The observed distributions of density and floating potential confirm that convective loss plays an important role in plasma transport in the stellarator field. To suppress the convective motion, the effect of viscosity damping of the motion is utilized. As the kinetic viscosity perpendicular to the magnetic field is proportional to (ρi, mi and νii are ion Larmor radius, mass and collision frequency, respectively), heavy ion plasmas such as argon and xenon plasmas are used. The experimental results confirm the effect of the viscosity damping, and the observed diffusion coefficient of the xenon plasma is, within a factor of 2, the same as the neoclassical one in the plateau region.