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Description
Hermes-3 is a multi-component plasma fluid code based on the BOUT++ framework [1] which simulates turbulence in the edge region and scrape-off-layer of tokamak plasmas with full 3D diverted tokamak geometry. The effect of turbulent magnetic fluctuations due to local turbulent currents has been implemented in Hermes-3, including ‘magnetic flutter’, how local magnetic fluctuations impact the evaluation of parallel gradients.
Flux-driven turbulence simulations were performed with evolving electron and ion density, momentum, and pressure. The scenario is based on a DIII-D plasma with magnetic fluctuations observed in the dynamics of L-H and H-L transitions [2]. The plasma evolves self-consistently from a given grid and input power to the core. The model has upper single null diverted geometry, unfavourable ion grad-B drift direction, deuterium fuel, toroidal magnetic field BT = 2.0T, plasma current IP =1.0MA, major radius R = 1.72m, and minor radius a = 0.6m. The radial extent of the domain is between normalised radius 0.9<𝜌<1.07, where 𝜌 is the normalised toroidal flux radial coordinate.
Three simulations were performed with varying levels of electromagnetism active in the model: an electrostatic simulation (ES), an electromagnetic simulation without flutter enabled (EM), and an electromagnetic simulation with flutter enabled (Flut). A comparison of the saturated equilibria shows EM has increased turbulent transport than ES, and the Flut simulation shows that inclusion of magnetic flutter reduces this turbulent transport back to levels comparable to the ES simulation.
Magnetic flutter has been seen to be crucial for the GRILLIX team to model their H-mode-like edge profiles [2]. The implementation of flutter in Hermes-3 paves the way for H-mode plasmas and L-H transitions to be simulated.