Instability Thresholds Alessandro Drago Super B General Meeting
Instability Thresholds Alessandro Drago Super. B General Meeting Perugia 16 -19 June 2009
Preliminary considerations • The bunch-by-bunch feedback systems for Super. B will be a direct evolution of the previous PEPII / DAFNE systems • Extrapolating the measurements done in DAFNE, it is possible to foreseen the thresholds to maintain control of the instabilities • Limits to the feedback performance can be given by undesired events 2
DAFNE, single horizontal feedback: I=560 m. A, mode -1 [=119] , grow=34. 5 (ms-1), damp=-127(ms-1) Damping time in 7. 9 microsecond i. e. in ~24 revolution turns 3
DAFNE, double horizontal feedback: I=712 m. A, mode -1 [=119] , grow=43. 7 (ms-1), damp=-233 (ms-1) Damping time in 4. 3 microsecond i. e. in ~13 revolution turns 4
Grow rates at higher e+ current: the unstable mode changes and becomes slower ! m=-2 m =1 m=-3 The beam current does not seem limited by the horizontal instability 5
Scalability • Double feedback in the same oscillation plane to use at the best the power output • A proved example of the scalability advantages • Possibility to have and manage easily more than one feedback in a single oscillation plane • Capability to damp coherent high order modes even if faster than foreseen 6
Numerical considerations • 500 w feedback damps in ~24 revolution periods • 2 x 500 w feedbacks damp in ~13 revolution periods • 3 x 500 w feedbacks should damp in ~7 revolution periods • 4 x 500 w feedbacks should damp in ~4 revolution periods • 5 x 500 w feedbacks should damp in ~2 revolution periods (? ? ? ) 7
Limit by tune spread 8 Measured by D. Teytelman & A. Drago
Longitudinal quadrupole instability DAFNE e- beam: longitudinal feedback off DAFNE e- beam: longitudinal feedback on Unable to damp longitudinal quadrupole instability 9
Conclusions • It possible to consider feedback systems that should be able to damp in ~4 revolution turns • Costs (for power amplifiers) and space in the main rings (for kickers) should be considered • Limits to feedback correct behavior could come from not foreseen reasons 10
- Slides: 10