Contact resistivity due to oxide layers between two REBCO tapes
Contact resistivity due to oxide layers between two REBCO tapes
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由于两个 REBCO 胶带之间的氧化层而产生的接触电阻率
DOI：
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Jeremy Levitan
中科院分区：
文献类型：
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作者：
Jun Lu;Y. Xin;E. Lochner;K. Radcliff;Jeremy Levitan
在无绝缘（NI）REBCO磁体中，匝间接触电阻率（ρc）决定了其失超自保护能力、充电延迟时间和磁场斜坡期间的能量损失。因此，能够控制适用于各种NI磁体线圈的ρc值范围至关重要。在这项工作中，我们研究了两种可能性来控制ρc：通过控制REBCO带材的铜表面的氧化物层;以及通过控制不锈钢共卷带材中的氧化物层。我们使用商用氧化剂Ebonol® C处理REBCO带材的铜表面。铜的氧化物层，其特征在于通过横截面透射电子显微镜（TEM）和X射线光电子能谱（XPS）。在Ebonol® C中在98 °C下持续1分钟形成的氧化物层是0.5-1 μm的Cu 2 O。在4.2K下，两种氧化REBCO之间的ρc约为35 mΩ cm ~ 2，在30000次接触压力循环后，ρ c降至10 mΩ cm ~ 2。ρc在77 K时仅增加5%。我们还研究了不锈钢共卷带的氧化对ρc的影响。用TEM和XPS研究了316不锈钢带表面的自然氧化物以及在200 °C-600 °C空气中加热的自然氧化物。原生氧化物层约为3 nm厚。在300 °C加热8分钟和600 °C加热1分钟后，其厚度分别增加到约10和30 nm。对于表面氧化层厚度约为10 nm的不锈钢带，经30000次压力循环后，ρc下降了近4个数量级。而在77 K时，它仅减少3倍。对于具有30 nm氧化物的表面，ρc随着负载循环适度降低。结果表明，对于氧化的不锈钢，要在大量的负载循环中获得稳定的ρc，需要相对厚的氧化膜。
In a no-insulation (NI) REBCO magnet, the turn-to-turn contact resistivity (ρc) determines its quench self-protection capability, charging delay time and the energy loss during field ramps. Therefore it is critically important to be able to control a range of ρc values suitable for various NI magnet coils. In this work, we investigate two possibilities to control ρc: by controlling the oxide layer of the copper surface of REBCO tapes; and by controlling the oxide layer in stainless steel co-wind tapes. We used a commercial oxidizing agent Ebonol® C to treat the copper surface of REBCO tapes. The copper oxide layer was characterized by cross-sectional transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The oxide layer formed in Ebonol® C at 98 °C for 1 min is Cu2O of 0.5–1 μm. The ρc between two oxidized REBCO is in the order of 35 mΩ cm2 at 4.2 K which decreases to 10 mΩ cm2 after 30 000 contact pressure cycles. The ρc increases but only by 5% at 77 K. We also investigated the effect of oxidation of stainless steel co-wind tape on ρc. The native oxides on 316 stainless steel tape as well as those heated in air at 200 °C–600 °C were examined by TEM and XPS. The native oxides layer is about 3 nm thick. After heating at 300 °C for 8 min and 600 °C for 1 min, its thickness increases to about 10 and 30 nm respectively. For the stainless steel tapes with about 10 nm surface oxides, pressure cycling for 30 000 cycles decreases ρc by almost 4 orders of magnitude. Whereas at 77 K, it only decreases by a factor of 3. For a surface with 30 nm oxide, the ρc decreases moderately with load cycles. The results suggest that for an oxidized stainless steel to achieve stable ρc over large number of load cycles a relatively thick oxide film is needed.