Extraction of a negative hydrogen ion beam from a microwave ion source

A microwave ion source has been developed for negative-ion-based neutral beam injection. The plasma generator of the test source is a 15 cm diameter, 16.5 cm long cylindrical chamber. Two ring-shaped permanent magnets are set around the chamber. The microwave power (2.45 GHz) is introduced into the chamber through a ceramic window and a rectangular waveguide, which are biased positively with reference to the chamber. The reflection power of the microwave is reduced effectively by biasing the waveguide and the window. A negative hydrogen ion beam with a current density of 3.4 mA cm−2 was extracted steadily at an operating pressure of 0.3 Pa without cesium seeding, with a net microwave power introduced into the chamber of 2.8 kW.