Negative ion source

Details Negative ion source Negative ion source

1986-01-23

1987-03-10

Anderson, Bruce C.

Radiant energy

Ion generation

Electron bombardment type

250424, 31511181, H01J 2720

Patent

active

046492798

ABSTRACT:
A method and apparatus for providing a negative ion source accelerates electrons away from a hot filament electron emitter into a region of crossed electric and magnetic fields arranged in a magnetron configuration. During a portion of the resulting cycloidal path, the electron velocity is reduced below its initial value. The electron accelerates as it leaves the surface at a rate of only slightly less than if there were no magnetic field, thereby preventing a charge buildup at the surface of the emitter. As the electron traverses the cycloid, it is decelerated during the second, third, and fourth quadrants, then reeccelerated as it approaches the end of the fourth quadrant to regain its original velocity. The minimum velocity occurs during the fourth quadrant, and corresponds to an electron temperature of 200.degree. to 500.degree. for the electric and magnetic fields commonly encountered in the ion sources of magnetic sector mass spectrometers. An ion source using the above-described thermalized electrons is also disclosed.

REFERENCES:
patent: 2935634 (1960-05-01), Lerbs
patent: 4213043 (1980-07-01), Dawson
patent: 4303865 (1981-12-01), Swingler
patent: 4329586 (1982-05-01), Dagenhart et al.
patent: 4486665 (1984-12-01), Leung et al.
Delmore, "Isotopic Analysis . . . ", International Journal of Mass Spectrometry and Ion Physics, 43(1982) 273-281.

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