LHC Emittance Preservation Checks MD I Preliminary o
- Slides: 7
LHC Emittance Preservation Checks - MD I Preliminary o o Effect of damper gain on emittance growth − At injection − During ramp Mitigation of growth due to IBS at 450 Ge. V with long. batch-by-batch blow-up − o Analysis still ongoing IBS and transverse blow-up – longitudinal impedance MD − Analysis still ongoing 1
From Evian/Chamonix Presentation LHC o Effect of reduced damper gain during ramp? Reduce damper gain before ramp for tune feedback →Increase of BBQ amplitude W. Hofle 2
Damper gain @ 450 Ge. V (1) o LHC Changed damper gain back and forth while waiting at 450 Ge. V − Single bunch (~ 1. 4 -1. 5 e+11), damper single bunch settings − Wait time ~ 10 minutes after each change Injection gain Ramp gain High gain NO NEGATIVE EFFECT Growth rather due to other effects 3
Damper gain @ 450 Ge. V (2) o LHC Results for beam 2 Growth in H due to IBS, independent of damper gain Beam 2 V: emittances growing with lower damper gain (chromaticity slightly negative? ) High damper gain: POSITIVE EFFECT 4
Ramp: damper gain modulation o o LHC 3 Ramps − 8 bunches with different gains, single bunches, 21/4/2012 − 8 bunches with different gains, single bunches, 22/4/2012 − 2 x 12 bunch batches with different gains, 50 ns, 22/4/2012 Analysis shows puzzling effect → no conclusion on damper effect Measured betas taken into account: Emittances shrinking through the ramp!! Emittances slightly over -estimated due to tail population 5
What is happening? o Wrong betas? o Wrong wire scanner settings? Did another check… 7/5/2012 o Emittance shrinkage coincides with intensity loss… o Probably not betas, wire scanner settings not reason. LHC 6
Summary LHC o Higher damper gain better for emittance preservation – at least at injection o Effect of different damper gains on emittance growth during ramp not clear yet o Puzzling effect: emittances shrinking through the ramp for (B 1 H, B 1 V and B 2 V) o More studies required: − Ramp with intermediate collimator settings to not lose intensity and measure emittance? 7
