Advanced center post electron gun

An electron gun for producing a hollow electron beam for use in an interaction region of a microwave device, the gun having a voltage source electrically connected thereto and comprising:

• an annular cathode;
• an anode spaced a fixed distance from said cathode, said anode having an aperture for passage of said beam therethrough, said cathode being negatively charged by the voltage source with respect to said anode;
• a center post located within a center region of said cathode positioned axially along an axis of said gun and said interaction region extending through said cathode, said center post terminating at said aperture of said anode, wherein an angle which is defined between said cathode and said anode is equivalent to an angle which is defined between said cathode and said center post;
• control means spaced between said anode and said cathode for electrostatically focusing said beam to control a convergence point of said beam;
• means for providing a magnetic field in a region of said beam convergence point;
• and
• more than one polepiece secured between said anode and said interaction region for creating a magnetic field reversal region, said polepieces including a central polepiece and an outer polepiece, wherein said magnetic field reversal region occurs along the axis of the electron gun and the microwave device downstream of said beam convergence point, away from said cathode, said beam being a large orbit beam in which the electrons spiral about the axis of the electron gun after passing said magnetic field reversal region.

An electron gun for producing a hollow electron beam for use in a microwave device having a voltage source electrically connected thereto and a region in which said beam interacts with a propagating RF signal, the gun comprising:

• an annular cathode having a conic surface;
• an anode spaced a fixed distance from said cathode, said anode having an aperture for passage of said beam therethrough, said cathode being negatively charged by the voltage source with respect to said anode;
• a center post located within a center region of said cathode along an axis of said gun and said interaction region, said center post terminating at said aperture of said anode, wherein an angle which is defined between said cathode and said anode is equivalent to an angle which is defined between said cathode and said center post;
• control means located between said anode and said cathode for electrostatically focusing said beam to control a convergence point of said beam;
• and
• means for providing a magnetic field in a region of said beam convergence point, and means for reversing direction of said magnetic field, wherein a magnetic field reversal region occurs along the axis of the electron gun and the microwave device downstream of said beam convergence point, away from said cathode, said beam being a large orbit beam in which the electrons spiral about the axis of the electron gun after passing said magnetic field reversal region, wherein said magnetic field reversing means is secured between said anode and said interaction region and comprises a plurality of polepieces.

An electron gun for producing a hollow electron beam for use in a microwave device having an RF interaction region, the electron gun having an annular cathode and an anode with an inter-electrode region defined therebetween, said anode having an aperture for passage of said beam therethrough, the gun comprising:

• a ferromagnetic cylinder enclosing said inter-electrode region electrically connected to said anode;
• means for producing a magnetic field coupled to said ferromagnetic cylinder between said anode and the interaction region;
• a center post electrically connected to said ferromagnetic cylinder, said center post terminating at said aperture of said anode and located along an axis of the inter-electrode region, wherein magnetic flux of said magnetic field is conducted through said center post and said ferromagnetic cylinder providing a magnetic field free region within the inter-electrode region;
• and
• wherein said magnetic field producing means further comprises more than one polepiece secured between said anode and said interaction region for creating a magnetic field reversal region, said polepieces including a central polepiece and an outer polepiece for reversing the direction of the magnetic field in a region of said beam convergence point, wherein a magnetic field reversal region occurs along the axis of the electron gun and the microwave device proximate the beam convergence point, said beam being a large orbit beam in which the electrons spiral about the axis of the gun after traversing said magnetic field reversal region.