In this work, we deal with topology optimization for designing electromagnetic devices circuits. The considered problems are inverse ones. One of the difficulties of such problem is the derivative informations because in general the cost function is an implicit function (in our case, it provides from the computation of a PDE which is a Maxwell equation). The design sensitivity is calculated from the Lagrangian formulation of the objective function with the adjoint variable method and it allows us to use first order optimization algorithms and also to solve numerically large scale problem in a relatively short CPU-time. Our method is based on the SIMP method (Solid Isotropic Material with Penalization) which is a variant of the homogenization method. For the numerical simulations, we have built our own solver which includes the finite element software FEMM (Finite Element Method Magnetics) and the Matlab optimization fmincon routine. The talk will be ended by the presentation of our topology optimization solver and the numerical results of some problems for designing Plasma Hall effect Thrusters.