1. PSB rf manipulations PSB cavities
Cavity
Frequency range
Maximum voltage
Use (for protons; no more ions foreseen)
C02
0.6  2 MHz
8 kV
Acceleration on h=1
Acceleration with h=2
C04
1.2  3.9 MHz
Bunch shaping (flattening) in dual harmonic mode
Bunch splitting (h=12) at 1.4 GeV
Acceleration on h=2
C16
5  16 MHz
6 kV
Controlled longitudinal blow-up
In total 12 cavities; 3 per ring.
31/03/2004
A. Blas Shutdown lecture

2. PSB rf manipulations PSB cavities
31/03/2004
A. Blas Shutdown lecture

3. PSB rf manipulations PSB cavities
31/03/2004
A. Blas Shutdown lecture

4. PSB rf manipulations Low level rf basic scheme
31/03/2004
A. Blas Shutdown lecture

5. PSB rf manipulations Injection
Injected Linac coasting beam:
50 MeV average kinetic, energy spread Dp/p ≈
31/03/2004
A. Blas Shutdown lecture

6. PSB rf manipulations Set Capture Frequency
The average energy together with the main dipolar field will determine the optimal frequency for capture.
RFBINJ is set to the B value measured at injection +1 ms.
GSFOFFC02 is set to a value that lowers the transients when closing the phase loop.
31/03/2004
A. Blas Shutdown lecture

7. PSB rf manipulations Set Capture rf Voltage
The rf voltage is kept at the minimum level during injection so as to have a minimal effect on the energy spread.
The voltage needs also to be big enough so as to allow the cavity tuning loop to function. VRF > 200 V
31/03/2004
A. Blas Shutdown lecture

8. PSB rf manipulations Set Iso-adiabatic Voltage
adiabatic means that the emittance remains constant and “iso” means that the adiabaticity is constant during the capture process (this also means that we are not absolutely adiabatic)
A is the bucket area
KA is the adiabaticity coefficient
TS the synchrotron frequency
Red: theoretical law with KA = 0.5
Green: actual function ; straight line in dB scale.
31/03/2004
A. Blas Shutdown lecture

9. PSB rf manipulations Iso-adiabatic Voltage (2)
Iso-adiabatic law:
Vi : initial voltage
Vf : final voltage
Tr : Rise time
Approximated by
straight line in dB scale
Lin/Log conversion
31/03/2004
A. Blas Shutdown lecture

10. PSB rf manipulations Open loop acceleration
The beam can be captured and accelerated (not synchronized) without closing any feedback loop
Although the overall efficiency is poor, if the beam is completely lost in this operation, the problem might well not be rf.
On top of all the signals applied during capture, just let the system adapt its frequency to the magnetic field raise by enabling STBRF
31/03/2004
A. Blas Shutdown lecture

11. PSB rf manipulations Open loop acceleration
31/03/2004
A. Blas Shutdown lecture

12. PSB rf manipulations Acceleration with phase loop
The phase loop should be closed as soon as the beam has enough rf structure (typ 300 μs) with SPL
GSPOFFC02 and BAi.GSFOFFC02 are set such as to minimize the transient on BAi.C02PHBEAM
31/03/2004
A. Blas Shutdown lecture

13. PSB rf manipulations Acceleration with phase loop
31/03/2004
A. Blas Shutdown lecture

14. PSB rf manipulations Acceleration with phase and radial loop
The radial loop should be closed as soon as there is enough room in the rf bucket to make it shrink in the acceleration process (typ inj + 1 ms) without loosing beam
STBRF (allows to update the B field at the frequency program level) should be applied at the same time.
The radial loop is not mandatory and cannot be used without the phase loop or with a low intensity beam
31/03/2004
A. Blas Shutdown lecture

15. PSB rf manipulations Synchronization
Just after flattop, the frequency beating process can start, followed by the phase synchronization.
The flattop frequency should be set with RFBEJ close to the reference to avoid transients
Check on Naos the error signal BAi.BEAMPHSYREF
31/03/2004
A. Blas Shutdown lecture

16. PSB rf manipulations Synchronization
31/03/2004
A. Blas Shutdown lecture

17. PSB rf manipulations Blow-up
Phase modulation around a high harmonic of the revolution
with:
Resonance condition: ; k, l integers
5 degrees of freedom !
31/03/2004
A. Blas Shutdown lecture

18. PSB rf manipulations Blow-up
31/03/2004
A. Blas Shutdown lecture

19. PSB rf manipulations Blow-up
31/03/2004
A. Blas Shutdown lecture

20. PSB rf manipulations Dual Harmonic Acceleration
31/03/2004
A. Blas Shutdown lecture

21. PSB rf manipulations Dual Harmonic Acceleration
Capture, acceleration can be performed with the main rf and its second harmonic to perform a bunch shaping.
Typically the harmonic are in opposite phase, resulting in a flat bunch with a lower peak current (less space charge effect)
Stability is less critical when the second harmonic cavity phase is referenced to the beam fundamental rather than to the main cavity.
31/03/2004
A. Blas Shutdown lecture

22. PSB rf manipulations Dual Harmonic Acceleration
As soon as the beam has an rf structure, switch the servoing reference from h1 cavity to beam with BAXi.SH2SYNCBEAM
31/03/2004
A. Blas Shutdown lecture

23. PSB rf manipulations Dual Harmonic Acceleration
The second harmonic voltage is lowered before extraction to ease synchronization and to permit longitudinal matching with the PS
31/03/2004
A. Blas Shutdown lecture

24. PSB rf manipulations Bunch splitting
31/03/2004
A. Blas Shutdown lecture

25. PSB rf manipulations Bunch Splitting
The voltage ratio C04/C02 should increase adiabatically until the splitting starts to occur.
When the h2 structure is important enough and some h1 is remaining, the loops can be switched from C02 to C04 as the main cavity
31/03/2004
A. Blas Shutdown lecture