------------------------------------------------------------ Minutes of the ABP-RLC section meeting of 07.11.2006 present: OB, FC, WH, JJ, EM, TP, FR, GR, BS, FZ web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Reports from Meetings ------------------------- There was an APC but none of the participants in the RLC meeting had attended it. OB received a message from FR, whose return to CERN is further delayed. In view of this situation OB announced that a reorganization of the ABP group will be necessary. He welcomes suggestions. The ABMB meeting next week will discuss resources at the department level. OB was already contacted by J.-P. Delahaye and R. Garoby regarding support for CLIC/CTF-3 and Linac-4/SPL activities. (2) Modified Y-Chamber and ATLAS Chamber (EM,OB) ------------------------------------------------ EM presented drawings of the Y-chamber in IR2 and IR8, including a modification of this chamber on the injection side, which is being proposed by B. Jeanneret. The proposal foresees to change the circular chamber with 28.15 mm radius into an elliptical with smaller half aperture equal to the present radius of 28 mm, and a larger half aperture of 38 mm. An answer on the impedance of the new Y chamber is needed within two months. EM will contact Bruno Spataro in an attempt to recuperate the original MAFIA input files for the Y chamber. FZ recalled that many of Bruno's files had been lost in a computer crash a few years ago. Verification after the meeting confirmed that this indeed was the case. However, according to FZ's old email exchange, pertinent information and input files may instead be obtained from Derun Li at LBNL. Also when writing these minutes, FZ remarked that it is not obvious whether the Spataro-Li model would apply to IRs 2 and 8, or only to 1 and 5. => ACTION = > Contact Bruno Spataro and/or Derun Li for Y-Chamber MAFIA input files (EM) OB recommended that data like Bruno's input file should be stored in ZDATA or equivalent. On Wednesday, OB will meet with Ray Verness to discuss the vacuum chamber for ATLAS detector upgrade. He inquired who in the RLC team is now doing HOM and loss factor calculations. It was reported that according to Erk Jensen, TK may take over the impedance calculation from AG. AG will become a machine supervisor. FC however commented that TK and he have not yet been asked. OB will contact Trevor to find out what AG is doing or who else can help in these calculations. => ACTION => Contact Trevor for help with impedance calculations (OB) OB recommends an interface which should run the programmes, such as available in the old ZBASE programme. WH suggests a discussion in one of the next meetings. JJ commented that the functionality of the impedance database could be provided in mathematica. After the meeting he began with an implementation. => ACTION => Organize team meeting on impedance database plans (WH) (3) PS Beam Stability and 48 Bunch Filling Scheme (EM, WH) ---------------------------------------------------------- EM reported an important news on the PS instability at high energy, namely that since last Friday the PS beam is stable. Suspected culprits include the PS kickers and feedback. Indeed at the morning of the day of the meeting, Steve Hancock reported that the CB is disconnected now. A similar correlation between beam stability and feedback was observed in 2004. Even without the feedback all bunches now have the same short bunch length, while there is no instability. This week, 1.5e11 protons per bunch were achieved at extraction from the PS. In any case, WH has developed an injection scheme for 5x48 bunches in LHC, for the case it is needed. The number of bunches is 8% lower than in the nominal scheme, which would lower the luminosity by the same fraction, if we do not increase the bunch charges. FC inquired the status of the transverse PS damper. EM responded that tests are presently being done at 26 GeV/c, whereas the damper was built to damp the injection oscillations and not for extraction. FC clarified he was more worried about kicker heating. EM responded that until now nothing was seen. (4) Highlights from PEP-II MAC (FZ) ----------------------------------- FZ presented the past & present performance of PEP-II, the proposed strategy for increasing the luminosity by almost another factor of 2 to 2e34, and the comments of the MAC, which advised the PEP-II team to exercise caution in reducing the bunch length and beta*, and rather push specific luminosity by improved optics corrections. The PEP-II MAC talks can be found at http://www.slac.stanford.edu/grp/ad/pep-ii/MAC-Review/MAC-Oct2006/ (5) Finite Length Impedance (EM) -------------------------------- EM reported that a 1st theory and a 2nd more refined resistive-wall theory had been developed by R. Gluckstern and B. Zotter (released on 9 August and 20 October 2006, respectively). The theories describe the impedance for a cylindrical object with finite resistivity of length g. EM presented a scan in g expected from the 1st and 2nd theory, considering graphite with a thickness of 2.5 cm. There are severe numerical problems above 100 MHz. EM also re-derived an analytical approximation, which differs from R Gluckstern's by some factor. EM emphasized that the new theory of Gluckstern and Zotter applies for any thickness and includes the inductive bypass, unlike Gennady Stupakov's published earlier. The final result suggests that even in the inductive bypass regime the impedance of an element is equal to its impedance per unit length multiplied by its length. FC asked whether the formula would apply to the experiments he had done in EPA. He summarized the basic message of the EPA experiments which is that the resistance of the coating determines the longitudinal impedance of a thinly coated ceramic structure. FC indeed has a formula for the longitudinal impedance which describes the EPA case. He expects the transverse impedance to be pretty small. EM proposes to review the paper by Stupakov in a future meeting. => ACTION => Review of Stupakov paper (EM) (6) AOB ------- Concerning collimator impedance measurements in the SPS, FC remarked that characteristic changes in sideband amplitude were observed in the 2004 measurements. He recommended that similar data be taken this year. FZ commented that many of the previous week's measurements were done in a so-called PLL mode, where the amplitude or width of the signal is not available. EM indicated that last week's collimator MD in SPS seemed to confirm the 2004 data. OB asked about the open LTC action on collimator impedance scaling. It is now scheduled for the 6th of December. FZ announced that a 1.5-days CARE-HHH & EUROTeV joint mini-workshop on technological solutions to the e-cloud problem will be held beginning of March. The highlight of this min-workshop will be the enamel based clearing electrodes invented by FC. FC added that the first enamel strip prototype electrode are under production in Germany. Concerning microwave measurements in the SPS and ongoing discussions, FC emphasized that a clear signal of the cyclotron resonance was seen, which proves that the measurement detects the electron cloud. Posted on the web: Slides by EM & FZ Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/