Total pressure measurements in the Elettra storage ring according to the performance of the sputter-ion pumps

Abstract

In the storage ring and the transfer line of the Elettra synchrotron radiation facility the total pressure measurements are not only performed by cold cathode gauges which, however, suffer from known start up problems, but also by utilising the electrical discharges of sputter ion pumps (SIPs). The throughput Q of a SIP is proportional to the ion current I and the real current is considered constant at each applied voltage. In this case the current I [A] absorbed in the pump is proportional to the pressure P [mbar], I=K P/sup n/, where K and n are constants depending on the nominal pumping speed and have to be specified for each applied voltage. The system developed in our laboratory allows to supply up to 8 SIPs using one power supply. The absorbed current for each pump can be measured and an automatic current to pressure conversion made. This system was calibrated in the UHV pressure range for 45, 120, 400 and 900 l/s SIP's, and was succesfully tested during the commissioning of Elettra.