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T. Garvey Labratoire de l’Acc é l é rateur Lin é aire – Orsay, W.D.-M ö ller , DESY-Hamburg

The RF Power Coupler Development Program at LAL-Orsay and DESY-Hamburg for TESLA and the European X-FEL. T. Garvey Labratoire de l’Acc é l é rateur Lin é aire – Orsay, W.D.-M ö ller , DESY-Hamburg. Function of the power coupler.

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T. Garvey Labratoire de l’Acc é l é rateur Lin é aire – Orsay, W.D.-M ö ller , DESY-Hamburg

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  1. The RF Power Coupler Development Program at LAL-Orsay and DESY-Hamburg for TESLA and the European X-FEL T. Garvey Labratoire de l’Accélérateur Linéaire – Orsay, W.D.-Möller, DESY-Hamburg SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  2. Function of the power coupler • Transmit the radio-frequency waves from the power source (klystron) to the accelerating cavity. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  3. Additional coupler functions • • Minimise forward loss of power from klystron to cavity. • • Isolate the evacuated cavity from the air filled wave-guide • • Protect the cavity against ‘contamination’. • • Minimise the thermal losses between the wave-guide (room temperature) and the cavity (2 K). • • Allow flexibility for thermal cycling of cryomodule. • • Allow variable “coupling” to the cavity. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  4. Coupler power requirements Operating frequency: 1300 MHz SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  5. The solution…. the TTF-III coupler SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  6. Design of the TTF-III Couplers • Co-axial is easy for: - variable coupling • - fabrication • - assembly • two windows for: -clean assembly • -safe operation • cold coax:-at 70 Ohm, 40 mm diameter • warm coax: -at 50 Ohm, 62 mm diameter • D.C. bias: -suppress multipacting flexibility: -bellows in the warm and cold coax ceramics:-Al2O3 with TiN coating copper plating:-20 μm -high thermal conductivity -high purity, hydrogen free SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  7. Multipacting – resonant discharge when mixing vacuum and RF with surfaces having SEE > 1. Apply thin coating (~ 10 nm) of TiN to reduce SEE of Al2O3 ceramic surface. Power levels scale as ~ Z.(diameter)4 SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  8. Warm assembly Warm ceramic protection cap SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  9. Cold assembly SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  10. Wave-guide assembly HV input coil SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  11. RF Coupler in Module warm window cold window cavity module 70K shield 4K shield SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  12. Coupling to the VUV-FEL LINAC Cavities Power towards cavity Coupler SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  13. Coupler development • RF design • Electromagnetic, multipactor, mechanical, thermal. • Fabrication • Reception, preparation, assembly • High power tests SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  14. RF design of couplers • Extensive use of electro-magnetic simulation codes • coupler well matched; VSWR < 1.2 • - minimise E-fields in critical areas. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  15. Laser weld of bellows Copper coated bellows Ceramic-metal brazing E-beam welding TiN coating TTF-III coupler production requires many technologies. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  16. Cleaning with ultra-pure water Inspection Assembly in Class 10 clean room High temperature vacuum bake-out Coupler reception, preparation and mounting SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  17. The RF Power Source SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  18. Pair of couplers under test at Orsay. High power test configuration SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  19. RF “conditioning” RF conditioning (or processing) is the procedure whereby the coupler power is gradually increased from zero to its nominal operating level. Corresponds to ‘controlled’ desorption of gases from RF surfaces ⃕ multipacting Surfaces “cleaned-up” as result of conditioning. Cold surfaces can re-collect gas following periods of operation. Interlocks required to protect coupler during processing ⃗ monitor vacuum levels, electron activity, light signals reflected and transmitted power, window temperature. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  20. Photo-multiplier Vacuum port Electron pick-ups Diagnostics used as interlocks SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  21. Control and Data Acquisition SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  22. Conditioning procedure • Pulse length 20 ms, ramp power to 1.0 MW in 0.2 dB steps • Pulse length 50 ms, ramp power to 1.0 MW in 0.2 dB steps • Pulse length 100 ms, ramp power to 1.0 MW in 0.2 dB steps • Pulse length 200 ms, ramp power to 1.0 MW in 0.2 dB steps • Pulse length 400 ms, ramp power to 1.0 MW in 0.2 dB steps • Pulse length 800 ms, ramp power to 0.5 MW in 0.2 dB steps • Pulse length 1300 ms, ramp power to 0.5 MW in 0.2 dB steps • Sweep power @ 1.3 ms, 50 to 500 kW. • Interlocks • e- pick-ups, photo-multiplier, vacuum, ceramic temperature • Wave-guide sparks – stop operation! SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  23. RF Coupler Performance @ DESY • Total of 40 RF power couplers connected to the superconducting cavities in the VUV FEL linac, eight per module. • All couplers in the VUV FEL linac have been processed and operated up to the limit of the cavity performance. • RF power couplers have been tested up to 1 MW of pulsed power at 1.3 ms pulse length, 2 Hz on the test stand. • RF power couplers operated ~270,000 coupler*hours. • TTF-III couplers have been tested together with cavities at gradients of 35 MV/m (600 kW) 5 Hz without degradation of cavity or coupler. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  24. Coupler processing data RF power as a function of time for different pulse widths. Electron activity as a function of RF power and pulse width. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  25. Conditioning times for couplers • Why are the conditioning times different ? • - real differences between couplers ? • differences in preparation / installation ? • Answer is object of our present studies. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  26. R&D to reduce conditioning time • Investigate new threshold levels for safe operation • Apply titanium-nitride on all RF surfaces • Use glow-discharge treatment of RF surfaces • DC bias sweep to provoke multipactor • Alternative anti-multipactor coatings SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  27. Measures towards cheaper coupler production Industrial study of coupler “mass” production for X-FEL. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  28. TTF-V Proto-type • Essentially = TTF-III “warm” part + 62 mm f • “cold” part. • Larger diameter – to transmit more power and • push multipactor levels to higher power • Candidate coupler for a two x 9 cell TESLA/ILC • cavity • Engineering drawings and technical specifications • completed. • Four such couplers will be built in 2005 • for high power tests in early 2006. • Will be subsequently used for studies on RF • conditioning times. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  29. TW60 Coupler Proto-type Radically different from TTF-III coupler, uses “thin” planar ceramic windows. Easy to braze, low dielectric loss. Insensitive to multipactor Warm transition is matched with reduced-height wave-guide  standing wave. “Line of sight to cavity” Cold window matched with reactive impedance elements on inner co-ax. Low power measurements already performed. High power tests planned for 2006 on four proto-types to be built by ACCEL. SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

  30. Summary The TTF-III coupler performance is adequate for the X-FEL project R&D is in progress to reduce processing times Industrial studies will lead to reduced costs The TTF-III coupler may also be acceptable for ILC Alternative ILC designs are being studied I thank all my DESY and Orsay colleagues for their contributions to this work Thank you for your attention SPIE Conference - Photonics Applications in Industry and Research, Warsaw, 30 August, 2005

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