Shear velocity stabilization of reactive trapped electron modes

One of the main candidates for the explanation of anomalous electron transport in tokamaks is the reactive trapped electron mode driven by compressibility (curvature) and electron temperature gradient. The influence of flow shear on this mode is studied by solving the radial eigenvalue problem. It is found that the Waltz rule stabilization criterion usually gives too strong a stabilization of this mode. The spatial-temporal evolution of unstable trapped electron modes is also investigated. It is found that it is strongly influenced by the continuum part of the spectrum. It is shown that the modes propagate with an acceleration from the source region, thereby widening the region of instability.