Accommodation Pumping—A New Principle for Low Pressures

A new principle of vacuum pumping, termed accommodation pumping, has been tested experimentally. Two volumes at room temperature are joined by a passage, the walls of which are alternately atomically rough and atomically smooth. When alternate smooth-rough junctions are held at a temperature other than room temperature, a pumping action develops and gas is transferred from one volume to the other. Experimental parameters studied are: time, location of temperature transition, pressure, number of pumping stages, nature of gas, nature of surfaces, effect of preadsorbed layers, and temperatures. A simple theory is given which yields first order agreement with pumping performance.