Gyrokinetic Simulations of JET Pedestals

Gyrokinetic simulations using the GENE code target a fundamental understanding of JET pedestal transport and, in particular, its modification after installation of an ITER like wall (ILW). In a representative carbon wall discharge, magnetic diagnostics identify washboard modes, which preferentially affect the temperature pedestal. Linear gyrokinetic simulations identify microtearing modes with scale lengths and frequencies comparable to magnetic fluctuation data. A similar ILW discharge is examined, which recovers a similar value of H98, albeit at reduced pedestal temperature. This discharge is distinguished by a much higher value of η, which produces strong ion temperature gradient (ITG) and electron temperature gradient driven instabilities. Global nonlinear simulations indicate that ITG turbulence produces substantial heat flux and very little particle flux. Sensitivity tests varying the density gradient demonstrate an ITG particle pinch that balances diffusion, suggesting that ITG may mediate the density profile. The ITG heat flux exhibits a scaling with ExB shear rate that agrees with basic theory [Hatch et al PPCF 2018] and suggests high sensitivity to ρ*.