Basic research of cryogenic low contact resistance switches for persistent operation of superconducting coil

在具有大电流超导线圈的大型螺旋装置等实验装置中，需要能够保持线圈电流恒定。如果可能，恒流操作显然比恒流控制操作更可取。然而，由于目前还没有像其30kA级电流容量那样的大电流恒流开关，所以现在不可能实现恒流操作。因为在超导技术的现阶段，还没有开路时介电强度达到几千伏，闭合时达到零电阻和几十千安的开关。然后选择了普通导电式机械开关的研制。目前的结果如下：触点由铜基制成，其接触面镀有铅锡焊料。接触点由鼓形凸起(曲率半径：20 mm，长度：20 mm)和平板组成。这些接触器用在液氦浴缸中，彼此接触，然后滑动。焊锡的厚度为0.15-0.5 mm。接触力为70-80公斤。获得的接触电阻在100A时为0.01微欧姆，200A时为0.1微欧姆，300A时为0.3微欧姆。如果100个触点并联运行，每个接触器的流量为300A，则30kA，0.003微欧。如果用于1H级线圈的电路，其倾倒时间常数为10年。

It is necessary to be able to keep coil currents constant in the experimental devices such as Large Helical Device which has large current superconducting coils. Persistent current operation is obviously preferable to constant current control operation, if possible. However, the persistent current operation is nowadays impossible because there is no such a high current persistent current switch as its current capacity of 30kA class. Because at the present stage of superconducting technology, there are no switches which have dielectric strength of several thousand volts in the open state and zero resistance and current capacity of several ten kA in the closed state. Then we chose development of normal conductive mechanical switches. Present results of are as follows ;The contact points are made of copper base and their contact surface are plating with Pb-Sn solder. The contact points are formed from both a drum shaped projection (radius of curvature : 20mm, length : 20mm) and a flat plate. These contactors are used in the liquid helium bath and contacted and then slides each other. The thickness of the solder plating is 0.15-0.5mm. The contacting force is 70-80kg. Obtained contact resistance are 0.01 micro ohm at 100A,0.1 micro ohm at 200A,0.3 micro ohm at 300A.It seems almost zero ohm in the range less than 100A.If 100 contacts are operated at parallel connection and each contactor is flowed 300A,then 30kA,0.003 micro ohm. If it is used in the circuit of 1H class coil, the dumping time constant is 10 years.