Study of ion pumps for operation in the low magnetic bending field of a large electron storage ring

The large amount of gas which is desorbed by the synchrotron radiation in high energy electron storage rings is commonly removed by linear sputter ion pumps operating in the magnetic bending field of the machine. To maintain the total synchrotron radiation power losses within acceptable limits, in spite of increases beam energy, the proposed Large Electron and Positron Storage Ring (LEP) will operate with a magnetic field swing between 0.02 and 0.12 Tesla. Diode ion pump models which work satisfactorily over this range of magnetic field are presented. The pumping speed for nitrogen has been measured as a fonction of the magnetic field. The dependence of pump performance on various factors such as anode voltage, cell diameter, perforated anode plates versus complete cylinders, bakeout and operational temperatures has been investigated. Comparison with recent semi-empirical formalism will be discussed