---------------------------------------------------------------- Minutes of the ABP-LCE team meeting of 13.06.03 present: TdA, AK, WH, EM, FR, DS, LV, FZ ---------------------------------------------------------------- (1) follow up on action items ----------------------------- A review of beam excitation devices in the LHC will be held next week Wednesday. WH will represent the LCE team. NEW ACTION ==> WH will attend beam-excitation review old ACTION: FR will ask Bruno Spataro to perform MAFIA calculations for the following list of items: - recombination chambers at IR2 - tanks for the OTR screens and wire scanners - geometric impedance of LHC collimators ALMOST DONE. FR has sent a list to Bruno Spataro. ACTION ==> LV will send informations on IR2 recombination chamber. old ACTION: AK will compare his results with the classical expectation and further discuss future plans for his PhD work with BZ and FR. Simulation run was completed for 2808 bunches. The rise time is 180 turns. The classical theory predicts about 50 turns (LV and AK). The origin of the factor 4 discrepancy is not clear. The simulation includes r.w. impedance of cold and warm parts and of the collimators, but without the inductive bypass. Only a single bunch is excited initially. The other bunches show an exponential growth in oscillation amplitude after an initial transient, during which they remain quiet. A graphical example for the results would be useful (suggested by EM). AK has discussed his future PhD workplan with FR and will give priority to the implementation of a new idea by DS to substantially reduce CPU time for multi-bunch resistive wall instability simulations using convolution theorem for resistive wake times bunch displacement and then FFT. This new alghorithm is linear rather than quadratic in the number of bunches. Next priority is to compute resistive collimator wake with inductive bypass effect, then implementing space charge using TRISIM approach and finally optimizing multi-bunch mode visualisation techniques with MATLAB. The ultimate goal is to put all these ingredients together, including resonator impedance with time-dependent frequency to simulate temperature effects, to study SPS experiments and LHC predictions. ACTION ==> prepare pictures of simulation results; understand the factor 4 discrepancy between prediction and simulation; discuss future plans with FR and BZ. old ACTION: identify and instruct a 'user' for Z-base (FR) NOT DONE. In addition to EM there could be two further users (DS and FZ). The task of the users also includes to decide what to do with the database, as well as to incorporate all available knowledge about the LHC impedance. ACTION ==> DS and FZ will discuss with FR. P. Sievers has asked how much Cu coating would be required to substantially reduce the impedance of graphite. LV's spontaneous answer was a couple of microns, but he will confirm this later. FR recalled that this might have been 0.5 mm. old ACTION: LV will confirm thickness of Cu coating for effective shielding. DONE. EXcellent news. 10 micron Cu layer reduces the effective impedance by a factor of 5. The resistivity of a thin layer deviates from the bulk. For the estimate the resistivity of beryllium was assumed for the Cu layer. The relevant corner frequencies (from the inductive bypass) are 6 MHz for carbon and 20 kHz for copper. With a thin coating the corner frequency is somewhere in between. It also depends on the aperture. The 8 kHz line is most important. It was recommended to publish a formula which describes the dependence on resistivity, thickness of coating, and gap size. LCE team recommends coating of secondaries, since surface roughness due to possible damage is not important for the long bunches in the LHC, and cleaning efficiency is not compromised. FR informed the team that RA has distributed the draft of a new collimation scheme. LV noted that the opening of the collimators is increased compared with the earlier design. old ACTION: impedance simulations The GdfidL program is already installed, but it does not yet run on all CPUs (DS). ACTION ==> EM and DS will meet Erk Jensen next Wednesday to discuss GdfidL simulations. EM recommends to make first run for the stripline BPM of Luc's note. The time when a first GdfidL result for the collimators may be expected is not yet known. H. Tsutsui who will arrive on Sunday can in parallel perform simulations of the collimator impedance using HFSS. FR has received 3 reports from R. Gluckstern. The transverse impedance for the collimators estimated by Bob Gluckstern grows linearly with the relativistic gamma of the beam, for large gamma, which is unphysical. old ACTION: ecloud studies DS reports that his and FZ's versions of ECLOUD were merged. The new version contains the modified elastic reflection and the corrected image-charge calculation for an elliptical chamber. The reference charge is also modified to avoid overflow in the number of macroelectrons. FZ mentioned that this version should be merged with another version from GR which includes changes to the on-line RK routines and to the description of a long uniform bunch. ACTION ==> new ECLOUD version 2.3 shall be released before the weekend. ACTION ==> ECLOUD version control will be converted to CVS (FZ with help from TdA) (2) announcements and other informations ---------------------------------------- F. Caspers has measured the microwave transmission with the fixed target beam. Here he gets a smaller signal and observes a slow build-up time of the order 5-10 microseconds, which could be consistent with ionization. The APC next Friday is devoted to high-intensity beams. Following a suggestion by GA there will be an excpetional APC meeting in the week thereafter, presumably Wednesday morning, which will be dedicated to results of the scrubbing run and the kicker-heating problem. I. Collins informed FZ that in surface physics an effective potential is used which is different from, and often larger than, the work function of a material. SR simulations results for the ideal LHC optics without errors (but with crossing angles) are imminent (FZ) and will be delivered to AR. FZ reported that the MADX difficulties were resolved with the help of FS and HG. They were all identified as user errors. The closed-orbit routine in some LHC examples does not function with the default settings. There was some discussion as to whether the default settings should be such that MAD always finds a solution. Concerning the aperture, FZ re-stated that it would be extremely helpful to have a MAD and/or database description of the LHC optics providing all apertures including the arcs and in particular those of the drift spaces. ACTION ==> FR will discuss the aperture question with OB The MD program in the SPS was discussed. No definite dates are known at the moment. Among others, MDs with LCE input are planned on the long-range beam-beam (LRBB) compensation using a wire, SPS impedance, SPS space charge, and the suppression of e-cloud instabilities by linear coupling. FR encourages the team to participate more strongly in MDs, and in particular to profit from the friendly environment in the PS control room. EM is a good contact for any PS study. Presently ongoing on the parasitic cycle are measurements on resonance extraction (5 islands and high intensity), organized by MG. LV recommended 1970+ papers by E. Keil and L. Evans on the nonlinear lens in the ISR, which could provide ideas for the LRBB wire studies. It was remarked that only about 2/3 (or less) of the group members attended the ABP group meeting. Further, the wish for an ABP forum on one (or more) of the hadron sources was expressed.