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J-PARC負水素イオン源LaB$$_{6}$$フィラメント形状の最適化

A Survey of optimal filament shape in the J-PARC H$$^{-}$$ ion source

池上 清*; 上野 彰; 小栗 英知; 滑川 裕矢; 大越 清紀

Ikegami, Kiyoshi*; Ueno, Akira; Oguri, Hidetomo; Namekawa, Yuya; Okoshi, Kiyonori

J-PARCイオン源は、セシウムを使用しないLaB$$_{6}$$フィラメント駆動型負水素イオン源である。このイオン源から引き出される負水素イオンビーム強度は、LaB$$_{6}$$フィラメントの大きさや形状によって異なることがわかった。そこでLaB$$_{6}$$フィラメント形状の最適化に向けイオン源テストスタンドでこの形状差異によるビーム強度の変化をアーク電流300A固定で測定検証した。実機で使用している二重螺旋の29.5mm$$phi$$のLaB$$_{6}$$フィラメントではビーム強度35.2mA、同じく15mm$$phi$$の物では41.8mA、3重ヘアピンの厚さ1.5mm幅3.5mmフラットLaB$$_{6}$$フィラメントでは43.4mAであった。このほか、多くの形状のLaB$$_{6}$$フィラメントに対してのビーム強度測定も行った。

A cesium-free H$$^{-}$$ ion source driven with a LaB$$_{6}$$ filament is under operation at the Japan Proton Accelerator Research Complex (J-PARC). The ion source succeeded in producing the maximum beam current of 38 mA, which is satisfied with the requirement for the J-PARC initial stage of 36 mA. The operating beam current, however, is within 30-33 mA during the accelerator beam commissioning run because we restrict the maximum arc current to 300 A for a highly stable beam operation. In order to improve the arc power efficiency for the beam current and to examine the possibility to satisfy with the requirement for the J-PARC final goal, we started to survey about the optimal size and shape of the LaB$$_{6}$$ filament by using the H$$^{-}$$ ion source test stand. All the tests were carried out with the same condition such as the arc current (300A), the beam energy and the magnet configuration of the plasma chamber. The beam current of 35.2 mA was extracted using a double spiral LaB$$_{6}$$ filament with a diameter of 29.5 mm and length of 35.5 mm, which is the same dimension as the present J-PARC ion source. By using a smaller one with a diameter of 15 mm and length of 34 mm, the beam current was increased to 41.8 mA. Furthermore, it was increased to 43.4 mA by using a flat triple hairpin shape LaB$$_{6}$$ filament.

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