Automated Determination of T_c for a High T_c Superconductor During Electron Irradiation Experiments in the Argonne HVEM

Abstract

Over the more than twenty years of operation of the 1.2 MeV AEI/Kratos HVEM at Argonne (Fig 1.), the primary emphasis by the user community has been on a wide variety of in situ irradiation effects studies involving both electrons and ions. in many cases it has been essential for the success of experiments for the professional technical staff of the Facility to develop specialty devices and techniques. This contribution deals with one such system which we have developed, namely, the design, assembly and operation of a system for in situ automated measurement of specimen electrical resistivity as a function of temperature in the range 15-135 K. A major problem is associated with this situation, which involves a small gauge-section conductor, requiring stable amplification and measurement of very minute electrical signals. The specific set of experiments for which this application was developed involved determining the effect of electron irradiation on the superconducting transition temperature T_c of YBaCuprate (YBCO) in order to distinguish between two possible theories of the conduction mechanism. in this type of experiment the critical temperature T_c is determined from a plot of electrical resistivity as a function of temperature following irradiation at 100 K at zero applied magnetic field to preclude the Meissner Effect. in these experiments T_c is 89 K prior to electron irradiation and drops to <15 K with increasing electron fluence. The analysis also revealed an oxygen-disorder-induced superconductor to normal-metal transition after sufficient electron fluence. Fig. 2 shows typical measurement results for two temperature ramps. The detailed results of these experiments are described elsewhere by Giapintzakis et al.