I am trying to make a .4 Tesla AC (50Hz) magnetic coil. Originally I used ID-38MM, OD-155MM & Length of Solenoid 50MM. Using 3.5MM X 1.5MM wire 380 Turns. I get 0.27 Tesla at 75Amp. but the wire allows me to work only for around 5 Min with Forced air cooling. I do not know the relationship how the field will depend on ID,OD & Length (just that the field is directly proportional to Amp Turns). It would be great if some could give a conditions for maximum field. Any guidance will be great help since i was not able to find anything on NET.