A cold atomic hydrogen beam source has been built and tested at BNL. The flow channel of the source, consisting of a discharge tube, a constricting nozzle, a thermal transition section, and an accommodator, was designed to operate in the laminar flow range. A novel feature of this source is a 0.3‐mm gap between the transition Teflon tube which guides the flow and an accommodator which cools the flowing gas; across this gap the wall temperature may step from 100 K in the Teflon to 3 K in the accommodator. A record pulsed H° beam flux of 9.4×1018H° sr−1 s−1was obtained at an accommodator temperature of 5.8 K. The gas dynamic analysis of the system is in excellent agreement with the experimental results.