Abstract A high power electron beam machine for operating on a workpiece is disclosed in which the beam focus is automatically maintained constant without the necessity of lens current variation regardless of changes in beam current. The electron gun assembly for the machine consists of a Rogowski gun having a square ribbon filament recessed from an enlarged filament aperture, and a pin type anode with a reduced height and an increased gap from the bias electrode. The electron gun produces a stationary image or apparent source of electrons even though the beam current or the high voltage operating level of the electron gun is varied. Increased life of the ribbon filament is obtained by using a ribbon filament consistng of tungsten with 3 percent rhenium added thereto.
The apparatus as in claim 1 in which said sleeve member terminates a short distance below a plane defined by the outer edge of said bias electrode.
Claim 2
Dependent Claim
14 words
The apparatus as in claim 2 in which said distance is approximately 0.312 inch.
Claim 3
Dependent Claim
17 words
The apparatus of claim 2 in which the height of said sleeve member is approximately 1.3 inches.
Claim 4
Dependent Claim
28 words
The apparatus as in claim 1 in which said filament includes first and second leg portions extending into said aperture from opposite sides of said flat emitting face.
Claim 5
Dependent Claim
33 words
The apparatus of claim 1 in which the diameter of said first aperture is about 0.186 inch, and said filament is recessed from the concave surface of said bias electrode about 0.025 inch.
Claim 6
Dependent Claim
18 words
The apparatus as in claim 1 in which the flat emitting face of said filament is approximately rectangular.
Claim 7
Dependent Claim
24 words
The apparatus of claim 1 in which the width of said filament emitting face is about one-third of the diameter of said first aperture.