Research activities of RF-based negative ion source in the ASIPP

The Comprehensive Research Facility for Fusion Technology (CRAFT) is a large scientific programme that is preferentially deployed for the construction of major national science and technology infrastructures. A negative ion-based neutral beam injector (NNBI) with beam energy of 400 keV, beam power of 2 MW and beam duration of 100 s is one of the projects. A radio frequency (RF) based negative beam source was designed for the CRAFT NNBI system. In order to understand the physics and pre-study the engineering problems for RF negative beam sources, a prototype source with a single driver was developed. Recently, this source was tested on a test facility with RF plasma generation, negative ion production and extraction. The long pulse plasma discharge and negative ion beam extraction with a three electrode accelerator were achieved successfully. The extracted ion current is 153 A/m2 with Cs injection and the ratio of electrons to negative ions is around 0.3. It lays good foundations for the R&D of negative ion sources for the CRAFT NNBI system. The details of design and experimental results of the beam source are given in this paper.