COMPACT ECR ION SOURCES WITH PERMANENT-MAGNETS IN A CUSP GEOMETRY AND IN A MAGNETIC-MIRROR STRUCTURE

Two compact Electron Cyclotron Resonance (ECR) ion sources exclusively built with permanent magnets in a cusp geometry and in a magnetic mirror structure are compared. The microwave discharge power is 60-120 W at a frequency of 2.45 GHz. The cusp structure enables to produce an argon-ion current of 1.5 mA at an extraction voltage of 2 kV with an aperture of 4 mm diameter at a gas pressure of 10-3 mbar. The ion source built with a magnetic mirror operates at lower pressure (10-4 mbar) with an ion current density of 5 mA/cm2 (the total current is 0.6 mA). Spectroscopic measurements of photons emitted by an oxygen plasma enable us to detect multicharged ions such as O4+ and O 5+ ions. With these two magnetic structures, sharp variations of current density with gas flow rates are observed and the different ranges of operating pressure are presented.