Trim in Q1 for β ∗ measurements R. Tom´ as, J. Coello, A. Garcia and M. Hofer for WP2 March 30, 2017
Goals of β ∗ measurement ⋆ Ensure beam aperture & machine protection. Requires ≈ 10% accuracy in β ∗ ⋆ Provide same luminosities to CMS and ATLAS within 5% rms. Requires 2% accuracy in β ∗
Techniques to measure β ∗ ⋆ K-modulation: ◮ without tune feedback . Demonstrated accuracy in LHC ≈ 1%. ◮ with tune feedback ⋆ β from amplitude of betatron oscillations with calibrated BPMs.
K-modulation accuracy versus Q1A trim Potential solution: Q1a trim? Q1 Q3 Q2a Q2b IP ktrim1 ktrim2 ktrim3 ktrimA1 kpc Factor 2 improvement in 𝛾 ∗ control (round optics): • Adding trimA1 Target reached! Target achieved for round 15cm optics and approaching the spec for flat 10/40cm optics. J. Coello in 2017 HL-LHC Circuit Review
K-modulation with tune feedback I This was tried in the LHC in 2016: Late response of feedback, partial correction...
35 0.4 0 5 10 15 20 25 30 0.6 0.5 0.0 0.1 0.2 0.3 K-modulation with tune feedback II Systematic error from Q1 β -beating in MQTs: ∆ Q ( Q 1) − ∆ Q ( MQT )[10 − 3 ] tune jitter from PC stability ∆ Q ( Q 1)[10 − 3 ] Systematic error above random error for ∆ Q > 0.01.
β from amplitude - BPM calibration 5 after calibration before calibration 4 3 Counts 2 1 0 12 10 8 6 4 2 0 2 4 6 ∆ β β kmod (%) Optics-measurement-based BPM calibration helps improving the accuracy but does not reach requirement.
Tightening imperfection tolerances? ⋆ Uncertainty of 10 units in MQFX TF could not be reduced (we already asked) ⋆ Improve longitudinal alignment accuracy from 5 mm to 1 mm for all triplet quadrupoles: ✸ Significant ✑ ✑✑✑✑✑✑✑✑ → 5.5% in flat improvement but not enough, lumi imb. 8% → 3% in round WP2 meeting to address feasibility of 1 or 5mm.
Summary ⋆ K-modulation without tune feedback is the best technique for β ∗ control. Current configuration gives 11% luminosity imbalance (4% in β ∗ ). ⋆ The only known solution to meet the 5% luminosity imbalance tolerance (2% in β ∗ ) is the Q1A trim with 30 Amps. ⋆ Longitudinal alignment uncertainty has limited impact on β ∗ control. 1 mm uncertainty gives 8% lumi. imbalance (3% in β ∗ ) How good could it be?
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