fThe optimal wire angles of inclination for maximum recovery of deuterium, maximum production rate and minimum column height in a concentric-tube thermal diffusion column operated with transverse sampling streams and inserted in annulus with a wire spiral for the improvement in recovery of deuterium. Considerable improvement in performance is obtainable if the wired column is operated at the optimal wire angles of inclination, instead of operating without wire spiral, so that the convection strength can be properly reduced and controlled, resulting in suppressing the undesirable remixing effect while still preserving the desirable cascading effect.