Local Transverse Coupling Control

The brightness of light produced at a point (s) in a light source is inversely proportional to ψ(s)f(β), where ψ(s) is the local coupling angle, f(β) is a function of the transverse beta-functions and n depends on photon diffraction effects and ranges from 1 to 2. As well, brightness is proportional to the circulating current, which, for a given lifetime, is proportional to the average vertical beam size and hence to the average coupling angle, ψav, over the entire lattice. At a given point, then, brightness is proportional to ψav/[ψ(s) f(β)]. Simulations performed on the Canadian Light Source (CLS) lattice indicate that it is possible to decrease the coupling locally resulting in enhancements of the local brightness by factors of 3 to 8. This is achieved with an array of independent skew quadrupoles. Corrections are applied using the Singular Value Decomposition (SVD) algorithm to adjust the coupling angle. A practical beam-coupling monitor as suggested by Teng has also beam demonstrated. Other techniques for controlling local coupling are also discussed. All techniques are well suited for global coupling control as well.