Vacuum system design for a 1.2 GeV electron storage ring with non-evaporable getter pumping

Abstract

We describe the design for the vacuum vessel and vacuum pumping system for a 1.2 GeV electron storage ring for light source applications. The hybrid vacuum vessel design consists of eight extruded aluminum (6063‐T4) dipole chambers curved to the ring radius of 2.93 m, with interconnecting stainless (304 L) steel straight vessel segments. The dipole chambers contain two 60 milliradian photon exit ports on the outer midplane, and an integral pumping chamber on the inner midplane which provides 500 1/s ⋅ m of active gas pumping with a circumferential array of a non‐evaporable getter (NEG) material. Ion pumping stations are distributed along the straight vacuum vessel segments to provide for pumping of CH4 and noble gases. The distributed pumping provided by the NEG offers a factor of five to ten times larger pumping speed in comparison to conventional designs based solely on the use of discrete or distributed ion pumps. Externally bonded cooling tubes on the dipole chambers offer a cost effective and fault tolerant means of removing the x‐ray heat load. Estimates of the conditioning time for the vacuum vessel are presented based on the recent photodesorption data from aluminum surfaces.