LOW-IMPEDANCE VACUUM CHAMBERS

The impedance of vacuum chambers has for long been the subject of many theoretical and experimental investigations. After impedance issues h ave been properly addressed by accurate three dimensional wake field c omputations, beam dynamics simulations showed that the effects of impe dance of the vacuum chamber in e(+)e(-) storage rings can be very impo rtant for both single bunch and multibunch operation. Comparison with measured data have proven that the impedance can be predicted rather a ccurately.(1) We analyze here a method to suppress the impedance of pu mping slots in vacuum chambers by orders of magnitude by applying mode ls and numerical computations with MAFIA.(2) While basically simple, t he scheme of hidden slots is extremely efficient in suppressing both n arrow-band and broad-band impedances by orders of magnitude. This tech nique was first used in the design of the HERA electron ring vacuum ch amber components.(3) Although developed for e(+)e(-) accelerators, the same technique may be used to suppress the impedance in high current proton machines such as the LHC.