US 4,528,474 A · Method and apparatus for producing an electron beam from a thermionic cathode

Abstract

Disclosed is a method and apparatus for producing a high electron beam current having a low energy spread at a high brightness of the beam and a uniform intensity distribution. The electron beam is extracted from an emission current which consists of used emission current and unused emission current. The used emission current has a uniform intensity distribution. The apparatus produces a negligibly small unused emission current by using both a frustum shaped cathode and a multi-electrode. The cathode comprises a thermoelectron emissive material having a low work function and one or more thin layers which cover the side surface of the cathode. A material of the outermost thin layer has a high work function. The multi-electrode consists of the cathode, a first grid electrode, a second grid electrode and an anode electrode. The used emission current is generated from the top surface of the cathode. The unused emission current that is generated from the side surface of the cathode is negligibly small. The top surface is immersed into a strong accelerating electric field. By adjusting the field at the top surface, an emission current density from the top surface can be varied in the range of one to several hundred times of the saturation current density at an operating temperature. Methods for manufacturing the cathode are provided.

Claims39

Dependent claims

Electron beam apparatus comprising:

frustum shaped cathode means composed of a thermoelectron emissive material having a low work function and a high operating temperature to provide a high emission current density, said temperature also causing such material to be highly reactive, said cathode means being a single crystal, having a flat single crystal plane top surface and a conical side surface, said flat single crystal plane top surface providing a high saturation emission current density having a uniform angular emission pattern which is essentially normal to said crystal plane and having a uniform intensity distribution at said operating temperature;
a thin coated layer which covers the side surface of said shaped thermoelectron emissive material and whose material has a high work function so as to provide a low saturation emission current density from said side surface relative to said top surface so that side lobes in said beam are prevented even under full exposure to a positive accelerating field, hardly reacts chemically with said thermoelectron emissive material at said operating temperature, has a high melting point, and has a low vapor pressure at said operating temperature;
and
electrode means for producing an electric field at said top surface for providing an emission region of the Schottky or thermal field type where said top surface is exposed fully to positive accelerating potentials of said electrode means.

1 more element

Electron beam apparatus comprising:

frustum shaped cathode means composed of a thermoelectron emissive material having a low work function and a high operating temperature to provide a high emission current density, said temperature also causing such material to be highly reactive, said cathode means being a single crystal, having a flat single crystal plane top surface and a conical side surface, said flat single crystal plane top surface providing a high saturation emission current density having a uniform angular emission pattern which is essentially normal to said crystal plane and having a uniform intensity distribution at said operating temperature;
a first thin coated layer, which covers the side surface of said shaped thermoelectron emissive material and whose material hardly reacts with said thermoelectron emissive material, has a high melting point and has a low vapor pressure at said operating temperatures;
a second thin coated layer which covers said first thin layer, and whose material has a high work function so as to provide a low saturation emission current density from said side surface relative to said top surface so that side lobes in said beam are prevented even under full exposure to a positive accelerating field, has a high melting point, and has a low vapor pressure at said operating temperature;
and
electrode means for producing an electric field at said top surface for providing an emission region of the Schottky or thermal field type where said top surface is exposed fully to positive accelerating potentials of said electrode means.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for producing an electron beam from a thermionic cathode

Life of this patent

Method and apparatus for producing an electron beam from a thermionic cathode

Life of this patent

Abstract

Claims39