Theory of High-Mode Phenomena for Stellarators

It is shown that besides the ion orbit loss mechanism, which occurs in a region $a-{\varepsilon }_t{\rho }_p<r<a$, the drift-orbit transport flux driven by the collisionless helically trapped particles can also drive the poloidal $\overrightarrow{E}\times \overrightarrow{B}$ velocity in a region $r<a-{\varepsilon }_t{\rho }_p$ in stellarators. Here, $r\left(a\right)$ is the minor (plasma) radius, ${\varepsilon }_t$ is the toroidal amplitude of the magnetic field spectrum, $\overrightarrow{E}\left(\overrightarrow{B}\right)$ is the electric (magnetic) field, and ${\rho }_p$ is the poloidal ion gyroradius. The transport-flux-driven $\overrightarrow{E}\times \overrightarrow{B}$ velocity can be triggered most efficiently by an increase of the ion temperature gradient. The theory is applied to the high-mode phenomenon observed in stellarators.