Non-destructive assessment of the critical current density in large superconducting pellets

We present a new method of rapidly determining the local critical current density (Jc) in large superconducting pellets without destroying the sample. We show that magnetoscan data averaged over a certain small sample area can be mapped directly onto absolute values of Jc. This conclusion and the corresponding calibration curve are based on results from magnetoscan and from SQUID measurements of the same sample regions, which were found to show an excellent correlation. Numerical simulations help to extend the calibration curve, to improve the resolution of the method and to reduce possible errors. (Some figures in this article are in colour only in the electronic version)