Optimization of the e - e - Option for the ILC M. Alabau Pons, LAL, Orsay and IFIC, Valencia

1. Optimization of the e-e- Option for the ILC M. Alabau Pons, LAL, Orsay and IFIC, Valencia R. Appleby, Cockcroft Institute and the University of Manchester P. Bambade, O. Dadoun, LAL, Orsay A. Faus-Golfe, IFIC, Valencia The e-e- running mode is one of the interesting physics options for the International Linear Collider (ILC). Beam-beam effects reduce the luminosity for the e-e- collisions. The dependence of the luminosity and deflection angles with the vertical transverse offset for different beam sizes has been analyzed to optimize performances for the e-e- mode, taking into account the requirements of the beam-beam deflection intra-train feedback system. A first study of the implications for the final focus and extraction line optics is also presented. Optics studies for the 20 mrad crossing-angle geometry Beam-beam effects e-e- collision anti-pinch effect Final focus e-e- Luminosity: ~20 of the e+e- drops rapidly with the vertical offset Quadrupoles upstream of the chromatic correction ssection and sextupoles have been refitted to obtain the new ß-fuctions at the IP for the alternative beam parameters. steeper deflection curve Final focus optics for the parameter set 2 Optical bandwidth for the different e-e- sets of parameters The distribution of particles at the entrance of the Final focus is created with PLACET for different average momentum offsets. The beam is then tracked with MAD8 and used as an input for GUINEA-PIG to compute the luminosity. (Results for nominal ILC parameters [1] at 500 GeV cms) Feedback simulation Extraction Line Power losses along the extraction line for the parameter set 2 for e-e- are smaller than for the high luminosity parameters for e+e- A simplified simulation of the beam-beam based feedback [2] has been carried out, for different initial train offsets and different jitter bunch-to-bunch, for e+e- and e-e- collisions with nominal parameters: ß-functions for the disrupted outgoing beam for the parameters set 2 Average train luminosity almost independent of the initial offset High Luminosity e+e- Parameters 2 e-e- because of greater sensitivity of e-e- collision e-e- luminosity loss a factor 2 greater for the same assumption on jitter alternative beam parameters: Sets of alternative beam parameters for the e-e- option with smaller disruption have been derived by varying the beam sizes, in order to maximize the luminosity by limiting beamstrahlung energy loss to 5%. Optics studies for the 2 mrad crossing-angle geometry In the 2 mrad crossing-angle geometry the spent beam is transported off-axis through the last defocussing quadrupole which produces a kick used to extract the spent beam. For the e-e- option it is necessary to reverse the signs of the final doublet, while keeping at least the strength of the last quadrupole to maintain the extraction scheme. A first attempt in this direction [3] indicated that this was feasible, but large ßy-value had to be used at the IP to keep reasonable collimation depth. This resulted in about a factor 2 lower peak luminosity. Improvements with half bunch lengths are also been investigated, for example, ßx/y=10/3 mm. In this case, more acceptable overall performance may hopefully be obtained. More work to improve the performance is going on. Feedback simulation for different jitter bunch-to-bunch: Acceptance of the detector (one side) Average train luminosity versus r.m.s. vertical offset difference between the beams • References • D. Schulte, “Beam-Beam Simulations of the Proposed ILC Parameters”, EUROTeV-Memo-2005-004-1. • G. White, N. Walker, D. Schulte, “An Example of Integrated Simulations- A LINAC to IP Simulation of the TDR TESLA Accelerator”, CARE/ELAN Document-2004-013. • A. Seryi, “Running 2mrad IR in the e-e mode: BDS constraints”, presented at Snowmass, August 2005. The alternative parameters have increased luminosity compared to the obtained for the nominal case for e-e-