Surface conditioning of synchrotron radiation source to improve beam lifetime

Surface cleanliness is of prime importance to achieve the desirable vacuum condition for long beam lifetime in all synchrotron radiation sources. The Photon Factory at KEK resolved the severe gas load from synchrotron radiation by in-situ Ar glow discharging the whole storage ring. Sufficient experience had been gained in the past two years operation on the synchrotron radiation source, especially on the VUV ring of the National Synchrotron Light Source (NSLS), to allow the authors to decide to glow discharge the VUV ring. In hoping to obtain higher circulating current and to reveal the cause of lifetime limitation, a better understanding of the beam loss mechanism is needed. Photodesorption is the major gas load in all existing electron (positron) storage rings. It is generally believed that these photodesorbed species (neutral and charged) provide the major loss mechanism to lessen the beam lifetime. The interaction of these species to the beam give rise to the various loss mechanisms, such as multiple Coulomb scattering, single scattering, bremsstrahlung and ion trapping. All these mechanisms has been under intense study at NSLS. This report only describes the result of surface condition and beam lifetime