Study on coupling and coupling correction for the SOLEIL ring

One main figure of merit of 3rd generation synchrotron radiation sources is the brilliance of the emitted light. In the presence of magnetic errors, this brilliance is spoiled when the coupling factor, defined as the ratio between the vertical and horizontal emittances, is enlarged. To reach the SOLEIL target coupling of 10−2 and to possibly go further down, we look for a correction strategy aimed at correcting the coupling at the error sources themselves. For this, we study the correction procedure which consists in minimising the vertical dispersion (Dz) together with the Cross-Talk Closed Orbits (CTCOs) i. e. the non-zero vertical closed orbits created by horizontal dipolar correctors. We show that this procedure is quite effective provided we use a sufficient number of correctors, with judicious location. A detailed statistical study will indicate the values expected for SOLEIL coupling before and after correction: a coupling as low as some 10−4 can be numerically obtained in most error configurations. Furthermore, the relevance of the use of the CTCOs in any corrector distribution will be discussed, and a correction procedure will be given when there are less correctors than the minimum number required. Finally, we demonstrate that the coupling can be precisely controlled between its minimum value and full coupling.