Multiple Andreev reflections and enhanced shot noise in diffusive superconducting-normal-superconductor junctions

We study the de conductance and current fluctuations in mesoscopic diffusiv e SNS junctions at subgap applied voltages eV < 2 Delta. We find that in sp ite of the multiple Andreev reflections, the current-voltage characteristic of a long SNINS structure obeys Ohm's law. At the same time, nonequilibriu m heating of subgap electrons produces giant shot noise with pronounced sub harmonic gap structure which corresponds to stepwise growth of the effectiv e transferred charge. At eV --> 0, the shot noise approaches the magnitude of the Johnson-Nyquist noise with the effective temperature T* = Delta/3. W e analyze the role of inelastic scattering and present a criterion of stron g nonequilibrium.