Resistive-wall impedances of a thin non-evaporable getter coating on a conductive chamber

Abstract

The resistive-wall impedances of a thin non-evaporable getter (NEG) with constant conductivity coating on a copper chamber are studied in both longitudinal and transverse directions. The copper chamber has a finite thickness and is surrounded by air. As the frequency increases, wake fields see mostly the air first and then the copper chamber next, and then finally the NEG coating. Both longitudinal and transverse impedances slowly undergo transitions from the resistive-wall impedances of the copper-only chamber to those of the NEG-only chamber over a 0.1-100 GHz frequency range. They start to deviate from the conventional impedance lines for the NEG-only chamber at ∼100 GHz. They increase first to ∼1 THz and then decrease rapidly as a function of the frequency. Numerical examples of the resistive-wall impedances are presented up to ∼100 THz using similar parameters to those of the SLS-II (Swiss Light Source) upgrade. We briefly discuss the characteristic of a loss factor for the chamber with NEG coating.