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=12) 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
PSB rf manipulations PSB cavities 31/03/2004 A. Blas Shutdown lecture
PSB rf manipulations PSB cavities 31/03/2004 A. Blas Shutdown lecture
PSB rf manipulations Low level rf basic scheme 31/03/2004 A. Blas Shutdown lecture
PSB rf manipulations Injection Injected Linac coasting beam: 50 MeV average kinetic, energy spread Dp/p ≈ 1.6 10-3 31/03/2004 A. Blas Shutdown lecture
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
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
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
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
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
PSB rf manipulations Open loop acceleration 31/03/2004 A. Blas Shutdown lecture
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
PSB rf manipulations Acceleration with phase loop 31/03/2004 A. Blas Shutdown lecture
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
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
PSB rf manipulations Synchronization 31/03/2004 A. Blas Shutdown lecture
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
PSB rf manipulations Blow-up 31/03/2004 A. Blas Shutdown lecture
PSB rf manipulations Blow-up 31/03/2004 A. Blas Shutdown lecture
PSB rf manipulations Dual Harmonic Acceleration 31/03/2004 A. Blas Shutdown lecture
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
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
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
PSB rf manipulations Bunch splitting 31/03/2004 A. Blas Shutdown lecture
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