Crossedelectric-magnetic field electron-capture ion source

A method for thermalizing electrons is presented which involves the acceleration of electrons away from a hot filament with crossed electric-magnetic (EXB) fields in a magnetron configuration. It is shown that during a part of the resulting cycloidal path the electron velocity is significantly less than the initial velocity. The electron accelerates as it leaves the surface at a rate only slightly less than if there were no magnetic field, which prevents charge build-up at the surface. As the electron traverses the cycloid it is decelerated during the 2nd, 3rd and 4th quadrants, then re-accelerated as it approaches the end of the 4th quadrant to regain its original velocity. The minimum velocity occurs during the 4th quadrant, and corresponds to an electron temperature of 200–500°C for the electric and magnetic fields commonly encountered in the ion sources of magnetic sector mass spectrometers. An ion source modeled from this principle is presented.