Calculation and Analysis of Helium-permeation-induced Frequency Drift of the Rubidium Atomic Clock

Due to the collision-shift effect, helium permeation into the vapor cell causes a time-dependent frequency drift in rubidium atomic clock. To quantify this shift, a cylindrical vapor cell with dimensions of 1.8 cm in diameter, 1.6 cm in height, and 1 mm in thickness, operating at a temperature of 65 ℃, is selected for analysis. Numerical methods are employed to simulate the temporal variation of helium gas pressure within atomic vapor cells composed of Pyrex (Corning 7740) and low helium-permeable aluminosilicate (Corning 1720). The results of the calculations indicate that for Pyrex vapor cells, after 12 years of operation, the drift rate attributable to helium permeation decreases to less than 1.0×10-14/day. In contrast, the frequency drift rate due to helium permeation in aluminosilicate vapor cell rubidium atomical clocks remains below 3.0×10-17/day throughout their operational lifetime, rendering its contribution to the drift rate negligible. This computational approach is also applicable to the investigation of the permeation processes of other gaseous species in various glass materials.