Self-consistent simulations of beam-beam interaction in future e + e - circular colliders including beamstrahlung and longitudinal coupling impedance

For the past generation {e}^{+}{e}^{\ensuremath{-}} storage ring colliders, we usually used natural bunch length or its impedance lengthened value in beam-beam simulations instead of considering the impedance directly. In the future colliders, such as FCC-ee and CEPC, the beam-beam interaction becomes essentially three dimensional. In order to increase the luminosity, the future accelerators will collide very intense beams of high energy with low emittances and small beta functions at the collision points exploiting the crab waist collision scheme with a large Piwinski angle. For these extreme parameters several new effects become important for the collider performance such as beamstrahlung, coherent X-Z instability, 3D flip-flop so that the longitudinal beam dynamics should be also treated in a self-consistent manner. In this paper we describe the numerical code for the self-consistent 3D beam-beam simulations including beamstrahlung and the longitudinal beam coupling impedance and study interplay of different effects arising in beam-beam collisions of the future colliders

Beam-beam effects in crab crossing and crab waist schemes

To boost up the luminosity performance in B factories, crab crossing and crab waist schemes are proposed. The crab crossing scheme compensates crossing angle, while the crab waist scheme compensates nonlinear terms induced by crossing angle with sextupole magnets. We discuss which nonlinear terms in the beam-beam map are enhanced by the crossing angle and which terms are compensated by the crab waist sextupole

Electron Cloud Instability in SuperKEKB Low Energy Ring

Abstract We study the issue of coherent instabilities due to electron clouds by numerical simulations for SuperKEKB. We first calculate electron cloud density by simulating the motions of the electrons emitted from the chamber wall. By introducing an ante-chamber we can reduce the number of eletrcons emitted from the chamber wall. We evaluate the relation of the electron density and the efficiency of the ante-chember. Next we study a perturbation to the beam motion (bunch by bunch wake field) and the growth rate of the coupled bunch instability. From those studies we estimate the effective value of quantum efficiency safe for avoiding coherent instabilities. Finally the threshold of the electron cloud density for the stability is estimated for SuperKEKB by single bunch numerical simulations

Simulations of the Electron Cloud Build Up and Instabilities for Various ILC Damping Ring Configurations

In the beam pipe of the positron damping ring of the International Linear Collider (ILC), an electron cloud may be first produced by photoelectrons and ionization of residual gases and then increased by the secondary emission process. This paper reports the assessment of electron cloud effects in a number of configuration options for the ILC baseline configuration. Careful estimates were made of the secondary electron yield (sometimes in the literature also referred as secondary emission yield SEY or {delta}, with a peak value {delta}{sub max}) threshold for electron cloud build-up, and the related single- and coupled-bunch instabilities, as a function of beam current and surface properties for a variety of optics designs. When the configuration for the ILC damping rings was chosen at the end of 2005, the results from these studies were important considerations. On the basis of the joint theoretical and experimental work, the baseline configuration currently specifies a pair of 6 km damping rings for the positron beam, to mitigate the effects of the electron cloud that could present difficulties in a single 6 km ring. However, since mitigation techniques are now estimated to be sufficiently mature, a reduced single 6-km circumference is presently under consideration so as to reduce costs

Beam-Beam Studies in LHC- Beam Loss and Bunch Shortening

In Hadron colliders, luminosity degrade various mechanism. Beam-beam related emittance growth is caused by resonances induced by crossing angle. Tune spread due to chromaticity enhances the resonances effect. A bunch shortening phenomenon related to beam-beam interaction has been observed in LHC. The bunch length has an anti-correlation with transverse emittance. This phenomenon has been studied using a weak-strong beam-beam simulation (BBWS code)

Study of Beam-beam Effects in FCC-he

Beam-beam effects of the ring-ring scheme of FCC-he and LHeC are being studied using weak-strong simulations. The beam-beam tune shift of the electron beam is one order larger than that of proton beam. The study of the electron motion under the beam-beam interaction is the main subject. Luminosity and equilibrium beam size and beam lifetime are analysed

Fundamental beam-beam limit from head-on interaction in the Large Hadron Collider

The beam-beam limit at hadron colliders manifests itself in the form of degraded luminosity lifetime and/or reduced beam lifetime. In particular, for increasing beam intensity, the nonlinear beam-beam force causes incoherent emittance growth, while the (linear) coupling force between the two colliding beams can result in coherent beam-beam instabilities. These phenomena may be enhanced (or suppressed) by lattice errors, external noise, and other perturbations. We investigate the luminosity degradation caused both by incoherent emittance growth and by coherent beam-beam instability. The resulting beam-beam limit for an ideal machine and the of question how it is affected by some of the aforementioned errors are discussed in theory and simulation