Summary notes of the LCU meeting on 27/01/2009

Present: IA, MA, GB, CB, FC, SF, MG, BH, JJ, EL, YL, JLN, SP, FeRo, AR, FS, YS, RT, TW, SW, FZ

Report from meetings

• SLM and general information -> MG
  MG thanks IA (whose contract ends on 31 January) for the work on the on-line model and the MAD-X activities (aperture module). IA will come back in April for a seminar.
• MG introduces BH, who will work on Whit paper-related activities.

Impact of possible IR7 optics changes on collimation performance -> JJ

 Postponed to the last meeting of February.

Status report of studies on putting beams in collision -> SW (pdf)

The motivation of this work is the study of the impact of the power converter performance used to put beams into collision (collapsing the separation bump) on beam parameters (emittance, mainly).
The request of ensuring the maximum speed to have maximum flexibility was already communicated to power converter responsible.
A new tracking code was developed and cross-checked against HFMM in the case of Gaussian profiles. The main features are reproduced (for the static), but the details have to be analysed. The next steps will be the analysis of the dynamic case.

E-cloud heat load with wrongly oriented saw tooth -> FZ (pdf)

 Due to missing spare beam screen of the type required for sector 3-4, an ECR is being prepared to announce the use of wrongly-oriented beam screens. This implies that the saw tooth will be still on the outside of the beam screen, but with the wrong orientation.
FC and EM checked that the impedance is invariant for reversal of the saw tooth.
The proposed slots are compatible with the current pre-allocation list of dipoles and SSS.
the additional heat load is being studied by FZ. The main issue is the assumptions to be made to describe the behaviour of a wrongly-oriented beam screen. No measurement data are available, hence it is assumed to use the measured photoelectron yield for flat samples plus about 20% diffusive component. FC raises the question of the actual behaviour of the copper hit by eV photons, as it should behave as a dielectric. These questions might be solved by performing additional measurements with the wrong orientation of the saw tooth (it would  be a useful to repeat some measurements to clarify some discrepancies, too).
Simulations of the heat load (assuming that a cryogenic cell has all the beam screens with the wrongly-oriented saw tooth) show that for 25 ns spacing, the local (the exact meaning of local has to be established) heat capacity limits the maximum intensity to 1-2×10¹¹ protons/bunch depending on the value of the secondary emission yield. In case 50 ns bunch spacing is considered, the intensities are limited to 3-3.6×10¹¹ protons/bunch depending on the value of the secondary emission yield. This means that the proposed installation will be a performance limitation for upgrade scenarios and a replacement of the beam screens should be envisaged at the time of the installation of the new triplets.
The incoherent effects (emittance growth) should be tested as well to quantify the impact of the wrongly-oriented beam screens.

A Landau octupole puzzle -> FZ (pdf)

Frank reports a puzzle concerning the strength of the Landau octupoles. This issue was triggered by the studies on the crab cavities performed by A. Morita. SF comments that the observed factor of two difference is due to the definition (rms) used in the specifications. This clarifies the situation and closes the case.

Beta-beating measurement and understanding -> RT (pdf)

 A review of the first beta-beating measurement is presented. Three methods are used to analyze data: SVD, SUSSIX, and harmonic analysis. The first is the most accurate.
The peak beta-beating is 30-40% and 100% for the horizontal and vertical plane, respectively. B2 errors and sextupole misalignments (including realistic closed orbit) do not explain the measurements.
The new development is the error fitting based on an iterative procedure (implemented by MA) or segment-by-segment analysis (implemented by RT). With six iterations the first methods yields a model in nice agreement with the measurements. Both methods find a big error in IR3 (then in IR2 and IR7). The measured data in IR3 could be explained by switching off MQTLI.7.R3.b2.
After the meeting the measured current in MQTLI.7.R3.b2 was checked to be different from zero. It was then proposed that a  swap of beam aperture occurred. This hypothesis is confirmed by the beta-beating as well as the dispersion measurements. Furthermore, N. Catalan Lasheras confirms that an inversion was found during the hardware tests following the sector 3-4 incident, thus confirming the beam measurements!

AOB

None

Last update: 3-February-09

MG

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