Summary notes of the LCU meeting on 3/04/2012

Present: JA, HB, RdM, OD, MG, JJ, EM, MS, MSt, RT, RV, FZ, PH, AL

Report from meetings

• SLM and general information -> MG
  As from the beginning of this month, Riccardo works with us as staff member and Pascal Hermes joined us as technical student supervised by John Jowett. The board with a post on collimation took place and a candidate was selected.
  Our internal deadline to submit IPAC contributions to the group leader is the 7 May.
  A general ABP group meeting followed by a grill-lunch is planned for the 18 or 22 June.
• LHC Status
  There is good progress on the LHC re-commissioning. Top energy and beta*=60 cm were reached and look ok. See the LHC-latest-news.
• LMC -> FZ
  The last LMC discussed commissioning progress, orbit stability and collimator settings. For further subjects and details see the link to the LMC.

Update on high-beta optics situation and impact on quadrupole powering -> HB   (slides)
HB reported from recent activities related to high-beta optics. The question of adding return cables in LS1 to eliminate the 0.5 < beam1/beam2 < 2 current ratio limitation is followed up with experts from power convertors and magnets as action item for the LMC.
A decision is required  before summer to allow for the ordering of cables.
High-beta optics have been matched beyond 90 m and look acceptable within standard aperture criteria to a beta*= 500 m for both TOTEM and ATLAS-ALFA.
Strength files were prepared up to a beta*= 1000 m and were checked to be compatible with the power converter and magnet limitations. Keeping quadrupole currents within the beam1/beam2 ratio limit has been very difficult and required many iterations and  compromises. A constant +/- 2mm separation is kept throughout the unsqueeze.
The scheduling of the high-beta runs was discussed in the last LPC. The first high-beta runs are presently foreseen to start shortly after the June deadline to collect maximum luminosity for ICHEP 2012.

Position of DS collimators in IR2 -> JJ   (slides)

The upgrade of the dispersion suppressor region in LS2 could allow to install collimators and detectors in the dispersion suppressor to detect off-momentum particles, which is interesting for physics studies as proposed by R. Schicker et al. from  ALICE. In particular, it was proposed to measure bound free pair production at 6.5 ZTeV at low beta* = 0.55 m. It would require a position beyond Q8 at Q9 to get sufficient horizontal dispersion.

An extremely-flat beam optics with large crossing angle for the LHC -> JA   (slides)

Jose reported about his studies which are done supervised by Frank Zimmermann in the framework of EUCARD. He was looking at very flat optics with a beta* of 1.5m in the horizontal plan, and a factor of 100 smaller beta* of 1.5 cm in the vertical plane. He gets a significant vertical dispersion which allows for a local chromatic correction with sextupoles. The crossing angle grows to 2 mrad. The Piwinski angle becomes rather large. Resonance excitation and the luminosity loss from the large Piwinski angle could potentially be minimized using a crab-waist scheme. A key element for such an optics would be special double-half quadrupoles. A very preliminary design of such magnets was studied by Stefan Russenschuck. As mentioned by SF the issue of field quality will be crucial for the special field configuration.

The scheme presented would certainly be very challenging. There are still many open questions at this point (field quality, dynamic and physical aperture including separation bumps etc). JA will present the current status at the annual EUCARD meeting later this month.

Simulations of IBS for protons at injection in 2012  -> MS   (slides)

Michaela reported about her recent studies on intra-beam scattering for protons at 450 GeV at injection in the LHC.

She uses the CTE (Collider Time Evolution) program by Mike Blaskiewicz, Roderik Bruce and Tom Mertens, which is based on the Nagaitsev formulas for intra-beam scattering. This allows to take into account non-Gaussian longitudinal beam shapes. She showed results on beam losses and emittance growth for 1 ns and 1.5 ns  bunch length (4 sigma). Longer bunches result in increased beam losses. The growth from IBs is more significant for the shorter bunch length. She also compared with the MAD-X predictions and finds results to be in broad agreement. Small differences are seen as can be expected from the more detailed bunch shapes taken in to account only in CTE.

Last update: 04-April-2012

MG & HB

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