Fig. 2-16 The status of negative ion source development for fusion research, and application areas to other sciences, technologies and industries

Fig. 2-17 Cross section of a negative ion source with the four-stage, electrostatic acceleration fields

Fig. 2-18 Accelerated negative ion beams The beam from each hole is distinguishable separately at 2 m downstream in the accelerated negative ion beams that come from the apertures of 14 mm diameter and the 3 x 3 lines. It can be said that the convergence is very high.

The neutral particle injection system needs an acceleration voltage of 1 MV for heating and controlling the ITER plasma. In addition, the accelerating current needs some tens of amperes for each injector. Negative ion sources are used in this range of acceleration voltage, because of the high efficiency of charge-exchange conversion. We have made 1 MV particle acceleration experiments successfully, as a part of the ITER technology R&D. To accelerate and focus only negative ions, plans were made taking into account the structure of electrodes which control the electrons in a negative ion source, the arrangement of the peripheral permanent magnets to get a high efficiency of the ion source and so on. The status of the development of source acceleration voltage and current is shown in Fig. 2-16. Figure 2-17 shows the cross sectional view of the ion source structure and the acceleration electrodes. An image of the accelerating beams is shown in Fig. 2-18. We have to achieve both the accelerating voltage and current for the ITER technology R&D. This kind of technology will have many spin-off effects in sciences, technologies and industries, such as large accelerators, advanced material developments with larger sizes and so on.

Reference K. Watanabe et al., Development of a Multiaperture, Multistage Electrostatic Accelerator for Hydrogen Negative Ion Beam, Rev. Sci. Instrum., 69 (2), 986 (1998).

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