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PS Landau RF System Study Group

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864/2-B14 - SALLE J.B.ADAMS (CERN)

864/2-B14 - SALLE J.B.ADAMS

CERN

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Present: F. Bertin, R. Calaga, H. Damerau, N. Esfahani, A. Lasheen, L. De Mallac, M. Morvillo, M. Paoluzzi

Parameters of lambda/4 resonator (Nasrin)

  • Nasrin presents a 1st iteration design of a lambda/4 resonator with on-axis ferrite tuner.
  • The R/Q is expected in the range of 30 to 50 Ohm.
  • The tuning range has been adjusted to ~5% with capacitive tuning.
  • A transmission line mode has been prepared in MatLab to check the scaling from the Fermilab parameters to the PS cavity; it also agrees well with the CST simulations
  • The shunt impedance (256 kOhm) of the 1st iteration design should be checked, in particular with respect to losses in the ferrite (the PS 40 MHz fixed frequency cavity has a shunt impedance of about 330 kOhm)
  • Capacitive loading has been introduced to shorten the cavity
  • Next steps are:
    • Optimization of the capacitive loading
    • Check influence of power module geometry on cavity parameters
    • Add practical considerations concerning ferrite/garnet geometry

Discussion with Fermilab colleagues and 2018 beam studies (Heiko)

  • Heiko reported on a first Skype discussion with R. Madrak, W. Pellico and C. Tan from Fermilab
    • The Fermilab 2nd harmonic cavity pushes the technical limit to achieve 100 kV (75...106 MHz)
    • The garnet material is AL800 (National Magnetics Group Inc.), mu = 1.5...3.5
    • No fast feedback and no passive gap short-circuit
    • R. Madrak scaled the Fermilab design to the PS parameters. Her CST model has been an important bench-mark for Nasrin's simulations
  • MD studies to guide/confirm cavity parameter choices during the 2018 run include:
    • Re-check the existing 40 MHz as Landau RF system (with new anode power supply)
    • Stabilization with 20 MHz and possibly 80 MHz to confirm stability scaling with synchrotron frequency spread
    • Quadrupole coupled-bunch oscillation measurements with full machine (21 bunches)

AOB

  • For 1st estimates for the coupling of the cavity to an amplifier, as well as the direct feedback, Giorgia will take Nasrin's cavity parameters as a starting point
  • To launch calculations for longitudinal beam stability, Alexandre needs figures for the cavity impedance (with direct feedback) → Nasrin, Giorgia
  • Mauro explained that, thanks to the low gap voltage, the transformation ratio of the power coupling would be significantly lower than with the existing 40 MHz cavities. The additional impedance reduction due loading with the amplifier output impedance would be beneficial. This relaxes the constraints on the direct feedback.
  • The existing gap short circuit system seems too large for a Landau cavity.
  • Mauro will propose a wide-band cavity solution based on Finemet material.
  • Mechanically tunes cavities (with air cushion or magnetically floating) have been built as prototypes, but a solution without mechanical movement is preferred.
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