------------------------------------------------------------
Minutes of the ABP-RLC team meeting of 16.06.2006 
Present full time: WH, GR, AG, EM, UD Present part time: TP, FC, Ernst Radermacher
Excused: FR, FZ (LHC-MAC), RT (time conflicting with the CLIC meeting, which ended
at 11:00)
web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/
------------------------------------------------------------

Concerning the TOTEM roman pots, E. Radermacher said that measurements were done 
with FC in order to see the influence of the beam on the wire and they put ferrite 
around the pot. The question was whether Cu coating would be needed. This could be 
harmful since there are welded bellows and some Cu could remain in the bellow during 
the coating treatment. FC thinks that Cu coating is not needed. The final decision 
is not to have Cu coating in the TOTEM roman pot. An official statement from our 
section is awaited on this subject. FC said that he supports the decision.

Reports from meetings
------------------

-> WH briefly reported from Wednesday's Commissioning Committee: first
collisions are expected in LHC at 450 GeV in November 2007. There could also be a 
ramp to 1 TeV. Luminosity will be in the order 10^(28)-10^(30) cm^(-2) and experiments
could acquire data for the detector calibration. Different scenarios are actually 
considered for the first stage of LHC operation, our team should give statements on 
their feasibility in terms of collective effects.

-> GR reported from the APC Meeting held on the previous Thursday.  
There were 3 presentations: F. Roncarolo showed results from SPS machine studies 
aiming at finding a better working point for the LHC beam. These studies included: 1)
dynamic crossing of resonance lines to determine their stop-bands, and 2) static 
working point scans with beam current and emittance measurements, as well as resonant
driving term analysis to try and localize sources of non-linearity along the machine.
All measurements were done in low current. The region 26.11<Qx<26.14 26.16<Qy<26.18 
turned out to be favorable both in terms of losses and for the available space to 
accept tune shift-spread in high current operation. Then H. Burkhardt presented his 
proposal for 2006 MDs on the SPS scrapers. The reason is that scrapers are useful to 
send to LHC a clean beam, i.e. without significant tails at more than 3.5 sigma, which
do not contribute to luminosity. The current SPS scraper system does not have the 
option of diagonal scraping and lacks a simple user interface, but from previous 
experience it appears to work well. H. Burkhardt requested few hours for setup of the 
equipment, and then at least two dedicated MD sessions to try scraping at different 
energies. Instrumentation needed for these MDs consists of BCT, profile monitors 
(possibly synchrotron light monitor at the higher energies for measurements with a 
good tail resolution), BLMs. Operation in coast would be desirable to measure the tail
re-population times.  
Last talk on the APC was from G. Arduini, who only presented the updated schedule of 
the MDs after the delay induced by the break-down of the PS rotating machine. This has
caused a general delay of 5 weeks on the general schedule, with 2 weeks possibly 
recovered at the end of the run if it is proven to be cost neutral in terms of power 
consumption. Minutes of this meeting will be soon available on the web:

https://ab-div.web.cern.ch/ab-div/Meetings/APC/2006/apc060608/minutes_060608_draft.html

Work reports
-----------------

EM presented the follow up on the study of the transverse impedance of kickers. More 
measurements were done with 2-wires on the shielded kicker MKE-L10, where all ferrite 
cells were equipped with serigraphed interleaved metallic stripes and results can be
viewed from the slides of his presentation. The contribution of the kickers to the 
imaginary part of the impedance is 0.6 MOhm/m in the low frequency (this should be the
part responsible for the coherent tune shift) per kicker, which means a total further 
contribution of about 5.4 MOhm/m given by the newly installed kickers.

EM reported on the the work done by him and GR on the scaling of the TMCI and electron
cloud instability thresholds with energy (core of their EPAC paper). Analytical 
estimates would suggest that the TMCI threshold scales like |eta|, the electron cloud 
instability threshold should scale like 1) |eta|^2/gamma if the pinch enhancement of 
the cloud density is not taken into account, or 2) like |eta|/gamma taking that also 
into account. HEADTAIL simulations confirm the scaling like |eta| for the TMCI 
thresholds, even if the numbers seem to be about a factor 2 below the analytically 
predicted ones. About the e-cloud instability, HEADTAIL simulations predict that a 
bunch at 60 GeV is more unstable than a bunch a 26 GeV. This is not in complete 
agreement with the expected scaling like |eta|/gamma, which would basically predict 
equal instability thresholds for a bunch at 26 or 60 GeV, but more detailed work on 
this issue has been foreseen.

Finally EM commented on some results on Landau damping with octupoles and space charge
presented by V. Kornilov at the the 39th ICFA Beam Dynamics Workshop on "High Intensity
High Brightness Hadron Beams" held at Tsukuba in Japan (http://indico.kek.jp/). 
Apparently, Kornilov's newly reported results change by 180 degrees the results 
presented in the GSI-CERN HHH bilateral meeting held on 30-31 March 2006 at 
GSI-Darmstadt (http://care-hhh.web.cern.ch/care-hhh/Collective%20Effects-GSI-March
-2006/default.html). In the conclusions of Kornilov's talk from the GSI meeting, it was
stated that PATRIC simulations support Laclare's conclusions (there is damping due to
nonlinear space charge) rather than Moehl's (there is no damping due to nonlinear 
space charge). In the conclusions of his talk from the Tsukuba workshop, it now comes
out that PATRIC simulations support Moehl's theory rather than Laclare's (which is in
agreement with what EM had presented in the GSI meeting).

AOB
------

Next RLC section meeting will take place on Friday 07.07.06 because on the 30th June
there will still be EPAC going on and part of the group will be attending it.