Summary notes of the LCU meeting on 06/07/2012

Present: AL, PS, SW, PH, TP, MG, AB, RV, LD, SF, MF, JJ, RT, OB, RdM, FZ.

Report from meetings

• SLM and general information -> MG
  The 2012 physics run has been extended by about two months in 2013. The year 2012 will be entirely devoted to proton physics, while the short 2013 run will be devoted to p-Pb physics.
  LS1 will be delayed accordingly.
  The sign oft he octupoles is becoming a key issue for LHC performance (see also next presentation).
  The beam-beam team considers that the crossing angle in IR2 is marginal and that it should be increased. Aperture checks have been carried out by Roderik.
  Plasma wakefield activities at CERN will be lead by E. Gschwendtner.
• LMC -> FZ
  FZ reported highlights from the LMC, in particular relatively recent observation of heavy losses, very frequently followed by a beam dump, occurring during the collapsing beam process.

...The sign of the LHC octupoles -> SF (slides)
SF presents his views on the problem, illustrated by several movies showing the tune footprint evolution during the collapsing process (nominal bunches, IP8 private bunches, variation from bunch to bunch).
He stresses that the source of the problem is the long-range of IR1 and IR5, which is enhanced by a factor of 2 during the collapsing process. This effect is compensating the octupole tune spread, first on the anti-diagonal for parallel separation of the order of 15 sigma*, then both on the diagonal and anti-diagonal at a very small separation around 2 sigma*.
This explanation matches very well with the observation that the so-called IP8 private bunches have now much less long-ranges in IR1 and IR5 with the new LHC filling scheme, and are not lost any longer during the levelling process.
There is a general consensus that these results shold be cross-checked by the beam-beam team.
There is a general consensus that these results should be presented at the next LMC, recommending a change of octupole polarity.

Last update: 24-July-2012

MG & HB

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