Methods and apparatuses for emitting electrons from a hollow cathode are provided. The cathode includes a plasma holding region configured to hold a plasma, a gas supply source configured to supply gas to the plasma holding region, and an orifice plate disposed on a periphery of the plasma holding region. The orifice plate comprises a plurality of openings constructed to receive electrons from the plasma. The plurality of openings decouple gas conductance and electrical conductance across the orifice plate. The diameters of the plurality of openings are within a range of 20%-60%, inclusive, of a diameter of a circular opening with an area equal to a sum of the areas of the plurality of openings.

An electron gun comprising a cathode having an electron emitting surface and whose planar shape is circular, a heater to increase the temperature of the cathode, and an anode to apply a positive electric potential relative to the cathode to extract electrons in a predetermined direction is provided. The cathode comprises a through hole at a central portion thereof along a central axis of the cathode, and either the cathode comprises a no-emitting layer at at least one of an opening edge on the electron emitting surface side of the through hole and an inner surface of the through hole, or the opening edge on the electron emitting surface side of the through hole is a chamfered C surface or a chamfered R surface.

A hollow cathode includes an insulation plate having cathode holes. Bottom electrodes are below the insulation plate. The bottom electrodes define first holes having a width greater than a width of the cathode holes. Top electrodes are at an opposite side of the insulation plate from the bottom electrodes. The top electrodes define second holes aligned with the first holes along a direction orthogonal to the upper surface of the insulation plate.

In one embodiment, a system includes a cathode and a thermionic emitter installed at least partially within the cathode tube of the cathode. The thermionic emitter is in a shape of a hollow cylinder. The hollow cylinder includes an outer surface and an unsmooth inner surface. The outer surface is configured to contact an inner surface of the cathode tube. The unsmooth inner surface includes a plurality of structures that provide an increase in surface area over a smooth surface.

An electron gun may include a cathode with an emitting surface configured to emit electrons. The cathode may include a through hole that goes through the emitting surface and is configured to allow back-streaming electrons of the emitted electrons to pass through. The electron gun may also include an anode configured to attract the emitted electrons from the cathode to the anode and focus the emitted electrons into an electron beam. The electron gun may also include a grid structure configured to facilitate the focusing of the emitted electrons, the grid structure being positioned corresponding to the through hole.

A hollow cathode includes an insulation plate having cathode holes. Bottom electrodes are below the insulation plate. The bottom electrodes define first holes having a width greater than a width of the cathode holes. Top electrodes are at an opposite side of the insulation plate from the bottom electrodes. The top electrodes define second holes aligned with the first holes along a direction orthogonal to the upper surface of the insulation plate.

The present disclosure generally pertains to devices and methods for generating thrust in vehicles, for instance in space applications. A heaterless, insertless hollow cathode utilizes AC and pulsed DC electric fields to ionize the propellant gas and generate a plasma plume. The cathode uses an argon microplasma generated in a quartz tube with a tungsten filament and brass ion collector. Free electrons are then drawn from the plasma plume and supplied to a thruster engine.

The present invention relates to a high efficiency hollow cathode and a cathode system applying the same, and comprises: a tube comprising at least two refractory metal parts; a gas providing unit and a gas outlet which are respectively formed at the distal ends of the tube; and an insert mounted inside the tube. According to the present invention, since the present invention constitutes a hollow cathode using more than two substances, the present invention can not only enhance thermal stability, lifespan and efficiency, but also can reduce costs accordingly.

In an example, a method to form a low work function insert includes preparing a mixture that includes a first powder that contains barium, a second powder that contains calcium, a third powder that contains at least one of aluminum, samarium, or magnesium, and a fourth powder that contains a refractory metal. The method may also include heating the mixture, contained in a crucible, in a furnace. Oxygen concentration in the furnace may be maintained at a low partial pressure during heating of the mixture in the furnace. The low work function of the insert allows electrons to be readily extracted from its surface.

Aspects include a method for treating a polycrystalline material, the method comprising: exposing a surface of the polycrystalline material to a plasma thereby changing the surface of the polycrystalline material from being characterized by a starting condition to being characterized by a treated condition; wherein: the surface comprises a plurality of crystallites each having the composition MB.sub.6, M being a metal element; the plasma comprises ions, the ions being characterized by an average ion flux selected from the range of 1.5 to 100 A/cm.sup.2 and an average ion energy that is less than a sputtering threshold energy; the starting condition of the surface is characterized by a first average work function and the treated condition of the surface is characterized by a second average work function; and the second average work function is less than the first average work function.