A high‐yield radio‐frequency ion source is described in which the ionization efficiency has been considerably enhanced by arranging for the radio‐frequency oscillator to excite the lowest‐order (m=0) helicon wave in the plasma. It has been used to produce intense beams of H+, H+3, He+, Ne+, Ar+, Li+, K+, Na+, and Cd+. A proton beam of up to 10 mA H+ is attainable, with a proton fraction in excess of 96%, using only 300 W of excitation power.

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