simulate a suqare inductor

Hi,

i'm new in Comsol and I want to simulate a square inductor, firstly I used a external current density in Magnetic field Module i get the magnetic field is near to the theorattical MF but the probleme I can not see the current density when i want to draw the 3D arrow volume, what does mean??
then I tried to used the single turn coil like a sample of single coil gap feed but I don't have success

thank's for your help,