A 13.56MHz multicusp ion source for gaseous ion-beam production

Abstract

Abstract A 10 cm×9 cm cylindrical radio-frequency (RF) driven multicusp ion source has been developed for producing high-current ion beams from gases. An inductively coupled 13.56 MHz RF plasma is produced in the presence of 20 rows of Sm–Co 5 magnets which form a longitudinal line-cusp field configuration. The field design was generated using the computer program magnus . By using a 0.35 Tesla magnet, the 100 eV electrons were confined in the source chamber. The RF antenna coil, coated with a thin layer of hard flexible glass to prevent electrical leakage and contamination, has power inlets into the source chamber. A 10:1 turns-ratio matching transformer was used in order to match the 50 Ω output impedance of the RF generator to the impedance of the plasma load. A test run has been performed with 0–500 W of RF power. The source parameters were measured with a Langmuir probe, a mass analyzer and a Faraday cup. For oxygen at 3 mtorr and power set at 500 W, the ion-current density is 36 mA cm −2 , representing an ion density of 1.5×10 11 cm −2 . The value for nitrogen operating at the same pressure is 34 mA cm −2 and, for argon and helium at 10 mtorr source pressure, it is 29 and 27 mA cm −2 , respectively.