High current density cathode structure

A compact cathode assembly having high electron emission current densities for producing a dense gas plasma, comprising:

• a high plasma density cathode enclosure,
• inlet means connected to said cathode enclosure for supplying gas to said cathode enclosure;
• a low plasma density utilization chamber coupled to receive plasma from said cathode enclosure through an aperture between said enclosure and said chamber;
• a lanthanum hexaboride cathode element having an electron emissivity of more than 10 amperes per square centimeter mounted within said cathode enclosure between said inlet means and said aperture;
• means for heating said cathode element to an elevated temperature without contaminating the electron emitting surface of said cathode element;
• and
• said system including means for providing a much higher plasma density within said cathode enclosure than in said utilization chamber, said higher plasma density being above the critical level required to support a cathode electron emission density of ten amperes per square centimeter.

A system including a compact cathode assembly having high electron emission current densities for producing a dense gas plasma, comprising:

• a high plasma density cathode enclosure;
• inlet means connected to said cathode enclosure for supplying gas to said cathode enclosure;
• a hollow cylindrical cathode element of solid lanthanum hexaboride, said cathode element having an electron emitting surface;
• means including at least two carbon rings having inner and outer peripheral notches, for mounting said cylindrical cathode within said cathode enclosure;
• means for heating said lanthanum hexaboride element to an elevated temperature without contaminating said electron emitting surface;
• and
• said system including means for producing a current density of more than ten amperes per square centimeter at the surface of the lanthanum boride element, said means including means for establishing a plasma density within said cathode enclosure above the critical level permitting cathode electron current densities of ten amperes per square centimeter.

A cathode system comprising:

• a cathode element of lanthanum hexaboride having an electron emitting surface;
• means for heating said cathode to electron emitting temperatures without contaminating said electron emitting surface;
• means for establishing a gas plasma density in the vicinity of said electron emitting surface having an electron density in the order of 2.times.10.sup.12 electrons per cubic centimeter or more;
• means for supporting said cathode with only carbonaceous material in engagement with said cathode;
• and
• power supply means for drawing current densities greater than 5 amperes per square centimeter from said emitting surface of said cathode.