Optics studies for the LHC beam in the TT2-TT10 line and effect of the QKE58 suppression E.Benedetto, A.Franchi Thanks: G.Arduini, D.Jacquet, O.Berrig, R.Steerenberg, E.Bravin, A.Guerrero, PS and SPS operators LII meeting, 11/12/2006

Motivations QKE58 was used in the past for the extraction of electrons and anti-protons from the PS. In 2001 section SS58 has been dismantled BUT historically QKE58 has always been kept switched on. What happens if we switch off QKE58? Changes in ,D ? Last dispersion measurements done in OTR in TT10 for beam matching

Outline Measurements of 10 th Nov ’06 MESPS (LHC beam, 26GeV, 1-4 bunches) w/o bunch rotation Dispersion measurements with Passerelle Beam profiles measurements with OTRs in TT10 →  emittance Comparison with model prediction (A.F.)

Dispersion measurements “Passerelle” provides access to PS and SPS equipments from Windows platform via Excel + Excel application by D.Jacquet and G.Arduini TT2-TT10 and first turn SPS For QKE58 on and off: –vary beam momentum (by change ref. freq. sent from SPS to PS) –record transverse positions with BPMs –for each momentum, the relative offset  p/p is computed from first turn measurements –3 rd order polynomial fit applied at the beam displacement function of  p/p → get dispersion D i at each BPM location –fit to calculate D 0 and D’ 0 at beginning TT2

Dispersion measurements The Dispersion measured at each BPM (blue) with error bars and the fitted curve (magenta). Measurements with QKE58 off. Horizontal Vertical

Dispersion measurements QKE58 onQKE58 off Horizontal dispersion (fitted curve) from 1 st turn measurements, compared with the expected periodic function in the ring. Large mismatch for QKE58 off.

Dispersion measurements measurements Dispersion at initial point Dispersion derivative at initial point H V error Dispersion at initial point Dispersion derivative at initial point H V measurements Dispersion at initial point Dispersion derivative at initial point H V error Dispersion at initial point Dispersion derivative at initial point H V Measurements in 2000 (QKE58 on) gave: DX0 = ; DPX0 = ; DY0 = ; DPY0 = ; Results with QKE58 ONResults with QKE58 OFF Larger horizontal dispersion (48% increase) at beginning of TT2 for QKE58 off

OTR measurements in TT10 2D beam profile  x,  y from projections on horiz and vertical plane + Gaussian fit MESPS with 4 bunches 4 monitors in TT10 (BTV1018, BTV1024, BTV1025, BTV1026) and MTV201 in TT2. Many problems (thanks a lot to the BDI people for help!!!) with CCD cameras and software acquisition. Hopefully will be solved during this shutdown.

OTR measurements 3-monitors method to derive  and emittance  at the beginning of TT2:    = M -1          M = C12C12 -2 C 1 S 1 S12S12 C22C22 -2 C 2 S 2 S22S22 C32C32 -2 C 3 S 3 S32S32           Combinations of 3 out of the 5 monitors in TT2-TT10. Dispersion from measurements 10/11/’06 Momentum spread (  p/p) 1  = NAMESALFXBETXMUXALFYBETYMUYDXDPXDYDPY BEGTT2A MTV BTV BTV BTV BTV with QKE58 on

OTR measurements Monitors in TT10 Less then 10% difference between QKE58 on and off in most of the cases –  x ~ 24m (was ~36m) –  y ~ 10m (was ~6.5m)  = ~ Completely different then the others

Including the monitor MTV201 (in TT2) Very small difference between QKE58 on and off in most of the cases  = ~ –  x ~ 24m (was ~36m) –  y ~ 10m (was ~6.5m) Results depends on the choice of the monitors

Comparison with model prediction Transfer matrix between end PS and beginning TT2

Comparison with model prediction Always ~30% difference in  x with w/o QKE58, ~10% in  y. With the “old” Twiss values, difference was >70% in  x Dispersion increase consistent with measur (was ~48%)

Summary Dispersion measurements: –Good agreement between measurements and model –Expected Dispersion increase if QKE58 off is ~50% OTR measurements for initial ,  –3-monitor methods –Good the determination of transverse emittance –Inconsistency between different monitor results –Inconsistency between measurements → show almost no effect of QKE58 the model → show large increase of  x (but the % depends on the assumed Twiss paramenters with QKE58 on) –Anyway, we managed to make them operative again !!!

What’s next Analysis of SEM-grid profiles in TT2 and TT10 –estimate about the initial Twiss parameters? Improve the analysis of OTR measurements –5-monitors method –Determination of the beam size from the 2D profile, not by fitting the projection on the x(y) plane, but by a 2D fit? –The software acquisition timing problem will be hopefully solved during the shutdown.