Local transverse coupling control

The brightness of light produced at a point (s) in a light source is inversely proportional to ψⁿ(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, ψ_av, over the entire lattice. At a given point, then, brightness is proportional to ψ_av/[ψⁿ(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 (1997) has also beam demonstrated. Other techniques for controlling local coupling are also discussed. All techniques are well suited for global coupling control as well