Possible Beam-beam and Levelling Scenarios for HL-LHC (original) (raw)
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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.
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.
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).
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.
The beam-beam interaction of finite length bunches in hadron colliders
2000
The influence of finite bunch lengths on the dynamics of head-on beam-beam interactions is studied analytically and by simulation. Compared to infinitesimally short bunches, the resonance widths of bunches in the Tevatron are an order of magnitude smaller. With finite length bunches we find that the strengths of beam-beam effects oscillate with decreasing amplitude as a function of the bunch length. The results suggest that it may be possible to increase the integrated luminosity delivered by a collider with a careful choice of bunch length. 29.20.Dh, 29.27.Bd,
Modelling and measurements of bunch profiles at the LHC
Journal of Physics: Conference Series, 2017
The bunch profiles in the LHC are often observed to be non-Gaussian, both at Flat Bottom (FB) and Flat Top (FT) energies. Especially at FT, an evolution of the tail population in time is observed. In this respect, the Monte-Carlo Software for IBS and Radiation effects (SIRE) is used to track different types of beam distributions. The impact of the distribution shape on the evolution of bunch characteristics is studied. The results are compared with observations from the LHC Run 2 data.
Simulations of Coherent Beam-Beam Modes at the LHC
2000
The transverse coherent oscillations of the two colliding LHC proton beams are studied via multi-particle tracking, using the beam-beam force of a Gaussian distribution with variable barycenters and rms sizes. In addition to head-on collisions, our simulation optionally includes the effect of long-range collisions and an external impedance. Simulation results are the coherent and incoherent oscillation frequencies, the emittance growth
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2016
At the LHC flat bottom the interplay between a series of effects (i.e. intrabeam scattering, longitudinal beam manipulations, non-linearities of the machine, etc.) can lead to an increase of the tails’ population of the beam distributions, which may become non-Gaussian. This paper presents observations of the evolution of particle distributions in the LHC flat bottom. Novel distribution functions are employed to represent the beam profiles, and used as a guideline for generalising emittance growth rate estimations due to IBS. Finally, an attempt is made to benchmark an IBS Monte-Carlo simulation code, able to track 3D particle distributions, with the measured beam profile evolutions.
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.