Cavity BPM Design, Simulations and Testing for the FERMI@Elettra Project

The cav­i­ty Beam Po­si­tion Mon­i­tor (BPM) is a fun­da­men­tal beam di­ag­nos­tic in­stru­ment for a seed­ed FEL, like FERMI@​Elettra.​ It al­lows the mea­sure­ments of the elec­tron beam tra­jec­to­ry in a non-de­struc­tive way and with sub-mi­cron res­o­lu­tion. The high res­o­lu­tion cav­i­ty BPM re­lies on the ex­ci­ta­tion of the dipole mode that is orig­i­nat­ed when the bunch pass­es off axis in the cav­i­ty. In this paper we pre­sent the pro­to­type of cav­i­ty BPM de­vel­oped for the FERMI@​Elettra fa­cil­i­ty. The RF pa­ram­e­ters of the cav­i­ties have been de­ter­mined by means of An­soft HFSS; while using the CST Par­ti­cle Stu­dio the level of the out­put sig­nals from the cav­i­ties have been also es­ti­mat­ed. Fur­ther­more, the de­sign of the RF fron­tend for the ac­qui­si­tion and con­di­tion­ing of the sig­nals from the BPM cav­i­ties is pre­sent­ed as well. The pro­to­type has been suc­ces­ful­ly in­stalled in the FERMI Linac dur­ing the last com­mis­sion­ing phase and pre­lim­i­nary re­sults with the elec­tron beam are also pre­sent­ed.