Summary notes of the LCU meeting on 17/05/2011

Present: CA, HB, LD, SF. MF, MG, BH, YL, TM, MS, GV, FZ

Report from meetings

• SLM and general information -> MG
  A general ABP group meeting with short presentation from all sections is planned for the 28 June starting at 11:00 to be followed by a lunch barbecue.
  The first LHC MD session was performed very successfully.
  The ATS optics worked well at injection, beta-beating was as for the nominal machine. Tune and coupling corrections worked nicely. One ramp was successfully performed and it was already possible to measure the optics (beta and dispersion) at 3.5TeV ramp as well as to perform the usual tune and coupling correction. The beta-beating at top energy was between 10-15% without any correction!
  The 90m optics for ALPHA and TOTEM were also successfully tested showing that the tune control by means of the main quadrupoles can be implemented in the machine.
  Using collision tunes already at injection was found to be feasible and the beam-beam studies allowed to reach five times the nominal beam-beam tune shifts in head on collisions.
• LHC -> BH
  Recovering from the short scheduled technical stop has been rather lengthy (as usual). A full session of VdM luminosity scans was successfully performed on Sunday and concluded with a length scale calibration for ATLAS on Monday. A special fill with Roman pot alignment for TOTEM/ATLAS-ALFA is currently in the machine.

• LBS -> HB
  The last LBS meeting had presentations from ATLAS and ALICE with details on the levels and time distribution of current beam-induced backgrounds and a presentation on LHC Performance and Statistics analysis. 

Demo of new LHC Fill Performance pages  -> YL  (slides)
Yngve has been working with Alick Macpherson / OP on a quick, automatic fill analysis. The data is extracted using JAVA and TIMBER interfaced with PYTHON with NUMPY and ROOT for analysis. The information is made available as web page http://cern.ch/LHC-Statistics with summary tables of fills and standard plots for luminosity, background and vacuum. A super-table with information for each fill, inspired by what was done for the TEVATRON is included. Feedback is more than welcome (After the meeting and following discussions at the SLM, it is proposed to add the evaluation of the transverse emittances using the intensity and luminosity information as well as to add the information concerning the beta* values).

11-T Nb3Sn dipole study -> BH  (slides)
Bernhard reported about progress on the hardware side on Nb3Sn dipoles as well as the consequences and related plans for optics.
The change of DS layout for IR3 does not match the availability of the proposed Nb3Sn shorter dipoles by the first long shutdown. Hence, it is planned to be performed by using the standard dipoles and moving the magnets in between Q8 and Q10 to make room to he cryo-collimators (the new layout was studied by JJ and TR).
It is presently foreseen to install 4 new Nb3Sn magnets both in IR7 and IR2 in the dispersion suppressor in the 2017 shutdown to gain space to allow the installation of extra collimators. The new magnets would be 5.5m long and straight. Changes on the overall LHC geometry will be small. BH showed a table of the expected multipole errors for these magnet and discussed the dynamic behaviour from persistent current effects.
The highly non-linear behaviour of the transfer function calls for a dedicated trim power converter to avoid closed orbit bumps, which would require a large fraction of the orbit corrector dipoles strength.
The dominant multipole error (b3) will be corrected with a spool piece corrector. As an alternative, SF proposes to replace the closed orbit corrector in Q8 and Q10 with combined dipole+sextupole corrector, which would allow gaining some additional space. The new error table refined with tracking simulations will be discussed with the magnet experts in order to agree on a target specification table.

AOB

None

Last update: 18-May-2011

MG & HB

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