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Minutes of the ABP-RLC team meeting of 23.09.2005
present: EB, UD, WH, EM, TP, FR, FZ
web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/
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(1) Minutes of last meeting, pending actions, announcements
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The list of outstanding actions was reviewed. EB will perform
HEADTAIL simulations with electron cloud in the LHC dipoles.
UD will complete and document the simulations for the SPS
experiment. WH has followed up on the optics with beta*=2 m
and he will compute the stabilization by long-range beam-beam
collisions at injection.
The CARE-HHH code repository is operational again, thanks to
help from Romain Basset, who has also moved it to the ORACLE
production server. Now the database has to be filled with
information. FZ commented on the low rate of responses.
Giuliano Franchetti would like to visit CERN for a week
some time after October 15, to continue the electron-cloud
collaboration. FR assumed that his travel could be financed
by the GSI CARE-HHH budget.
(2) PS Kicker Impedance (EM)
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Four kickers are foreseen to be installed in the PS for the new CT,
increasing the total number of PS kickers from 6 to 10.
Measurements on two different new PS kickers were performed by F. Caspers
and T. Kroyer in the presence of FR. The longitudinal impedance was
measured with the single-wire method with varying transverse wire
position. EM used the Panofsky Wenzel theorem to extract the
transverse impedance. In the horizontal plane, both real and imaginary
part are negative at low frequencies. The vertical impedance components
are both positive at low frequencies and correspond well to a
broadband resonator. Kicker type 1 has a longitudinal impedance Z/n
of about 1 Ohm, kicker type 2 of about 0.5 Ohm. Since there are
2 kickers of each type, the total impedance contribution is
about Z/n~3 Ohm, or 15% of the present PS impedance of 20 Ohm.
In the vertical plane the kickers will add an impedance of
about 0.4-0.5 MOhm/m to about 1.5 MOhm/m (or 30%) at 700 MHz.
The PS impedance is most critical for the TOF beam with 7e12 protons
per bunch, for which a fast vertical instability is seen near transition
with a frequency that corresponds to about 700 MHz, i.e., close to the
peak of the kicker impedance. At present, this instability is
suppressed by increasing the longitudinal emittance to 2.2 eVs.
With the 4 additional kickers, the emittance may need to be raised
to 2.5-3.0 eV. EM did not know whether this value can be achieved.
Analytical predictions for the SPS gave a 2x higher resonance
frequency than the value suggested by certain measurements.
So there is uncertainty whether we model the kickers correctly.
EM will present a comparison of the analytical model and
the PS kicker measurements in a future RLC meeting.
FR pointed out that a proper APC discussion before installation
would be needed. (After the meeting M. Giovannozzi was informed
and further measurements of the other PS kickers were suggested).
(3) Coulomb'05 Workshop (EM)
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EM gave an interesting summary of Coulomb'05, which was
a workshop bringing together accelerator physicists and
mathematicians. There was only one presentation on electron
cloud, by Roberto Cimino. From CERN, EM and M. Giovannozzi
attended. Pusterla reviewed the non-conventional approach
to beam dynamics based on the nonlinear Schrodinger equation.
FR recalled an existing similar model by Renato Fedele et al.
Contact was established with Neishtadt, the creator of the
adiabatic theory, who explained that a different theory applies
at the beginning of the adiabatic trapping.
Y. Elskens et al. described a scheme of controlling chaos
by creating barriers introducing small terms to the
Hamiltonian. Similar work was published in a recent PRL article.
Zenkevich discussed the importance of non-Gaussian tails
for intrabeam scattering. Several other high-quality
presentations can be found on the web.
The web site of COULOMB05 is
http://www.physycom.unibo.it/coulomb05/scientific_program.html.
(4) Effective Luminosity for LHC and SuperLHC (FZ)
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FZ compared the importance of IP collisions, gas scattering and IBS
for the luminosity lifetime. The dominant process are the IP collisions,
which lead to a decay of the beam current as 1/(1+t/tau). Using this
model, the computed the optimum run tune as a function of turnaround
time, and presented examples for the nominal LHC and for an LHC with
1e35 cm-2 s-1 luminosity. The numbers are only slightly different
from those of an exponential model, about 10% higher. The expressions
are compact.
(5) AOB (FR)
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FR will be away for the next 2.5 weeks.
RLC meetings can be organized as needed.
Posted on the web: Slides by EM and FZ
Web site: http://ab-abp-rlc.web.cern.ch/ab-abp-rlc/