323 research outputs found
Summary of session on Beam Losses, Halo Generation and collimation
The session on beam losses, halo generation and collimation is the first of two sessions of the BEAM07 Workshop, which were devoted to specific CERN-GSI subjects and were meant to be the follow up of last year’s CERNGSI Bilateral Meeting on Collective Effects, which took place on March 30-31, 2006 at the GSI-Darmstadt
Simulation study of electron cloud build up in the SPS MKD kickers
During the 2008 run, an unusual behavior characterizing pressure and temperature increase in some of the dump kickers of the SPS was noticed. In particular, it was observed that 1) the MKDV2 kicker would exhibit maximum heating with 75 ns spaced LHC beams and 2) the pressure rise was specially critical in MKDV1 in presence of 50 ns spaced LHC beams [1]. While the anomalous heating of MKDV2 with 75 ns beams could be tentatively explained by the denser beam current spectrum that would more likely hit one of the kicker impedance peaks, the fast pressure rise in MKDV1 with 50 ns spaced beams was ascribed to a surface effect, namely beam induced multipacting leading to electron cloud formation. This report summarizes a simulation study that was done in order to check whether the electron cloud behavior in the dump kickers could explain the experimental observations
Operational beams for the LHC
The variety of beams, needed to set-up in the injectors as requested in the
LHC, are reviewed, in terms of priority but also performance expectations and
reach during 2015. This includes the single bunch beams for machine
commissioning and measurements (probe, Indiv) but also the standard physics
beams with 50 ns and 25 ns bunch spacing and their high brightness variants
using the Bunch Compression Merging and Splitting (BCMS) scheme. The required
parameters and target performance of special beams like the doublet for
electron cloud enhancement and the more exotic 8b4e beam, compatible
with some post-scrubbing scenarios are also described. The progress and plans
for the LHC ion production beams during 2014-2015 are detailed. Highlights on
the current progress of the setting up of the various beams are finally
presented with special emphasis on potential performance issues across the
proton and ion injector chain.Comment: Submitted for publication in a CERN Yellow Report (YR
Benchmarking headtail with electron cloud instabilities observed in the LHC
After a successful scrubbing run in the beginning of 2011, the LHC can be
presently operated with high intensity proton beams with 50 ns bunch spacing.
However, strong electron cloud effects were observed during machine studies
with the nominal beam with 25 ns bunch spacing. In particular, fast transverse
instabilities were observed when attempting to inject trains of 48 bunches into
the LHC for the first time. An analysis of the turn-by-turn bunch-bybunch data
from the transverse damper pick-ups during these injection studies is
presented, showing a clear signature of the electron cloud effect. These
experimental observations are reproduced using numerical simulations: the
electron distribution before each bunch passage is generated with PyECLOUD and
used as input for a set of HEADTAIL simulations. This paper describes the
simulation method as well as the sensitivity of the results to the initial
conditions for the electron build-up. The potential of this type of simulations
and their clear limitations on the other hand are discussed.Comment: 7 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Fast Ion Instability in the CLIC Transfer Line and Main LINAC
The Fast Ion Instability is believed to be a serious danger for bunch trains propagating in the CLIC electron transfer line and main linac, since it may strongly affect the bunches in the tail of the train if the vacuum pressure is not below a certain threshold. We have developed the FASTION code, which can track electrons through a FODO cell line and takes into account their interactions with the produced (and possibly trapped) ions. We describe how this tool can be used for setting tolerances on the vacuum pressure and for giving specifications for the design of a feedback system
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