A method and apparatus for plasma modifying a workpiece such as a syringe barrel, cartridge barrel, vial, or blood tube is described. Plasma is provided within the lumen of the workpiece. The plasma is provided under conditions effective for plasma modification of a surface of the workpiece. A magnetic field is provided in at least a portion of the lumen. The magnetic field has an orientation and field strength effective to improve the uniformity of plasma modification of the interior surface of the generally cylindrical wall. A vessel made according to the process or using the apparatus described above. A pharmaceutical package comprising the syringe barrel or vial containing a pharmaceutical preparation, secured with a closure.