2020同步年報

Facility Status 097 A New-Type Standard Leak Element Using Femtosecond Laser Micromachining A vacuum device with a known artificial leak, herein called a standard leak element (SLE), is a useful tool that can serve to supply a reference gas flow for the calibration of vacuum instruments ( e.g ., ionization gauges, leak detectors and residual gas analyzers) and the measurement of pumping speeds for a vacuum pump or a vacuum system. Many studies have consequently been conducted to develop such devices. The NSRRC vacuum group has been collaborating with the ultrafast dynamics laboratory of the National Chiao Tung University to develop successfully a flange-type SLE ( Fig. 1 ); the new design can be compatible with an ultra-high vacuum environment to overcome the issues related to the use of an epoxy resin sealant in a SLE of other types ( i.e ., large rates of outgassing and low baking temperature < 120 o C). To measure the conductances of the SLE for various test gas species at varied inlet pressure, five non-condensable gases (H 2 , He, CH 4 , N 2 and CO 2 ) were introduced into a measurement chamber through the SLE and the measurement results show ( Fig. 2 ) the minimum conductance 2.54 × 10 -9 L s -1 for N 2 can be attained and its molecular flow regime can be extended from high vacuum up to 1000 mbar ( i.e ., the con- ductance in molecular flow C SLE is independent of inlet pressure P CDG and depends on only tem- perature, the molecular mass of a test gas and the geometric structure of the micro-hole). Figure 3 indicates a strong dependence of the conductance values on the inverse square root of the molecular mass for all these test gases, according to which one can readily calculate the conductance for any non-condensable gas once one conductance value of these gases is known. Fig. 1 : Manufacturing processes of a flange-type SLE: (a) preparation of a double-sided 16CF flange; (b) CNC (computer numerical control) milling to drill a blind hole on the flange, and (c) micro-hole drilling through the blind hole using femtosecond laser micromachining. [Reproduced from Ref. 2] Fig. 2 : Conductance of a SLE as a function of inlet pressure for various non-con- densable gases. Fig. 3 : Dependence of molecular flow conductance on the gas molecular mass.