Ion source having plasma control means

Claim 1

IN AN ION SOURCE HAVING A GAS IONIZATION CHAMBER AND AN EVACUATED PLASMA FORMING CHAMBER, PLASMA CONTROL MEANS COMPRISING AN ANODE, AN EXTRACTOR ELECTRODE AT A HIGH POTENTIAL WITH RESPECT TO THAT OF SAID ANODE, SAID ANODE CONSTITUTING A COMMON PARTITION BETWEEN SAID IONIZATION CHAMBER AND SAID PLASMA FORMING CHAMBER AND HAVING AN APERTURE THEREIN ADAPTED TO COMMUNICATE A CONTROLLED QUANTITY OF IONS THEREBETWEEN, SAID ION SOURCE PRODUCING A CONCENTRATION OF IONS AT SAID APERTURE SUFFICIENTLY GREAT SO THAT THERE WOULD BE A TENDENCY FOR SPACE CHARGE REPULSION TO PRODUCE A HIGHLY DIVERGENT BEAM UPON EXTRACTION OF POSITIVE IONS AT THAT POINT, AND AN ANNULAR MEMBER CONTIGUOUS THERETO DISPOSED IN CONCENTRIC RELATIONSHIP TO SAID APERTURE, SAID ANNULAR MEMBER BEING AT THE SAME ELECTRICAL POTENTIAL AS THAT OF SAID ANODE AND BEING OF SUFFICIENT LENGTH TO FORM A REGION FREE OF INFLUENCE OF THE FIELD EFFECT TO THE EXTRACTOR ELECTRODE UNTIL SUCH TIME AS SAID PLASMA HAS DIFFUSED TO A SUFFICIENT EXTENT TO REDUCE SPACE CHARGE EFFECTS IN THE ION BEAM TO BE EXTRACTED THEREFROM, SAID ANNULAR MEMBER THUS PROVIDING A DRIFT SPACE AND EXIT APERTURE FOR SAID PLASMA AND HAVING A GEOMETRY ADAPTED TO PROVIDE OPTIMUM DIVERGENCE CHARACTERISTICS OF AN ION BEAM EMANATING THEREFROM.