P. Butta', F. Manzo, C. Marchioro A simple Hamiltonian model of runaway particle with singular interaction (211K, PostScript) ABSTRACT. We consider a Hamiltonian system given by a charged particle under the action of a constant electric field and interacting with a medium, which is described as a Vlasov fluid. We assume that the action of the charged particle on the fluid is negligible and that the latter has one dimensional symmetry. We prove that if the singularity of the particle/medium interaction is integrable and the electric field intensity is large enough then the particle escapes to infinity with a quasi-uniformly accelerated motion.