Bifurcation theory of poloidal rotation in tokamaks: A model for L-H transition

TLDR

The theory is used to explain the L‑H transition in tokamaks. The model predicts bifurcated poloidal momentum solutions, where decreasing ion collisionality abruptly increases poloidal flow, deepens the radial electric field, suppresses turbulence, and enhances confinement.

Abstract

It is shown that the poloidal momentum balance equation in tokamaks has bifurcated solutions. The poloidal flow velocity ${U}_{p}$ can suddenly become more positive when the ion collisionality decreases. The corresponding radial electric field ${E}_{r}$ becomes more negative and hence suppresses the turbulent fluctuations. Thus, plasma confinement is improved. The theory is employed to explain the L-H transition observed in tokamaks.