Dispenser cathode with emitting surface parallel to ion flow

A dispenser cathode for use in a gas filled tube as an electron emitting surface with said cathode fabricated from a porous refractory metal interspersed with an electron emitting material, with said cathode when in operation subjected to ion back bombardment which undesirably can deplete said electron emitting material from said surface, the improvement herewith comprising:

• at least one aperture located on said emitting surface and characterized in having steep vertical walls separated one from the other by a given distance such that said steep vertical walls of said at least one aperture extend to a specified depth not to exceed the thickness of said cathode with respect to said given distance whereby said at least one aperture does not pass through said cathode to enable said cathode to emit electrons when heated with said steep vertical walls operating to cause bombarding ions which impinge upon said wall to cause emitting material to deposit on the opposite wall.