Summary notes of the LCU meeting on 10/09/2007

Present: IA, MA, CB, RB, HB, RdM, MG, WH, JJ, PL, MM, TP, VP, TR, FR, FS, TW

Report from meetings

• SLM -> MG
  No meeting last week (Jeûne Genevois).
• ICC -> MG
  As already reported last time, a problem with several of the vacuum plug in modules (PIMs) was observed after the warm up of sector 7-8 (see slides presented by P. Strubin - AT - at the last ICC meeting). Some non-conformities were identified, like insufficient length of some PIMs and increased bending angles on the RF-fingers. It is speculated that the latter might have been introduced at the manufacturing stage to improve the electrical contact and hence reducing the resistance. A working group was set up to study the problem and to come up with solutions.
  Another issue discussed was on the subject of the RF-shields for TCLI collimators. One part of the shield is made in stainless steel (304L) and high magnetic permeability regions could form when forming the required profile. These regions, could eventually get magnetized by the beam-induced magnetic field. Evaluation of the magnitude of this effect is in progress by AT experts.

Progress in the MADX on-line model -> IA (pdf file)
IA reported about progress in the ongoing work on the MADX on-line mode.
It will give full access to MADX tools in the control room and provide a realistic model of the actual machine.
It has a graphical interface based on Java, allows for scripts in python and provide measurement and analysis tools. IA mentioned neural network fitting as a possible option. There was some concern on the speed of neural network fitting. MG comments that the use of such an option within the control system it doubtful.
JJ would like to see the possibility to save a full machine similar to what was possible in LEP using MAD8. MG urged to assign highest priorities to issues which would be needed early in commissioning. Another presentation is foreseen in two weeks.

Chromatic beta-beating and aperture for V6.501 optics -> TR (pdf file)
Simple phase advance differences like 0.25 or 0.75 between high-beta insertions allow obtaining good chromatic corrections with few sextupole families and less spread of the strength between the various families (see the LOC presentation and LHC project note 103 and LHC project report 308). The insertion re-matching done for V6.501 resulted less favourable in terms of phase differences between IR1 and 5 for chromatic corrections.
TR found a satisfactory solution using 32 sextupole families in which the chromatic beating in one half of the LHC is very small. In principle it is possible to select in which half circumference the small chromatic beating is located. Two settings were computed depending on whether the correction optimizes the chromatic beta-beating in IR3 or IR7. Input from the collimation team is needed to see if small chromatic beta beating is more important for IR3 or IR7.
These settings were obtained by imposing the special phase advances: once it is agreed where to locate the minimum of chromatic beating, it will be necessary to tune the machine in order to obtain the appropriate phase advance.

AOB
none

Last update: 18-September-07

MG & HB

Back to LCU Minutes