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C oupled C avity L inac RF design

C oupled C avity L inac RF design. G. De Michele, PhD. Outline. CCL RF design Tank Design Bridge Coupler Design RF F eedthrough Design Low Power Measurements Beadpull Measurements and Tuning High Power Measurements. Outline. CCL RF design Tank Design Bridge Coupler Design

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C oupled C avity L inac RF design

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  1. CoupledCavityLinacRF design ADAM SA G. De Michele, PhD

  2. Outline • CCL RF design • Tank Design • Bridge Coupler Design • RF Feedthrough Design • Low Power Measurements • Beadpull Measurements and Tuning • High Power Measurements ADAM SA

  3. Outline • CCL RF design • Tank Design • Bridge Coupler Design • RF Feedthrough Design • Low Power Measurements • Beadpull Measurements and Tuning • High Power Measurements ADAM SA

  4. CCL Overview ~24 m CoupledCavityLinac ADAM SA • Use 10 power units, 7.5 MW each • Maximum power /unit = 5.2 MW (70% of 7.5MW) • Kilpatrick factor < 2.0 • ΔETOT : 32 MeV  230 MeV • ΔEp ≤ 20 MeV / klystron 20cm beam CouplingCells AcceleratingCells End Cells ~27cm

  5. CCL RF Design • A tank is designed with the main design parameters: • Cell length, gap length, septum thickness, the number of cells • With the following objectives: • The tankis resonant at the design frequency of 2998MHz • The cell length is consistent with the particle speed (l=β·λ/2) & RF phase • The effective shunt impedance is maximum (within constraints) • The constraints are: • The peak field • The feasible range of geometrical dimensions • Tracing the synchronous particle, we find a new energy & RF phase. • Design the next tank until: • The design energy is reached or • The available klystron power is used up ADAM SA

  6. Double Chain of Resonators • The double chain of resonatorsoperates in the so-calledπ/2 mode • Very stable working mode w.r.t. the geometry variations • The spacingbetween the workingfrequency and itsneighbor modes is largerthan in anyother mode • Requirements • Stop Band (SB) about 1MHz • Couplingbetween the accelerating (ACs) and coupling (CCs) cells at about 3%  better modes separation • Field uniformity • Field in CCs about 1% fields in ACs ADAM SA SB=fπ/2-(f+ - f-)/2 π/2 mode

  7. SimplifiedGeometry for RF 3D Design • 5 cells (2 ACs and 3 CCs) geometry • Adjustcells dimensions to uniform the E field, right workingfrequencyand minimize the E fieldinside the CCs • Replicatethe geometry for the full tank design and introduce at the same time the End Cells • Nowthe structure isfinite. The End Cells have to beadjusted in order to keep the fielduniformitywithinspecs Advantages: simulation time drasticallyreduced. Only fine tuningwillbeperformed on the wholesimulated tank. ADAM SA

  8. CCL Tank Design Vacuum Model • Hic suntleones ADAM SA k=2.8% SB=950kHz

  9. Final Geometrical Tank Parameters ADAM SA

  10. Tolerances The fielduniformity of the tank willdramaticallyget worse for a variation of +/-20um on the outer corner radius of the end cells. ADAM SA ±10um The freq. variation of the accelerating cellis1.3MHz/10um. ± 20um

  11. Outline • CCL RF design • Tank Design • Bridge Coupler Design • RF Feedthrough Design • Low Power Measurements • Beadpull Measurements and Tuning • High Power Measurements ADAM SA

  12. Bridge Coupler Design Input Power Input Power ADAM SA

  13. Bridge Coupler for the First Unit ADAM SA Tank 2 Tank 1

  14. Outline • CCL RF design • Tank Design • Bridge Coupler Design • RF Feedthrough Design • Low Power Measurements • Beadpull Measurements and Tuning • High Power Measurements ADAM SA

  15. RF Feedthrough Design • Magnetic pick-up (loop) for high power operation. • The coupling has to belessthan 40dB in order to couple few watts, to reduce at minimum the operating mode frequency shift, to reduce at minimum the losses on the pick-up thatcouldbring at a reduceQ-value ADAM SA 3.50mm 1.52mm L_pk

  16. Different pick-up length 3.50mm 1.52mm ADAM SA L_pk

  17. CCL RF Design – Conclusions • Consistent • Particle Energy & Phase • Design Parameters & Constraints • Complete • Tank and Module Design • Tuners for Stabilization • Power Coupler & Feedthroughs ADAM SA

  18. Outline • CCL RF design • Tank Design • Bridge Coupler Design • RF Feedthrough Design • Low Power Measurements • Beadpull Measurements and Tuning • High Power Measurements ADAM SA

  19. Low Power Measurements - Motivation • Low power measurements have to be performed in order to find the resonance frequency, quality factor, coupling parameter beta of the power coupler, length of the tuners • Tolerances, thermal expansion, possible numerical code frequency deviation, define the maximum frequency error • The tuners in the accelerating and coupling cells will compensate part of these frequency errors • All cells have tuners in order to actlocally. The fielduniformitycouldbeadjusted by local tuning ADAM SA

  20. Low Power Measurements - How • RF pick-ups(antennas, loops) willbeused in order to find the spectrum of each tank, so the operating frequency and the quality • Beadpullmeasurementswillbeperformed in order to check the E fielduniformity ADAM SA

  21. Outline • CCL RF design • Tank Design • Bridge Coupler Design • RF Feedthrough Design • Low Power Measurements • Beadpull Measurements and Tuning • High Power Measurements ADAM SA

  22. High Power Measurements - Motivation • Modules AcceptanceTest • Pre-conditioningprior to acceleratoroperation Goal: stable operationwithrequired input power and reflected power below 10% Locations where power measurementswillbeperformed (Pfw, Prev, Pcav) ADAM SA

  23. Thank you for your attention ADAM SA

  24. Back up ADAM SA

  25. Drawbacks of RelaxedTolerances • Local temperaturerisedifferentfromexpected • Couldbring to an important frequency shift of single cellsthatcouldbecovered (if in the acceptable tuning range) by tuners BUT only if ALL cellswillbemeasuredaftermachining • Field uniformity off fromdesignedvalue • Differentacceleration in eachcell: the particlewillbe out of phase in the nextcell • Frequency shift • Couldbecovered by tuners at the cost of more dissipated power • Extra field in the coupledcells • Low power efficiency i.e. more dissipated power ADAM SA NB. The number of tuners has been limited at 2 per cell in order to preserve the quality factor of the cells and to reducecomplexity

  26. Testing and conditioning procedure • Low power to high power • Short to long pulses • Low to high repetition rate • Limitation of power rise by hardware thresholds (vacuum, powers, water temperature) • Vacuum and reflected power feedback loop to keep the SW interlocks far from the HW interlocks ADAM SA • HW interlocks • modules temperature, input water temperature • vacuum • water flow • forward, reverse, cavity powers • SW interlocks • all the HW interlocks • thresholds are tighter than HW interlocks in order to reduce RF-off time

  27. 5cells - half CC termination – fπ/2 vs tuner length(4mm diameter) ADAM SA

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