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SPL power coupler. Possible proposed designs Part II : designs comparison. Summary. Comparison of proposed designs: SPL-CEA coaxial disk water cooled window SPL-SPS coaxial disk air cooled window SPL-LHC cylindrical air cooled window Design issues Waveguides Titanium coating

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spl power coupler
SPL power coupler

Possible proposed designs

Part II : designs comparison

Eric Montesinos / CERN-BE-RF-SR

summary
Summary
  • Comparison of proposed designs:
    • SPL-CEA coaxial disk water cooled window
    • SPL-SPS coaxial disk air cooled window
    • SPL-LHC cylindrical air cooled window
  • Design issues
    • Waveguides
    • Titanium coating
    • RF simulations
    • Coupling box
  • Construction process
  • Conditioning process
  • Mass production
  • New proposed schedule
  • Conclusion

Eric Montesinos / CERN-BE-RF-SR

three possible remaining designs
Three possible remaining designs
  • All use the same double walled tube
  • All use the same vacuum gauge, electron monitor and arc detector
  • We have designed them to be compatible without modifying the cryomodule

Eric Montesinos / CERN-BE-RF-SR

three possible remaining designs1
Three possible remaining designs
  • SPL-CEA HIPPI coaxial disk water cooled window
  • SPL-SPS coaxial disk air cooled window
  • SPL-LHC cylindrical air cooled window

Eric Montesinos / CERN-BE-RF-SR

coaxial disk water cooled window
Coaxial disk water cooled window
  • CEA design based on a coaxial disk ceramic window as in operation at KEKB and SNS, modified for 704MHz
  • Advantages
    • High power capability, tested up to 1MW with 2ms / 50Hz on warm test cavity and on cold cavity last week
    • Matched window, this allows to easily change the waveguide position
    • Commercially produced window (Toshiba)
  • Drawbacks
    • Window and antenna are water cooled:
      • Not following CERN vacuum group recommendations
      • Needs accurate mounting
    • Difficult DC HV biasing due to water:
      • Need insulating pipes (X-rays, radiation,... More maintenance and operational costs)
    • Need a second air cooling circuit for the waveguide:
      • Doubles the operational needs: water and air systems

Waveguide air cooling

Antenna and outer ceramic water cooling

Eric Montesinos / CERN-BE-RF-SR

coaxial disk water cooled window1
Coaxial disk water cooled window
  • Quite complex brazing process (compare to SPS and LHC)
  • Water seal to be modified from organic (acceptable for test) to metallic (for long term operation without maintenance)
  • the tolerances are very tight
  • No flexibility for the antenna:
    • Stress to the ceramic
    • RF contact depends on tolerances
    • Possible water leak if misalignment (already happened)

Eric Montesinos / CERN-BE-RF-SR

coaxial disk air cooled window
Coaxial disk air cooled window
  • Design based on a coaxial disk ceramic window similar as the one in operation on the CERN SPS TWC 200MHz power load
  • Advantages
    • Very simple and well mastered brazing of ceramic onto a titanium flange
    • High power capability (500kw cw)
    • Very easy to cool with air
    • Waveguide as “plug and play” mounting, absolutely no stress to the antenna
    • DC HV biasing very simple, with again a “plug and play” capacitor fitting, and again no stress to the ceramic due to finger contact
    • Least expensive of the three couplers !
  • Minor drawback
    • Ceramic is part of the matching system, fixes the waveguide position

Ceramic and waveguide air cooling

Antenna and outer ceramic air cooling

Eric Montesinos / CERN-BE-RF-SR

coaxial disk air cooled window1
Coaxial disk air cooled window
  • Very simple brazing process:
    • Titanium outer flange:
      • Dilatation coefficient near ceramic
      • Surface hard enough for vacuum copper seals
    • Inner tube in copper 1.2mm thickness to allow easy brazing
  • Antenna inner upper part has been designed:
    • With spring washers for a good RF contact between the upper and lower inner conductor sections
    • Without any stress to the ceramic
    • Allowing a correct air flow

SPS Window: very simple brazing process

Spring washers

Air “cane”

RF contact

RF contact without stress to the ceramic

by compression of the outer line through the air “cane”

Eric Montesinos / CERN-BE-RF-SR

plug and play waveguide system
“Plug and play” waveguide system
  • Need additional 50 Ωouter lines:
    • Vacuum side for monitoring vacuum, electron, light, …
    • Air side for RF matching and for air cooling of the ceramic
  • “Plug and play” waveguide and biasing capacitor
  • There is a finger contact all around the capacitor to avoid stress on the ceramic
  • This waveguide mounting method has already been used successfully for the LHC couplers

Eric Montesinos / CERN-BE-RF-SR

cylindrical air cooled window
Cylindrical air cooled window
  • Design based on the same cylindrical window as the LHC couplers:
    • Long and difficult process to achieve reliability of the window, the final design was obtained after more than six years of studies
    • As the design was complex, we keep it exactly as it is
    • Instead of changing the ceramic design we have adapted the line to the ceramic
  • Advantages
    • High power capability window, LHC proven (575kW cw full reflection, could be more…)
    • Simple to cool with air
    • Absolutely free of mechanical stress on the antenna
    • Same “plug and play” waveguide and DC capacitor as previous design, no stress to the ceramic
    • Simplest version to assemble !
  • Drawbacks
    • Ceramic is part of the matching system, fixes the waveguide position
    • Possible multipacting due to the outer conical outer line

Ceramic and waveguide air cooling

Eric Montesinos / CERN-BE-RF-SR

cylindrical air cooled window1
Cylindrical air cooled window
  • LHC window is a huge improvement over the LEP window, with less losses and higher power capability
  • We still not know the upper power limit of the LHC window
    • The LHC coupler were powered up to 575kW cw full reflection (SW) for several hours all phases
    • Klystrons failed, not the coupler !
  • The LHC window appears to be really robust
    • To date 30 LHC couplers have been built and tested, 16 are in operation in LHC
  • A new coupler using exactly the same ceramic window is under construction for ESRF and SOLEIL → Standardization of the ceramic

ESRF-LHC new design

LHC window:

Two solid copper collars brazed to the ceramic

First EB welding

(mechanical)

Third EB welding

(mechanical and vacuum)

Second EB welding

(mechanical and vacuum)

Eric Montesinos / CERN-BE-RF-SR

plug and play waveguide system1
“Plug and play” waveguide system
  • Same “Plug and play” waveguide and biasing capacitor as with the coaxial air cooled window
  • The waveguide has just one contact with the body line
  • There is a finger contact all around the capacitor to avoid stress on the ceramic

Eric Montesinos / CERN-BE-RF-SR

comparison titanium coating
Comparison: Titanium coating
  • LHC, coating done twice:
    • First coating on the top and the bottom edges of the ceramic (electrical continuity)
    • Brazing of the copper collars
    • Second coating on the inside of the ceramic
    • → Double the costs
  • SPS, only one coating:
    • Straight forward
    • Done after brazing
  • Toshiba process:
    • Probably one coating
    • What about the part of ceramic masked by the chokes?

First coating:

R = 0.5 MΩ

Second coating:

R = 2 MΩ

One coating:

R = 2 MΩ

?

What about the part of ceramic behind the choke ?

One coating:

R = 2 MΩ

Eric Montesinos / CERN-BE-RF-SR

comparison s11 simulations
Comparison: S11 simulations

Cavity bandwidth

704 MHz / Qext (1.2 x 106) = 586 Hz

SPL-CEA

SPL-LHC

SPL-SPS

Eric Montesinos / CERN-BE-RF-SR

comparison field strength
Comparison: Field Strength

SPL-CEA

Max 751 kV/m

with 1MW

SPL-SPS

SPL-LHC

Max 880 kV/m

with 1MW

Max 866 kV/m

with 1MW

Eric Montesinos / CERN-BE-RF-SR

waveguides options
Waveguides options
  • If needed, LHC design could be done with a “coaxial conical” extension line to change the waveguide position
  • We simulated the waveguide with steps to check effects on the field distribution, it reduces the field strength
  • Using a waveguide without doorknob considerably eases the mounting and reduces the cost (as LHC)
  • Immediately after the coupler waveguide flange, there will be a flexible waveguide to reduce mechanical stresses
  • Nevertheless, a supporting tool will be necessary for the coupler waveguide, still to be studied

LHC design with a possible conical coaxial extension to change the waveguide axis

Two steps waveguide: slightly reduces the field strength

Doorknob / reduced height: ~ same field strength

Eric Montesinos / CERN-BE-RF-SR

comparison
Comparison

Eric Montesinos / CERN-BE-RF-SR

coupling box
Coupling box
  • Will be used to:
    • Connect two couplers in the vertical position for conditioning
    • Storage and transport chamber with springs to damp shocks
  • Solid copper:
    • Low RF losses
    • Strong enough to sustain deformation due to strong pressure effects
    • Extra external mechanical adjustment for frequency tuning
  • Could be EB soldered or assembled from two parts:
    • Vacuum seal
    • Easy to clean, we want to re-use it for 250 couplers !

Springs to avoid any shock while transporting

Eric Montesinos / CERN-BE-RF-SR

construction process

Vacuum leak detections after each major operation

Construction process
  • We plan to follow an upgraded LHC coupler construction process:
    • Build all components:
      • Metrologic controls
      • Mechanical and thermal tests
    • In clean room (class 100):
      • clean all parts in contact with beam vacuum with pure water or pure alcohol
      • Particle counting to validate the cleaning
    • In clean room (class10):
      • assemble a pair of couplers and mount them on a test cavity
    • Bake out
    • RF conditioning
    • In clean room (class 10): mounting of coupler with its double walled tube on SPL cavity

Eric Montesinos / CERN-BE-RF-SR

construction process1
Construction process
  • To be carefully followed-up:
    • Assembly tooling
    • Handling with special gloves only, avoid contamination of surfaces by hydrocarbons, finger prints,…
    • Optimize the process to minimize the number of handlings
    • Avoid intermediate packing in polymeric sealed bags (contamination)
    • Specially designed transport containers
  • Visit tomorrow of the three facilities:
    • Building 252 class 100 clean room
    • Building 252 class 10 clean room
    • Building SM18 class 10 clean room
    • Would like advice on what we could improve for high gradient cavities

Eric Montesinos / CERN-BE-RF-SR

conditioning process
Conditioning process
  • Install one cavity with its two power couplers and prepare for conditioning
  • List of interlocks and monitoring:
    • Vacuum gauges
    • Directional couplers
    • Light detector
    • Electron monitor
    • Thermal measurements
    • Gas analyzer
    • Air flow meter
    • Water flow meter (power load)
  • The tests will be done at CEA Saclay

TTF III power coupler test bench

Eric Montesinos / CERN-BE-RF-SR

conditioning process1
Conditioning process
  • The conditioning loop will be the same as the one used since 1998 with the SPS and LHC couplers:
    • A first direct vacuum loop (red) ensures RF is never applied if pressure exceeds 5.0 x 10-7 mbar
    • A second vacuum loop (blue), cpu controlled, executes the automated process
    • The interlock vacuum threshold of 5.0 x 10-7 mbar will be chosen, guided by our experience, to protect the couplers, but also to have an as short as possible conditioning time
    • The settings are adjusted to have minimum attenuation under 1.0 x 10-8 mbar and maximum attenuation over 2.5 x 10-7 mbar (~40 dB dynamic range with the attenuator)

Eric Montesinos / CERN-BE-RF-SR

conditioning process2
Conditioning process
  • The conditioning process will be similar to the LHC one:
    • The process always starts, under vacuum control, with very short pulses of 20 µs every 20 ms
    • Power level is increased using short pulses up to full power passing slowly through all power levels to avoid “de-conditioning”
    • Same procedure repeated for initially short then longer and longer pulses up to the maximum length
  • The conditioning process will be considered finished when the vacuum level decreases below a predefined level (1 x 10-8 mbar for example), while ramping the maximum length pulse

Eric Montesinos / CERN-BE-RF-SR

double walled tube rough estimate 15 000 chf coupling box rough estimate 25 000 chf
Double walled tube rough estimate: 15’000 CHFCoupling box rough estimate: 25’000 CHF

Eric Montesinos / CERN-BE-RF-SR

spl cea rough estimate 53 000 chf
SPL-CEA rough estimate:53’000 CHF

Eric Montesinos / CERN-BE-RF-SR

spl sps rough estimate 27 000 chf
SPL-SPS rough estimate:27’000 CHF

Eric Montesinos / CERN-BE-RF-SR

spl lhc rough estimate 30 000 chf
SPL-LHC rough estimate:30’000 CHF

Eric Montesinos / CERN-BE-RF-SR

mass production
Mass production

Eric Montesinos / CERN-BE-RF-SR

new proposed schedule
New proposed schedule
  • Integrate advice and launch as soon as possible:
    • One pair of coaxial air cooled window
    • One pair of cylindrical air cooled window
  • Have 2 pairs ready for tests beginning 2011
  • Decide which ones to construct in March 2011 (still three possible choices)
  • Construct remaining couplers in 2011
  • Have 8 fully ready and conditioned couplers beginning 2012

Today: coupler review

Confirm the Saclay test stand availability in 2011:

February and end of year?

Eric Montesinos / CERN-BE-RF-SR

conclusion still a lot to do
Conclusion: still a lot to do…
  • Eight couplers could be ready within two years:
    • Necessarily based on existing designs and very well known processes
  • Coaxial air cooled and cylindrical air cooled versions to be tried:
    • Potentially inexpensive for mass production
    • Interesting for large machines
  • Keep the coaxial water cooled option open:
    • Study the modification of the cooling from water to air
    • Redesign the waveguide transition for:
      • Less stress to the ceramic
      • Easier DC biasing

Eric Montesinos / CERN-BE-RF-SR

many thanks for your patience
Many thanks for your patience

Eric Montesinos / CERN-BE-RF-SR