JFT-2M NBI磁気浮上型TMPの振動測定試験

Abstract

The magnetic levitation type turbo molecular pump installed in the main exhaust system of the Neutral particle Beam Injector (NBI) system was damaged. This system was used for the highly heated density test for the JFT-2M (JAERI's (Japan Atomic Energy Research Institute) Fusion Torus-2M). After the damage, permanent countermeasures were employed and the results of the vibration test were reported. Vibration tests were made in order to investigate the cause of the damage. As a result, excess acceleration acted which was much larger than the guaranteed value by the manufacturer and the displacement was also large. Therefore, the cause of the damage was shown to be the excess force which acted on the turbo molecular pump. Hence new bellows for the purpose of vibration absorption were fabricated, and the turbo molecular pump was replaced by the one with higher guaranteed anti-vibration value. The exhaust manifold was also fixed. The test results indicated that both the acceleration and the displacement were reduced to 1/4 and 1/5 of the previous values, respectively. The safety of the new system was confirmed furthermore by the frequency analysis of the maximum acceleration. The output values of the gap sensor also indicated that the new arrangement has a sufficient room of safety with respect to the gap at the touchdown position.

高性能トカマク開発試験装置(JFT-2M)用高加熱密度試験用の中性粒子入射装置(NBI)主排気系の磁気浮上型ターボ分子ポンプの損傷発生から恒久対策後の振動測定試験について述べた。損傷の原因調査のために振動測定試験を行った結果、メーカの耐加振試験値を大きく超える加速度が働き、変位も大きかった。よって、ターボ分子ポンプに許容値を上回る過大な力が加わったことが損傷の原因であると裏付けられた。振動吸収用のベローズを新たに製作し、ターボ分子ポンプもより大きな耐加振試験値のものにかえた。排気マニホールド部も固定した。振動試験の結果、加速度、変位ともそれぞれ1/4、1/5に低減させることができた。最大加速度発生時の周波数分析から、安全性も確認された。ギャップセンサの出力からも、タッチダウンに至るギャップに対して充分余裕があることがわかった。