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Collimation Studies MD

Collimation Studies MD. G . Valentino, R. W. Assmann , R. Bruce, G. J. Mueller, S. Redaelli , B. Salvachua. Why the MD was requested. BLM Spike Quality Poor BLM spike quality was noticed for some horizontal collimator alignments.

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Collimation Studies MD

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  1. Collimation Studies MD G. Valentino, R. W. Assmann, R. Bruce, G. J. Mueller, S. Redaelli, B. Salvachua

  2. Why the MD was requested BLM Spike Quality Poor BLM spike quality was noticed for some horizontal collimator alignments. As this plane is affected most by dispersion, the idea was to observe the spike quality for different cuts in the momentum halo with the IR3 TCP. Setup Time In March 2012: setup time of 7.5 hours was achieved at 4 TeV flat top. If collimators need to be re-aligned this year (and after LS1), a faster alignment would allow for reduced time without physics. Instabilities @ 4 TeV with tight collimator settings (with E. Metral, N. Mounet, B. Salvant) High losses observed during a test alignment with many collimators close to the beam. Impedance increases exponentially with the gap in mm. Beam instability studies were originally foreseen, but had to be postponed to the next MD block due to a reduction in the overall MD 1 block time.

  3. MD Requirements Energy: 450 GeV & 4 TeV Injection optics Both beams, 1 nominal bunch (1.15E11 p) per beam Safe Beam Flag, BLMs and collimator movements masked

  4. Momentum Halo Cut Study Jaw stops moving TCL.5L1.B2 Loss Threshold At start of horizontal collimator alignment, the momentum halo is cut using IR3 TCP. Ensures that the alignment of the other collimators is done to the betatron halo. For some alignments, losses increased again after the first spike was observed. Aim of study: to align IR3 H collimator (TCLA) for different Dp/p cuts with the IR3 TCP, and observe any improvements in the BLM signal quality.

  5. Momentum Halo Cut Study • Shift in beam-based center observed after momentum halo cut with the IR3 TCP. • After first IR3 TCP alignment, TCLA beam-based center does not vary by > 10 µm. • Confirms requirement for momentum halo scraping with IR3 TCP before alignment. BB Centers Beam Size Ratio Measured-to-Nominal beam size ratio stabilizes already after the first IR3 TCP alignment.

  6. Momentum Halo Cut Study Example for TCLA.7R3.B1 BLM signal spike quality was found to be good, and similar for different Dp/p cuts: Poor spike quality in March alignments more likely due to: (a) non-optimized operational conditions, e.g. octupole strengths (b) beam oscillations at the TCTs / TCLs (?)

  7. Coarse BPM-interpolated alignment • BPM-interpolated centers were compared to all the beam-based centers for the 2011 and 2012 alignments. Average interpolation vs. measurement delta: 0.550 mm.

  8. Coarse Aligned Jaw Settings: Coarse BPM-guided Initialization GUI

  9. Improved Parallel Alignment Algorithm BB Center comparison to March alignments • Average Delta w.r.t. March 21 alignment: 0.155 mm. • Orbit corrected only initially in the MD. • Setup Time: 27 collimators in 1 hour 45 mins. • Extrapolated to 80 collimators = 5.5 hours. • 2 hours improvement over previous best time. Algorithm: move left and right jaws of collimators simultaneously to the beam while loss threshold < BLM. Previously: if one collimator stopped moving, parallel alignment would continue for the other collimators without checking which jaw of the stopped collimator is aligned. Now: after the “both jaws” movement has completed, all left jaws are moved, followed by all right jaws. Gain in setup time: before, if one jaw of each collimator is still far from the beam, more time is spent during the sequential fine alignment phase.

  10. Summary MD was successful: enough time for all proposed MD studies to be performed. BLM spike quality issue is thought to be related more to machine parameters such as octupole strengths or the jaw material rather than the depth of the momentum cut. IR3 study confirms the need for a momentum halo cut at the start of alignment. Time for full collimator alignment reduced from 7.5 to 5.5 hours. Coarse alignment using BPM-interpolated orbit will be used as a standard alignment procedure before BLM-based alignment.

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