• Follow up of actions
  • VELO detector and spectrometer strength for LHCb -> YP (pdf file)
  • YP first mentions that a bug was discovered on the MADX aperture module regarding the slicing of kickers. An easy by-pass of the problem is achieved by introducing slice lengths which are longer than the kickers. JBJ will look into the problem in due time.
  • YP presents a complementary study regarding the aperture on IR8 at 450 GeV when the spectrometer has its full strength. A request was made by the experiment to check if there is any possibility to have also the VELO detector closed at 5mm during the early run next year.
  • Using analytical estimates and simulations with MADX, it is shown that, provided that the instrument can be centered around the closed orbit, the VELO cannot be closed to less than 5.6 mm without internal crossing angle or 7.2 mm for the extreme internal crossing angle. However, a magnet-like 2.2 mm mechanical tolerance was used in the evaluation of the n1. With tighter mechanical tolerance for the VELO assembly, 2 extra mm can be gained for the closure of the VELO.
  • MG suggests that a table with the values for the closure of the VELO at top energy is included. The results will be refined and presented at the next LTC.
    
  • Squeeze study for LHCCWG -> MG (pdf file)
  • Proposed topic by Roger Bailey to be covered in LHCCWG of 29th of November
  • Shared in three presentations (LOC, collimators and operation) with the following questions
  • mechanics: is it any different from the ramp?
  • intermediate optics: how many and which ones?
  • influence of optics changes on crossing angle (when we have one)?
  • energy?
  • collimators: when do we move them?
  • do 1 and 5 together? what about 2 and 8?
  • machine protection
  • Proposal for LOC work
  • IR2 (JJ) and IR8 (YP), IR1-5 (MG and SF)
• Report from meetings
  • MEB -> MG
  • The big issue is the performance of Q5R5 magnet (SSS650). After the thermal cycle the magnet did not reach nominal performance. A decision was taken to stop the test, based on a statement by Ranko that operational currents were lower than nominal, without any communication from ABP-LOC. Actually, the current for 17 m β* presents only 10A safety margin and for TOTEM optics there is none. Nevertheless, the magnet was stripped and presented at MEB. At first it was considered as a viable option to repeat the test in the tunnel. After discussions, a possibility appeared to prepare a spare magnet to replace this one with minor hardware modifications. The cold test of this magnet will be redone and in case of failure, the transformation of the spare magnet for Q8 into a spare magnet for Q5R5 will be launched.
  • A complete reshuffling of the pre-allocation list of the SSS in Sector 2-3 was performed in order to cope with installation from the right side of IP3. 19 already approved magnets had to change slots.
• Beta correction at the KEKB rings -> Akio Morita (pdf file)
• Akio Morita presents the on-momentum beta correction used in KEKB in routine operation and the first attempts to do an off-momentum beta correction.
• Available monitors include the tune monitor and the TBT BPM system. The available knobs are the dipole and quadrupole currents.
• The basic idea is to fit the measured response of a dipole kick to an analytic formula using the beta function and phase advance. The fit is done either through least squares minimization of polynomial function, or by reducing dimension of the problem with some assumptions, or by brute force fitting, this last being very slow. An improved fitting scheme based on Newton-Raphson method exists.
• The beta correction is based on the fit between measurement and model using as knobs the quadrupole fudge factor and horizontal cosine-like bump around the sextupoles. An extra weight is applied for the tunes and the fudge factor of the real machine is iteratively updated.
• One correction is applied every two weeks, implemented on SAD and fully automatic. Each iteration takes 7 minutes and the usual correction time takes 30-60 minutes per ring. Typical performance is a final beta beating of 10% and tune correction to better than 3 x 10^-4.
• Off-momentum beta function correction is performed by minimizing the difference between measured and model optics using the 54 sextupole families around the ring. Disturbing effects can come from coupling close to the sextupoles. Examples are shown, but some disagreement is found between the measurement and model
• RT asks what is the initial beta beating. Akio Morita answers that it is 20%. The BPM resolution is 1μm.
• MG asks what happens with dispersion? Akio Morita answers that the dispersion remains uncorrected.
• Tunability of IR4 for the new optics scheme -> TR
• New aperture was introduced and test with latest optics of IR4 was made. No significant change with respect to what was found by André Verdier is observed. There are some problems with the automatic matching process.  Riccardo de Maria is informed.
• Aperture issues for vacuum chambers between D1 and D2 in IR2 and 8 -> JBJ (pdf file)
• JBJ explains that these are preliminary results taking into account all the changes in the injection kicker area.
• Initially, there was no dipole for the beam-beam crossing scheme. Since then, three orbit correctors and an extra BPM were added
• For an injected beam with no secondary halo and kicker misfire there are only 5σ at the entrance of the kicker. Then the BPMWB goes down to 3σ and the ZDC Y-chamber around 5σ
• On injection elements a 2mm orbit tolerance is being enforced. Again ZDC and y-chamber is problematic especially whenever 4mm orbit tolerance is used for both beams in conjunction with a non-elliptical chamber. The case of an elliptical chamber it is a bit better.
• Collective effects have to be discussed as well.
• For 450GeV run no crossing scheme is included but still the bottleneck is found in the Y-vacuum chamber area.
• YP asks if there will be more aperture bottlenecks between Q1 (L/R) especially for the high spectrometer values. JBJ replies that probably the TCT will do its job, but still some particles may flow around this area.
• MG suggests that this should be submitted to LHC Machine Protection Working Group.
• TR suggests to check the impact with the new topics.
• AOB

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