Uniformity correction for large area electron source

An electron emission apparatus, comprising:

• (a) a vacuum chamber;
• (b) a large surface area cathode in the vacuum chamber;
• (c) means for applying a negative voltage to the cathode in an amount sufficient to drive electrons toward a target in the vacuum chamber;
• (d) an anode spaced apart from the cathode and positioned between the cathode and the target;
• said anode comprising an electrically conductive grid having an array of spaced apart apertures therethrough extending from a center of the grid to an edge of the grid;
• said apertures having progressively increasing area from the center of the grid to the edge of the grid ,and said grid having a progressively decreasing thickness from a center of a grid to an edge of the grid ;
• and
• (e) means for applying a voltage to the anode which is positive relative to the voltage applied to the cathode;
• and
• (f) means for generating electrons between the cathode and the anode.

A charged particle emission apparatus, comprising:

• (a) a vacuum chamber;
• (b) a first electrode capable of directing charged particles in the vacuum chamber;
• (c) means for applying a voltage to the cathode and causing the first electrode to direct charged particles toward a target in the vacuum chamber;
• (d) a second electrode spaced apart from the first electrode and positioned between the first electrode and the target;
• said second electrode comprising an electrically conductive grid having an array of spaced apart apertures therethrough extending from a center of the grid to an edge of the grid;
• said apertures having progressively increasing areas from the center of the grid to the edge of the grid, and said grid having a progressively decreasing thickness from a center of a grid to an edge of the grid;
• and
• (e) means for applying a voltage to the second electrode which attracts the charged particles directed by the first electrode.

A method for producing a highly uniform electron beam emission, comprising:

• (a) applying a negative voltage to a large-area cathode positioned in a vacuum chamber, to direct electrons in the vacuum chamber toward a target in the vacuum chamber;
• (b) applying a voltage to an anode spaced apart from the cathode and positioned between the cathode and the target, which voltage is positive relative to the voltage applied to the cathode;
• said anode comprising an electrically conductive grid having an array of spaced apart apertures therethrough extending from a center of the grid to an edge of the grid;
• said anode having one or both of (i) and (ii):
• (i) apertures having progressively increasing area from the center of the grid to the edge of the grid;
• (ii) a progressively decreasing thickness from a center of the grid to an edge of the grid.

A method for producing a highly uniform charged particle emission comprising:

• (a) applying a voltage to a large-area cathode positioned in a vacuum chamber and causing the first electrode to direct charged particles toward a target in the vacuum chamber;
• (b) applying a voltage to a second electrode spaced apart from the first electrode and positioned between the first electrode and the target;
• which voltage attracts the charged particles directed by the first electrode;
• said second electrode comprising an electrically conductive grid having an array of spaced apart apertures therethrough extending from a center of the grid to an edge of the grid;
• said second electrode having one or both of (i) and (ii):
• (i) apertures having progressively increasing area from the center of the grid to the edge of the grid;
• (ii) a progressively decreasing thickness from a center of the grid to an edge of the grid.