------------------------------------------------------------ Minutes of the ABP-RLC section meeting of 21.11.2006 present: OB, UD, EM, WH, JJ, TP, FR, GR, BS, RT, FZ excused: FR web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/ ------------------------------------------------------------ (1) Reports from Meetings ------------------------- APC: GR reported from the last meeting, which was devoted to SPS impedance measurements. EM and R. Steinhagen there discussed collimator impedance measurements with collimator open and closed. Also the real part of the impedance was assessed at the SPS using growth rate measurements. Parasitically the tune shift with current could be inferred. Helmut presented the 2006 SPS transverse impedance measurements at 26 GeV/c. A small increase in impedance with respect o 2003 was seen, which is attributed to four newly installed kickers. The latest broadband-resonator impedance is 23.6 MOhm/m (for Comparison before the 20065 shutdown the value was 21 MOhm), J. Tuckmantel showed the measured longitudinal quadrupole oscillations as a function of frequency. They indicate that the longitudinal impedance increased more than expected. A probable explanation is that the bunch length was not the same as in the previous measurements. E. Gaxiola presented the result of the kicker improvements for reduced heating. A byproduct is a reduction of the transverse impedance. He showed the kicker temperature increase as a function of current for modified and unmodified kickers. The temperature rise was reduced by a factor of two by stripe coating. Tom Kroyer showed bench wire measurements of the kicker impedance with stripes. In the frequency range 50-100 MHz the impedance gets worse (a new peak appears), while at higher frequencies the impedance has indeed improved. LHCCWG: FZ reported that two presentations were given by F. Bordry on the tracking errors of the main power converters, and by J. Wenninger on beam measurements of tracking errors. The expected effect of the tracking errors is in the shadow of other uncertainties like p.c. decay or snap back. It can be corrected using beam-based measurements and/or feedback. ABMB: OB reported that in response to the DG's white paper, all group leaders are updating entries in the Activity Planning Tool (APT). The goal is the demonstration how many resources are missing. This issue will go to the SPC in December. SLM: Discussion of the new group structure has progressed. In view of imminent MAPS exercises, the goal is to reorganize the group before February. One possibility could be a combination of the linac4 and CLIC sections. An open question is the future RLC section. OB appreciates any feedback. New staff members: OB announced that the ABP group got two new staff members. Rosario will join the RTL section, working for shutdown coordination. Michel Sampson too will join RTL section, as well for shutdown coordination, and to assist Muriel with APT entries etc. OB explained the meaning of APT as Activity Planning Tool. WH confirmed a suspicion of FZ that it is accessible only for section and group leaders. (2) Open Actions ---------------- EM contacted Bruno. Bruno will meet with Derun Li in California. He will pass by CERN afterwards to inform EM about the outcome. OB talked to Trevor concerning the requested help on impedance calculations. After the RLC meeting, Trevor clarified that discussions in the RF group have not yet led to the identification of a possible replacement for AG. The present situation is that the RF group still does not have a solution. Erk will ask AG to continue doing these calculations for the time being. A longer-term solution will need to be found. WH has organized a meeting on impedance measurements (today); see below. EM is ready to discuss the Stupakov paper; see below. WH has presented scheme of 48 bunches to LOC. Later he will present it to the LHCCWG. A note is in preparation. (3) ZBASE (OB, WH, JJ) ---------------------- OB reiterated his wish to have a data repository with common format for all items. He clarified that not only the data, but also all the programmes and input files used for the calculations should be stored in this repository. FZ commented that in particular we need to collect such information from AG before he moves on to new activities. OB recalled his study of the incoherent loss factors for LEP and how it was facilitated by the existing ZBASE. WH stressed the goal to identify what we already have, and what is working, and to determine people willing to participate and to maintain the repository. Both OB and WH emphasized that we need to identify a person driven to take on this task and push it through. The ultimate goal is that a newcomer can run the code and update impedances in a couple of minutes. OB conceded that we could use another language. An advantage of Tcl/Tk is the interpretative nature of this language, and that is does not need to be compiled. A further goal announced by OB is the extension of ZBASE to the full CERN accelerator chain. OB recommends not dropping the existing ZBASE without having a functioning alternative, and that we should maintain the minimum feasibility which exists. WH agreed that the person doing the job can later choose the tool to use. JJ commented that Mathematica might be a good tool to implement the required functionality, He drafted a first basic implementation. The completion is not difficult, and it could be left as a job for a technical student or summer student. JJ explained that the structural description of the database is called a schema. But the classical relational model for the schema may not suit our specific needs. JJ prefers to think in terms of mathematical functions and not in terms of tables. Primary physics-driven requirements are the impedance and wake function for all objects in the LHC, the integrity of the LHC data, and the possibility of many kinds of manipulations. Secondary computer-driven requirements are the capability of reading unstructured output formats from various programmes, access to all platforms, and to be as simple as possible and future-proof. Database maintainer and applications are functions to be supported. Access can be via the web. JJ showed examples how data can be read in and assigned to rules. He presented example files and file contents, plots, and beam data. He commented on ways of reading URMEL/ABCI etc output files. He displayed a plot of a wake field from the database, with a lot of noise at the end. OB commented that a reason for the noise could be too short a time range in the wake computation. He explained that further examination is often necessary to judge the validity of the data, and that a good check is to make a Fourier transform. JJ next showed how the optics can be read in from LHC optics database using Madtomma. Specifically, the optical data for any specific element or for classes of elements can be extracted. OB commented that ZBASE had an interface to MAD. JJ's conclusions list a number of advantages of the Mathematica approach. Noteworthily, Mathematica interpolation functions would offer many advantages. OB agreed that the availability of interpolating routines would be a big plus of Mathematica. WH asked who will be the person to do this. EM volunteered for taking on this responsibility. JJ repeated his comment that the project could be completed by a technical student. OB says that the programme should be continually checked and debugged. EM will evaluate ZBASE and mathematica option and report back to the team before Christmas. OB suggested as a first step to follow up with AG to see what he has done and collect the data he has, and then, as a second step, think about how to link these tools to the database. EM also expects to receive a new MAFIA file from B. Spataro. Then beginning of next year, EM will make a proposal of organization and distribution of work packages. OB commented that the experiments' impedances stored in ZBASE are still up to date. EM reminded us that BS will derive a general formula for the resistive-wall impedance. WH concluded the discussion by stating that EM will come back when he has something to present or needs help. It is foreseen that EM will report back to the team early next year. Replying to question by WH, OB clarified that there will be no Chamonix meeting in 2007. An LHC commissioning meeting may be held in late spring. The ABOC/ATC days may take place end of January. Review of Stupakov's paper (EM) ------------------------------- EM reviewed the theory of Stupakov published in 2005 and compared it with an unpublished theory of Gluckstern and Zotter. Stupakov's paper represents the first attempt to compute the effect of finite-length RW impedance. A certain frequency regime is considered in this calculation. Stupakov employs the Leontovich boundary conditions. Zotter's approach is the most general, applying to any number of layers, any beam velocity, any conductivity, any permittivity, and any permeability. G. Stupakov's proof only applies to the intermediate, classical frequency regime. In addition, the Zotter-Gluckstern model is different from Stupakov's. In the Zotter-Gluckstern case, a perfectly conducting pipe is bypassing the resistive insertion. Preliminary results indicate however that about the same conclusion as Stupakov's could be obtained. Bruno Zotter presently is in the US, to further discuss this issue with Bob Gluckstern. AOB --- FZ reported that he has posted all LCE-RLC minutes starting from 2003 on the RLC web site. OB recalled that there will be a presentation on collimator impedance at the LTC of December 6. Posted on the web: Slides by JJ & EM Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/