For removal of disrupted beams at the ILC linear e+e- collider it is desirable to collide beams at some crossing angle. An especially large crossing angle, of about 25 mrad, is necessary for the photon collider, where disrupted beams are softer and wider than in the e+e- case. Some complications arise due to the solenoidal magnetic field of the detector. Radiation of particles in this field can increase the vertical beam size, leading to a loss of the luminosity. In addition, in the presence of a detector magnetic field the beam trajectories are not flat. Moreover, in the case of e-e- beams, the vertical collision angle is non-zero and larger than the beam diagonal angle sigma_y/sigma_z, and this should be corrected in some way. In this paper, possible solutions of these problems are considered. It is shown that at the ILC one can have the interaction region compatible both with e+e- and gamma-gamma, gamma-e modes of operation without loss of luminosity.
We develop theoretical expressions for the luminosity and beam-beam tune shifts in the presence of both a crossing angle and hourglass effects for the present and next generation of symmetric e$^+$-e$^-$ colliders. The theory is applied to the design of the Fermilab site filler Higgs factory and to the FCC-ee collider.
In this paper, we present the effects of linear transverse-longitudinal coupling on beam size at Interaction Point (IP) of a collider with local crab crossing scheme, when time dependent transverse deflection (crab kicks) and dispersive orbit intertwine near IP. The analytic propagation formula and the closed orbit form of the crab dispersion and momentum dispersion are derived. The non-zero momentum dispersion at crab cavities and the non-ideal phase from crab cavities to IP are detailed with the derived propagation formula to predict the beam size distortion at IP with or without the beam-be…
At this time, the design of the International Linear Collider (ILC) is optimized for e+e- collisions; the photon collider (gamma-gamma and gamma-electron) is considered as an option. Unexpected discoveries, such as the diphoton excess F(750 GeV) seen at the LHC, could strongly motivate the construction of a photon collider. In order to enable the gamma-gamma collision option, the ILC design should be compatible with it from the very beginning. In this paper, we discuss the problem of the beam crossing angle. In the ILC technical design, this angle is 14 mrad, which is just enough to provide en…
Crab crossing scheme is an essential collision scheme to achieve high luminosity for the future colliders with large crossing angles. However, when bunch length of one or both colliding beams is comparable with the wavelength of the crab cavity voltage, the nonlinear dependence of the crabbing kick may present a challenge to the beam dynamics of the colliding beams and impact the beam quality as well as the luminosity lifetime. In this paper, the results of nonlinear dynamics in the crab crossing scheme are presented, using both analytical and numerical studies. The result indicates that highe…
The ILC accelerator parameters and detector concepts are still under discussion in the world-wide community. As will be shown, the performance of the BeamCal, the calorimeter in the very forward area of the ILC detector, is very sensitive to the beam parameter and crossing angle choices. We propose here BeamCal designs for a small (0 or 2 mrad) and large (20 mrad) crossing angles and report about the veto performance study done. As illustration, the influence of several proposed beam parameter sets and crossing-angles on the signal to background ratio in the stau search is estimated for a part…
The ILC baseline consists of two interaction regions, one with a 20mrad crossing angle and the other with a 2mrad crossing angle. It is known that the outgoing beam losses in the final doublet and subsequent extraction line are larger in the 2mrad than in the 20mrad layout. In this work, we exploit NbTi and Nb$_3$Sn superconducting magnet technologies to redesign and optimise the final doublet, with the aim of providing satisfactory outgoing disrupted beam power losses in this region. We present three new final doublet layouts, specifically optimised for the 500 GeV and the 1 TeV machines.
The current status of the 2mrad crossing angle layout for the ILC is reviewed. The scheme developed in the UK and France is described and the performance discussed for a TeV machine. Secondly, the scheme developed at SLAC and BNL is then studied and modified for a TeV machine. We find that both schemes can handle the higher energy beam with modifications, and share many common features.
At the international linear collider, measurement of the beam profile at the interaction point is a key issue to achieve high luminosity. We report a simulation study on a new beam profile monitor, called the pair monitor, which uses the hit distribution of the electron-positron pairs generated at the interaction point. We obtained measurement accuracies of 5.1%, 10.0%, and 4.0% for the horizontal, vertical, and longitudinal beam size, respectively, for 50 bunch crossings.
A complete optics design for the 2mrad crossing angle interaction region and extraction line was presented at Snowmass 2005. Since this time, the design task force has been working on developing and improving the performance of the extraction line. The work has focused on optimising the final doublet parameters and on reducing the power losses resulting from the disrupted beam transport. In this paper, the most recent status of the 2mrad layout and the corresponding performance are presented.
In this paper we use current and proposed final doublet magnet technologies to reoptimise the interaction region of the International Linear Collider and reduce the power losses. The result is a set of three new final doublet layouts with improved beam transport properties. The effect of localised power deposition is considered, and its reduction using Tungsten liners.
Beam collisions with a crossing angle at the interaction point have been applied in high intensity colliders to reduce the effects of parasitic collisions which induce emittance growth and beam lifetime deterioration. The crossing angle causes the geometrical reduction of the luminosity. Crab cavity can be one of the most promising ways to compensate the crossing angle and to realize effective head-on collisions. Moreover, the crab crossing mitigates the synchro-betatron resonances due to the crossing angle. Crab cavity experiment in SPS is proposed for deciding on a full crab-cavity implement…
The Supper Proton-Proton Collider is a next-generation hadron collider that is now being designed. A baseline design aims for a peak luminosity of about 1*10^35 cm^-2 s^-1. The focus of this article is the effect of beam-beam interactions which are expected to strongly influence stability in the beams. We start with a discussion of a scheme to generate the crossing angles at the interaction points while also correcting the dispersion thus created. The optics constraints on the achievable \b{eta}* were studied. Weak-strong simulations were performed to study single particle dynamics via tune fo…
In DAFNE, the Frascati $e^+e^-$ 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…
A method proposed to preserve the electron beam polarization at the VEPP-4M collider during acceleration with crossing the integer (imperfection) spin resonance at energy E=1763 MeV has been successfully applied. It is based on full decompensation of the $ 0.6\times3.3$ Tesla$\times$meter integral of the KEDR detector longitudinal magnetic field due to the anti-solenoids 'switched-off'.
Current bearing wire compensators were successfully used in the 2005-2006 run of the DAΦNE collider to mitigate the detrimental effects of parasitic beam-beam interactions. A marked improvement of the positron beam lifetime was observed in machine operation with the KLOE detector. In view of the possible application of wire beam-beam compensators for the High Luminosity LHC upgrade, we revisit the DAΦNE experiments. We use an improved model of the accelerator with the goal to validate the modern simulation tools and provide valuable input for the LHC upgrade project.
We discuss a low energy $e^+e^-$ collider for production of the not yet observed ($μ^+μ^-$) bound system (dimuonium). Collider with large crossing angle for $e^+e^-$ beams intersection produces dimuonium with non-zero momentum, therefore, its decay point is shifted from the beam collision area providing effective suppression of the elastic $e^+e^-$ scattering background. The experimental constraints define subsequent collider specifications. We show preliminary layout of the accelerator and obtained main parameters. High luminosity in chosen beam energy range allows to study $π^\pm$ and $η$ -m…
A Super Proton-Proton Collider (SPPC) that aims to explore new physics beyond the standard model will be built in China. Here we focus on the impact of beam-beam interactions in the SPPC. Simulations show that with the current optics and nominal tunes, the dynamic aperture (DA) with all the beam-beam interactions is less than 6σ, the dominant cause being the long-range interactions. First, we show the results of a tune scan done to maximize the DA. Next, we discuss the compensation of the long-range interactions by increasing the crossing angle and also by using current carrying wires.
A formula of luminosity of asymmetric e+e- collider with coupled lattices is derived explicitly. The calculation shows how the tilted angle and aspect ratio of the beams affect the luminosity. Knowing the result of the calculation, we measure the tilted angle of the luminous region of the collision for PEP-II using two dimensional transverse scan of the luminosity. The method could be applied to correct the coupling at the collision point.
Physically speaking, the delta function like beam-beam nonlinear forces at interaction points (IPs) act as a sum of delta function nonlinear multipoles. By applying the general theory established in ref. 1, in this paper we investigate analytically the beam-beam interaction limited dynamic apertures and the corresponding beam lifetimes for both the round and the flat beams. Relations between the beam-beam limited beam lifetimes and the beam-beam tune shifts are established, which show clearly why experimentally one has always a maximum beam-beam tune shift, ξ_{y, max}, around 0.045 for e-^+e$^…
In future normal-conducting linear colliders, the beams will be delivered in short bursts with a length of the order of 100 ns. The pulses will be separated by several ms. In order to maintain high luminosity, feedback is necessary on a pulse-to-pulse basis. In addition, intra-pulse feedback that can correct beam positions and angles within one pulse seem technically feasible. The likely performances of different feedback options are simulated for the NLC (Next Linear Collider) and CLIC (Compact Linear Collider).
The design luminosity for the future linear colliders is very demanding and challenging. Beam-based feedback systems will be required to achieve the necessary beam-beam stability and steer the two beams into collision. In particular we have studied the luminosity performance improvement by intra-train beam-based feedback systems for position and angle corrections at the interaction point. We have set up a simulation model which introduces different machine imperfections and can be applied to both the International Linear Collider (ILC) and the Compact Linear Collider (CLIC).
Luminosity upgrade at the LHC collider using longitudinally flat bunches in combination with the large crossing angle (large Piwinski angle scheme) is being studied with renewed interest in recent years. By design, the total beam-beam tune shift at the LHC is less than 0.015 for two interaction points together. But the 2010-11 3.5 TeV collider operation and dedicated studies indicated that the beam-beam tune shift is >0.015 per interaction point. In view of this development we have revisited the requirements for the Large Piwinski Angle scheme at the LHC. In this paper we present a new set of …
We present a concept for control of the ion polarization, called a transparent spin method. The spin transparency is achieved by designing such a synchrotron structure that the net spin rotation angle in one particle turn is zero. The polarization direction of any ions including deuterons can be efficiently controlled using weak quasi-static fields. These fields allow for dynamic adjustment of the polarization direction during an experiment. The main features of the Transparent Spin method are illustrated in a figure-8 collider. The results are relevant to the Electron-Ion Collider considered …
The idea of plasma suppression of beam-beam effects at muon colliders is discussed. It is shown that one should take into account collisions in the plasma that were ignored before. Rough estimates show that this effect leads to a fast ``recovery'' of the beam magnetic field. For beam parameters characteristic for muon colliders the suppression of the magnetic component of the beam field (1/2 of the total force) is almost absent. It is also shown that the presence of the dense plasma (Li jet) at the interaction point leads to enormous hadronic background (due to photo-nuclear reactions) in the …
