The driving toroidal electric field in Tokamaks is shown to lead to a significant pinching effect at low collision frequency. For ${\beta }_{\theta }=\frac{8\pi p}{B_{\theta }^{}{}_{}{}^2}<1\mathrm{}$, where $B_{\theta }$ is the poloidal field, this pinching is more rapid than outward diffusion in the banana and plateau regimes of toroidal transport theory.

• Received 27 July 1970

DOI:https://doi.org/10.1103/PhysRevLett.25.1090