A new method for the measurement of low outgassing rate of materials based on torsion balance

Outgassing, defined as the continuous release of gas molecules from the surface of materials, is a common issue in vacuum research. Although the quantity of desorbed molecules is generally small, its impact becomes significant in high-precision scientific missions, such as the space-borne gravitational-wave (GW) detection. The detailed evaluation of this noise source relies on the outgassing rate for materials applied, while the current measurement methods all show insufficient precision, lacking practicability in measuring small-sized samples. In this paper, a new outgassing rate measurement method based on high-precision torsion balance is proposed. Unlike the general methods that rely on monitoring pressure variation, this approach detects the extremely weak force exerted by the released gas molecules. Verified through principle experiments, the detection limit for the present apparatus can be evaluated to be better than 1.9 × 10-12 Pa m3/s in water molecule equivalent at room temperature. The typical test results show a measurement uncertainty of less than 4%. In addition, the apparatus can monitor the fluctuation of outgassing rate with a noise level of 3 × 10-11 Pa m3/s/Hz in the mHz frequency band. In conclusion, this first-time proposed method is especially valuable for studying the outgassing rate of small-sized samples. It can be applied in the monitor of outgassing of the inertial sensor used in the space-borne GW detection during the on-ground testing and in other high vacuum demanded scientific missions.