Ion mobility measurements and thermal transpiration effects in helium gas at 4.3 K

The thermal transpiration effect, which means a significant pressure difference between the two ends of a pipe due to a large temperature difference, has been discussed in ion mobility measurements in helium gas at 4.3 K. A modified Takaishi–Sensui’s empirical formula for the pressure correction is obtained from the experimental results. We propose to use this formula instead of the original Takaishi–Sensui equation for helium gas. By using the new formula, the reduced mobilities of He+4 and Ar+40 ions in He4 gas have been obtained with the measurements of drift velocities at the gas temperature of 4.3 K and comparisons have been made with the recent theoretical calculations by Dickinson et al. [J. Phys. B: At. Mol. Opt. Phys. 32, 4919 (1999)] and Viehland et al., [J. Chem. Phys. 105, 11143 (1996)], respectively, which show fairly good agreements with the experimental results.