79 research outputs found
Numerical Calculations of Wake Fields and Impedances of LHC Collimators' Real Structures
The LHC collimators have very complicated mechanical designs including
movable jaws made of higly resistive materials, ferrite materials, tiny RF
contacts. Since the jaws are moved very close to the circulating beams their
contribution in the overall LHC coupling impedance is dominant, with respect to
other machine components. For these reasons accurate simulation of collimators'
impedance becomes very important and challenging. Besides, several dedicated
tests have been performed to verify correct simulations of lossy dispersive
material properties, such as resistive wall and ferrites, benchmarking code
results with analytical, semi-analytical and other numerical codes outcomes.
Here we describe all the performed numerical tests and discuss the results of
LHC collimators' impedances and wake fields calculations.Comment: Invited Talk at ICAP 2015, Shanghai, China, 11 pages, 11 figure
Beam-Beam Interaction in Novel, Very High Luminosity Parameter Regimes
In order to achieve luminosities significantly higher than in existing
machines, future storage-ring based colliders will need to operate in novel
parameter regimes combining ultra-low emittance, large Piwinski angle and high
bunch charge; implementation of techniques such as a "crab waist" will add
further challenges. Understanding the beam-beam interaction in these situations
will be essential for the design of future very high luminosity colliders.
Recent developments in modeling tools for studying beam-beam effects, capable
of investigating the relevant regimes, will be discussed and examples,
including tests with crab waist collisions in DAFNE, will be presented.Comment: Invited Talk at 1st International Particle Accelerator Conference
(IPAC10), Kyoto, Japan, May 23-28, 2010. 5 pages, 7 figure
Numerical Calculations of Wake Fields and Impedances of LHC Collimators' Real Structures
The LHC collimators have very complicated mechanical designs including
movable jaws made of higly resistive materials, ferrite materials, tiny RF
contacts. Since the jaws are moved very close to the circulating beams their
contribution in the overall LHC coupling impedance is dominant, with respect to
other machine components. For these reasons accurate simulation of collimators'
impedance becomes very important and challenging. Besides, several dedicated
tests have been performed to verify correct simulations of lossy dispersive
material properties, such as resistive wall and ferrites, benchmarking code
results with analytical, semi-analytical and other numerical codes outcomes.
Here we describe all the performed numerical tests and discuss the results of
LHC collimators' impedances and wake fields calculations
Aplication of Frequency Map Analysis to Beam-Beam Effects Study in Crab Waist Collision Scheme
We applied Frequency Map Analysis (FMA) - a method that is widely used to
explore dynamics of Hamiltonian systems - to beam-beam effects study. The
method turned out to be rather informative and illustrative in the case of a
novel Crab Waist collision approach, when "crab" focusing of colliding beams
results in significant suppression of betatron coupling resonances. Application
of FMA provides visible information about all working resonances, their widths
and locations in the planes of betatron tunes and betatron amplitudes, so the
process of resonances suppression due to the beams crabbing is clearly seen.Comment: 11 pages, 10 figure
Single Bunch Instabilities in FCC-ee
FCC-ee is a high luminosity lepton collider with a centre-of-mass energy from 91 to 365 GeV. Due to the machine parameters and pipe dimensions, collective effects due to electromagnetic fields produced by the interaction of the beam with the vacuum chamber can be one of the main limitations to the machine performance. In this frame, an impedance model is required to analyze these instabilities and to find possible solutions for their mitigation. This paper will present the contributions of specific machine components to the total impedance budget and their effects on the beam stability. Single bunch instability thresholds will be estimated in both transverse and longitudinal planes
Coupling impedances and collective effects for FCC-ee
A very important issue for the Future Circular Collider (FCC) is represented by collective effects due to the selfinduced electromagnetic fields, which, acting back on the beam, could produce dangerous instabilities. In this paper we will focus our work on the FCC electron-positron machine: in particular we will study some important sources of wake fields, their coupling impedances and the impact on the beam dynamics. We will also discuss longitudinal and transverse instability thresholds, both for single bunch and multibunch, and indicate some ways to mitigate such instabilities
Suppression of the longitudinal coupled bunch instability in DANE in collisions with a crossing angle
In DAFNE, the Frascati collider operating since 1998, an innovative
collision scheme, the crab waist, has been successfully implemented during the
years 2008-09. During operations for the Siddharta experiment an unusual
synchrotron oscillation damping effect induced by beam-beam collisions has been
observed. Indeed, when the longitudinal feedback is off, the positron beam
becomes unstable with currents above 200-300 mA due to coupled bunch
instability. The longitudinal instability is damped by colliding the positron
beam with a high current electron beam (of the order of 2 A). A shift of about
-600 Hz in the residual synchrotron sidebands is observed. Precise measurements
have been performed by using both a commercial spectrum analyzer and the
diagnostic capabilities of the longitudinal bunch-by-bunch feedback. The
damping effect has been observed in DAFNE for the first time during collisions
with the crab waist scheme. Our explanation, based both on theoretical
consideration and modeling simulation, is that beam collisions with a large
crossing angle produce longitudinal tune shift and spread, providing Landau
damping of synchrotron oscillations.Comment: 6 pages, 9 figures, ICFA mini-Workshop on "Mitigation of Coherent
Beam Instabilities in particle accelerators" MCBI 2019, 23-27 Sep 2019,
Zermatt, CH. arXiv admin note: substantial text overlap with arXiv:1006.178
Wakefields of the FCC-ee collimation system
The purpose of this paper is to calculate the longitudinal and transverse
wakefields of the FCC collimators by using the electromagnetic codes ECHO3D and
IW2D. We cross-checked our results using CST particle studio for long bunches,
and found them to be in good agreement. The obtained results show that the
collimators give one of the highest contributions to the overall FCC-ee wake
potentials. Using the code PyHEADTAIL, we have found that the presence of the
geometric wakefield of the collimators leads to the occurrence of transverse
mode coupling instability (TMCI) at a significantly lower bunch population as
compared to that of all other contributions and solutions to reduce this
geometric term must be found
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