Actively-cooled plasma electrode for long pulse operations in a cesium-seeded negative ion source

セシウム添加型負イオン源長パルス運転用強制冷却型プラズマ電極

藤原 幸雄; 渡邊 和弘; 奥村 義和; Trainham, R.*; Jacquot, C.*

Fujiwara, Yukio; Watanabe, Kazuhiro; Okumura, Yoshikazu; Trainham, R.*; Jacquot, C.*

セシウム添加型の負イオン源における長パルス運転用のプラズマ電極を開発した。セシウム添加型負イオン源では、プラズマ電極の温度を負イオン生成に適する300C程度に維持することが必要である。冷却パイプを熱絶縁のためのスペーサを介してプラズマ電極にロー付けする構造を新たに提案、3次元熱解析により設計を行い製作した。実際に負イオン源に組み込み負イオンビーム生成試験を行った結果、長パルス試験において温度が約280Cに維持できることを確認でき、本強制冷却方式が長パルス運転用電極に有効であることを確認できた。

A new actively-cooled plasma electrode has been developed for long pulse operation in a cesium-seeded negative ion source. To keep the electrode temperature at about 300 C, which is optimum range of temperature to enhance cesium effects, the electrode cooling structure has been designed using three-dimensional numerical simulation assuming that the heat flux from the source plasma was 15 W/cm. Water cooling tubes were brazed to the plasma electrode substrate with spacers made of stainless steel which acts as a thermal resistance. The fabricated plasma electrode has been tested in a cesium-seeded volume negative ion source called Kamaboko source. The temperature of the electrode reached 280 C for the arc power of 41 kW, which is operating condition required for producing D- beams with current densities exceeding 20 mA/cm. It was demonstrated that the actively-cooled plasma electrode is applicable to long pulse operations, meeting the temperature requirement for optimizing the surface-production process of negative ions in the cesium seeded ion source.