Summary notes of the LCU meeting on 15/07/2008

Present: MA, RA, GB, HB, MG, WH, JJ, MM, JN, TP, VP, FR, FS, TW, SW, NH

Report from meetings

• ICC -> MG
  A short (weekend) injection test into the LHC bringing beams from IR2 to IR3 could technically be performed at the beginning of August, but still requires the ok from the safety authorities. Injection for a full turn will likely not be attempted before the end of August. The vacuum leak in the ATLAS toroid is under repair. Meanwhile, CMS plans to install the second end-cap.
• SLM -> MG
  A fault on a refurbished PS magnet stopped the injectors for about a week. The other refurbished PS magnets are checked as well.

JJ introduced Nina Hagen. She works for 6 month with us as technical student from Oslo university on programming for ICOSIM, the code used for ion simulations.

Recent optics studies for IR8 -> MM (pdf)

Optics for the IR8 squeeze down to 2 m and un-squeeze up to 30m including crossing scheme were studied by MM with the help of WH and TR.
The warm corrector MCBWH.5L8.B1 is used for the crossing scheme. It is found to limit the achievable crossing angle for beta* > 20 m. In case the cold corrector in Q5.L* is used, the limitation is removed. A report on this work by Malika, Werner and Yannis is being prepared.
The files are ready for storing in the optics database.

Aperture checks in collaboration with TW are planned. There is little margin in aperture at injection when the LHCb spectrometer is fully on.

Collimation Phase II approach -> RA (pdf)
RA introduced the subject of phase II collimation. Phase I collimation is only safe up to 40 % of the nominal intensity. Phase II collimation aims for significant (factor 10) improvements in collimation efficiency, impedance, and setting up speed.
Factor 10 efficiency for protons and ions: use metallic, advanced phase 2 collimators as well as cryogenic collimators into SC dispersion suppressor.
Factor 10 in set-up time: integration of pick-ups into collimator jaws.
Factor 10 in impedance: factor 2 seems possible.
These studies profit from EU support under FP7, USLARP and Darmstadt-FAIR collaboration. 

Collimation Phase II proton efficiency simulations -> TW (pdf)
TW showed loss maps from simulations of phase II collimation.
A very significant improvement is expected from the cryogenic collimators in the dispersion suppressor. They will however require moving pairs of cold dipoles such that the missing dipole in the dispersion suppressor is closest to the quadrupole, allowing to install the cryogenic collimators at the peak of off momentum particle losses. The simulations predict gains by a factor of 30 for the losses in arc magnets and also a significant reduction in the machine induced backgrounds to the experiments.
Detailed feasibility studies should be performed.

Effects of ultra peripheral nuclear collisions in the LHC and their alleviation -> RB (pdf)
RB reported on peripheral nuclear collisions which are a major source of off momentum particles in operation with lead ions. The most relevant process is the Bound Free Pair Production (BFPP) resulting in Pb81+ ions with deltap of -1.2% and local losses in the dispersion suppressors around the IRs.

Electromagnetic Dissociation (EMD) with single neutron loss from Pb208 to Pb207 results in deltap of -0.48% and does not produce local losses and is therefore less of an issue. EMD with loss of two neutrons resulting in deltap of -0.96% instead is a source of local losses.
RB proposes to use local orbit bumps, tuned with the help of BLM signals, to distribute the local losses peaking at a single quadrupole equally over three quadrupoles. The required local bumps maybe as large as 3.8 mm. RA commented that this is potentially dangerous and should be discussed with the machine protection experts.

Cryogenic collimators for heavy ions in the LHC -> JJ (pdf)
JJ produced MAD-X (seqedit) files with moved dipoles in dispersion suppressors for phase II collimation studies. 

The displaced dipoles imply changes of betas and dispersion by few percent and will require some re-matching.

Preliminary ion simulations for a phase II system with cryogenic collimators  -> GB (pdf)
The multistage collimation system designed for protons will be much less efficient for ions and is expected to limit ion operation at 30% of nominal.
A main issue are losses in the dispersion suppressors.
The proposed phase II cryogenic collimators in the dispersion suppressor were simulated for ions. Their effectiveness is remarkable: at a position of about 25 sigma there is essentially no more power deposited on the dipoles in cells 9R7 and 11R7.

Brainstorming meeting with CICs on applications for the online model -> FS (pdf)
FS reported from a meeting with the Commissioners In Charge (CIC) of our group. He recalled the mandate for the online model and described the requests which were discussed in that meeting. A list of requests will also be circulated by email. It includes luminosity scans, search for imperfections, aperture with collimators and the effect of triplet alignment.
FeRo will help as major user and also to follow up on requests. Further ideas are welcome and should be discussed with IA and FS.

AOB

Last update: 23-September-08

MG & HB

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