Resistive drift wave instability is one of the driving sources of turbulence in linear devices, and its ion mass dependence on structural formation is investigated by turbulence simulation. Modes are less unstable in the case with smaller mass ions, because the normalized density gradient length becomes larger with larger Larmor radius, but can be unstable considering the change of ion-neutral collision frequency. Nonlinear calculations show that a large number of modes with larger axial mode

more »

... mbers are linearly unstable and their nonlinear couplings induce turbulence with a zonal flow in the case of smaller mass ions as helium.