High Luminosity Issues for DAPhNE Upgrade

We give an overview of presentations and discussions during the Accelerator Working Group Session dedicated to High Luminosity Issues for a future upgrade of the Frascati e+e- Phi-Factory DAPhNE at the Workshop "e+e- in the 1-2 GeV range: Physics and Accelerator Prospects" held at Alghero (Italy) on 10-13 September 2003.Comment: Invited talk at the Workshop on e+e- in the 1-2 GeV range, Alghero, Italy, September 2003 (eConf c0309101

Aplication of Frequency Map Analysis to Beam-Beam Effects Study in Crab Waist Collision Scheme

We applied Frequency Map Analysis (FMA) - a method that is widely used to explore dynamics of Hamiltonian systems - to beam-beam effects study. The method turned out to be rather informative and illustrative in the case of a novel Crab Waist collision approach, when "crab" focusing of colliding beams results in significant suppression of betatron coupling resonances. Application of FMA provides visible information about all working resonances, their widths and locations in the planes of betatron tunes and betatron amplitudes, so the process of resonances suppression due to the beams crabbing is clearly seen.Comment: 11 pages, 10 figure

Study of collective effects in the CERN FCC-ee top-up booster

The CERN FCC-ee top-up booster synchrotron will accelerate electrons and positrons from an injection energy of 20 GeV up to an extraction energy between 45.6 GeV and 182.5 GeV depending on the operation mode. These accelerated beams will be used for the initial filling of the high-luminosity FCC-ee collider and for keeping the beam current constant over time using continuous top-up injection. Due to the high-intensities of the circulating beams, collective effects may represent a limitation in the top-up booster. In this work we present a first evaluation of the impedance model and the effects on beam dynamics. Methods to mitigate possible instabilities will be also discussed

Strong RF Focusing for Luminosity Increase

A luminosity of a circular collider can be increased by squeezing the bunch length at the interaction point (IP). A natural way to decrease the bunch length is to decrease the momentum compaction factor and/or to increase the RF voltage. However, in such a way we cannot obtain short bunches with high currents since wakefields prevent this due to the potential well distortion and the microwave instability. In present paper we propose to use a strong RF focusing (with high RF voltage and high momentum compaction factor) to obtain very short bunches at the IP with progressive bunch elongation towards the RF cavity. This allows placing the most important impedance generating elements near the RF cavity where the bunch is longest thus minimizing the effect of the wakefields.Comment: 6 page