Calibration of extremely low leak rate by static expansion

A novel technique was developed to calibrate extremely low leak rate by static expansion. In the newly-developed calibration technique, the rising rate of He-ion current and calibration coefficient of quadrupole mass spectrometer were evaluated. Good repeatability was obtained in measuring the rising rate of He ion current, originated from an extremely low leak rate of the magnitude of 10-10 Pa·m3/s. Furthermore, a two-stage static expansion of a gas-mixture not only provides better calibration coefficient of the quadrupole mass spectrometer, but also bypasses the complicated expansion involved. The new technique was tested by calibrating a leak rate of 10-10 Pa·m3/s with satisfactory results. We suggest that with decreased volume of calibration chamber, the new technique may reduce the lower calibration limit down to 10 -13 Pa·m3/s.