Simulate eddy current induced by switching off current source in short time

Hello,

I am using COMSOL to simulate eddy current induced by switching off current source in short time. The most simplified model consists of a single turn coil and a copper plate. By switching off current in coil, we should see eddy current in copper plate. Now I am using magnetic field to simulate this problem. The current is defined by a step function 10 * step(t[1/s]) [A]. For coil, I try both single conductor and multi-turn with N=1. However, I always get error. If I use single conductor, COMSOL complains current excitation is not supported. If I use multi-turn with N=1, COMSOL complains the result does not converge. So how can I simulate this problem.

Thanks, Yukai