Longitudinal broadband impedance of the Aladdin vacuum chamber and new dipole chamber design

Abstract

An estimate of the longitudinal broadband impedance is obtained by summing estimated impedance contributions from the radiofrequency (RF) cavities, bellows, beam position monitors, Q electrode, vacuum chamber transitions, dipole chambers, pumping holes and slots, kickers, flanges, sector valves, resistive walls and space charge. The estimated total reduced impedance is |Zn/n| = 11.5 Ω. The RF cavities are estimated to contribute 5.8 Ω to the reduced impedance |Zn/n|, while the vacuum chamber is estimated to contribute 5.7 Ω. The vacuum chamber impedance of 5.7 Ω is expected to excite the microwave instability. If the dipole vacuum chambers are replaced by a design with an antechamber connected by a slot of height 24 mm, and the attached large formed bellows are effectively shielded (or shortened), the estimated ring impedance is decreased by 0.5 Ω. This impedance reduction may improve performance of the standard low-emittance lattice at high ring currents, where increased beam dimensions attributed to the microwave instability are observed.