A linear plasma mass filter includes a container which is shaped as a rectangular prism. Magnetic coils encircle the container for generating a uniform magnetic field (B) in the container, and electrodes are mounted on the container for generating an electric field (E) in the container. Specifically, the electric field is rectilinear in that all of the electric field lines are parallel to each other. Further, the electric field is oriented perpendicular to the magnetic field to create crossed electric and magnetic fields (E.times.B). A plasma source is provided for injecting a multi-species plasma into the container which includes relatively low mass particles (M.sub.1), and relatively high mass particles (M.sub.2). Both M.sub.1 and M.sub.2 are responsive to the magnetic field with respective cyclotron orbits of a first diameter (D.sub.1) and a second diameter (D.sub.2). A first collector is positioned in the container at a projected distance d.sub.1 from the plasma source for collecting the relatively light mass particles (M.sub.1) and a second collector is positioned in the container at a projected distance d.sub.2 from said plasma source for collecting the relatively high mass particles (M.sub.2). For the present invention: d.sub.1 <D.sub.1 <d.sub.2 <D.sub.2.
