Trajectories of a charge in a magnetic field on Riemannian manifolds with boundary

We prove an existence result for trajectories of classical particles accelerated by a potential and a magnetic field on a non–complete Riemannian manifold M . Both the potential and the magnetic field may be not bounded and have critical growth. We state a suitable convexity assumption involving the magnetic field in order to prove that the support of each trajectory is entirely contained in M .