Vacuum system of the 3-GeV RCS in J-PARC

J-PARC 3GeVシンクロトンの真空システム

荻原 徳男; 金正 倫計  ; 神谷 潤一郎   ; 山本 風海   ; 吉本 政弘  ; 引地 裕輔; 金澤 謙一郎; 三尾 圭吾; 瀧山 陽一; 菅沼 和明 ; 齊藤 芳男*

Ogiwara, Norio; Kinsho, Michikazu; Kamiya, Junichiro; Yamamoto, Kazami; Yoshimoto, Masahiro; Hikichi, Yusuke; Kanazawa, Kenichiro; Mio, Keigo; Takiyama, Yoichi; Suganuma, Kazuaki; Saito, Yoshio*

3GeV RCSの真空システムを設計するにあたっては、(1)保守時の放射線被爆を最小にすること、また、(2)圧力不安定性を引き起こさないように、ビーム運転中に超高真空を維持することが要求される。このため、イオン誘起脱離によるガス放出の抑制のみならず、ビーム運転中の効率良い排気を考慮したシステムの設計がなされた。具体的には、イオンポンプのみならずターボ分子ポンプを用いた排気を採用した。また、徹底したガス放出の低減対策を施した。さらに、3GeV RCSの特徴である25Hz, 1MW運転から要請される各種機器の開発を行った。その結果として、本真空システムは、現在、200kW運転に至るまで、良好な真空状態を維持している。

To minimize the radiation exposure during maintenance, it is necessary to compose the 3-GeV RCS vacuum system with reliable components which have long life time in such a high level of radiation. In addition, it is necessary to keep the operating pressure with beam in ultra high vacuum for suppressing the pressure instability. Thus we should think of not only the outgassing mainly due to ion desorption but also the pumping efficiency. From the above, the vacuum system was designed. The ring is divided by the isolation valves into 6 sections, which can be pumped down independently. For avoiding any eddy current loss ceramic ducts are used in the bending and focusing magnets. These ducts are connected to the Ti ducts, putting the Ti bellows between. Here, we adopt pure Ti as a material for the ducts and bellows because of its small residual radioactivity. The ring is evacuated with 20 ion pumps (0.7 m/s) and 24 turbomolecular pumps (TMPs) (1.3 m/s), which are attached to the Ti ducts. The TMPs are used for not only rough pumping but also evacuation during the beam operation. Especially a collimator system for localizing beam losses in a restricted area is evacuated with the TMPs, because the outgassing from this region will be probably the largest. On the other hand, each arc section is pumped by 4 ion pumps and 2 TMPs. To realize the above system, we have developed some components such as large aperture ceramic ducts and TMPs with high radioactive-resistance, as well as several kinds of heat treatment to reduce the outgassing. Finally, we have realized the UHV without baking in the RCS and the beam operation has been succeeded until now.