Summary notes of the LCU meeting on 15/12/2009
Present: MA, HB, RC, OD, SF, MF, MG, BH, JJ, YL, JN, AR, FS, MS, YS, DW, FZ, LH
Report from meetings
Linear imperfections in new cold D1 dipole for LHC upgrade -> BH (slides)
BH introduced the doctoral student Lutz Hein who works with him on Linac4.
BH described the LHC upgrade studies related to the planned new, large aperture D1 separation dipole.
The original field quality was studied by computing the resulting DA of the new layout.
Non-linear corrector packages have to be added and the high-order multipoles
should be reduced in order to achieve a nominal value for the DA.
Recently, the
low-order multipoles were also studied taking into account their impact on
beta-beating, tune shift, and coupling. The value of these low-order multipoles
is vital for the day-to-day operation, as any change in the crossing angle, or
separation bumps will have a direct impact on the beta-beating, tune shift and
coupling of the machine. It is clear that tighter bounds should be given to
these multipoles in order to reduce their impact on machine operation. This
study led to a new revised error table that should be communicated to US
colleagues for consideration. It is also worth mentioning that the field quality
of the proposed D1 cold magnet is currently much worse that the one of the D1
installed in the LHC in IR2/8 (not to mention the warm D1, which is better for obvious
reasons).
LHC optics studies with MAD-X, PTC, and beam measurements -> OD (slides)
OD reported about optics studies with MAD-X, PTC and
beam measurements during the LHC commissioning.
The analysis of the off-momentum beta-beating started with a comparison between
MAD-X and PTC: some of the differences are due to the different model used for
the two codes (in both cases thick lens to enable using the settings directly
extracted from the machine).
The dispersion measurements show a beating at the level of 10% in particular in
sector 3-4 and 4-5. The beating decreases with energy by about a factor of two.
It is planned to use the dispersion measurements to constrain the search for
optic errors from the beta-beating measurements.
The quality of the LHC measurements is general very good and allows to cross check BPMs. He showed a list of suspicious BPMs:
MG suggest to communicate this to BI (Rhodri Jones) for further
action. It is worth mentioning that systematic BPMs check were also performed by
OP and the results used to fix a number of monitors during dedicated accesses to
the LHC tunnel.
Noise in MADX thin-lens tracking module -> YS (slides)
YS has added features to MAD-X which allow to simulate ripple on magnets,
the so-called NOISE element. Amplitude, frequency, and phase can be specified. He showed that this can be used to study emittance growth.
MG suggest to use this to study the effect on the noise on the
damper recently observed during the beam commissioning.
MAD-X aperture modeling was extended to allow for offsets in the
description of the aperture. These offset will be active only in the MAD-X
tracking, but not in the aperture computation (for which the only way of
defining offset is via a separate offset file). SF
suggests to add the option of specifying a tilt in the transverse plane of the
aperture (the new implementation foresees only transverse shifts).
YS also presented a number of checks he made on the 6D
beam-beam elements. He used such an element when studying the beam-beam effects
for a crab cavity in the LHC. The 6D beam-beam element might be useful for the
parameter range of the LHC Phase I upgrade scenario. In this context SF
asked for clarifications concerning the conventions used for the sign of the
crossing angle (should it be that of the strong or of the weak beam). The checks
presented do not seem to be conclusive. It is decided that YS
will continue the investigations, while in parallel FS
clarifies the theory and the implementation in SixTrack.
AOB
None
Last update: 16-December-09
MG & HB
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