Olivier Napoly

An interaction region for gamma–gamma and gamma–electron collisions at TESLA/SBLC

Abstract Linear colliders offer a unique opportunity to study γγ and γe interactions. Using the laser backscattering method one can obtain γγ, γe colliding beams with an energy and luminosity comparable to that in e + e − collisions. This work is part of the Conceptual Design of TESLA/SBLC linear colliders considering a second interaction region for γγ and γe collisions. We consider here possible physics in high-energy γγ, γe collisions, e→γ conversion, requirements to lasers, collision schemes, attainable luminosities, backgrounds, possible lasers, optics at the interaction region and other associated problems.

A generalized method for calculating wake potentials

Abstract We describe a generalized method to compute wake potentials created in axisymmetric structures. It relies on expressing the wake potentials, of any multipole order, as integrals over the e.m. fields along an arbitrary one-dimensional contour spanning the structure longitudinally. For perfectly conducting structures, the integration along the axis can then be replaced by choosing a contour beginning and ending on the beam tubes. Thus it generalizes the former method of calculating the wake potentials by integrating along a straight line at the beam tube radius. Its usefulness is illustrated with the computer code ABCI which permits calculation of wake potentials in structures extending to the inside of the beam tube radius, or having unequal beam tube radii at the two sides.

Progress on the CLIC final focus system

The final focus system has been adapted to the revised parameter list for CLIC (CERN Linear Collider). It is expected that lower emittances are obtainable in the damping rings and the blowup in the main linac can be contained to 25%. In that case the luminosity would no longer be limited by synchrotron radiation in the final quadrupoles, and a luminosity above 10/sup 33/ cm/sup -2/ s/sup -1/ could be reached for bunches colliding head on. However, finite crossing angles are required so the disrupted beam can pass through a special aperture in the first interaction region quadrupole. The reduction of luminosity due to this crossing angle and due to unavoidable misalignments has been studied as a function of bunch length with a particle tracking code. Two designs of quadrupoles are being evaluated.<<ETX>>