I wonder what more or less direct measurements of the displacement current exist. I know that the existence of em waves demonstrates its existence, though somewhat indirectly. I also know that there have been sensitive magnetic field measurements between charging parallel plate capacitors, but it has been argued that these can be explained in terms of the conduction currents flowing within the plates (Bartlett, Am. J. Phys. 58 (12), 1168 (1990) ). Any others?
Update: I ran across an interesting article showing an alternative to the displacement current to make Maxwell's equations consistent with charge conservation, but it fails to predict em waves (Wolsky, Euro. J. Phys. 36 (2015) 035019). It's interesting because it underscores that the displacement current is a theoretical construct. Is there evidence for it that does not invoke Faraday's law?