
• Limitation overheating of metal rods

• High power test demonstrated
• 1MW x 1.5ms x 5pps and 2MW x 1.5ms x 3pps 9kW
  for matched load
• 500kW x 1.5ms x 5pps for short
• Effect of MP is weak. Upper limit is 200kW

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• Pair of coupler was tested in cryostat
• Achieved 61 kW CW
• 62mm diameter port (cold part)

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ILC coupler STF/KEK
Dynamic loss lt static loss

• Fixed coupling, Qext 2. 106
• No air cooling
• Dynamic losses 0.2W to 5K
• Static losses 1W to 5K (high)

Test results 1 MW 1.5 ms 5Hz Pav 7.5
kW Processing 50 hrs
ERL 20kW CW cold window ?104 Variable
coupling Gas cooled
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Two 60mm coupler designs (DESY, LAL)
Produced 4 prototypes of each coupler (ACCEL,
2006) and few tested at LAL.
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? 40mm vs. 60mm in cold part ?

• Few existing 1.3 GHz power couplers are using
  40mm or 60mm coax in cold parts.
• Both diameters were tested up to 2 MW peak power.
  No fundamental power limitations was identified,
  both should work at 500kW reliably.
• Cold part ? 60mm will facilitate MP problem, but
  not solve it. Demonstrated processing time in
  designs with 40 and 60 mm cold parts is
  comparable 10-20 hrs in the tests.
• Today only TTF-3 design has adjustable coupling.
  It is important feature for ILC and Project X
• TTF-3 couplers will require some redesign work to
  accommodate gt 5 kW average power (need air
  cooling in warm part).
• Field asymmetry for ? 60mm is more severe, it can
  cause RF kick and wakes. Need analysis.

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Assembly Processing Facility at SLAC

• Goals
• Setup a class 10 clean room at SLAC to clean and
  assemble cavity couplers from parts built by CPI
  (no welding required).
• Once assembled, pairs of couplers will be rf
  processed at the L-Band test area at End Station
  B and then shipped to FNAL.
• Develop less expensive means of producing
  couplers
• Project Status
• Received 12 couplers ordered from CPI by FNAL
  have been inspected three sent back to CPI where
  they have been repaired/replaced
• Class 10 clean room facility completed in FY09 Q2
• First coupler pair assembled in clean room, baked
  (150 degC for a day) and rf processed (in lt 10
  hours) - have been sent to FNAL
• Started program to build coupler cold section
  with induction brazing or TIG welding

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Coupler Assembly in Cleanroom Class 10
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Coupler Cleaning

• Warm and Cold parts are cleaned to a class 10
  level.
• Coupler parts be blown out with filtered nitrogen
  (surface particle might be disturbed during
  shipment).
• Hardware has been cleaned for processing and
  re-cleaned after teardown and bagged for
  shipment.

Ultrasonic Wash Station
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Coupler Pair Test Setup
RF In
RF Out
Ion Pump 10B
Ion Pump 10D
Ion Pump 10C
Couplers are baked at 300ºF for 30 hrs
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L-band Test Stand in ESB
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Coupler Sub-Assemblies and RF Processing Stand
Instrumented Coupler Test Stand at SLAC ESB
Processing of a Not-Cleaned Pair after a 150 C
Bake Power (MW) -vs- Time for Pulses of 50,100,
200, 400, 800, 1000 ms
Time (hr)
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RF Process History
Processing of a Cleaned Pair after a 150C Bake
Vacuum Process Threshold 100uA
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Warm Part
Cold Part

• Delivered NOT under vacuum but have been Nitrogen
  purged.
• Warm window is protected for shipment class 10
  wipe, then with a S.S. cover.
• CF-16 (e-pickup ports) leak tested.
• All other Con-Flat flanges need new copper
  gaskets for final configuration.

• Shipping CPC with Support Stand
• Cold Parts are under Vacuum (must vent before
  removal)
• CF-100 section is protected with Top Hat and
  has been purged with Nitrogen

CPC Support Stand
Top Hats
Warm window Ceramic Coverings
E-pickups in final configuration
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RD on Fabrication Simplification
Many of the above joints e-beam welded so bellows
and windows not heated looking at using
induction brazing or TIG welding in many places
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Plan for ARRA funds

• First set of couplers are developed by ILC funds
• ARRA would provide funds for couplers for planned
  RD cryomodules in FY09-FY12 (CM 3,4,5 Type-IV)
• ARRA funds will also be used to develop couplers
  that have both higher power handling capability
  and are easier/cheaper to manufacture and RF
  process.
• Milestones
• FY09 Initial order of 22 couplers from U.S.
  industry using ARRA funds
• FY10
• Evaluation of power handling capability of TTF3
  coupler complete
• Evaluation of induction brazing and coupler
  design changes complete
• FY11 Couplers, possibly with an improved design,
  are ordered from U.S. industry with ARRA funds.
  The exact number will be determined as costs are
  understood better.
• It is envisioned that this order will be
  combined with larger order that includes Px and
  ILC RD couplers leading to cost savings.

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Conclusion

• 12 couplers are manufactured, inspected and 2 of
  them are conditioned and shipped to Fermilab
• Infrastructure for coupler cleaning, assembling
  and processing at SLAC are completed and used for
  coupler processing.
• RD program on coupler design issues, processing
  and manufacture is underway (SLAC/FNAL)
• Plans for FY09-12 are based on expected ILC and
  ARRA funds to provide couplers for planned RD
  cryomodules.
• An order for 22 couplers would be placed in FY09
• RD on easy/cheap to manufacture (SLAC with
  vendors)
• Evaluation of power handling capability of TTF-3
  coupler in FY10 and ordering of 20 modified
  couplers