US 5,675,606 AGranted

Solenoid and monocusp ion source

AssigneeThe United States of America as represented by the United States Department of Energy

InventorsJohn Paul Brainard, Erskine John Thomas Burns, Charles Hadley Draper

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Abstract

An ion source which generates hydrogen ions having high atomic purity incorporates a solenoidal permanent magnets to increase the electron path length. In a sealed envelope, electrons emitted from a cathode traverse the magnetic field lines of a solenoid and a monocusp magnet between the cathode and a reflector at the monocusp. As electrons collide with gas, the molecular gas forms a plasma. An anode grazes the outer boundary of the plasma. Molecular ions and high energy electrons remain substantially on the cathode side of the cusp, but as the ions and electrons are scattered to the aperture side of the cusp, additional collisions create atomic ions. The increased electron path length allows for smaller diameters and lower operating pressures.

Claims25

Dependent claims

An atomic-hydrogen ion source comprising:

(a) a nonmagnetic housing enclosing a vacuum envelope between a rear wall and a front wall, said front wall having an aperture for passage of ions and an ion beam from said housing;
(b) a cathode positioned within said housing near but electrically insulated from said rear wall;
(c) an anode supported between said cathode and said aperture within said housing, said anode for energizing electrons emitted from said cathode when a voltage is applied between said anode and said cathode, said anode being electrically insulated from said cathode and said housing;
(d) a reflector within said housing located between said anode and said aperture, said reflector being electrically insulated from said cathode, said anode and said housing;
(e) a monocusp magnet positioned on the exterior of said nonmagnetic housing behind and adjacent to said reflector, said monocusp magnet for forming a monocusp magnetic field on said reflector;
(d) at least two permanent solenoid magnets, each set positioned along the exterior of said nonmagnetic housing on each side of said monocusp magnet, one set towards said cathode and the other set towards said aperture, said at least two permanent solenoid magnets for forming an axial solenoidal magnetic field to extend the path length of electrons, the relative strengths and positions of the solenoid magnets with respect to the cusp magnet generates a unique magnetic field configuration inside the small volume ion source for generating atomic, not molecular, hydrogen ions;
(g) a gas source to fill said vacuum envelope with a gas which is ionized by electrons to form a plasma;
whereby electrons emitted from said cathode are accelerated toward said anode along lines of said axial solenoidal magnetic field and are reflected at said monocusp magnetic field at said reflector wherein said electrons travel between said cathode and said reflector along said line of said solenoidal and monocusp magnetic fields;
said electrons ionizes said gas within said vacuum envelope into molecular ions and said molecular ions pass through said monocusp magnetic field toward said aperture and dissociate into atomic ions by low energy electrons that have been scattered towards said aperture.

6 more elements

An ion source comprising:

(a) a coaxial cylindrical nonmagnetic housing enclosing a vacuum envelope between a rear wall and a front wall, said front wall having an aperture for passage of ions from said housing;
(b) a gas source to fill said vacuum envelope with a gas which ionizes to form a plasma;
(c) a hollow truncated cone cathode having lanthanum hexaboride as an electron emitting material, said cathode positioned coaxially within said housing near but electrically insulated from said rear wall;
(d) a coaxial anode ring supported between said cathode and said aperture within said housing so that said anode ring grazes an outer boundary of said plasma, said anode ring for energizing electrons emitted from said cathode when a voltage is applied between said anode ring and said cathode, said anode ring being electrically insulated from said cathode and said housing;
(e) a reflector ring within said housing located axially between said anode ring and said aperture, said reflector ring being at a potential between said cathode and said anode ring and electrically insulated from said cathode, said anode ring, and said housing;
(f) a permanent bar monocusp magnetic ring, positioned exterior to said vacuum envelope behind and adjacent to said reflector, said monocusp magnetic ring for forming a monocusp magnetic field on said reflector ring having a major monocusp magnetic field component axially perpendicular;
(g) at least one coaxial solenoid magnetic ring positioned exterior to said vacuum envelope on a side of said monocusp magnet towards said cathode, said solenoid magnet for forming an solenoidal magnetic field to extend the path length of electrons with said solenoidal magnetic field having a major component coaxially parallel and intersecting a surface of said cathode material;
whereby electrons emitted from said cathode and accelerated toward said anode ring along said solenoidal magnetic field lines and are reflected at said monocusp magnetic field at said reflector ring and travel between said cathode and said reflector ring along said solenoidal and monocusp magnetic field lines, which electrons ionize said gas within said vacuum envelope into molecular ions and said molecular ions pass through said monocusp magnetic field toward said aperture and dissociate into atomic ions by low energy electrons that have been scattered towards said aperture.

5 more elements

Dependencies are inferred from the claim text.