Notes about collision monochromatization in e+e−e^+e^- colliders

The manuscript describes several monochromatization schemes starting from A.~Renieri \cite{ref:Renieri} proposal for head-on collisions based on correlation between particles transverse position and energy deviation. We briefly explain initial proposal and expand it for crossing angle collisions. Then we discuss new monochromatization scheme for crossing angle collisions based on correlation between particles longitudinal position and energy deviation

Beam-beam effects investigation and parameters optimization for a circular e+e- collider TLEP to study the Higgs boson

Several proposals exist for future circular electron-positron colliders designed for precise measurements of the Higgs boson characteristics and electroweak processes. At very high energies, synchrotron radiation of the particles in a strong electromagnetic field of the oncoming bunch (beamstrahlung) becomes extremely important, because of degradation of the beam lifetime and luminosity. We present theoretical calculations of beamstrahlung (including the beam lifetime reduction and the energy spread increase) which are benchmarked against quasi strong-strong computer simulation. Calculation results are used to optimize TLEP project (CERN).Comment: 17 pages, 2 tables, 9 figure

Dynamic aperture limitation in e+e−e^+e^- colliders due to synchrotron radiation in quadrupoles

In a lepton storage ring of very high energy (e.g. in the $e^+e^-$ Higgs factory) synchrotron radiation from quadrupoles constrains transverse dynamic aperture even in the absence of any magnetic nonlinearities. This was observed in tracking for LEP and the Future Circular $e^+e^-$ Collider (FCC-ee). Here we describe a new mechanism of instability created by modulation of the particle energy at the double betatron frequency by synchrotron radiation in the quadrupoles. Energy modulation varies transverse focusing strength at the same frequency and creates a parametric resonance of the betatron oscillations with unusual properties. It occurs at arbitrary betatron frequency (the resonant detuning is always zero) and the magnitude of the parameter modulation of the betatron oscillation (strength of the resonance driving term) depends on the oscillation amplitude. Equilibrium between the radiation damping and the resonant excitation gives the boundary of the stable motion. Starting from 6d equations of motion we derive and solve the relevant differential equation describing the resonance, and show good agreement between analytical results and numerical simulation

The FCC-ee Interaction Region Magnet Design

The design of the region close to the interaction point of the FCC-ee experiments is especially challenging. The beams collide at an angle (+-15 mrad) in the high-field region of the detector solenoid. Moreover, the very low vertical beta_y* of the machine necessitates that the final focusing quadrupoles have a distance from the IP (L*) of around 2 m and therefore are inside the main detector solenoid. The beams should be screened from the effect of the detector magnetic field, and the emittance blow-up due to vertical dispersion in the interaction region should be minimized, while leaving enough space for detector components. Crosstalk between the two final focus quadrupoles, only about 6 cm apart at the tip, should also be minimized.Comment: Poster presented at IPAC16, May 8-13, Busan, Kore

Status and Challenges for FCC-ee

We report the design status and beam dynamics challenges for the electron-positron branch of the Future Circular Collider (FCC) study, as of August 2015. After recalling motivation and physics requirements for the FCC-ee, we briefly discuss configurations and parameters, collider layout, the superconducting RF system, possible staging scenarios, final-focus optics, interaction-region (IR) issues, machine detector interface and IR synchrotron radiation, dynamic aperture, beam-beam effects, top-up injection, mono-chromatization option, impedances, instabilities, energy calibration and polarization, and SuperKEKB as a key demonstrator, before presenting conclusions and outlook.Comment: Combination of two articles invited for the ICFA Beam Dynamics Newsletter, September 2015 issu