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Influence of magnetic fields on turbo-molucular pumps

磁場のターボ分子ポンプに与える影響

荻原 徳男; 金澤 謙一郎; 猪原 崇*; 和田 薫*

Ogiwara, Norio; Kanazawa, Kenichiro; Inohara, Takashi*; Wada, Kaoru*

ターボ分子ポンプ(TMP)は、核融合及び加速器等の分野でも広く用いられている。ここで問題となるのは、準定常的にかかる磁場の影響である。そこで、最初に、この磁場のTMPに与える影響を、(1)ローター回転軸に平行な磁場の場合と、(2)直交する磁場の場合にわけて調べた。平行な磁場による影響はなく、磁場のない場合と変わらないのに対して、直交磁場の場合にはローター駆動電力の増大及びローター温度の上昇が観測された。これは、渦電流損によるもので、その磁場依存性は、以下のとおりである。(a)磁場強度の2乗に比例して渦電流損は増加する。(b)ローター回転数に対する依存性は、回転数が高くなると回転数の1/2乗に比例して渦電流損は増加する。これらの特性は、簡単な渦電流のモデルにより説明される。

Recently turbo-molecular pumps (TMPs) have been widely used in nuclear fusion devices and sometimes in particle accelerators. Therefore, in order to use them in a quasi-static magnetic field the influence of the fields on TMPs has been exactly investigated. First of all, the influence for the two special magnetic fields has been examined: one is due to the vertical magnetic field, and the other due to the parallel component. The parallel magnetic field has no influence of the operation of the TMP. On the contrary, the driving power and the rotor temperature were largely affected by the vertical magnetic field. The eddy current loss in the vertical field increases rapidly with the field strength. It is proportional to the square of the field strength. The eddy current loss also increases as the revolution frequency, however, it has quite different dependence from the magnetic field strength. These dependences are well explained by the skin depth, which referred to the region where a localized magnetic field and current flow exists. Then we have successfully evaluated the influence of the magnetic field with an arbitrary direction by means of adding the contributions from the two magnetic components. Furthermore, from the demonstration experiment, it is generally found that the magnetic field with the symmetry around the rotor axis does not affect the operation of the TMP.

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パーセンタイル:30.25

分野:Materials Science, Multidisciplinary

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