Collisionless Drift Waves Ranging from Current-Driven, Shear-Modified, and Electron-Temperature-Gradient Modes

The specific history of collisionless drift waves is marked by focusing upon current-driven, shear-modified, and electron-temperature-gradient modes. Studies of current-driven collisionless drift waves started in 1977 using the Innsbruck Q machine and was continued over 30 years until 2009 with topics such as plasma heating by drift waves in fusion-oriented confinement and space/astrophysical plasmas. Superposition of perpendicular flow velocity shear on parallel shear intensively modifies the drift wave characteristics through the variation of its azimuthal structure, where the parallel-shear driven instability is suppressed for strong perpendicular shears, while hybrid-ion velocity shear cause unexpected stabilization of the parallel-shear-modified drift wave. An electron temperature gradient can be formed easily by control of thermionic electron superimposed on ECR plasma, and is found to excite low-frequency fluctuation in the range of drift waves.