There are multiple ways in Elmer to define coil currents in hierarchical simulations for the Whitney AV solver to compute magnetic fields. Basically one can give "Current Density i", i=1,2,3 or "Electric Potential" which is used to internally compute the current sources in the AV solver.

Now the caveat of the given source is that they must be divergence free. Elmer has built-in automated logic to do this but it only works for the given current density, not for the potential. To control the fixing there is the keyword

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```
Fix Input Current density = True
```

Attached is a simple case with five coils (including geo file for netgen). The coil currents are generated automatically to the coil solver. Of all the choices the elemental currents works the best by far

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```
Current Density 1 = Equals "CoilCurrent e 1"
Current Density 2 = Equals "CoilCurrent e 2"
Current Density 3 = Equals "CoilCurrent e 3"
```

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```
Current Density 1 = Equals "CoilCurrent 1"
Current Density 2 = Equals "CoilCurrent 2"
Current Density 3 = Equals "CoilCurrent 3"
```

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```
Electric Potential = Variable "time"
Real Procedure "CoilSolver" "CoilPotentialNormalized"
```

-Peter