Characteristics of trapped electron transport, zonal flow staircase, turbulence fluctuation spectra in elongated tokamak plasmas

Abstract

The effects of plasma elongation on trapped electron mode (TEM) driven turbulence and transport are investigated with detailed analyses of fluctuation, zonal flow and zonal pressure. For the study, global nonlinear TEM simulations with different elongations () are performed by employing a bounce-averaged gyrokinetic code gKPSP. From the simulations, -scalings of the electron heat conductivity (), ion heat conductivity (), and particle diffusivity () are found as , and , respectively. Higher plasma elongation is found to enhance zonal flows and their shearing rate at short radial scales, which in turn reduce the radial correlation length of turbulence and limit avalanche-like large scale transport events. Radial corrugations of density and temperature profiles also emerge due to quasi-stationary zonal flows at short spatial scales. In addition, it is found that the Doppler shift caused by the quasi-stationary zonal flows can modify the phase velocity of fluctuation in the laboratory frame and result in turbulence spectra consisting of components propagating in both electron and ion diamagnetic directions, while the transport is mainly governed by TEM.

Self-consistent model of the plasma staircase and nonlinear Schrödinger equation with subquadratic power nonlinearity

“…Concerning the units, "a" is the tokamak minor radius, "c s " is the ion acoustic speed, and ρ is the dimensionless radial coordinate. plasma to generate staircase structures proves to be an established fact [3,4], it has been confirmed computationally using different numerical codes [11][12][13][14][15][16]; discussed theoretically, especially invoking flux-gradient time delay, flux landscape bistability or wave trapping [17][18][19][20][21][22]; and observed experimentally other than on Tore Supra also on DIII-D [16]; KSTAR [23]; and lately in HL-2A L-mode discharges [24].…”

A new mechanism for increasing density peaking in tokamaks: improvement of the inward particle pinch with edge E × B shearing

“…The significant suppression of Ion Temperature Gradient (ITG) dominated plasma turbulence via electromagnetic fluctuations and fast ions [1,2], for instance, has opened up the scope of turbulence reduction by alternative mechanisms to the wellknown E×B shearing. Such effects have also been shown to play an important role in the so-called isotope effect [3,4] and the recently found E×B staircase phenomenon [5][6][7].…”

Wave trapping and E × B staircases

“…Zonal flows play a major role in the dynamics of "E × B" staircases, which are self-organised turbulent states observed in a number of gyrokinetic simulations [16,17,18,19,20,21]. Similar patterns were observed in simulations of a reduced 2D model of interchange turbulence [22] and also 2D ion temperature gradient (ITG) turbulence [23].…”