Superconducting tunnel junction (STJ) X-ray detector is promising for materials analysis because of its high energy resolution and high counting rate capability. In order to realize a practical analytical instrument based on STJ X-ray array detectors with hundreds of pixels [1], it is necessary to develop a scalable wiring system to connect between STJ array at a cold stage of a helium three cryostat and readout electronics in room temperature (RT) for its realistic operation including a maintenance. In our previous study, a scalable wiring system was realized utilizing a plug-in wire system, in which all electrical wires were attached to connectors at the both ends and the connections between the STJ array and the RT electronics were established via the connectors, as followings [2]. Harnesses of copper alloy miniature coaxial cables were used from RT to the 2.5 K stage, and NbTi woven looms were placed from the 2.5 K stage to the helium three stage. The number of conductors was fifty for each harness, and eight sets of harnesses were used to connect 200-pixel STJ array to RT electronics. However, the base temperature and the holding time of the helium three stage were degraded due to the heat load from RT to the 2.5 K stage. Copper alloys should be replaced with materials with low thermal conductivity.

 Stainless steel is a unique electronic conductor material with low thermal conductivity that can be used in printed circuit boards. Flexible flat cables with stainless steel conductors were manufactured and were used as connection of RT to the 2.5 K stage instead of harnesses of miniature coaxial cables of copper alloy. Cooling performance of the helium three cryostat was tested. The base temperature of the helium three stage is 302 mK, and the holding time is more than 115 hours. The holding time is 30 hours longer than that of the previous system.

 [1] “Development of superconducting tunnel junction array detectors with three-dimensional structure to exceed 1000-pixel array”, G. Fujii, M. Ukibe, S. Shiki, and M. Ohkubo, J. Low Temp. Phys., 184, 194-199, 2016.
[2] “Plug-in Wire for 200-pixel Superconducting Tunnel Junction X-ray Detector Array for Helium-3 Cryostat”, S. Shiki, G. Fujii and M. Ukibe, J. Phys. Conf. Ser., Volume 1293, 3 012049, 2019.

Keywords: X-ray, cryogenics, array detector