Method and apparatus for magnetic focusing of off-axis electron beam

An electron beam device having a longitudinal axis, comprising:

• a source of a plurality of electron beams disposed apart from the longitudinal axis, the plurality of electron beams arranged to form between said source and a collector assembly;
• a flux equalization assembly disposed between said source and said collector assembly and relatively near said source, said flux equalization assembly including:
• (1) a flux plate formed of a ferromagnetic material, the flux plate including at least one aperture for each of the plurality of electron beams, an aperture wall defining the aperture;
• (2) a flux equalization ring disposed concentrically about each of the plurality of electron beams and forming an azimuthally varying gap between said flux equalization ring and a corresponding aperture wall and (3) a flux equalization cylinder disposed concentrically about each of said plurality of electron beams;
• and
• a source of a magnetic field disposed to focus the electron beams,
• wherein the electron beams travel between the source and the collector in a substantially straight path parallel to the longitudinal axis of the device.

An electron beam device having a longitudinal axis and a magnetic circuit providing a magnetic focusing field disposed about the longitudinal axis focusing the electron beam(s) to a first diameter, the device having at least one electron beam disposed parallel to and a distance from said longitudinal axis, the device comprising:

• a cathode associated with said at least one electron beam;
• an anode associated with said at least one electron beam;
• and
• a flux equalization assembly disposed between said anode and said cathode, said flux equalization assembly including a ferromagnetic flux plate having a beam aperture through which said at least one electron beam is arranged to pass, said flux equalization assembly including local magnetic perturbators acting to cancel local magnetic field asymmetry, and said flux equalization assembly including a portion extending toward said cathode to surround at least a portion of the at least one electron beam in a region adjacent the cathode where it is of greater diameter than said first diameter.

An electron beam device having a longitudinal axis and a magnetic circuit providing a magnetic focusing field disposed about the longitudinal axis focusing the electron beam(s) to a first diameter, the device having at least one electron beam disposed parallel to and a distance from said longitudinal axis, the device comprising:

• a cathode associated with said at least one electron beam;
• an anode associated with said at least one electron beam;
• and
• a flux equalization assembly disposed between said anode and said cathode,
• said flux equalization assembly including a ferromagnetic flux plate having a beam aperture through which said at least one electron beam is arranged to pass,
• said flux equalization assembly including one or more magnetic perturbators local to and associated with said at least one electron beam and acting to cancel local magnetic filed asymmetry in said at least one electron beam.