Conveners
H– and D– sources for fusion: Oral session O1
- Motoi Wada (Doshisha University)
- Yuri Belchenko (Institute of Nuclear Physics)
Large-scale sources for negative hydrogen (or deuterium) ions are used in some present and many future fusion devices in neutral beam injectors (NBI). Several test facilities contribute to the development of the RF source for the ITER-NBI in order to achieve simultaneously the ITER requirements, e.g. beam pulse of 3600 s, beam current density of 286 A/m2 and co-extracted electron...
Negative-ion based neutral beam injectors (N-NBI) are utilized for plasma heating and current drive in the Large Helical Device (LHD). In the previous operation, we achieved 2.9 MW deuterium beam injection using the negative ion source optimized hydrogen operation. The deuterium negative ion current was reduced to 55.4 A and the average current density was 223 A/m$^3$ which is 0.65 times lower...
Plasma meniscus is widely believed to be formed in negative ion beam extraction boundary as well as positive ion beam extraction boundary, because very similar perveance dependence of beam divergence is generally observed. However, several difference properties of plasma meniscus formation were revealed in recent studies of negative ion beam focusing. In this talk, the different responses...
Flow of charged particles near the plasma grid in negative ion sources affects the extraction efficiency of negative hydrogen / deuterium (H- / D-) ion beams [1][2]. In our previous research, the flow of the charged particles was measured with a four-pin directional Langmuir probe by rotating the tips around the center axis of the tips [3]. In the case of the four-pin probe, spatial resolution...
Good understanding of negative ion beam optics is crucial to the development of the ITER NBI system. The Large Helical Device (LHD) has such a negative ion beam. Recently, an unexplained splitting of the beam in the horizontal, but not the vertical, direction has been observed in the emittance diagram. This indicates a large influence of the plasma meniscus on the negative ion beam optics. As...
Long term stability of a plasma heating system is indispensable for realizing a DEMO nuclear fusion reactor. One possible cause for deteriorating the accelerator/ion source system of negative ion based neutral beam injection (N-NBI) heating is the damage due to energetic positive ions back-streaming from the beam produced plasma. The positive ions strike the surfaces of downstream sides of...
The Comprehensive Research Facility for Fusion Technology (CRAFT) is a large scientific device that is preferentially deployed for the construction of major national science and technology infrastructures. A negative beam source 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 device. A radio frequency (RF) based...
A Negative-ion based Neutral Beam Injection (NNBI) prototype is under conceptual design in Southwestern Institute of Physics for China Fusion Engineering Test Reactor (CFETR). The aim in the first stage is to extract an H- beam >3A for 1000s and acquire an energy of 200keV. In this presentation, a single beamlet model for optimization of the CFETR NNBI prototype accelerator’s beam optics is...
An external RF antenna based cusp free negative H ion source has been designed and developed as shown in figure 1. This source is operated at 10% duty factor and the key experimental result is shown in figure 2. The extracted H- ion beam current is 11 mA with 2 ms pulse duration and 50 Hz repetition rate at 50 kV beam energy. Operation of the H- ion source at high duty factor results in...
Negative ion production in the hydrogen plasma of a fusion grade negative ion source relies on the surface production mechanism. Surface production is associated with the resonance electron capture (REC) by neutral hydrogen atoms and ions impinging on a low work function surface. In order to reduce the surface work function, a Cesium (Cs) layer is deposited in situ primarily on the first grid...
Negative ion or anion density measurement is frequently done non-invasively by employing Cavity Ring-Down Spectroscopy (CRDS) diagnostic system. The optical cavity in the CRDS system is created by installing two highly reflecting concave mirrors on two collinear opposite ports of the ion source chamber; so that the cavity encloses the plasma as an absorbing medium. In a continuously fed cesium...
