Minutes of the ABP-LCE team meeting on 13.02.04 present: EB, WH, AK, FR, DS, EV, FZ ---------------------------------------------------------------------- (1) Minutes & Pending Actions ----------------------------- Old ACTION: FZ will inform Gerhard Schneider. Done. FZ also pointed out that the calculated impedance will change if the magnetic permeability is largely different from 1. There was no immediate answer as to what the actual value is. (2) Geometric Collimator Impedance (DS) ----------------------------------------- DS presented new Gdfidl calculations of the LHC collimator impedance. He considered 3 different geometries for the collimator. Longitudinal trapped modes exist inside the tank. The strongest mode is at 120 MHz. Assuming copper as material, the total heating obtained by summing over all modes and resonances is 300 W in the worst case that all resonances interact with the beam. 1 kW is acceptable. Transverse trapped modes are located on the jaw. The predominantly driven coupled-bunch head-tail mode is m=4, due to the frequency of the resonator. The growth rates or imaginary tune shifts for m=4 are of order 5e-6. For higher resistivity the tune shift is reduced. FR asked how the m=4 values enter into the stability diagram. ACTIONS (mainly DS): => clarify geometry of trapped modes => compute longitudinal impedance => practical advice for collimator design => redo estimate for larger gap => understand stability diagram for m=4 => what can be measured in the SPS? => perform full simulation for the SPS (AK) (3) SPS losses during CNGS beam extraction (EV) -------------------------------------------------- The particle losses in the 2nd batch after extracting the first batch for CNGS was estimated by integration, for various apertures and residual-kick amplitudes. The kick experienced by the first bunch of the second batch is 21% and in total 2e-4 of the second batch would be lost. If a gap of additional 50 missing bunches is introduced, the fraction of lost beam is only 1e-8. Beam in the gap was recently identified as another, perhaps larger problem. This is under discussion with W. Hofle. Plans for future work: documentation of damper simulation application to LHC rf voltage modulation for LHC FR recommended a presentation by EV. (4) Review of resistive wall formulae and measurements (FZ) ------------------------------------------------------------ FZ contacted F. Caspers. His measurement results are summarized in AB-2003-051, written with A. Mostacci, and U. Irizo. The measurements are consistent with the formula by Burov&Lebedev and also, in the low frequency regime, with an inductive bypass formula that is different from L. Vos'. Overall, applying the various existing expressions to the warm LHC BPMs gives predictions that vary by more than an order of magnitude. => The same formulae should be applied to the measurement of Fritz and to the collimator computed by H. Tsutsui. => Some unclear expressions should be discussed with F. Caspers and A. Mostacci. (5) AOB -------- LHC Design Report. The revised LCE chapter for the LHC design report is finished and available from FR. The arc SR heat load may still need to be updated (peak values to be replaced by averages). The figures showing LHC cryogenic capacity for electron-cloud heat loads were updated. The numbers have not yet been confirmed by L. Tavian. EM has updated res.-wall rise times at injection. This may have implications for the feedback damping times. RA has reduced the number of collimators by 30%. This change will not be part of the design report. WH has worked on MKI kicker specifications for CNGS. These are related to the required stability on the target. The maximum acceptable ripple is of order +/-1.5-2%. WH is working on a report on tune spectra with beam-beam. He will send a figure to JPK for the tune-meter specification. WH, EV and W. Hofle held a meeting on feedback measurements with beam-beam. WH will do simulations for beam-beam. EV's feedback simulations may be integrated. FR mentioned a question on the feasibility of a window in the feedback system, that would allow measuring the tune of a single undamped bunch. He recommended discussions with BDI to make sure that the tune can be measured at injection into the LHC. We should have a meeting on MD plans for 2004. These may include collimator study, single-bunch collective effects, e-cloud, BB compensation. Enclosed: Slides by FZ.