In a plasma ion source having an induction coil adjacent to a reactor chamber for inductively coupling power into the plasma from a radio frequency power source and designed for negative and positive ion extraction, a method for operating the source according to the invention comprises providing radio frequency power to the induction coil with a RF amplifier operating with a variable frequency connected to a matching network mainly comprised of fixed value capacitors. In this device the impedance between the RF power source and the plasma ion source is matched by tuning the RF frequency rather than adjusting the capacitance of the matching network. An option to use a RF power source utilizing lateral diffused metal oxide semiconductor field effect transistor based amplifiers is disclosed.