Single-ring magnetic cusp low gas pressure ion source

A single-ring magnetic cusp low gas pressure ion source for a neutron generator, said source comprising:

• a nonmagnetic housing comprising a rear plate and a front wall spaced from said rear plate, said front wall including an aperture plate having aperture means for passage of ions from said housing;
• cathode means for emitting electrons positioned within said housing, said means being near and electrically insulated from said rear plate, an axis of said source extending from said cathode to said aperture means;
• nonmagnetic anode ring means coaxially aligned with said axis and positioned between said cathode and said aperture plate for receiving electrons from said cathode when a positive voltage is applied between said anode and said cathode, said ring being electrically insulated from said cathode and housing;
• a nonmagnetic cylinder coaxial with said axis within said housing and surrounding said anode, said cylinder being electrically insulated from said cathode and housing;
• an electron reflector plate located between said cathode and said rear plate, said reflector plate being electrically insulated from said cathode, anode, housing and cylinder;
• and
• magnetic ring means for forming a magentic field having a continuous single-ring cusp on said cylinder said single-ring cusp being the only cusp formed on said cylinder, the magnetic field lines from said cathode to said cusp passing adjacent said anode ring;
• whereby electrons are confined between said cathode and said magnetic ring cusp, and ions can pass through said magnetic field to said aperture means.