Journal Club presentation LHC optics commissioning: A journey towards 1% optics control Helena Pikhartova June 27, 2018
Summary of article 2/8
Beta beating ✽ Maximum relative deviation of the β function with respect to the model ✽ Traditionally not required to be very precise ✽ LHC is the first high energy collider with tight design tolerances on optics errors to guarantee the machine protection during operation with beam Beta beating for some other machines: 3/8
β ∗ waist ✽ In 2015 it was discovered that there was a systematic offset of the β ∗ waists in both IP1 and IP5 resulting in an increase of the β ∗ causing about 5% luminosity loss 4/8
Orbit drift ✽ Without varying any parameters, orbit will change through hours of operation ✽ Need to have feedback on orbit drift and correct 5/8
Beam Position Monitors ✽ BPMs are used to measure the turn-by-turn data of betatron oscillations, which are excited adiabatically by an AC dipole ✽ 11 BPMs installed to measure phase advance between each other and calculate β at their location ✽ 6/8
K-modulation ✽ K-modulation is a method for measuring beta functions at locations of individually powered quadrupoles ✽ Changing the strength of a quadruple results in a tune change → tune change is proportional to the change of strength and the beta function at the location of the quadrupole ✽ If the tune change can be measured accurately, the beta function can be calculated from the change in quadrupole strength 7/8
Conclusion By the end of 2016: ✽ β ∗ = 0 . 4 m (better than design value) at 6.5 TeV ✽ Smallest beta beating ✽ Optics control 1% ✽ Luminosity leveling due to detector pileup and cryogenic power limits done by varying β ∗ during run 2017 and beyond: ✽ β ∗ = 0 . 3 m at 7 TeV ✽ Keeping up good optics control 8/8
The end of presentation 1/2
Discussion 2/2
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