Longitudinal impedance and coherent synchrotron radiation models for ThomX storage ring

This article deals with the design of an impedance model (including geometric, resistive wall and coherent synchrotron radiation (CSR) wakefields) for ThomX, a 50 MeV electron storage ring designed to work in pulsed mode. The beam dynamics is very different from usual damped storage rings and is strongly dominated by collective effects. The geometric and resistive wall impedance model is obtained using simulation or analytical modelling of the individual elements and is checked using wire measurements on prototypes. The CSR is simulated in a rectangular vacuum chamber to take into account transient effects and resonances. From these models, two distinct regimes of beam dynamics stand out, driven respectively by the CSR and by the geometric impedance.