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Contribution Poster

H– and D– sources for fusion, accelerators and other applications

Design of Negative Ion Source Using a Plasma Electrode of C12A7 Electride


  • Mr. Masumi KOBAYASHI

Primary authors



Alkali metal such as cesium covers the plasma electrode to enhance the negative hydrogen ion surface production in a negative ion source. Accumulation of Cs in the source shortens the maintenance cycle of the apparatus. In this research, inorganic material, C12A7 electride, which has low work function and high electric conductance, is studied as a candidate material for a new type of cesium-free plasma electrode. One of the key issues of this type of ion source design is in-situ baking mechanism and the temperature control system of the plasma electrode made of C12A7 electride. Figure 1 shows the result of the ohmic heating test of electride; i.e., direct electrical current was induced to the sample. The value of conductivity increases with increasing temperature. The sample heating up to $328.5 {}^circmathrm{C}$ caused non-uniform temperature distribution, and the material became fragile. Another key issue is removal of impurity layer formed on the electride. We design a negative ion source having an ECR plasma source and a three electrode extractor: acceleration and deceleration grids, with the electride plasma grid having an indirectly heating system. The preliminary results on the characteristics measurements of the ion source will be presented.