Concept for a cesium-free negative ion source based on microwave heating of a low work function granular material

Matsubara, Akihiro*; Kokubu, Yoko   ; Nishio, Kazuhisa*; Kimura, Kenji*; Kashimura, Keiichiro*; Shimada, Koji   ; Fujita, Natsuko   

We propose a concept for a cesium-free negative ion source based on microwave heating of granular low work function materials, which allows for both safety and high efficiency. This negative ion source features a structure where the plasma region and the negative ion generation region are adjacent within a microwave cavity. In the negative ion generation region, granular low work function materials heated by microwaves are placed. The sample gas entering the plasma region is excited, then it enters the negative ion generation region. Subsequently, it comes into contact with the surface of the low work function material, changes into negative ions, and finally, is extracted by an electric field. One advantage of this negative ion source is that, by using low work function materials in granular form, the reactive area is more than ten times larger compared to conventional negative ion sources using low work function materials.