A new method is proposed to induce a negative radial electric field in the edge region of tokamak plasmas utilizing the fast ion loss mechanism induced by a toroidal field ripple. In this method, low energy hydrogen isotope beams are perpendicularly injected into the edge plasma. A modest beam power is sufficient to exceed the threshold of the edge radial electric field required for the L- to H-mode transition, derived by Shaing and Crume (SHAING, K.C., CRUME, E.C., Jr., Phys. Rev. Lett. 63 (1989) 2369), in the presence of a small toroidal field ripple; such a ripple is included in existing designs of the next generation of fusion machines