----------------------------------------------------------- Minutes of the ABP-RLC team meeting of 08.07.2005 present: EB, WB, FC, UD, AG, WH, TP, FR, DS, FZ web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Minutes of last meeting, pending actions, announcements ----------------------------------------------------------- The list of actions is posted at http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/Actions/actions.htm . There were no comments to the minutes of the previous meeting. (2) Wire measurements of LHC MKI kicker impedance (FC) ------------------------------------------------------ FC reported on the wire impedance measurement of the MKI kicker. 1 Ohm corresponds to 20 W losses. The main outcome of the study is that the total losses are below 100 W for the whole 3-m long unit. The measured MKI kicker was fully assembled including ceramic beam pipe and straight metallic stripes. It is characterized by a filling time of 1 microseconds and ~100 ns rise time, as defined by the kicker group. Three measurement methods were employed: (1) ordinary transmission and reflection measurement, (2) time domain gating, (3) resonator measurement. The last one is the most precise. Resonances occur if the length of the kicker equals (n lambda/2) with n=1,2,... . There are 38 resonances below 1.5 GHz. The error of the final result is about 10-20%. Enhanced absorption is seen at around 400 MHz and 800 MHz. The corresponding Z/n is only about 60 microOhm. The ceramic coating reduced the real part of the impedance by a factor 100 and the imaginary part by a factor of 20, comparing with earlier measurements for an uncoated chamber. Larger impedances are found below 40 MHz. For example, at 1.5 MHz the impedance is close to .5 kOhm for 3 m length, which translates into Z/n~5 Ohm, about 100 times the estimated total Z/n value. In this regard, the microwave threshold should be revisited. The impedance of a kicker with helical metallic stripes was also measured, but the data are not yet analysed. The helical shape should lower the induced voltage and prevent sparking, but the expected reduction is only about 20%. (3) Wire measurements of LHC collimator (FC) -------------------------------------------- The same concept as for the kicker was applied to the collimator. The jaws were moved rather than the wire, to determine the magnitude of the transverse wake field. FC showed a synthesized step response. The most accurate results were, also here, obtained, with the resonator measurement. When the jaws are closed, the resonances do not stay equally spaced. The absolute position of the collimator jaws during this experiment was known only to within 1-2 mm. The position reading even changed over periods of two hours. A transverse sweep of the jaws reveals the transverse impedance, via the Panofsky-Wenzel theorem. The measurement gave some indication that one may be able to decrease the transverse impedance at the expense of increasing the longitudinal. => Action => The measurements will be compared with HFSS simulations (AG). => ACTION = > Extract transverse impedance from the data (FZ?) (4) Beam-beam compensation studies (UD) --------------------------------------- UD has written a new code BBEAMSIM in Fortran 95, modeled after FZ's code WSDIFF. The new code shall be better documented, more flexible and faster. First simulations were done for the SPS, using R matrices between wires computed by MAD. The survival of tracked particles was explored with one and two wires, as a function of the starting position in x-y space, and in x-x' phase space. The variation of instability threshold with betatron phase is of order 0.5 sigma. Going from 1 to 2 self-compensating wires increases the dynamic aperture by about 1 sigma. Some small regions are unstable with 2 wires and stable with a single wire. In the latter case, an island structure is found (5th order resonance). The unstable trajectories are characterized by step-like increases in the particle amplitude. A tune scan was performed. It showed tune regions where either 1 or 2 wires provided more stability. The variable tune and the wires were both taken to be horizontal ones, while in the real SPS experiments the wires were mounted in the vertical direction and the vertical tune was varied. => ACTION => Simulations for the real SPS conditions will be performed (UD). DS suggested to use different colors to indicate various levels of instability. UD described his plans for the near future. FR recommended to benchmark simulations against experiments. The proposed wire experiment at RHIC will be discussed at the FNAL LHC IR upgrade meeting and probably also at a general US-LARP meeting in October. (5) Highlights from the 2005 Lepton-Photon Symposium (FZ) ---------------------------------------------------------- FZ summarized some highlights from LP2005, mainly from the sessions on neutrino physics, astrophysics & cosmology, and new facilities, including ILC schedule & plans. Posted on the web: Slides by FC (2x), UD, FZ Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/