833 research outputs found
Summary of session 3 on synchrotron radiation and beam dynamics
Below we summarize presentations, discussions and general conclusions of the
Workshop session on "Beam Dynamics Issues". Major subjects include effects due
to synchrotron radiation (SR), cryogenic loads, electron cloud, impedances,
intra-beam scattering (IBS) and beam-beam interactions.Comment: 2 pp. EuCARD HE-LHC10 AccNet mini-workshop on a High-Energy LHC,
14-16 Oct 2010: Villa Bighi, Malt
Simulations of Coaxial Wire Measurements of the Impedance of Asymmetric Structures
Coaxial wire measurements have provided a simple and effective way to measure
the beam coupling impedance of accelerator structures for a number of years. It
has been known how to measure the longitudinal and dipolar transverse impedance
using one and two wires for some time. Recently the ability to measure the
quadrupolar impedance of structures exhibiting top/bottom and left/right
symmetry has been demonstrated. A method for measuring the beam coupling
impedance of asymmetric structures using displaced single wires and two wire
measurements is proposed. Simulations of the measurement system are presented
with further work proposed
Transverse Instabilities of Coasting Beams with Space Charge
Transverse beam stability is strongly affected by the beam space charge.
Usually it is analyzed with the rigid-beam model. However this model is only
valid when a bare (not affected by the space charge) tune spread is small
compared to the space charge tune shift. This condition specifies a relatively
small area of parameters which, however, is the most interesting for practical
applications. The Landau damping rate and the beam Schottky spectra are
computed assuming that validity condition is satisfied. The results are applied
to a round Gaussian beam. The stability thresholds are described by simple fits
for the cases of chromatic and octupole tune spreads.Comment: 6 pages, 2 figures, accepted by Phys. Rev. ST - Accel. Beam
Comparison of the current LHC Collimators and the SLAC Phase 2 Collimator Impedances
One of the key sources of transverse impedance in the LHC has been the
secondary graphite collimators that sit close to the beam at all energies. This
limits the stable bunch intensity due to transverse coupled-bunch instabilities
and transverse mode coupling instability. To counteract this, new secondary
collimators have been proposed for the phase II upgrade of the LHC collimation
system. A number of designs based on different jaw materials and mechanical
designs have been proposed. A comparison of the beam coupling impedance of
these different designs derived from simulations are presented, with reference
to the existing phase I secondary collimator design
Concevoir en partenariat une EcoViticulture ECOnomiquement viable et ECOlogiquement responsable par rapport aux pesticides (EcoViti)
InitiĂ© en 2010, le projet Casdar EcoViti a proposĂ© et testĂ© une dĂ©marche sâappuyant sur des connaissances expertes pour la conception de systĂšmes viticoles innovants Ă bas intrants phytosanitaires. LâĂ©valuation des performances et le rĂ©-ajustement des prototypes conçus se fait au sein dâun rĂ©seau de plateformes dâexpĂ©rimentation installĂ©es dans les grandes rĂ©gions viticoles françaises. Une mĂ©thode et des outils adaptĂ©s Ă la viticulture ont Ă©tĂ© produits et formalisĂ©s. Les premiers rĂ©sultats dâEcoViti montrent des performances environnementales et Ă©conomiques satisfaisantes pour encourager lâĂ©volution des systĂšmes viticoles vers une moindre dĂ©pendance aux intrants
Evaluation of the Beam Coupling Impedance of New Beam Screen Designs for the LHC Injection Kicker Magnets
During the 2011 run of the LHC there was a significant measured temperature
increase in the LHC Injection Kicker Magnets (MKI) during operation with 50ns
bunch spacing. This was due to increased beam-induced heating of the magnet due
to beam impedance. Due to concerns about future heating with the increased
total intensity to nominal and ultimate luminosities a review of the impedance
reduction techniques within the magnet was required. A number of new beam
screen designs are proposed and their impedance evaluated. Heating estimates
are also given with a particular attention paid to future intensity upgrades to
ultimate parameters
Coaxial Wire Measurements of Ferrite Kicker Magnets
Fast kicker magnets are used to inject beam into and eject beam out of the
CERN accelerator rings. These kickers are generally transmission line type
magnets with a rectangular shaped aperture through which the beam passes.
Unless special precautions are taken the impedance of the yoke can provoke
significant beam induced heating, especially for high intensities. In addition
the impedance may contribute to beam instabilities. The results of longitudinal
and transverse impedance measurements, for various kicker magnets, are
presented and compared with analytical calculations: in addition predictions
from a numerical analysis are discussed
Assessing habitat-suitability models with a virtual species
This paper compares two habitat-suitability assessing methods, the Ecological Niche Factor Analysis (ENFA) and the Generalised Linear Model (GLM), to see how well they cope with three different scenarios. The main difference between these two analyses is that GLM is based on species presence/absence data while ENFA on presence data only. A virtual species was created and then dispatched in a GIS-model of a real landscape following three historic scenarios: 1° spreading, 2° at equilibrium and 3° overabundant species. In each situation, the virtual species was sampled and these simulated data sets were used as input for the ENFA and GLM to reconstruct the habitat suitability model. The results showed that ENFA is very robust to the quality and quantity of the data, giving good results in the three scenarios. GLM was badly affected in the case of the spreading species but produced slightly better results than ENFA when the species was overabundant; at equilibrium, both methods produced equivalent results. The use of a virtual species proved to be a very efficient method, allowing to fully control the quality of the input data as well as to accurately evaluate the predictive power of both analyses
Chromaticity dependence of the transverse effective impedance in the CERN Proton Synchrotron
The current knowledge of the transverse beam coupling impedance of the CERN Proton Synchrotron (PS) has been established with beam-based measurements at different energies. The transverse coherent tune shift as a function of the beam intensity has been measured in order to evaluate the total effective imaginary part of the transverse impedance in the accelerator at the energies of 7, 13 and 25 GeV. Measurements have been performed changing the vertical chromaticity
for each vertical tune scan with intensity. The data analysis revealed an increase of impedance with chromaticity for all the considered energies. The transverse impedance
can be compared with the previously evaluated theoretical impedance budget taking into account the individual contribution of several machine devices
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