ODE with double integral operation

Have you ever tried to evaluate you double integral on its own outside the solve block? You should have done so, as you get an error doing so.

What I have noticed is

1) E.r obviously should have unit Joule, so the integral limits must have this unit, too. This means that l=7 J, not dimensionless

2) The argument of the exp function must be dimensionless!!  But your first argument ist Joule squared and the argument in the second exp function is J. This can't work.

3) I doubt that Mathcads odesolve can solve an DE with the function as integral limit. Not sure, though. You should try if thats possible using a simple example.

WE