the invention adds one or more surface contour to the bombarded area within ion columns to greatly reduce the likelihood that back sputtered material will reach the ion generating source . a number of different surface contours are disclosed including angled surfaces , surfaces defining cups to capture back sputtered material , pre - textured and forested surfaces . the different surfaces can be used in any combination . the reduction in back sputtered material reaching the ion source reduces the time to stability , greatly increases the working stability , and increases the lifespan of the source .