Operation of the PF ring vacuum system without an in situ bake-out

The vacuum system of the PF ring was commissioned without an in situ bake-out after its upgrading reconstruction in which a great number of vacuum beam ducts were replaced by new or improved ones. The degassing of the ring was decreased suf®ciently by synchrotron-radiation irradiation as expected from previous experiments. The system was successfully commissioned and the required pressure was achieved within a reasonable short period. # 2001 Elsevier Science B.V. All rights reserved.