Non-linear transport due to collisional drift wave and interpretation of related experiments

The non-linear development of a plasma with an unstable collisional drift wave is studied by using two-fluid equations. The set of the non-linear equations for modification of background density and drift mode amplitude is derived by an asymptotic expansion method, which describes well the transition to higher instabilities and non-linear transport. It is shown that stable stationary convective motion exists only for limited values of a critical number, the ratio of viscosity damping to linear growth rate. As this critical number decreases, the number of unstable modes increases, and, usually, a bifurcation of non-linear steady states is obtained. Expressions for particle and heat transport are obtained. A comparison of these results with the experiments of a stellarator device is also made. (author)