Evaluation of mean time between accidental interruptions for accelerator klystron systems based on the reliability engineering method

信頼性工学に基づく加速器クライストロン系で発生するトリップ事象の平均時間間隔の算出

武井 早憲   ; 古川 和朗*; 矢野 喜治*; 小川 雄二郎*

Takei, Hayanori; Furukawa, Kazuro*; Yano, Yoshiharu*; Ogawa, Yujiro*

加速器駆動核変換システム(ADS)では、ビームトリップ事象が少ない、信頼性の高い加速器を開発しなければならないが、ビームトリップ事象がどの位の間隔で生じているか統一した手法で評価されていない。本研究では、統一した評価手法を得ることを目的として、高エネルギー加速器研究機構入射用加速器のクライストロン系の運転データを用いてクライストロン系が偶発的にトリップする平均時間間隔(MTBI)を信頼性工学に基づく手法で評価し、従来の結果と比較した。従来、クライストロン系のMTBIを評価する手法は少なくとも3種類あり、評価したMTBIは30.9時間, 32.0時間、そして50.4時間となった。一方、本研究では信頼性工学では一般的なノンパラメトリックな評価手法を用いてMTBIを評価したところ、57.3時間となり、従来の評価値と比較して1.14倍以上も長い時間となった。今後、本研究で述べた信頼性工学に基づく手法でビームトリップの平均時間間隔を評価することが望ましい。

Experiences with existing high-power proton accelerators indicate that frequent beam trips are inevitable. One of the reasons for such frequent beam trips is the accidental interruption to protect accelerators against fatal failures. Generally, the failure frequency for the general machinery can be evaluated based on a reliability database for its components. On the other hand, the beam-trip frequency for the accidental interruption was not evaluated based on the reliability database because it has not yet been established. A principal reason for the lack of this reliability database is the inconsistency of data collection and analysis methods among laboratories. For example, there are at least three methods to estimate Mean Time Between accidental Interruptions (MTBI) for klystron systems. In the present study, the MTBI of the klystron systems of an electron/positron injector linac at the High Energy Accelerator Research Organization (KEK) was evaluated based on the reliability engineering method, in order to build the reliability database using the unified data collection and analysis method. As the result, the mean values of the MTBI by the traditional three methods were evaluated as 30.9, 32.0, and 50.4 hours. On the other hand, that by the reliability engineering method was evaluated as 57.3 hours, i.e., more than 1.14 times of the traditional results. Although these results are obviously different from traditional results, it appears that the present estimation based on the reliability engineering method is suitable for the MTBI of accelerator components as typified by the klystron system.