Simulations of Coherent Beam-Beam Modes at the LHC (original) (raw)
Coherent Beam-Beam Oscillations at the LHC
1999
The transverse coherent motion of the two colliding LHC beams is studied by multi-particle tracking, where the beam-beam force is calculated assuming a Gaussian beam distribution with variable barycentres and rms beam sizes. The simulation yields the coherent and incoherent oscillation frequencies, the emittance growth of either beam, and evidence for the existence or lack of Landau damping. The transverse
Simulations of coherent beam-beam modes at the Large Hadron Collider
Physical Review Special Topics - Accelerators and Beams, 2000
The transverse coherent motion of two colliding proton beams at the Large Hadron Collider is studied by multiparticle tracking. We use the beam-beam force for a Gaussian beam distribution with variable barycenters and rms beam sizes, and optionally include the effect of long-range collisions and external impedance. The simulation yields the coherent and incoherent oscillation frequencies, the emittance growth of either beam, and evidence for the existence or lack of Landau damping. For head-on collisions of beams with equal sizes, we find that the p-mode frequency lies outside of the continuum frequency spread, if the ratio of the beam-beam parameters exceeds 0.6, in accordance with predictions. For smaller ratios of the beam-beam parameters, or if, for equal beam-beam parameters, the beam sizes are widely different, the p mode is Landau damped. When long-range collisions are also included, undamped coherent modes do still exist outside the continuum, both with and without alternating crossing planes at two interaction points. However, separating the tunes of the two beams restores the Landau damping, provided the external impedance is sufficiently small.
Coherent Beam-Beam Effects in the LHC
In the Large Hadron Collider (LHC) two proton beams of similar intensities collide in several interaction points. It is well known that the head-on collision of two beams of equal strength can excite coherent modes whose frequencies are separated from the incoherent spectrum of oscillations of individual particles. This can lead to the loss of Landau damping and possibly to unstable motion. The beam-beam effect in the LHC is further complicated by a large number of bunches (2808 per beam), a finite crossing angle and gaps in the bunch train. The coherent beam-beam effects under various conditions and operational scenarios are studied analytically and with multiparticle simulations. We give an overview of the main results and present proposals to overcome these difficulties together with possible side effects.
Preliminary Simulations of Emittance Growth Due to an External Noise in Colliding Beams in the LHC
Preliminary results from simulations are presented using the COherent Multi-Bunch Interaction code (COMBI). Two bunches colliding head on, under the influence of an arbitrary sourced white noise are considered. The effect of noise on both flat and round beams is simulated and the emittance growth as a result is observed and studied. Preliminary results suggest that there is no significant difference in emittance growth due to the use of flat beams under the influence of uncoupled external white noise operating at HL-LHC parameters.
Studies of the beam-beam interaction for the LHC
Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)
We have used the beam-beam simulation code CBI to study the beam-beam interaction for the LHC. We find that for nominal LHC parameters, and assuming only one bunch per beam, there are no collective (coherent) beambeam instabilities. We have investigated the effect of sweeping one of the beams around the other (a procedure that could be used as a diagnostic for head-on beam-beam collisions). We find that this does not cause any problems at the nominal current, though at higher currents there can be beam blow-up and collective beam motion.
Coherent beam-beam interactions in electron-positron colliders
Physical Review Letters, 1991
We present the results of a new calculational technique that evaluates the beam-beam force due to an arbitrary cha.rge distribution. We find coherent instabilities that dominate at certain operating points and depend strongly on the degree of damping in the system. We conclude that while these resonances may play a significant role for colliders with low damping, with a careful choice of operating points they should present no danger to the new generation of high luminosity heavy-quark factories under design.
Weak-strong beam-beam simulations for the Large Hadron Collider
Physical Review Special Topics - Accelerators and Beams, 1999
A weak-strong simulation code is used to study the single-particle stability in the presence of triplet field errors, head-on collisions, and long-range beam-beam interactions at the Large Hadron Collider. We present the dependence of the simulated transverse diffusion rate on various parameters, such as starting amplitude, working point in tune diagram, crossing angle, beta function at the interaction points (IPs), beam current, triplet nonlinearities, tune modulation, and a transverse offset at one of two IPs.
Simulations of the strong-strong beam-beam interaction in hadron colliders
We develop weighted macro-particle tracking and the Perron-Frobenius operator technique for simulating the time evolution of two beams coupled via the beam-beam interaction. The πand σ-modes, with and without a sextupole perturbation, are studied based on the Vlasov-Poisson system. Extending standard averaging formalism to maps with a small collective force, we derive an approximation to the "kick-rotate" model of our simulation. This eliminates the delta function smoothing in the Vlasov equation, common in many theoretical approaches. Action densities are quasi-equilibria, consistent with simulation, and linearization leads to uncoupled Fourier modes and thirdkind integral equations. Extensions to 2-d.o.f. and a flexible general purpose code are being developed.
Beam Dynamics Studies to Develop a High-energy Luminosity Model for the LHC
2015
Luminosity, the key figure of merit of a collider as the LHC, depends on the brightness of the colliding beams. This makes the intensity dependent beam-beam effect the dominant performance limiting factor at collision. The parasitic interactions due to the electromagnetic mutual influence of the beams in the interaction region of a collider induce a diffusive behaviour in the tails of the beam. The evolution of charge density distribution is studied to model the beam tails evolution in order to characterize beam lifetime and luminosity. To achieve this, tools are developed for tracking distributions of arbitrary number of single particles interacting with the opposing strong-beam, to analyse the halo formation processes due to the combined effect of beambeam and machine non-linearities. This paper presents preliminary results of the simulations, both for the LHC Run I and nominal LHC parameters. The former will be used to benchmark simulations while the latter aims at supporting lum...
Study of offset collisions and beam adjustment in the LHC using a strong-strong simulation model
The bunches of the two opposing beams in the LHC do not always collide head-on. The beam-beam effects cause a small, unavoidable separation under nominal operational conditions. During the beam adjustment and when the beams are brought into collision the beams are separated by a significant fraction of the beam size. A result of small beam separation can be the excitation of coherent dipole oscillations or an emittance increase. These two effects are studied using a strong-strong multi particle simulation model. The aim is to identify possible limitations and to find procedures which minimise possible detrimental effects.
Beam-beam simulations of hadron colliders
2005
Simulations of beam-beam phenomena in the Tevatron and RHIC as well for the LHC are reviewed. The emphasis is on simulations that can be closely connected to observations.
2002
The bunches of the two opposing beams in the LHC do not always collide head-on. The beam-beam effects cause a small, unavoidable separation under nominal operational conditions. During the beam adjustment and when the beams are brought into collision the beams are separated by a significant fraction of the beam size. A result of small beam separation can be the excitation of coherent dipole oscillations or an emittance increase. These two effects are studied using a strong-strong multi particle simulation model. The aim is to identify possible limitations and to find procedures which minimise possible detrimental effects.
Review of Modern Physics
We develop the method of weighted macroparticle tracking (WMPT) for simulating the time evolution of the moments of the phase space densities of two beams which are coupled via the collective (strongstrong) beam-beam interaction in the absence of diffusion and damping. As an initial test we apply this method to study the p mode and the s mode in three different 1D limits of the beam-beam interaction. The three limits are flat beams and transverse motion in the direction of the small width, round beams, and flat beams and motion in the direction of the large width. We have written a code (BBDeMo1D) based on WMPT, which allows testing of all three limits and is suited for extension to 2 degrees of freedom.
Possible upgrade scenarios for the Large Hadron Collider (LHC) comprise the operation with either uniform (hollow) bunches or long super-bunches. We discuss the respective merits of these approaches with regard to beam-beam effects, electron cloud, and luminosity. Next, we compare the usual scheme of alternating collisions in the horizontal and vertical plane at two interaction points with that of inclined hybrid collisions at 45 o and 135 o . We then study the longitudinal dynamics for a barrier bucket rf system, including the effect of synchrotron radiation, and, finally, discuss the intrabeam scattering for both Gaussian and uniform bunches (or super-bunches).
The bunches of the two opposing beams in the LHC do not always collide head-on. The beam-beam effects cause a small, unavoidable separation under nominal operational conditions. During the beam adjustment and when the beams are brought into collision the beams are separated by a significant fraction of the beam size. A result of small beam separation can be the excitation of coherent dipole oscillations or an emittance increase. These two effects are studied using a strong-strong multi particle simulation model. The aim is to identify possible limitations and to find procedures which minimise possible detrimental effects. Abstract Abstract The bunches of the two opposing beams in the LHC do not always collide head-on. The beam-beam effects cause a small, unavoidable separation under nominal operational conditions. During the beam adjustment and when the beams are brought into collision the beams are separated by a significant fraction of the beam size. A result of small beam separation can be the excitation of coherent dipole oscillations or an emittance increase. These two effects are studied using a strong-strong multi particle simulation model. The aim is to identify possible limitations and to find procedures which minimise possible detrimental effects.
Advances in Large-Scale Computations of Multi-Particle Beam Dynamics
The design and operation of modern particle accelerators is making ever-increasing demands on computer simulations of beam dynamics. We describe recent large-scale computations of collective effects utilizing high-performance computing to address the problems posed by the leading accelerators in operation today and upgrades to these accelerators and facilities planned for tomorrow. We discuss electron cloud, beam-beam and space charge simulations of the Fermilab Tevatron, Main Injector and Debuncher, as well as CERN's LHC, SPS and proposed PS2. In addition, because accelerator science serves the larger purpose of basic physics research, we also describe some of the physics topics that will become accessible due to the upgrades to accelerators we simulate.
Of Instabilities in the LHC Due Tomissing Head-On Beam-Beam Interactions
2013
We report the observation of coherent instabilities on individual bunches out of the LHC bunch train. These instabilities occurred spontaneously after several hours of stable beam while in the other cases they were related to the application of a small transverse beam separation during a luminosity optimization. Only few bunches were affected, depending on their collision schemes and following various tests we interpret these instabilities as a sudden loss of Landau damping when the tune spread from the beambeam interaction becomes insufficient.
Longitudinal Beam Dynamics and Coherent Synchrotron Radiation at cSTART
2021
The compact STorage ring for Accelerator Research and Technology (cSTART) project aims to store electron bunches of LWFA-like beams in a very large momentum acceptance storage ring. The project will be realized at the Karlsruhe Institute of Technology (KIT, Germany). Initially, the Ferninfrarot Linac- Und Test-Experiment (FLUTE), a source of ultra-short bunches, will serve as an injector for cSTART to benchmark and emulate laser-wakefield accelerator-like beams. In a second stage a laser-plasma accelerator will be used as an injector, which is being developed as part of the ATHENA project in collaboration with DESY and Helmholtz Institute Jena (HIJ). With an energy of 50 MeV and damping times of several seconds, the electron beam does not reach equilibrium emittance. Furthermore, the critical frequency of synchrotron radiation is 50 THz and in the same order as the bunch spectrum, which implies that the entire bunch radiates coherently. We perform longitudinal particle tracking simu...
Observations of Beam-Beam Effects at the LHC
arXiv (Cornell University), 2014
This paper introduces a list of observations related to the beam-beam interaction that were collected over the first years of LHC proton physics operation (2010-12). Beambeam related effects not only have been extensively observed and recorded, but have also shaped the operation of the LHC for high-intensity proton running in a number of ways: the construction of the filling scheme, the choice of luminosity levelling techniques, measures to mitigate instabilities, and the choice of settings for improving performance (e.g. to reduce losses), among others.