RF measurements during floating MD in Week 30 25 th of July 2012

1. RF measurements during floating MD in Week 30 25th of July 2012 Participants: T. Argyropoulos, H. Bartosik, T. Bohl, H. Timko,H. Damerau, C. Lazaridis LIU-SPS BD WG 02/08/2012

2. General • MD title: • Longitudinal set up of the 50 ns LHC beam with Q20 optics • MD aim: • Improve capture losses and overall transmission • Achieve beam stability and acceptable beam parameters at flat top • Beam conditions: • Single batch of 36 bunches • Intensities at injection Np~1.6x1011 p/b • Varying parameters @SPS: • RF voltage amplitudes (V200 and V800 - operation always in double RF) • Longitudinal emittance blow-up (only turn on/off – not necessary to • optimize for this intensity) – not used in the past for Q20 optics • Longitudinal dampers’ gain (didn’t help) • Varying parameters @PS: • Controlled emittance blow-up

3. Outline • Losses • Stability • comparison between the two main 200MHz voltage programs used during the bunch profile measurements for the cases: • with SPS longitudinal emittance BUP • w/o SPS longitudinal emittance BUP • Summary

4. Losses • Increase 200 MHz voltage at flat bottom to reduce capture • losses  losses at flat bottom were increasing  Overall • transmission constant between (~ 8 - 9 %) Low voltage at flat bottom – 4.5 MV High voltage at flat bottom – 7 MV

5. Losses • Total losses were not much affected by the different longitudinal • emittances. correlation of losses with Vinj and εFB Comparable losses to those for Q26

6. Stability - RF voltage programs • Two main 200 MHz RF voltage • programs during the bunch • profile measurements • Stability at FT was a bit better • with the high voltage values • Change V800 at flat top didn’t • help stability • The V200 Low was chosen to • compare with the MD at • November 2011  stable • bunches at that time w/o • emittance BUP with similar • intensities (1.6x1011 p/b at • injection)

7. Stability – w/o emitt. BUP • unstable at ~350 – 370 GeV/c  • different from last year! • emittances at FB ~0.28-0.31 eVs • Losses ~ 8 - 9 % • Long. Emitt. BUP in PS : 3x3 kV • and 3x3.5 kV  only changed • the spread of τi , not <τ> V200Low V200High • unstable at ~360 – 390 GeV/c • emittances at FB ~0.33-0.34 eVs • Losses ~ 8 - 9 % • Long. Emitt. BUP in PS : 3x4 kV

8. Stability – w/o emitt. BUP V200 High • unstable at ~360 – 390 GeV/c • emittances at FB ~0.33-0.34 eVs • Losses ~ 8 - 9 % • Long. Emitt. BUP in PS : 3x4 kV V200High • unstable just before FT • emittances at FB ~0.34-0.36 eVs • Losses ~ 8 - 9 % • Long. Emitt. BUP in PS : 3x5 kV

9. Stability – with emitt. BUP V200Low • emittances at FB ~0.30-0.32 eVs • Losses ~ 8 - 9 % • Long. Emitt. BUP in PS : 3x5 kV V200High • emittances at FB ~0.34-0.36 eVs • Losses ~ 8 - 9 % • Long. Emitt. BUP in PS : 3x5 kV

10. Summary • Beam is more unstable and has more losses for the same injected beam • parameters and machine conditions than in 2011 (also in Q26 optics). • Stable beam always at FB • Instability observed w/o long. emittance blow-up during the ramp  • improved by increasing longitudinal emittance (injected or in the SPS • with higher RF voltage at injection) • changing the gain of the longitudinal dampers at flat bottom or • flat top didn’t help • Stable beam along the cycle with long. emittance blow-up • for Low V200 : τFT = 1.56-1.6 ns and εFT = 0.43-0.46 eVs • for High V200 : τFT = 1.68-1.7 ns and εFT = 0.49-0.5 eVs •  similar bunch lengths at FT with Q26 • more variation with low RF voltage  some adjustment in the BUP is • needed • Losses along FB were not understood • Measurements with only one batch  what can be obtained with • 4 batches?