Analysis of current and voltage distribution in the first Japanese qualification sample of an ITER TF conductor

日本のITER-TF導体の性能評価用短尺CICC導体の電流と電圧分布の解析モデル

小泉 徳潔; 松井 邦浩; 奥野 清

Koizumi, Norikiyo; Matsui, Kunihiro; Okuno, Kiyoshi

原子力機構はITER-TF導体の25%の調達を担当しており、原子力機構が開発したTF導体の性能検証試験をスイスのSULTAN試験装置で実施した。本サンプルでは導体長が2.5mと短く、導体内の電流分布はジョイントの影響を受けやすい。一方、ジョイント部は2Tから7Tの不均一な外部磁場を受けるため、銅の磁気抵抗効果によってジョイント抵抗にばらつきが生じる。このため、導体内に電流偏流が発生し、実験結果から正確に導体性能を評価することが困難となっている。そこで、集中定数回路モデル及び二次元の静電界モデルを用いて導体内の電流分布及びコンジット表面の電圧分布を計算するモデルを開発した。加えて、ジョイント内の素線と銅の接触部近傍の電流経路の形状を考慮したモデルを用いて、ジョイントの磁気抵抗効果を正確に評価し、この結果を、前記のモデルに反映した。これらの解析の結果、磁気抵抗の影響によって、分流開始温度が数百mK低く評価されていることがわかった。この影響は、ジョイント部に薄い高抵抗層を入れることで緩和できることもわかった。

Japan Atomic Energy Institute (JAEA), as Japanese Domestic Agency, has responsibility to procure 25% Toroidal Field (TF) coil conductor for ITER. The proto conductor was successfully developed and qualification test of these conductors were performed in the SULTAN test facility in Switzerland. Since the conductor length is only 2.5 m, the current distribution in the conductor is affected by joint. Because the joint is subjected to back ground magnetic field distributed from 2 T to 7 T, joint resistance is not uniform along the cable axis due to electromagnetic resistance of copper in the joint. This causes non-uniform current distribution in the conductor and voltage on surface of jacket is not a constant along circumference direction. It is therefore made difficult to correctly evaluate conductor critical current performance. Thus, the authors developed a simulation model to calculate current distribution in the conductor using a lumped circuit model and voltage distribution on the jacket using a 2-dimensinal steady state potential model. In addition, effect of electromagnetic resistance in the joint is carefully considered by using a model taking account of shape of current path. These simulation results show that the current sharing temperature estimated from the measured voltage is a few hundred milli-Kelvin lower than the one when the current distribution is uniform. In addition, it is figured out that the electromagnetic resistance in the joint originates relatively large non-uniform current distribution. This can be reduced by inserting high resistive thin layer in the joint to decrease the effect of the electromagnetic resistance.