Summary notes of LCU meeting on 18/06/2007

Present: IA, MA, RB, HB, FC, SF, MG, WH, AK, MM, EM, TP, VP, TR, FR, BS, FS, RT, SW, PL, RC

Report from meetings

• SLM -> MG
  MG received only very few comments on the forum. It was felt that the forum would be useful in principle, but that already a large number of meetings are organized. MG asks for further feedback and for possible subjects we would like to have discussed in a forum.
  He reminds that all PAC contributions should be sent to Oliver. For CLIC related subjects, please sent a copy to Hans Braun and J.P. Delahaye.
  We welcomed Paul Anton Letnes who started today as technical student under supervision of HB. His main work is to write operational software for the scrapers in the SPS and to participate in related MDs, and if time permits, to extend this to other LHC injection related work.

Discussion of a bench method for low frequency transverse impedance measurements on the collimators -> FC (pdf file)
FC recalled how transverse impedances of kickers and collimators can be measured using wire methods in the laboratory. A major challenge is that the impedances to be measured are very small, typically some mOhm: this can be overcome by using a coil instead of a single wire. A careful network analyzer setup and analysis is needed.
It is planned to apply these techniques to measure the transverse impedance of the LHC collimators. The main interest is to measure the impedance below frequencies of 1 MHz where differences exist between different models (check "inductive bypass"). Details on which collimators could be measured and when should be worked out with Ralph Assmann. FeRo and BS would be interested to be involved in measurements from September on.

Comparison of various formalisms for longitudinal and transverse resistive wall impedance -> BS (pdf file)
BS showed a comparison of predictions based on Henry/Napoly (HN) and Zotter. HN give predictions for any mode of the longitudinal impedance. The transverse impedance is obtained via the Panofsky-Wenzel theorem. Zotter's approach allows for non-relativistic effects (beta < 1), various materials and multiple layers. The predictions of HN and Zotter agree well up to 1 THz (but beyond this is a regime which is not so relevant for the LHC).

Trip report from BNL -> TP  (pdf file)
TP reported from her trip to BNL. The main goal was to get experimental information from transverse beam transfer function measurements at RHIC. Measured spectra were compared to three types of predictions: i) based on analytic models; ii) rigid bunch simulations; iii) multiple particle simulations. These comparisons are useful to benchmark codes used for the LHC. Good agreement between measurements and predictions were observed. The simulation of chromaticity and non-linear effects is under study.

Computing self-consistent beam-beam effects and consequences for bunch to bunch tolerances -> WH  (pdf file)

WH reported from beam-beam simulations and gave predictions of which bunch to bunch intensity and emittance variations would be acceptable in the LHC.
He uses the TRAIN program which is well adapted to simulate LHC filling and collision schemes. The program iterates to determine the closed orbits for all bunches in presence of beam-beam effects. He finds that bunch by bunch fluctuations of up to 10% in intensity and 20% in emittance should be tolerable.

Status of LHC MAD-X on-line model -> IA  (pdf file)
IA referred to our meeting on May 7 for an introduction of the online model. He showed schematically how the CAMIF, FIDEL/WISE, LSA,  the Layout database, the simulation manager and visualizations are connected in the on-line model. Possibilities for additional functionality include collective effects, IR geometry and a knowledge database.
There is some concern about FIDEL or WISE integration.
Practical tests of the on-line model in MD are planned for September.

AOB
MG announced that there will be no LHC-upgrade meeting next week.

Last update: 18-June-07

MG & HB

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