I got some peripheral involvement in shrinking coins in 1991 [ I showed
up, and got them to shrink some coins for me].
The large loft in Down town Seattle used for amateur experiments was
rented by two guys.
There is a wizard named Dan who suggested to those two guys to go buy
some surplus capacitors that had become available.
These were special caps used for Reagan's star wars research on high
velocity electric guns.
The caps were high capacitance value, high Voltage, low effective series
resistance, and low output inductance.
They would wind solid, not stranded wire around a coin.
A safety shroud that looked like a helmet, but was ~1/4" welded steel,
was put over the coil and coil.
The caps were charged up for ~10 minutes with a Neon light transformer,
An pneumatic compressed air solenoid had been fashioned. It was
something like a wooden arrow that was pushed by air very quickly to
close the circuit.
When the air valve was thrown, we would be hiding behind furniture and
covering our ears.
It was as loud as being indoors with a high power rifle.
The solid #12 AWG wire would break up into pieces 1/4" long and fly
outward making holes in most insulators. Nomex paper was the only thing
I saw tough enough to stand up to the explosion.
Dan suggested an explanation for the forces:
He said we had 1,000,000 peak Amps.
He said that the coil was a toroidal bundle that was being forced by the
magnetic force to have a smaller minor diameter and a larger greater
flux was then crowded into the coil major diameter and pushing
outwards. The flux set up eddy currents in the coin, that produced flux
that made more crowding. This is the force that made our Quarters shrink
in diameter and get twice as thick.