PERFORMANCE OF INSERTION DEVICE VACUUM CHAMBERS AT ELETTRA

Ten long straight vacuum chambers for insertion devices (ID) are currently installed at ELETTRA. Four different types are employed: a) four stainless steel (SS) vacuum chambers with a rectangular cross section 80 mm x (17-20) mm, pumped by two central 120 l/s sputter-ion pumps connected to an antechamber; b) one pump free SS vacuum chamber with an elliptical cross section of 82 mm x 14.8 mm; c) four pump free extruded aluminum vacuum chambers with an elliptical cross section of 81 mm x 14 mm; d) one pump free extruded aluminum vacuum chamber of the same cross section, coated with a low temperature activation NEG. Results of standard laboratory vacuum tests will be discussed. Vacuum measurements during commissioning, such as dynamic pressure and Bremsstrahlung (BS) radiation, are also reported. The lifetime variation due to the reduction of the total pressure for all types of ID chambers will be compared. 1 TYPES OF ID VACUUM CHAMBERS The ID chamber is a low conductance vacuum system. During machine operation its inner surface is exposed to an intense flux of synchrotron radiation. Consequently the local pressure rises; above a certain threshold other than reducing the beam lifetime, an unacceptable level of gas bremsstrahlung is exceeded. Besides the mechanical requirements, the design of an efficient ID vacuum chamber should take into account at least the following aspects: 1) the effective pumping speed should be as high as possible (this necessity is in contrast with the required small cross section of the chamber), 2) the outgassing rate should be low; materials and cleaning procedures have to be chosen carefully, 3) the photon stimulated desorption should be as low as possible. The ELETTRA storage ring (SR) contains twelve long straight sections: ten are currently equipped with ID’s (see Tab.1), one is reserved for future special components, and the last one is used for injection. Each ID chamber is connected to the SR by means of two vacuum vessels, which joint the rhomboidal cross section of the SR to the elliptical or rectangular internal shape of the ID chamber. Each of these vessel hosts a 120 l/s sputter-ion pump (SIP) and an inverted magnetron gaug