A device for separating a chemical mixture into its constituents includes a central cathode that is aligned axially within a cylindrical plasma chamber. An anode, made of the chemical mixture requiring separation is positioned near the cylindrical wall of the plasma chamber. A working gas is introduced into the chamber to sputter the chemical mixture into the plasma chamber where it is dissociated and ionized. To reduce the unwanted loss of the central cathode due to sputtering by the working gas, the central cathode is formed with a plurality of radial projections that extend outwardly from the axis of the cylindrical plasma chamber. These radial projections act to capture sputtered cathode material before it is lost to the plasma. Once the chemical mixture has been ionized in the plasma chamber, the ions are separated, according to their respective mass to charge ratio, using crossed electric and magnetic fields.