Linear particle accelerator

Quantum mechanics

Beam (structure)

Engineering

Materials science

Computational physics

Particle accelerator

Nuclear physics

Energy (signal processing)

Computer science

Classical mechanics

Thermal emittance

Transverse plane

Beam emittance

Physics

Mathematics

Optics

Environmental science

Geometry

Interaction point

Structural engineering

Dispersion (optics)

Betatron

Acceleration

Line (geometry)

In high energy linear colliders the transverse beam emittance has to be preserved in order to achieve small interaction spots. Beams with trajectory offsets in cavities excite transverse wakefields which kick the tail of the beam leading to an undesired emittance growth. Here we will concentrate on the longitudinal wakefield creating an energy deviation /spl Delta/E/sub W/ within the beam. At high dispersion /spl eta/ the beam will be spread out corresponding to its initial (and/or correlated) energy spread /spl Delta/E/sub 0/ (or /spl Delta/E/sub rf/) and is therefore very sensitive to energy changes. The energy variation /spl Delta/E/sub W/ will cause a transverse emittance blow up in the high dispersion regions. The effect can be estimated by comparing the betatron size /spl sigmasub x/=/spl radicspl betaspl epsi/ with displacement /spl Delta/a=/spl etaspl Delta/E/sub WE. Some kicks and displacements will compensate each other along the beam line. Simulation results are presented showing how much is really compensated and the final emittance contribution of this effect for the SLC Ring-To-Linac transport line is given. To minimize it, any vacuum pipe irregularities, like bellows, diameter steps, collimators, etc. should be smoothed or avoided at higher dispersion areas.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transverse effects of longitudinal wakefields at high dispersion