Effects of Parallel Wavelength on the Collisional Drift Instability

Abstract

An extensive investigation of the dependence of drift wave characteristics upon parallel wavelength in collisional potassium Q ‐machine plasmas is presented. Results are compared with a two‐fluid slab‐model theory which includes the effects of parallel resistivity and thermal conductivity for electrons and Larmor radius, collisional viscosity, and motion parallel to the magnetic field for ions. The general stability characteristics of the drift wave are confirmed: stability at low magnetic field (B/k ⊥ ≲0.4 kG · cm ) due to ion viscosity, stability at both long‐ and short‐parallel wavelength ( λ ‖ ≳ 200 and λ ‖ ≲100 cm , respectively) due to the combined effects of ion viscosity and parallel electron fluid expansion and stability of individual modes at high magnetic field (B/k ⊥ ≈ 1 kG · cm , λ ‖ ≈ 100 cm ) due to ion parallel motion. Quantitative agreement between experiment and theory is demonstrated for the detailed parametric dependences of instability onset, complex frequency, and oscillation amplitude on parallel wavelength, magnetic field, and density.