Summary notes of the LCU meeting on 18/09/2012

Present: HB, RdM, LD, SF, MF, MG, BH, JJ, Qe, MS, RV, AL

Report from meetings

• SLM and general information -> MG
  Several optics related MDs are proposed for the next MD session, including low and high beta and non-linearities.
  The Hamburg beam pipe for IP1 was discussed in the last LEB and requires further efforts to reduce the impedance. The request by LHCb for a smaller beam pipe allowing for a smaller radius for their VELO detector, both to be installed in LS2, is also followed up.
• LHC Status -> BH
  Last week had special runs last week with a pPb run and high beta as reported later in this meeting. This week is technical stop. For the up to date LHC status see the latest news.
• LBS -> HB
  The LBS meeting yesterday had two main items on the agenda. The first item was on LHCb in the context of running conditions and background estimates for future operation with a smaller beam pipe and vela.
  The second item was an update on ALICE backgrounds. Injection has been modified recently to minimize TDI heating and the induced vacuum rise: Beam 1 is injected first, and the TDI retracted, followed by Beam 2.
  For more details see the indico page of the meeting. 
• MAD-X status -> LD
  Laurent reported about on-going work on MAD-X, with a busy period of testing. He is in contact with Etienne and Piotr in the context of PTC_twiss.
  An ATS note on the MAD-X implementation of the RF multipoles is in preparation.
  Further bug reports were received.
  A new development version is planned soon.

Pilot p-Pb run  ->  RV (slides)
Reine reported about the proton - lead pilot run last week.
After a difficult start with many technical problems to solve, injection, and ramp of protons in Beam 1 and lead ions in Beam 2 worked well. This allowed for the first time in the LHC to collide proton and ion beams. Stable beams with p-Pb collisions were achieved and left colliding for several hours.

The horizontal emittance for the lead beam increases as expected from intrabeam scattering. A smaller increase of the vertical emittance was also observed and is presently less well understood. The special MD on the effect on the moving parasitic collisions later in the week failed due to problems to inject train with low intensity bunches and another run will be requested.

Current plans for the p-Pb physics run at the end of this LHC running period are to use 1 m or 0.8 m beta* in IP1,2, 5 and 2 m in IP8. TOTEM will participate and take data together with CMS. LHCf will also be back for the p-Pb run.

High beta study on 13/14 September  -> HB (slide)

Helmut showed a slide that summarizes the 24 hour high-beta run last week. Three fills were lost with technical problems: collimator energy interlock, a new RQTX1 limit, which was recently introduced without verifying its compatibility with all running options, and orbit feedback.
The actual program then worked very well and both major planned milestones for beta* = 1000 m were achieved: correcting and measuring the corrected optics, and obtaining for the first time collisions at beta* = 1 km. Another challenge will be to get collimators and roman pots very close to the beams. This was only just started last week.
More work on this is planned in MD3 to be prepared for the 1 km physics run planned for week 43.

Thins lens slicing  -> HB (slides)

Thin lens versions of the optics are important for tracking and error assignment. TEAPOT slicing is very effective, but has been limited so far to four slices, at least in the MAD-X implementation.

Helmut compared the transfer matrices of thick quadrupoles, with SIMPLE, i.e. equidistant, and TEAPOT slicing. He showed, that it is possible with a single distance parameter delta = 0.5 / (n+1) to reproduce the focusing term (2,1 matrix element) of the thick quadrupoles to the third power in L by means of quadrupolar kicks. The result is identical with the known TEAPOT for n=2, 3, 4, and continues to converge well for larger n (as can be seen from the formulas shown in the backup slides).
A test version of MAD-X with the extended TEAPOT as default for any n is available on afs as ~hbu//hbu/public/madx64. As before, SIMPLE equidistant slicing can be selected.

He prepared a draft ATS note which gives further details.

In the following discussion, Helmut confirmed, that this works equally for focusing and defocusing quadrupoles. The other matrix terms and higher orders are very similar to SIMPLE slicing, and converge equally well with n. All these findings will be collected in the note, together with a test of the method with the ATS optics.

Last update: 18-September-2012

MG & HB

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