ETG Instability in the Mega Ampere Spherical Tokamak Pedestal

We present a gyrokinetic analysis of turbulent transport from electron temperature gradient (ETG) driven turbulence in the MAST pedestal. During ELM cycles, the electron density profile builds up faster than the electron temperature profile, suggesting that an electron thermal transport mechanism must be active. ETG transport is considered a plausible candidate because of its large electron heat diffusivity and low electron particle diffusivity. ETG has been investigated recently in NSTX and shown can be important in spherical tokamaks' (ST) pedestals [1]. Local linear and nonlinear results derived from the gyrokinetic code GENE also show that heat flux produced by ETG modes is 10-30% of the neutral beam injection in the MAST upper pedestal and pedestal top during the pre-ELM (80-99% inter-ELM period) and post-ELM (0-20%) periods. A reduced ETG model for conventional tokamak heat flux prediction is tested on MAST's pedestal [2]. Another reduced gyrokinetic model developed for instability identification for the core of conventional tokamaks will also be tested and improved for STs' pedestals [3].



[1] W. Guttenfelder et al., Nucl. Fusion 62 042023 (2022)

[2] D. R. Hatch et al., Phys. of Plasmas 29, 062501 (2022)

[3] D. B. Verma et al, (Nov.2021), 63^rd APS DPP; Pittsburg PA