An apparatus for generating a plasma in the lumen of a small diameter tube includes a housing (12) having a diaphragm (18) which separates the housing into a first chamber (14) equipped with a gas inbleed (26) assembly and a second chamber (16) connected to a vacuum source. Parallel plate electrodes (58) in the first chamber are encased in a dielectric (42) which prevents substantially all plasma discharge external of a plasma zone between the electrodes. A conduit (64) maintains gas flow between the chambers. A bore (52) through the dielectric includes the plasma zone and receives the tube (54) to be plasma treated.
A method for treating the luminal wall of a plastic tube (54) includes positioning a tube in the plasma zone, evacuating the chambers, bleeding a gas into the chambers, and delivering radiofrequency power to the electrodes (58). A long tube may be drawn through the plasma zone, or the dielectric and electrodes may be moved past the tube.