Probe size to capture data - synchronous generator

The research i am busy with continues with the development of a proto-type hybrid field generator, which has taken the first step towards solving the problem of matching a permanent magnet generator with variable speed operation. I would like to capture the real time flux/ flux density in the air gap between the armature (stator) and the field (rotor) of the synchronous machine. The one constraint is that the size of the air gap is 0.5mm. Is there a coil that is small enough to fit to the tooth of the stator of this machine? Your input would be appreciated Best Regards Raymond