A sputtering wind

A directional pressure probe extending from a capacitance manometer and rotatable over 360 deg of orientation was inserted at midlength near a high-rate magnetron sputtering source. Actuating the cathode at currents up to 12 A gave rise to a pressure difference between probe orientations facing toward and away from the source. The greater pressure was observed when facing away. The difference was as large as 10% of the base pressure and varied systematically with the base pressure and the cathode current. It appears that energetic particles emanating from the source collide with the ambient gas, pumping it preferentially toward the ends of the cylindrical magnetron and driving opposed toroidal circulation cells that return the gas to the cathode at midlength. A freewheeling fanblade was installed and observed to rotate when the sputtering source was on. Blocking the direct incidence of condensible particles with a shutter caused the direction of rotation to reverse. This counter-rotation was in accord with the gas circulation model and confirmed the existence of a brisk ‘‘sputtering wind.’’