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PSC40 Automatic Tuner Control

PSC40 Automatic Tuner Control. P. Maesen 27 May’09. Presentation. PS 40 MHz RF system 2 cavities in SS77 and SS78 used for LHC beams in PS ring Buncher system that creates the 25,50 and 75 ns spaced bunches beams Copper coated steel cavity Operating at 40.055 MHz R/Q = 33 Ω

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PSC40 Automatic Tuner Control

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  1. PSC40 Automatic Tuner Control P. Maesen 27 May’09

  2. Presentation • PS 40 MHz RF system • 2 cavities in SS77 and SS78 used for LHC beams in PS ring • Buncher system that creates the 25,50 and 75 ns spaced bunches beams • Copper coated steel cavity • Operating at 40.055 MHz • R/Q = 33 Ω • Strong capacity loading to fit in PS straight section • Loaded Q around 10000 • Acceleration field : 300kV • 300 kW pulsed RF amplifier

  3. Tuner • Variable capacitor tuner system inductively coupled (range 40.055 MHz +- 50 kHz) • Needed to compensate the geometrical deformation due to external atmospheric temperature and pressure variations. • Despite strong feedback, the system is strongly detuned for the high intensity LHC beams. • But the same cavity is also used for low intensity pilot beams for LHC in the same super-cycle. • And the tuner mechanism has not been designed for constant re-adjustment within the super-cycle

  4. PS 40 MHz Automatic Tuner Control

  5. Problem • The tuning must be done without beam • But then the frequency is wrong, stacked to a limit of the phase loop • Needs: • to switch to a frequency reference during tuner pulse. • to release the AVC Veto and send a voltage program for 50 kVp of acceleration field • Then send the proper pulse number to the tuner driver on the right direction.

  6. Variable capacitor Cavity Coax line Final amplifier Cryostat

  7. Status & conclusions • Ready to make a test on one cavity soon (this Friday ?) • But : • still try to find software solution for voltage program instead of additional hardware • Based on old LINAC boards to be replaced by modern PLC control • And who is or will be responsible of, in which RF section ?

  8. Acknowledgement • Alain Marmillon for operational records • Heiko Damerau for Central Building arrangement • Matthias Haase for database • REFERENCES • E. Jensen “Frequency adjustment needed for the 40 MHz cavity”, PS/RF/Note 95-29. • R. Garoby, D. Grier, E. Jensen, “The PS 40 MHz Bunching Cavity”, PAC 1997, Vancouver • A.K. Mitra, R.L. Poirier, E. Jensen, “ Coarse and Fine Tuners for the CERN PS 40 MHz Buncher Cavity”, 1998

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