  Here we describe a three-dimensional current mapping technology developed for
a superconductor using an array of Hall sensors distributed around it. We
demonstrate this in a prototype similar to a conventional resistive
superconducting fault current limiter (SCFCL). By calibrating the Hall sensor
voltage, we can directly measure the distribution of the currents in the
superconductor and the shunt. Using pulsed measurements, we measure the
fractions of current distributed between the superconductor and shunt resistor
parallel combination when a fault-like condition is mimicked in the system.
Using the Hall array measurements, we generate a real-time three-dimensional
map of local average current distribution around the superconductor used in our
prototype of SCFCL. Our measurements show that, even for currents less than the
critical current a non-uniform current flow pattern exists around the
superconductor which we have used in the prototype. The capability of
real-time, three-dimensional monitoring of the average local current
distribution offers a way for the early detection of instabilities like
hotspots developing in a superconductor. We discuss the use of this technique
to not only show how it offers early detection and protection against
instabilities developing in the superconductor, but also how it offers an added
flexibility, namely, a user-settable fault current threshold.
