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Minutes of the ABP-LCE team meeting of 28.05.04
present: EB, AK, WH, DK, EM, FR, DS, FZ
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(1) Visit by DK and Beam-Beam Studies
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Dobrin Kaltchev is visiting for 40 days.
He will perform beam-beam tracking with linear
imperfections. Another beam-beam priority
item is a tune scan being done by WH.
After linear imperfections have been
included, crossing schemes can be simulated.
(2) Impedance Calculations
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EM noted that the collimation and machine
protection comprises many elements
(like TCDI , TCDQ, ...) which could harbor
trapped modes. FR comments that the rf
group cannot compute so many different
elements as a background activity, and that
we should resort to analytical estimates
or extrapolate from similar devices such
as the main collimators.
FR also replied to a question by FZ
that impedances of the LHC experimental
chambers had already been computed by OB.
(3) BBLR Impedance
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FZ reported a numerical calculation of the BBLR
impedance by Alexej Grudiev, with results
from GdfidL and HFSS. There was some discussion
how the impedance should be computed for an
asymmetric structure. AG computed the
impedance off axis and subtracted the on-axis
value. The on-axis impedance yields the
closed-orbit deflection.
Based on these impedances the closed-orbit
deflection for a single nominal LHC bunch is
estimated as 2 nrad and the tune shift 1e-5.
These values are insignificant.
Fritz Caspers had several proposals for
further calculations and measurements.
(4) EPAC Papers
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EM is 1st author on papers about the Montague resonance
and space charge with octupoles; FZ on papers about the
beam dynamics challenges in future circular colliders,
electron-cloud benchmarking in the SPS, electron-cloud
code comparison, SPS impedance measurements using
current-dependent phase advance, QCD explorer, and BBLR;
EB on papers about electron-cloud instabilities and
electron-cloud pinch; AK on papers about simulation
codes and inductive bypass; WH on papers about CNGS;
DK on papers about Lie algebra and FFAG; DS on none;
FR on papers about collective effects and cheap options
for an LHC upgrade.
FR recommended that collaborators be reminded to update
their results for the code comparison.
It was unclear how BZ's result fort he inductive
bypass could be reconciled with formulae from the
other coauthors.
(5) AOB
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EM reminded us that Alexej Burov will visit CERN
from May 30 to June 11 to work on resistive-wall
impedance, kicker impedance, comparisons etc.
FR suggested to schedule a special AB forum.
It was commented that AB could become coauthor on
the inductive bypass paper.
(6) Some Pending Actions
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ACTION => Clarify relation between loss factor & synchronous phase shift.
PENDING. EM ? (Energy loss depends on t and theta)
ACTION => Clarify why B. Zotter's results are an order of
magnitude larger than the results from Vos,
Burov&Lebedev. BZ will give a presentation in one of
the next LCE meetings. AK plans to repeat the derivation
with field matching and four em potentials.
PENDING.
ACTION => Clarify the origin of the difference in graphite
resistivity.
Attached: Slides by FZ.