Summary notes of the LCU meeting on 19/11/2007

Present: IA, CB, HB, RC, RDM, SF, MG, WH, JJ, MM, VP, TR, FR, FS, RT, SW

Report from meetings

• SLM -> MG
  MG reminded us about the deadlines for EPAC'08, which had already been circulated by email. Proposal should be sent to him by Dec. 12 for a selection on the group level, which will be further passed on to Steve Myers on Dec. 17 for the selection at the department level. Conference participation is discussed today in the AB management board. MG reminds that paper acceptance requires that at least one of the authors will be present at the conference.
• ICC -> MG
  The status of the FP420 experiment was discussed. It is proposed to install FP420 in the missing dipole region of the dispersion suppressor. Lyn Evans and Jos Engelen pointed out that FP420 is currently not an officially accepted experiment, even though recommended by the LHCC.
  The cool down of sector 4-5 is progressing and a temperature of 4.5 K was reached last week. Next steps are 1.9 K and powering tests.
  Another item discussed was the experience with radiation issues in CNGS and possible lessons learned from this for the LHC. The key message was to cross-check the simulation results against measurements for the CNGS case and then to draw conclusions about the reliability of the studies for the LHC.

Final results for the new V6.501 optics release -> TR (pdf)

TR has finalized the injection optics V6.501, and showed the tables of phase advances and apertures for the insertions. All the aperture bottlenecks observed during the MEB activity were fixed, but those in the horizontal plane in IR3 (Beam 1/2) for the region between Q6 (left and right). This is due to the large value of the dispersion function, which is required for the momentum collimation system. An isolated aperture bottleneck is observed in at Q6 in IR2 (horizontal plane) for Beam 1.

IR2,3,4 and 7 have different phase advances compared to V6.501.
IR8 could be rematches at constant phase advance. The optics in the injection regions in IR2/8 from Q6 to Q6 were kept the same as in V6.500 to avoid any clash with the optics of the injection lines.
IR4 was used to rematch the overall tunes. It was possible to do this well within the tuning range choosing betas which are favorable for the transverse feedback (at least at the pick-ups). Feedback from the feedback specialist is expected to decide whether additional fine tuning is required.

For IR3 and IR7 the rematching was performed outside the region delimited by Q6 (left and right) to leave the optics of the collimation system unperturbed. A new de-tuned (i.e. with a standard value of the dispersion funcion) optics for IR3 compatible with the new phase advances was also computed and no aperture bottlenecks are present.
V6.501 for injection is now considered to be ready from our side and to become final, unless issues are found by other groups.

Analysis of MD data using the on-line model tools -> IA (pdf)
IA showed that the recent TI2 test and SPS MDs were used for work on the tools of the online model. He looked at beam sizes at screens and compared this with mad predictions. In the SPS, he looked at orbits and tune along the cycle. Distinguishing between noise, experimental effects and reproducibility of the beams can be tricky. MG asks whether any attempt to analyze the data in view of disentangling beam parameters' from optics parameters fluctuations were made. SF suggested to look at the correlation between the beam size in the various monitors. These type of tools should be part of the on-model as will be extremely useful during the LHC commissioning.  
FS added (see slides), that C-code was tested successfully to acquire data in SDDS format and transform it for use in SUSSIX. He also showed coupling measurements comparing horizontal and vertical tune peak height measured as a function of the skew quad excitation, which confirmed that the SPS was well decoupled (globally and hence also locally).

New options for the High beta optics -> SW (pdf)
As shown by MA in the meeting on the 29 October, other insertions like IR2/8 can be used to compensate for the tune loss in high-beta insertions at top energy. SW recalled the known issues with the high beta* (>2600 m) Atlas optics solution from André/Angeles, namely:
lower vertical integer tune
inverted Q4s polarity
200 m beta* at injection leaving insufficient aperture for separation

SW presented possible new solutions for the injection. He illustrated two alternatives.
Alternative 1 : inverted Q4 polarities at injection and top energy combined with high beta* also at injection. The injection beta* can be lowered from 200 m (original solution proposed by A. Verdier) to 50 m. This increases the aperture (to n1 = 3.9 sigma for the standard emittance), but would be sufficient to accommodate the high-beta* design emittance of 1 micrometer for Atlas including separation. However, in this scenario IR4 would not be sufficient to restore the nominal value of the injection tune and the arcs should be used. This means that this option would still require a dedicated injection and ramp for the high-beta operation.
Alternative 2 : using the standard injection and ramp. This would potentially allow for a much faster commissioning and gradual implementation of the high-beta* optics for Atlas with the potential to operate at any intermediate beta* values. It would however require fully bipolar Q4 powering. According to F. Bordry, this is not inconceivable, but would be quite expensive and could easily require 2 years of development time for new power convertors.
MG suggested to base aperture estimates on the design 1 micrometer normalized emittance and to work out few complete options from injection to final high beta* including overall tune compensation and running scenarios. HB thinks it would be difficult to keep 1 micrometer from injection and that scraping at top energy might be necessary to reach the very low 1 micrometer emittance. SF proposed to see to which value beta* could be increased at injection compatible with aperture and separation.
Further work will also have to cover Totem, including also an update of the 90 m option for optics V6.501.

AOB
None

Last update: 22-November-07

MG & HB

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