ONERA is involved in the testing and development of new current-free electric thruster (helicon thruster or ECR thruster), using magnetized plasmas. For this development, a numerical tool is desirable to model the magnetized plasma, and assess the overall performances of the system. For this reason, a model for the plasma produced in the thruster has been developed. It boils down to a single-fluid MHD model, where the steady-state solutions, in a static magnetic field, are sought using a finite element approach. First, this model is used to address a simple test problem: the cylindrical vessel, with a purely axial magnetic field. This shows the operation regimes of the discharge: magnetized, non magnetized and a transitional regime. Second, a more realistic thruster configuration is modeled, and the results of the code are used to understand the behavior of the plasma. The strong effect of the magnetic field topology is shown, and in particular the use of a purely diverging magnetic field appears to enhance significantly the performances.