High-current, low-pressure plasma-cathode electron gun

• US 5,537,005 A
• Filed: 05/13/1994
• Issued: 07/16/1996
• Est. Priority Date: 05/13/1994
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Schumacher, Robert W., Goebel, Dan M.
• Primary Examiner(s): Lee, Benny T.
• Application Number:
  US08/242,569
• Time in Patent Office: 795 Days
• Field of Search: 315/111.81, 315/39, 250/427, 313/360.1, 313/362.1, 313/230, 313/231.71, 313/588, 313/632
• US Class Current: 315/111.81
• CPC Class Codes: H01J 3/025 Electron guns using a discharge in a gas or a vapour as electron source gas-filled discharge tubes with gaseous cathodes H01J15/00

Abstract

Plasma-cathode electron gun structures capable of operation in low-pressure, e.g., <5×10^-3 Torr, ionizable gas environments are disclosed. They utilize a thermionic emitter within an enclosure with a partially transparent electrode defining a plasma face. Spaced anodes are disposed adjacent the electrode to extract an electron beam from the plasma face. A magnetic system forms an inward directed field, and a portion of the plasma electrons are directed through this field to enhance ionization efficiency.

Claims

1. A plasma-cathode electrode gun for extracting an electron beam from an ionizable gas having a pressure less than 5×

10^-4 Torr, comprising;

an enclosure having a wall and and configured to contain said ionizable gas;

a thermionic electron emitter positioned within said enclosure;

an outlet defined in said wall;

a discharge anode defining a plurality of apertures and positioned across said outlet;

a beam anode defining a plurality of apertures and spaced from said discharge anode to define an acceleration region between said discharge anode and said beam anode;

a magnet system that is arranged around said enclosure and configured to generate magnetic flux line in said enclosure which are adjacent said wall;

a discharge supply arranged to apply discharge voltage pulses across said emitter and said discharge anode to generate a plasma of ions and electrons by ionization of said ionizable gas;

a beam supply coupled to said discharge anode and said beam anode to generate an electric field across said acceleration region for extraction of a first portion of said electrons as said electron beam; and

a voltage differential device that connects said wall and said discharge anode for coupling a sample of said discharge voltage pulses to said wall to direct a second portion of said electrons through said magnetic flux lines for enhancement of said ionization and said extraction.

2. The electron gun of claim 1 wherein said voltage differential device comprises a resistor having a selectable range of resistance and said resistor connects said enclosure with said discharge anode.

3. The electron gun of claim 2, wherein said selectable range is between 1 and 2 ohms.

4. The electron gun of claim 1, further including a mesh coupled across said discharge anode to establish a face of said plasma.

5. A method of extracting an electron beam from an ionizable gas having a pressure less than 5×

10^-4 Torr, the method comprising the steps of;

containing said ionizable gas within an enclosure;

emitting electrodes from a thermionic emitter into said ionizable gas;

impression discharge voltage pulse across said ionizable gas to form a plasma of ions and electrons by ionization of said gas;

with a magnetic flux source, forming magnetic flux lines within said enclosure;

applying an electric field to said ionizable gas to extract a first portion of said electrons and form said electron beam; and

coupling a selectable sample of said discharge voltage pulse to said enclosure to direct to a second portion of said electrons through said magnetic flux lines for enhancement of said ionization and said extraction.