Profiles of temperature, safety factor, and magnetic shear for an RF-heated NSTX e-ITB, shot 129354 at 232 ms (solid). The electron temperature, safety factor, and magnetic shear for a non e-ITB RF NSTX plasma, shot 124948 at 300 ms, are shown for comparison (dashed).
Linear critical electron temperature gradients, for the parameters of NSTX 129354 during an e-ITB, testing the effects of and ion model. ETG-ki uses gyrokinetic ions, and ETG-ai uses the adiabatic ion approximation. The boxes represent possible and mostly likely experimental values of and within the e-ITB, where .
Radial profiles of experimental and ETG linear critical gradients, NSTX 129354, using Eq. (3) to estimate the linear critical gradients. For reference, the critical gradient formula for positive shear large aspect ratio tokamaks,4 Eq. (1), is also plotted where . The lower bounds on the critical gradients represent , the dashed profiles , and the upper bounds .
Electron heat flux as a function of driving gradient for and . The experimental temperature gradient lengths and electron heat fluxes are, respectively, given by and .
Electron heat flux as a function of driving gradient and magnetic shear for .
Critical gradients as a function of magnetic shear, . ETG becomes linearly unstable at gradients above (solid with square). Above (dashed with circles), turbulent thermal diffusivities exceed . The dotted line with diamonds represents the nonlinear upshift of the critical gradient, . For comparison, the original cyclone ITG test case found an upshift in the critical gradient for transport that extended by 2, from to at .24
Poloidal cross sections of saturated density fluctuations below and above for . The flux-surface widths have been enhanced by a factor of four for visual clarity.
Density fluctuations as a function of poloidal angle and , showing off-midplane peaking at .
Time averaged heat flux spectra for different values of z = 21.8, and the spectrum of the fastest growing linear mode.
Plasma parameters and simulation domain used in the NSTX 129354 global simulations.
Cross-section of electron density fluctuations, 129354 global simulation, showing an electron internal transport barrier. . Although peak amplitudes of exist, for clarity only are shown.
Time evolution of radial heat flux profile, 129354 global simulation, . The white line marks the location of minimum . Heat fluxes as calculated by transp increase as one moves radially from to .
Time-averaged heat flux profiles for global simulations with different values of . For reference, experimentally inferred levels range from to .
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