Sintered wire cathode
A porous cathode structure is fabricated from a plurality of wires which are placed in proximity to each other in elevated temperature and pressure for a sintering time. The sintering process produces the porous cathode structure which may be divided into a plurality of individual porous cathodes, one of which may be placed into a dispenser cathode support which includes a cavity for containing a work function reduction material such as BaO, CaO, and Al 2 O 3 . The work function reduction material migrates through the pores of the porous cathode from a work replenishment surface adjacent to the cavity of the dispenser cathode support to an emitting cathode surface, thereby providing a dispenser cathode which has a uniform work function and therefore a uniform electron emission.
1. A cathode for electron emission, said cathode having:
a porous cathode formed from a plurality of continuous wires having linear regions, said wires joined to each other by partially melting said wires along said linear regions substantially coaxial to said wires, said partial melting thereby forming substantially continuous and linear pores adjacent to said melted linear regions, said porous cathode having an emission surface and a replenishment surface, said linear pores coupling said emission surface to said replenishment surface;
a dispenser cathode support including a cavity adjacent to said porous cathode replenishment surface, said cavity containing a work function lowering material and allowing said work function lowering material to travel from said cavity to said emission surface using said pores.
2. The cathode of claim 1 where said work function lowering material in said cavity includes at least one of BaO, CaO, and Al 2 O 3 .
3. The cathode of claim 1 where said porous cathode emission surface is planar.
4. The cathode of claim 1 where said porous cathode emission surface is concave.
5. The cathode of claim 1 where said wires are tungsten.
6. The cathode of claim 5 where said tungsten wires have a diameter prior to sintering of 10 u to 20 u.
7. The cathode of claim 1 where said wires are a refractory metal.
8. The cathode of claim 1 where said wires have substantially equal diameters.
9. The cathode of claim 1 where at least one said wire is formed from a different refractory metal.
10. The cathode of claim 1 where said work function lowering material increases the thermionic emission of free electrons.
11. The cathode of claim 1 where said sintered wires are coated with said work function lowering material prior to sintering, and said pores are thereby substantially filled with said work function lowering material.
12. A porous cathode having:
a plurality of wires partially melted to each other and thereby forming linear and substantially continuous pores adjacent to each said partially melted wire, said porous cathode having a replenishment surface and an opposing emission surface, said replenishment surface and said emission surface coupled to each other by said substantially continuous pores, said pores supporting a work function lowering material.
13. The porous cathode of claim 12 where said work function lowering material moves through said pores to said emission surface as either said wires or said work function lowering material of said emission surface is consumed.
14. The porous cathode of claim 13 where the movement of said work function lowering material through said pores is the result of capillary action.
15. The porous cathode of claim 12 where said work function lowering material contains at least one of BaO, CaO, or Al 2 O 3 .
16. The porous cathode of claim 12 where said work function lowering material is introduced into said pores after sintering of said wires.
17. The porous cathode of claim 12 where said work function lowering material is coated on said wires before said sintering, said sintering causing said work function lowering material to substantially fill said pores.
18. A porous cylinder formed from a plurality of substantially linearly arranged wires partially melted to each other along substantially linear regions of adjacent contact of said wires, said partial melting such as by sintering, whereby regions of said wires which are not melted to each other form pores which are substantially continuous along said wires, said porous cylinder having a replenishment surface and an opposing emission surface coupled to said replenishment surface by said substantially continuous pores.
19. The porous cylinder of claim 18 where said substantially continuous pores contain a work function lowering material.
20. The porous cylinder of claim 18 where said porous cylinder includes a reservoir for the storage of a work function lowering material, said reservoir coupled to said replenishment surface which is also coupled to said emission surface through said pores.
21. The porous cylinder of claim 19 where said work function lowering material is at least one of BaO, CaO, or Al 2 O 3 .
22. The porous cylinder of claim 18 where said wires are tungsten and have diameters in the range 10 u to 20 u.