초록 ▼

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 b

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°to 500°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.

대표청구항 ▼

An apparatus for producing negative ions of a gaseous sample comprising: an electron emitter; a draw-out electrode lying in a first plane and having an axis extending perpendicular to said first plane; a chamber having an ionization region and containing said electron emitter in said ionization regi

An apparatus for producing negative ions of a gaseous sample comprising: an electron emitter; a draw-out electrode lying in a first plane and having an axis extending perpendicular to said first plane; a chamber having an ionization region and containing said electron emitter in said ionization region and containing said draw-out electrode removed from said ionization region; means for providing at least between said electron emitter and said draw-out electrode, an electric field aligned with said axis of said draw-out electrode and oriented to attract negative particles toward said draw-out electrode; means for providing in said ionization region of said chamber, a uniform magnetic field orthogonal to said electric field throughout said ionization region, such that when a gaseous sample is introduced into said ionization region of said chamber, and electrons are emitted from said electron emitter, said electrons accelerate toward said draw-out electrode under the influence of said electric field, said magnetic field causes said moving electrons to travel in a direction orthogonal to said magnetic and electric fields, with a generally cycloidal trajectory effected by said orthogonal electric and magnetic fields, molecules of said gaseous sample capture said cycloidally moving electrons to become negative ions which are preferentially accelerated by said electric field toward said draw-out electrode, free electrons not captured being retained in said ionization region.