Abstract: The vacuum leak detection is an important technology to obtain high vacuum in the drift tube linear accelerator (DTL). The quadrupole mass spectrometer is an important tool for analyzing the components of the residual gas in the vacuum system, and can also be used as a means of leak detection. In this paper, the DTL1^# cavity was detected by two means of helium mass spectrometer leak detector and quadrupole mass spectrometer. When the coil of the 12^# drift tube was applied current, the pressure, leakage rate and residual gas composition of the cavity were all changed, and the spectral peak of water increased most significantly. So there's something wrong with 12^# drift tube. The cavity quickly obtained the high vacuum of 10^-6 Pa by proper treatment, which met the requirements of the linear accelerator for vacuum system.

Key words: leak detection, drift tube, mass spectrometer leak detection, residual gas analysis