Summary notes of the LCU meeting on 29/11/2010

Present: HB, RdM, OD, SF, MG, BH, JJ, TM, RT, SW, FZ

Report from meetings

• SLM and general information -> MG
  This and the next LCU meeting have exceptionally been moved to Monday morning.
  A report on the planning of the HL-LHC studies was sent to the EU with requests for support. Discussions with external collaborators should wait for a first response from the EU on these requests.
  Frank Schmidt negotiates with IT to get a better share of lxplus batch resources. We have now two groups, u_coll for collimation and u_slap for general tracking. These groups date back to 2004 and the last review of our shares was made in 2008.
  There are ongoing discussions on LHC parameters for 2011 and the minimum beta* in preparation of the Evian workshop next week.
  BH asks to sent him proposals for subjects for students. He will be teaching in JUAS in January and could look for good candidates for the subjects proposed.
• LMC->FZ
  Katy Foraz presented an update of the technical stop planning which allows to accommodate extra activities like the installation of snap-back capacitors required for 4 TeV. JJ gave a report on the current ion run. Further subjects and details will be available from the LMC minutes.

Nb3Sn dipoles in the LHC DS: preliminary results -> BH (slides)

BH studied the implications on optics and geometry, if shorter, stronger Nb3Sn dipoles would be installed in dispersion suppressors (DS)  at Q8, Q10, to make space for cryogenic collimators. As Nb3Sn material is very brittle, it is proposed to have rectangular magnets (with the appropriate aperture - about 60 mm) instead of sector dipoles. The change in geometry is small, but in any case the affected elements should be re-aligned. The impact of the edge focusing on the tune and beta-beating is also very small. As the new dipoles should be in series with the nominal ones, any difference in transfer function would generate an orbit distortion. The amplitude of this orbit distortion is such that orbit correctors would use a too large fraction of their strength. This means that a trim power converter should be used. Persistent current effects are very large and also for spool pieces a trim power converter should be envisaged. Next point will be the study of dynamic aperture and specification of an error table.

The installation of the new dipoles is discussed for the DS of IR7 and IR2 (in IR3 the solution proposed by JJ with displaced nominal main magnets was endorsed in July 2010 at a collimation review). JJ reminded that the DS of IR7 and IR2 are different and that a single Nb3Sn dipole on either side of the DS around IR2 should be sufficient. For IR2 more input from the collimation team is required, but MG comments that tracking studies could be launched already with an educated guess of the layout.

15 cm beta* round optics for crab-cavity using SLHCV3's techniques --> RdM (slides)

RdM and SF work on options for LHC upgrade optics. One option is for 15 cm beta* with 580 murad total crossing angle, with round beams and would rely on crab cavities. The proposed layout is based on the sLHCV3 approach of using the neighbouring arcs of IR1/5 to correct the off-momentum chromaticity. This presentation was given to allow for discussion and feedback before the crab cavity workshop in two weeks. The squeeze down to 60 cm would be with local chromaticity correction, while the neighboring insertions would be required to squeeze down to the target value of 15 cm. So far this looks promising but a number of details remain to be checked. The crab cavities should be located next to the D2 separation dipole. In particular, the required strength of the crab cavities calls for further optimisation. Increasing the beta-functions at the location of the crab cavities would allow reducing the voltage, but this would have impact on the aperture requirement for D2. The dogleg option is still on the table for improving the optical conditions at the location of the crab cavity.

AOB

None

Last update: 02-November-2010

MG & HB

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