-----------------------------------------------------------
Minutes of the ABP-RLC team meeting of 19.05.2006
present: EM, WH, TP, GR, RT, FZ
excused: UD, FR
web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/
------------------------------------------------------------
(1) Minutes of Last Meeting, Pending Actions
--------------------------------------------
Actions from 05.05.2006:
=> ACTION => Discussion with Elena Shaposhnikova & rf group on strategy for
longitudinal parameters at LHC injection (FR).
Pending since FR is absent
=> ACTION => SPS e-cloud simulations at 26 and 60 GeV for a dipole field (GR).
Simulations were run for the two energies and also for 450 GeV, both without field and for a dipole.
The 450 GeV case is more stable thanks to increased longitudinal emittance.
=> ACTION => Contact rf group for possibly higher-quality bunch profiles (GR).
This question was addressed in the APC of 18.05.2006. Higher resolution is possible with the
Faraday-cage scope according to Thomas Bohl.
Other and older actions:
=> follow-up impedance of LHC septa, 07.04.2006, EM
PLANNED
=> add 2003 minutes and presentations to the RLC web site, 17.03.2006, FZ
IN SLOW PROGRESS
=> contact D. Macina to organize meeting with experiments on TCTV aperture, 17.03.2006, FR
STATUS UNKNOWN
=> contact M. Mayer to question chamber dimensions, 17.03.2006, EM, AG
PROBABLY DONE, TO BE CHECKED WITH AG
=> contact Stefano Redaelli to clarify number of TCTV, 17.03.2006, EM, AG
DONE, RESULT PRESENTED ON 07.04.2006 by EM
=> GR and FR will follow-up ideas on debunching transverse impedance measurements
with GA, EM, and FZ, 10.03.2006
PLANNED. FZ commented that raw data from earlier MD should be available from Thoms Bohl.
He recommended performing a HEADTAIL debunching simulation, with for example 2 resonators,
to check whether growth rate indeed is proportional to impedance at the chromatic frequency.
EM reported that the FP420 Cu-pipe thickness was checked. It is only 200 micron instead of several cm.
Federico Roncarolo is now re-computing the impedance as a function of the Cu thickness.
WH encouraged all RLC members and friends to inspect the list of actions posted at
http://ab-abp-rlc.web.cern.ch/ab%2Dabp%2Drlc/Actions/actions.htm
and to send any comments to FZ. Especially team members should let it be known when
an action under their responsibility has already been completed and reported.
(2) Follow-up of GSI-CERN Meeting: Simulation Results from Burkhardt Doliwa on SPS MKE
Kicker Impedance and Numerical Results from Rainer Hasse on LHC Collimator (EM)
--------------------------------------------------------------------------------------
At GSI, it was agreed that the Darmstadt team computes the impedance of SPS kickers and
LHC collimators using their own simulation programmes and formulae, respectively,
for benchmarking purposes.
The impedance of the SPS MKE kicker was simulated by Burkhardt Doliwa, using his
code, which was developed in the group of T. Weiland. Both real and imaginary part
of the simulated kicker impedance are close to the curves which EM has computed
previously using either the Burov-Lebedev or Bruno Zotter's theory, as well as
to the result of the two-wire measurement by Fritz Caspers and Tom Kroyer.
EM and GR discussed that in order to include the kicker impedance in the HEADTAIL
code, either the wake field of AK could be used, which corresponds to Luc Vos'
approximate bypass impedance, or a new wake field may be derived possibly starting
from Bruno Zotter's most general expression.
Rainer Hasse has numerically calculated the impedance of an LHC collimator
in the LHC and in the PS booster, respectively, using Al-khateeb's formulae.
The PS booster case was chosen for investigating the effect of a beta much
smaller than 1. The impedance was computed with or without the space-charge
contribution. All the results are preliminary.
The transverse impedance from Rainer Hasse peaks at about the same frequency,
~1 MHz, as the one computed from B-L's or Zotter's theory, but the value of the
maximum impedance is larger by a significant factor. Also strikingly, in
Rainer Hasse's calculation the imaginary part of the impedance approaches zero
for low frequencies and not a constant large value. The large differences
between the CERN and GSI results need to be clarified.
Rainer Hasse has also computed the longitudinal impedance, for which no
CERN prediction exists. Unlike for the transverse case, the imaginary component
of the longitudinal impedance goes towards a constant large value as the
frequency decreases.
FZ suggested to calculate the longitudinal impedance using the old LAWAL code.
Even if not fully exact, it might allow for a verification of the order of
magnitude at least.
EM informed the team that the derivation of the longitudinal impedance
will be a first task of the new student, Benoit Salvant?, together with debugging
the transverse notebook of Bruno Zotter (the impedance values derived by which
appear to be closer in magnitude to Rainer Hasse's, as remarked by FZ).
(3) AOB
-------
If FR does not return next week, the meeting on 26.05.2006 (Friday after
Ascension) will be cancelled.
Posted on the web: Slides by EM
Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/