LHC Momentum in 2008 J. Wenninger December 2008
Injection Test No. 1 SPS momentum set to Pnom,SPS = 450 GeV which corresponds to 449.16 GeV (calibrated with ions in 2002). Synchronization test 8-11 August: Sector 23 offset : -33 units with SPS @ Pnom,SPS = 450 GeV Sector 23 offset : -7.3 units with SPS @ Pnom,SPS = 451 GeV >> Obtained a difference of 0.26%, expected 0.22% >> PSPS = 450.31 GeV @ Pnom,SPS = 451 GeV LHC : fRF,LHC = 400'788'790 Hz SPS : fRF,SPS = fRF,LHC /2 = 200'394'395 Hz SPS central frequency (2002) fc,SPS = 200'394'215 Hz (+- 70 Hz) >> fRF,SPS – fc,SPS = 144 Hz >> Delta E = -0.039% = -3.9 units >> ES23 = 449.2 x 1.0033 (S23 traj) x 0.9994 (central f SPS) = 450.5 +- 0.2 GeV
10th September first turn offsets LHC fRF,LHC = 400'788‘790 Hz ?? Average offsets b1-b2 differ only by ~ 0.01% = 1 units. Statistically consistent…
12th September closed orbit LHC fRF,cap,LHC = 400'788'963 Hz LHC theoretical fRF,nom-LHC = 400'788‘734 Hz Average energy offset of CO : -0.094% = 9.4 units. Ft offset consistent with CO within 0.01-0.02%. >> Why did it change with respect to 10th ?
FT and CO b1 & b2 FT dp/p offsets on Sept 10th are consistent / show no significant difference. dp/p = -4 units fRF,LHC = 400'788'790 Hz (??) b2 CO dp/p offsets on Sept 12th : dp/p = -9.4 units FT seems well centered on CO, i.e. similar shift as CO within 1 unit. fRF,LHC = 400'788‘963 Hz >> The RF frequency difference of 173 Hz (wrt 10th) can explain a shift of the FT of -2.2 units due to the energy change in the SPS. Is the remaining shift of -2 to -3 units due to LHC ? >> A shift of -119 Hz is required to center b2 on the CO: fRF,LHC = 400'788‘884 Hz >> The SPS field must be increased by 8 units to re-center FT. Beam2 data
Central orbits – b2 To center the beam2 closed orbit and compensate for the radial offset (-9.4 units): The b2 central frequency (central = ~ centered in the BPMs) : LHC fRF,c,b2 = 400'788‘884 Hz >> 150 Hz higher than design : Ring 2 radius is 1.6 mm smaller than nominal. >> Note that the SPS radius is 1 cm larger than nominal. The corresponding SPS extraction frequency is: SPS fRF,ext = LHC fRF,c,b2 /2 = 200‘394’442 Hz To be compared with the SPS central frequency (central ~ centered in sextupoles, 2002- 2004): SPS fRF,c = 200’394’239 +- 70 Hz >> SPS fRF,ext - fRF,c = 203 +- 70 Hz >> Offset of -0.5 permill >> SPS radial position shifted inwards by -2 mm - OK