In recent years, the vacuum degree of SSC chamber hasn't been reached ideal value all along. In the condition of running two HIRFL-800 cryo-pumps, the pressure of vacuum system still kept in the level of 10-4 Pa. For this reason, the HIRFL national laboratory determined to transform SSC vacuum chamber. At first, we had to find the leak sources of the system, knowing the affection to the vacuum degree of the chamber. Water ingredient was detected very high in vacuum system by quadrupole mass spectrometer, it meant the big leaks being in the system. We used the pause time of accelerator to detect leak sources. After leak points were found and repaired, not only the pressures of the system were decreased, but also the cryo-pumps running efficiency was improved.
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