An Isochronicity-Tunable Achromat Module

This note provides closed form expressions (in the thin lens approximation) for the quadrupole strengths required to tune the R56 parameter of the isochronous module based on three identical dipoles [2] and lists the eight sets of possible ranges for the three lengths of the drift spaces separating the magnetic components. Thus it permits the design of an insertion satisfying precise geometric constraints as in the future CLIC test facility CTF3 and which is able to compress or stretch longitudinally the beam according to the settings of the quadrupoles. An application to a CTF3 transfer line is also shown.