Estimation of beam trip frequencies of ADS accelerator based on the operational data of J-PARC Linac

J-PARC運転データに基づく加速器駆動核変換システム用加速器のビームトリップ頻度の評価

武井 早憲   

Takei, Hayanori

現存する大出力陽子加速器では頻繁にビームトリップ事象が発生するため、加速器駆動核変換システム(ADS)の未臨界炉を構成する機器に対して熱疲労損傷を生じる可能性がある。すでに、この影響を熱過渡解析に基づき評価し、ビームトリップ時間毎に許容されるビームトリップ頻度を求め、既存の加速器(米国LANSCE及びKEK電子・陽電子線形加速器)の運転データよりADS用加速器のビームトリップ頻度を推定した。両者を比較した結果、ビームトリップ時間が10秒以下のビームトリップ頻度は許容ビームトリップ頻度以下となったが、トリップ時間が10秒を超えるビームトリップ頻度は許容値を635倍上回っていた。本研究では、新たにJ-PARCリニアックの運転データを解析し、モンテカルロ法を用いてADS用加速器のビームトリップ頻度を推定した。その結果、ビームトリップ時間が10秒以下のビームトリップ頻度は既報と同様に許容値以下となった。一方、ビームトリップ時間が10秒を超えるビームトリップ頻度は既報の値よりも小さくなったが、まだ許容値を310倍上回っていることがわかった。

Frequent beam trips as experienced in existing high-power proton accelerators may cause thermal fatigue in Accelerator-Driven System (ADS) components, which may lead to degradation of their structural integrity and reduction of their lifetime. In the previous study, the thermal transient analyses were performed to investigate the effects of beam trips on the reactor components. In order to consider methods to reduce beam-trip frequency, we compared the acceptable beam-trip frequency with the performance of the ADS accelerator, which was estimated based on the operational data on existing accelerators, the Los Alamos Neutron Science Center (LANSCE) and the High Energy Accelerator Research Organization (KEK). The comparison showed that for beam trips with a duration of 10 s or less, the beam-trip frequency was acceptable. On the other hand, for beam trips with durations exceeding 10 s, beam-trip frequencies were about 6 to 35 times larger than acceptable values. In the present study, the operational data on J-PARC Linac were newly analyzed and probability density functions (pdf) of beam trips for the ion source and the accelerator tube of the J-PARC Linac was obtained. Using the Monte Carlo method based on the beam-trip pdf, the beam-trip frequencies of the ADS accelerator were estimated. As the result of the estimation, it was found that the type of the beam-trip pdf was the initial failure type, i.e., the beam-trip frequency for the ion source and the accelerator tube was larger at the beginning and decreased monotonously with the operation time. And the beam-trip frequency of the ADS accelerator with a duration of 10 s or less was acceptable, as same as the previous value. On the other hand, beam-trip frequencies with durations exceeding 10 s were less than the previous values, but about 3 to 10 times larger than acceptable values.