Development of a Conduction-Cooled Low Temperature Superconducting (LTS) Pulse Coil

电导冷却LTS脉冲线圈具有优良的特性，足以满足短时间不间断电源（UPS）的要求。与液氦池沸腾或超临界氦强制流动等传统冷却方式相比，传导冷却具有可靠性高、操作简便等优点。超导导体要求具有低的交流损耗和高的稳定性。研制了一种铝挤压NbTi/Cu压实股绞线电缆的SC导体。线圈形状是183转x 14层缠绕在GFRP筒管上的单个螺线管。Dyneema FRP （DFRP）垫片和Litz线（绝缘铜股编织线）插入每层。DFRP垫片与Dyneema长丝具有良好的导热性，增强了绕组中层与层之间的传热。另一方面，Litz导线增加了绕组之间的热量传递，并通过将Litz导线的末端直接连接到制冷机的冷头上，实现了更多线圈的传导冷却。该盘管连接了3台GM制冷机，其制冷量在4 K时为4.5 W，在50 K时为240 W。而盘管冷质量为1100千克，热负荷为2.3 W在4 K和186 W在65 K。它花了大约两周的时间来冷却盘管作为专门利用制冷机。在冷却过程中，线圈内部的空间温度分布可以忽略不计，这表明线圈具有良好的热性能。为了评估线圈的热性能，线圈电流从1000 A的额定电流以4 s的时间常数迅速减小。由于447j的交流损耗，线圈的温度从3.9 K上升到4.4 K。然而，线圈的温升只有0.5 K。这意味着交流损耗产生的热量在线圈绕组内被很好地分布，并且在几秒钟内也被转移到制冷机的冷头上。由于线圈的组件在低于10 K的低温下具有很高的热扩散率，因此线圈的热扩散率增强导致温度快速稳定。我们成功研制了1兆焦耳导冷LTS脉冲线圈。通过冷却和激励试验验证了导冷线圈的优良性能，并通过UPS-SMES的能量提取试验验证了其适用性。少

A conduction-cooled LTS pulse coil has excellent characteristics, which are adequate for a short-time uninterruptible power supply (UPS). The conduction cooling has higher reliability and easier operation than the conventional cooling schemes such as pool boiling with liquid helium or forced flow of supercritical helium. A low AC loss and a high stability are required for the superconducting (SC) conductor. The SC conductor of a NbTi/Cu compacted strand cable extruded with an aluminum has been developed. The coil shape is a single solenoid of 183 turns x 14 layers wound on the GFRP bobbin. The Dyneema FRP (DFRP) spacers and the Litz wires (braided wires of insulated copper strands) are inserted in each layer. The DFRP spacers have a good thermal conductivity along with Dyneema filaments, which enhance the heat transfer from layer to layer in the windings. On the other hand, the Litz wires increase the heat transfer from turn to turn in the windings and enable conduction cooling of the … More coil by attaching the end of the Litz wires directly to the cold heads of the cryocoolers. The coil was connected with three GM cryocoolers which have cooling capacity of 4.5 W at 4 K and 240 W at 50 K. Whereas the coil cold mass is 1, 100 kg and the heat loads are 2.3 W at 4 K and 186 W at 65 K. It took approximately two weeks to cool-down the coil as exclusively utilizing cryocoolers. The spatial temperature distributions within the coil were negligible during the cool-down, which indicated good thermal properties of the coil. To evaluate the thermal performance of the coil, the coil current was reduced rapidly from the rated current of 1000 A with a time constant of 4 s. Due to the AC loss of 447 J, the temperature of the coil increased from 3.9 K to 4.4 K. However, the temperature increase of the coil was only 0.5 K. It means that the heat generated by the AC loss was well distributed within the coil winding and was also transferred to the cold heads of cryocoolers during a few second. Since the components of the coil have high thermal diffusivities at the cryogenic temperature below 10 K, the enhanced thermal diffusivity of the coil results in the rapid temperature stabilization. We have successfully developed the 1 MJ conduction-cooled LTS pulse coil. The high performance of the conduction-cooled coil has been demonstrated by the cooling and excitation tests and its applicability was also confirmed by the energy extraction tests as the UPS-SMES. Less