A dedicated synchrotron radiation source, SORTEC SOR ring, was built and started its operation in 1989. The vacuum performance that is responsible for the fast startup and long beam lifetime of the ring is evaluated by comparing the measured pressure and beam lifetime with a simulated pressure profile. When 30% is assumed as an effective pumping speed of nominal value, the outgassing yield of q
0=5·10
-13 (Torr·l/s/cm
2) and effective photodesorption coefficient of η
eff= 1.5·10
-6 (molec/ph) are obtained at an integrated beam dose of 250 (A·h) thereby demonstrating the cleanliness of our vacuum duct. By choosing the optimum operating point, in addition to the ion clearing, a beam lifetime of over 50 hrs at 200 mA beam current has been achieved after a year of machine commissionings.
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