RF System models for the Decay Ring. G. Burt , A. Dexter (Lancaster Uni) With thanks to E. Jensen (CERN). Issues. Huge beam current 50-250 Amps. Huge RF power is required. Beam Current in quadrature with the RF (cavity will be detuned when the beam arrives).
G. Burt, A. Dexter (Lancaster Uni)
With thanks to E. Jensen (CERN)
V before beam arrives
A simple code has been written to understand the behaviour of such a system.
It includes a simple LLRF system that responds instantly (unrealistic) and can look at the effect of a varying current or frequency.
If we do not detune the cavity and we only have a small RF power available the gap voltage quickly rises to 750 kV and the phase tends towards 180 degrees.
To keep the cavity on amplitude and phase with the cavity tuned to 40 MHz takes ~9 MW.
If the charge in the beam varies we need more power to keep the cavity on phase as the capacitive loading of the cavity by the beam varies (real parts of the voltage no longer cancel).
This doesn’t include the generator mismatch which will mean even more power is required.
During filling and other slow charge variations this can be corrected with a tuner in the cavity to keep the cavity frequency correct for minimum beam loading.
Coarse and fine tuners for the CERN PS 40 MHz buncher cavity, A. Mitra