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

It is shown that the poloidal momentum balance equation in tokamaks has bifurcated solutions. The poloidal flow velocity Uₚ can suddenly become more positive when the ion collisionality decreases. The corresponding radial electric field Eᵣ 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.