The Experimental Advanced Superconducting Tokamak (EAST) is one of the fully superconducting tokamak, its aim at the long-pulse operation (1000s) to study the physics of steady-state operation for nuclear fusion sciences. In order to support the steady-state operation and physical research, the high power neutral beam injection (NBI) system need to be employed on the EAST for the plasma heating and current driving. According to the scientific study schedule of the EAST, the designed NBI system includes two beam lines which will be constructed in two phases. Each beam line will deliver a deuterium neutral beam with beam energy of 50–80 keV with beam duration of 10–100 s. Each beam line has the maximum beam power of 4MW.
The high current ion source is one of the most important parts in the high power NBI. A hot cathode positive ion based source was developed for EAST-NBI, which shown in Fig. 1. The ion source contains a bucket hot cathode arc chamber with 650 mm long, 260 mm width and 300 mm depth. There are 32 hairpin filaments with diamond of 1.5 mm and 160 mm long to supply primary electrons. A tetrode type accelerator with slit type used to extract the ions from the plasma and accelerated to the desired energy. The beam extraction area is 120 mm × 480 mm (can be changed) with beam transmittance of 60 %. The designed beam species is deuterium with beam power of 2–4 MW and beam energy of 50–80 keV and beam pulse length of 10–100 s.
The ion source needs to be conditioning before operation on the EAST-NBI. An ion source test bed was designed and developed for the ion source performance tests and the optimization verification. The characteristics of ion source were tested with hydrogen beam, and each ion source should achieve 4MW ion beam with beam energy of 80 keV. The optimum beam perveance and arc efficiency were analyzed too. The optimum beam perveance was 2.8 μp with beam energy of 50 keV and the arc efficiency was 0.55A/kw.
Long pulse operation was one of the requests of EAST ion source. The real-time feedback control method was employed and can got stable plasma and ion beam. The beam extraction was tested to achieve 100 s on the test bed. Consider the high power deposited on the calorimeter, the beam was modulated with suitable frequency and duty ratio. When the conditioning finished, the ion sources were moved to the EAST-NBI. The deuterium beam was extracted and injected into the EAST plasma. Details of the performance of positive ion source on the test bed and EAST-NBI will be presented.
Beam Species Characteristics of High Current Ion Source for EAST Neutral Beam Injector
