CERN SPLFundamental Power CouplerProgress report

SPL meetingCERN, 6 - 7 December 2012Eric Montesinos, CERN BE-RF-PM

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Contents• Introduction

▫ CERN RF Fundamental Power Coupler team

• SPL coupler project▫ SPL FPC initial design

proposals▫ March 2010 Coupler review▫ June 2010 SPL Coupler

project▫ Construction▫ Assembly in DESY clean room▫ Double walled Tubes (DT)▫ LLRF tests▫ High Power tests at CEA : TW▫ High Power tests at CEA : SW

• Next steps

• Key R&D results :▫ Mono bloc waveguide▫ Test box▫ Double walled Tube as

support for cavity▫ High Average power air

cooled couplers

5-6 December 2012

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CERN RF Fundamental Power Coupler teamCERN Machine Design Prototype Series

SPS 200 2001 LHC 400 2006

Linac 4 Under Way

SPL cylindrical Under test

SPL planar Under test

HIE-Isolde Under test

Crab Cavities

To come

SPS 800 To come

LIU- SPS 200

To come

5-6 December 2012

SPS 200 MHz coupler

LHC 400 MHz coupler

Linac 4352 MHz coupler SPL 704 MHz

couplers

HIE Isolde 100 MHz couplers

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CERN RF Fundamental Power Coupler team

5-6 December 2012

Machine Design Prototype Tests

ESRF 300 kW CW

ANL-APS 100 kW CW

SOLEIL Under way

ESRF 352 MHz coupler Argonne APS 352 MHz coupler

SOLEIL 352 MHz coupler design

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SPL FPC initial design proposals

5-6 December 2012

RF Characteristicsf0 704.4 MHz

Power levels

1000 kW pulsed0.4 + 1.2 + 0.4 = 2.0 ms50 Hz (20 ms)100 kW average

Cavity design gradient 19-25 MV/m

Qext of input coupler 1.2 x 106

Input line Ø100 / 43.5 mm = 50 Ω(from the cavity design)

Waveguides WR 1150

2009 2010 2011 2012 2013

CEA HIPPI(baseline)

CylindricalWindow

Disk WGWindow

DiskCoaxial window

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SPL FPC initial design proposals

5-6 December 2012

2009 2010 2011 2012 2013

30 kCHF8.25 MCHF

15 kCHF4.125 MCHF

15 kCHF4.125 MCHF

14 kCHF3.85 MCHF

Baseline: CEA Saclay coupler

To be upgraded for SPL cryomodule compatibility

Kept open the possibility to use another design, to be fixed in March 2010

Comparison basis: RF power capability Low heat load Tuning capability (fixed coupling,

adjustable coupling) Conditioning time Contamination during beam part

assembly Easy installation Integration with the cryomodule Easy operation Cost

Window-Ceramic-Antenna275 Series 4-8 MCHF

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March 2010 Coupler review• Review committee members :

▫ Ali Nassiri (Chair)▫ Wolf Dietrich Moeller▫ Mark Champion▫ Sergey Kazakov▫ Mircea Stirbet

• Presenters :▫ Amos Dexter & Rama Calaga

(Multipacting simulations)▫ Miguel Jimenez (Vacuum)▫ Sergio Calatroni (DT Coating)▫ Ofelia Capatina & Vittorio

Parma (Cryomodule integration)

▫ Eric Montesinos (FPC)

5-6 December 2012

2009 2010 2011 2012 2013

Technical ChoicesSingle window couplerFixed couplerWith a Double Walled TubeMounted in clean room with its double walled tube horizontally in only one operationVertically below the cavity and will be a support for the cavity (first time worldwide)

With a HV DC biasing capacitorAir cooled

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Two designs have been validated

5-6 December 2012

Cylindricalceramic window

Coaxial diskceramic window

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5-6 December 2012

Same Double Walled Tube(Outer line of a coaxial

transmission Line)With same interface flange

to cryomodule

Same Waveguide with integrated matching step (instead of a doorknob)And same DC capacitor

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Cylindrical window• Advantages

▫ LHC window with high power capability due to its solid copper collars

▫ Simple to cool down with air▫ Absolutely free of mechanical

stress onto the antenna▫ “plug and play” waveguide

and DC capacitor, no stress to the ceramic

• Drawbacks▫ Ceramic is part of the

matching system, imposing the waveguide position

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Coaxial Disk window• Advantages

▫ Very simple and well mastered brazing of ceramic onto a titanium flange

▫ Simple to cool down with air

▫ “plug and play” waveguide and DC capacitor, no stress to the ceramic

• Drawback▫ Ceramic is part of the

matching system, fixing the waveguide position

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SPL coupler project (June 2010)• Four vacuum lines:

▫ 4 cylindrical window couplers

▫ 4 disk window couplers▫ 8 Double walled Tubes▫ 4 test boxes

• DESY clean process assembly▫ (Jlab also proposed to help)

• CERN LLRF measurements

• CEA RF power tests▫ (BNL also proposed to help)

5-6 December 2012

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Couplers construction• All parts have been

produced by May 2011 (10 months)

• All components have been individually vacuum leak free tested before being sent to DESY for assembly

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Couplers construction• All parts have been

produced by May 2011 (10 months)

• All components have been individually vacuum leak free tested before being sent to DESY for assembly

• Specific transport boxes with springs as per tetrodes have been designed to avoid any shocks

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Assembly in DESY clean room• In June 2011, the four

cavities were assembled in DESY clean room

• Use of a specially designed helicoflex seal

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Assembly in DESY clean room• In June 2011, the four

cavities were assembled in DESY clean room

• Use of a specially designed helicoflex seal

• Thanks to DESY colleagues who have performed a very good job and to a very good preparation job of the jointing surfaces all four cavities were leak free

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Double walled Tube (DT)• Copper sputtering removed with

simple water Ultra Sonic cleaning process

• Mistake in the machining process :▫ An additional machining step not

included in the lists has erased all the care put into the preparation of DT

• Decision to continue the first two vacuum lines with NOT copper sputtered DT :▫ Lead into a very important delay

onto the schedule▫ Will limit average power during

tests

5-6 December 2012

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LLRF measurements at CERN (summer 2011)

5-6 December 2012

• S11 with 2 x N/WG adaptors + 2 couplers + 2 DT + test box :▫ Cylindrical windows = -26.5 dB▫ Coaxial planar disk = -18 dB

• Pfwd/Prev (S11) at CEA premises with 2 couplers + 2 DT + test box :▫ Cylindrical window = -17 dB▫ Coaxial planar disk = -40 dB

• Even with only -16 dB, 1 MW will reverse 25 kW, acceptable with CEA premises, thanks to their circulator

2009 2010 2011 2012 2013

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RF power tests at CEA cylindrical window• First test were to check RF,

so No bake out to take no risk with the test box helicoflex gasket

• Static vacuum ~ 2 x 10-7 mbar

• Pulse mode process

• After 3 weeks, 50 kW 20 s - 20 Hz

• We Stopped the test

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RF power tests at CEA disk windows• In the meantime, second test box

with two disk window couplers has been baked out at CERN

• No helicoflex leak▫ Very slow heating up and

heating down ramps 10 C / hour▫ Maximum temperature during

48 hours was only 150 C▫ Nitrogen onto copper rings to

avoid any oxidization

• Very good static vacuum after the process ~ 1 x 10-10 mbar (vs 5 x 10-7 mbar before starting the bake out)

• Pulse mode process

• After two weeks :▫ 1000 kW 2 ms - 20 Hz

• Ultimate goal of 1000 kW 2 ms - 50 Hz was not possible due to losses in uncoated DT limitation

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RF power tests at CEA cylindrical window• We also baked out the first

test box with two cylindrical windows at CERN

• No helicoflex leak

• Very good static vacuum after the process ~ 1 x 10-10 mbar (vs 2 x 10-7 mbar before starting the bake out)

• Pulse mode process

• After 1 week:▫ 1000 kW 2 ms - 20 Hz

• Ultimate goal of 2 ms - 50 Hz was not possible due to losses in uncoated DT limitation

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TW tests ok (May 2012)

•Both coupler versions have reached TW maximum values of 1 MW 2 ms - 20 Hz

•Limitation of average power to 20 Hz instead of 50 Hz due to uncoated TD

•Successful TW tests

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SW tests with cylindrical window• A variable short

circuit has been designed and constructed at CERN for SW test

• Steps of 20 mm to have enough accuracy performing tests within all phases

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SW tests with cylindrical window• We started SW tests in pulse

mode

• With 500 µs – 8Hz :▫ Up to 500 kW, no trouble▫ Arcing when reached 575 kW

• It seemed to be air side as there was no vacuum activity

• There was no arc detector to stop the test, a photomultiplier modulated RF, and it was possible to hear arcing in the WG system

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SW tests with cylindrical window• Air side arcing were

confirmed when dismounting WG

• Input coupler presented some impressive arcing traces

• Output coupler was without any trouble

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SW tests with cylindrical window• Analyzing black deposit, we

only identified :▫ Gold coming from upper

gold platted copper collar▫ Copper coming from lower

copper collar

• There were without any doubt electrical arcing (>1’000) between two copper brazed collars

• The only positive point is that ceramic remained vacuum leak free

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2009 2010 2011 2012 2013

0 2 4 6 8 10Energy (keV)

0

10

20

30

cps

C

OCu

Au

Cu

Cu

Au

0 2 4 6 8 10Energy (keV)

0

10

20

30

cps

O

Cu

Al

Cu

Cu

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Improvement of cylindrical window• A trick given by Michel

Langlois (ex-Thales tube designer) is to improve air flow in the critical area in order to avoid ionization of the air around the ceramic itself

• improve air cooling around ceramic with a short circuit as air inlet

• Inserting PEEK screen all around ceramic

5-6 December 2012

Air inlet throughWG short circuit

PEEK Screen all around ceramic

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SW tests with coaxial disk windows• We then decided to start

SW tests with coaxial disk windows

• Up to date, we performed:▫ 1000 kW 1.5 ms – 4 Hz

• Some RF leaks were observed

• CEA was finally not sure if these RF leaks were coming form couplers

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SW tests with coaxial disk windows• Last week, while

preparing test box with copper coated DT, we observed some arcing traces on the outer line in front of the inner contact

• These traces were not present after TW test

• There were no arc detector fault during the whole SW test (interlock active)

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Arcing traces on inner line

Arcing traces on outer line

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SW tests with coaxial disk windows

• Still waiting items to find an explanation

• Possible candidates :

▫ Not enough springs ensuring specific 1MW RF contact :

1. Inner ceramic is brazed with a stainless steel nut

2. Air cane is built with a specific bolt

3. Air cane is screwed compressing springs which when relaxed ensure 1 MW RF contact

▫ Contact surfaces were not flat enough

5-6 December 2012

1.

2.3.

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SW tests conclusion• Cylindrical window couplers have performed

575 kW 500 µs - 8 Hz full reflection all phases -> very strong arcing, interlock not operative

• Coaxial disk window couplers have performed1000 kW 1.5 ms - 4 Hz full reflection all phases, no interlock (operative), but few arcing traces (to be understood and explained)

• SW tests are not conclusive, work still have to be done

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Coated DT• 6 DT with new copper sputtering have been processed :

▫ Test with 150 Bars water have been performed▫ TD qualified▫ 2 have been provided to cryomodule team

• Unfortunately DESY clean room was not anymore available

• CEA proposed to assemble couplers and copper sputtered DT onto test boxes in ‘L’orme les Meurisiers’ premises :▫ One Test box with two copper plated DT and two coaxial disk

window has been assembled last week

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Next steps

• Second test box will be assembled beginning 2013

• Cylindrical or Disk windows ? Decision after cylindrical arcing analysis

• Beginning 2013, final tests at CEA with :▫ 1000 kW TW 2 ms – 50 Hz▫ 1000 kW SW limited to 200 µs – 50 Hz

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Next steps• EB welding of cryostat

flanges will be done afterward

• Study of clean room tooling for assembly onto SPL cavity has started

• Assembly of couplers onto cavities in CERN clean room goal remains mid-2013

• RF power tests on cavity asap

5-6 December 2012

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Next steps• Provide a CERN clean assembly premises for

couplers

• Continue all remaining couplers power tests with CERN amplifiers when available

• Longer term basis :▫ After qualification of SPL cavities, make a test with

‘dirty’ couplers (ISO 7 instead of ISO 4 for example, tbd), to quantify coupler cleanliness impact onto cavity field

5-6 December 2012

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Key R&D resultsMono bloc waveguides

• ‘Plug and Play’ waveguide with matching step and DC capacitor included :

1. Connect the waveguide to the body line2. Insert the contacts ring3. Final assembly of air cooling system

• No doorknob, reduced height, with no mechanical stress to the ceramic

5-6 December 2012

1. 2.

3.

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Key R&D resultsTest box

• All in one, only two covers conditioning test box

• Pros :▫ Easier (not easy) copper

sputtering▫ Self supporting shape▫ Easily cleanable for SRF needs,

can be used for several sets of coupler (if large series : SPL, ESS, …)

• Cons :▫ Helicoflex faces to be very well

prepared▫ Self-supporting structure : heavy

weight

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• Successfully made available 3D printing for RF tests with a special silver paint

5-6 December 2012

S21 = 0.01 dBS11 = -40 dB

S21 = 0.03 dBS11 = -25 dB

@ 400 MHz

Machined 3D printed

Delay [days] Cost [CHF]

Machined 3D Machined 3D

15 5 9000 3800

Key R&D results3D printing & RF

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Key R&D results High average power air cooled couplers

• Cylindrical window : ▫ TW : 1000 kW 2 ms - 20

Hz▫ SW : 550 kW 500 µs - 8

Hz

• Coaxial disk window : ▫ TW : 1000 kW 2 ms - 20

Hz▫ SW : 1000 kW 1.5 ms - 4

Hz

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Acknowledgements• SPL coupler review committee :

▫ Ali Nassiri, Wolf Dietrich Moeller, Mark Champion, Sergey Kazakov, Mircea Stirbet, Amos Dexter, Rama Calaga, Miguel Jimenez, Sergio Calatroni, Ofelia Capatina, Vittorio Parma

• DESY :▫ Wolf-dietrich Moeller, Axel Matthaisen,

Birte Van der Horst, and local team

• CEA :▫ Stephane Chel, Guillaume Devanz, Michel

Desmond, and local team

• ESRF :▫ Jorn Jacob, Vincent Serriere, Loys, Jean-

Maurice Mercier, Didier Boillot

• APS :▫ Ali Nassiri, Doug Horan, Gian Trenko, Dave

Brubenker, and local team

• CERN :

▫ Mechanical & Material Engineering group : Francesco Bertinelli, Ramon Folch, Serge

Mathot, Agostino Vacca, Thierry Tardy, Thierry Calamand, Thierry Renaglia, Ofelia Capatina, Marc Polini, Laurent Deparis, Philippe Frichot, Jean-Marie Geisser, Jean-Marc Malzacker, Pierre Moyret, Alain Stadler

▫ Vacuum, Surface & Coating group : Miguel Jimenez, Sergio Calatroni,

Wilhelmus Vollenberg, Marina Malabaila, Nicolas Zelko

▫ Magnets, Superconductors & Cryostats : Vittorio Parma, Arnaud Van de Craene,

▫ RF group : Sebastien Calvo, Antoine Boucherie, all

FSU-BE03 members

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Thank you very much for your attention

5-6 December 2012