Nonlinear saturation of ETG turbulence

Magnetic-confinement-fusion devices such as tokamaks aim to sustain plasmas at temperatures and densities high enough for the energy produced by fusion reactions to outpace the losses. The dominant source of these losses is from turbulence --- a chaotic, nonlinear ensemble of Larmor-scale fluctuations driven by the gradients of the plasma density and temperature --- that transports particles and heat across the confining magnetic field. Electron-temperature-gradient (ETG) turbulence can constrain the performance of the tokamak pedestal --- the steep-gradient region near the plasma's edge --- in present-day devices [see, e.g., Turica et al. (2026); Field et al. (2026)]. Despite recent advances in our understanding of ETG turbulence and its transport scalings [see, e.g., Hatch et al. (2022); Chapman-Oplopoiou et al. (2022); Adkins et al. (2026)], the mechanisms governing its nonlinear saturation across different parameter regimes remain poorly understood. In particular, local gyrokinetic simulations of toroidal ETG turbulence can exhibit streamer-dominated states in which the transport fails to reach a statistically steady level [see, e.g., Jenko et al. (2000)]. This behaviour raises two related questions: which parameter regimes permit such runaway transport, and what physical effects ultimately regulate it in real plasmas? Answering these questions is essential for reliable predictions of pedestal performance in future fusion devices. In this project, the student will investigate the non-saturation of ETG-driven transport and its behaviour near marginality within the local gyrokinetic framework using a combination of analytical theory, reduced modelling, and high-fidelity gyrokinetic simulations. The student will seek to identify where non-saturation occurs, determine the physical mechanisms responsible, and develop reduced criteria for predicting its onset. These criteria will then be used to assess pedestal behaviour in high-performance scenarios. Prior familiarity with gyrokinetic or drift-kinetic plasma theory would be advantageous but is not essential.