Zonal profile corrugations and staircase formation: Role of the transport crossphase

Recently, quasi-stationary structures called E × B staircases were observed in gyrokinetic simulations, in all transport channels [Dif-Pradalier et al. Phys. Rev. Lett. 114, 085004 (2015)]. We present a novel analytical theory—supported by collisional drift-wave fluid simulations—for the generation of density profile corrugations (staircase), independent of the action of zonal flows: turbulent fluctuations self-organize to generate quasi-stationary radial modulations Δ θ k ( r , t ) of the transport crossphase θk between density and electric potential fluctuations. The radial modulations of the associated particle flux drive zonal corrugations of the density profile via a modulational instability. In turn, zonal density corrugations regulate the turbulence via nonlinear damping of the fluctuations.