---------------------------------------------------------------- Minutes of the ABP-LCE team meeting of 20.06.03 present: TdA, AK, WH, JJ, EM, DS, HT, LV (chair), FZ, BZ excused: FR ---------------------------------------------------------------- (1) report from meetings ------------------------ WH reported on a meeting of the BI specification working group (summary attached). For LCE the most important item is the future of the aperture kickers. It was decided that there will be no kicker able to generate 8-sigma oscillations at top energy in the 1st year of LHC. The money saved will be used to finance the AC dipole development. For studies at injection the Q kickers will be upgraded. They will become stronger (producing 8 sigma kicks) and the pulse length will be l longer as well (affecting 1/4 of the beam). Also dicussed was a bunch tickler for exciting individual bunches. This could be used to measure beam-transfer functions as in the ISR and also to detect coupled-bunch modes. The question was asked to LCE team which amplitude would be required (ACTION). The answer is that the amplitude should be sufficient to detect the signal. (2) ongoing activities (round table) ------------------------------------ LV calculated the effective collimator impedance with the help of WH, and using latest set of parameters from Ralph Assmann. The impedance effect is reduced by a factor of about 3. HT studied the power deposition in MKE kickers. He will also compute the collimator impedance with the HFSS code. JJ mentioned that no current item is related to LCE. DS was instructed in the use of GdfidL and is ready to launch computations. WH is computing a new consistent set of crossing angles and beta functions for all IRs. BZ mentioned a PAC paper on tune shift for a small number of bunches ion the SPS. More experiments are needed and will be done this year. AK has worked on 3 items: (1) he is looking for a closed expression for the res-wall impedance with inductive bypass, with the help of SF; (2) he has tested a fast computation scheme using convolution theorem and FFT, suggested by DS, which looks promising, and which will be implemented in the fortran code to speed it up; (3) he is in contact with EM on the res.-wall instability; at the moment he still runs the old version of the code. FZ has computed photon fluxes and critical energies along all 4 LHC experimental insertions, in collaboration with A. Rossi, for the Insertion Region Review held this week. Simulations with PHOTON addressed the effect of reflectivity, quadrupole radiation, angular distribution of photon emission, optics and orbit errors, beam 1 and beam 2. The simulated fluxes are at least 10 times lower than those in the arc. The photon energies are ~3 times lower as well. Reducing the reflectivity does not change the average flux. Therefore, and for various other reasons, it was recommended to not install a sawtooth chamber in the experimental regions. FZ discussed the CVS implementation of ECLOUD with TdA. JJ recommends using the Windows version of CVS. TdA mentions that an 'fsplit' command can split the code into modules automatically (FS). ECLOUD version 2.3 was posted on the web and distributed. Already feedback from R. Wanzenberg (DESY). A first look at electron cloud for the collimators will be made in the next few days. At the Insertion Region Review, FR has raised the question of the LHC experimental background and possibly other effects associated with synchrotron radiation photons from one proton beam being back-scattered by the other proton beam. What is the cross section for this process and the associated high energy gamma flux? Do we need dedicated masks to reduce background in the experiment? ACTION -> FS+DS? TdA is working on a problem of the MADX plot routine discovered by E. Keil, which occurs if one plots after performing tracking. With FS he found that multipole and particle keywords are missing. MAD8 is taken as a guide to fix this problem. EM was occupied by MDs and PS supervision. He discussed with AK the resistive-wall instability. He confirmed LV's prediction that the RW growth time of the most unstable mode is about 50 turns without inductive bypass. The factor 3-4 discrepancy with AK's simulations is still unaccounted for. (3) discussion of transverse damper ----------------------------------- Responding to question by EM, LV explained that the damping time at injection is limited by the amplitude of the injection oscillations and the available power. At top energy any stable gain less than 0.3 may be possible, and conceivably one could achieve damping times as low as a couple of turns.