2024 – The role of SOL flows and recycling in neutral fueling asymmetries and the impact on pedestal performance

The role of SOL flows and recycling in neutral fueling asymmetries and the impact on pedestal performance

2024 Research Campaign, Thrust: High Opacity and Density Operation

Purpose of Experiment

The primary goal of this experiment is to characterize the role of scrape-off-layer (SOL) flows and divertor recycling in inducing in-out and up-down asymmetries in main chamber neutral fueling. Our current understanding is that this asymmetry arises from the combined effect of SOL flows, magnetic topology, recycling, wall conditions and divertor regime. Depending on the plasma flows and location of stagnation points in the SOL, the recycling flux is typically not evenly distributed between the divertor targets. Therefore, the spatial distribution of the recycled neutrals penetrating into the confined plasma region leads to fueling asymmetries.

Experimental Approach

This proposal is aiming to modify near-SOL flows by scanning the injected NBI torque and to disentangle the effect of toroidal rotation, parallel and E✕B flows, magnetic topology, inner divertor detachment and opacity on neutral fueling asymmetries. We will run experiments at different external torque levels to study the effect of toroidal rotation on the near-SOL flows through viscous coupling, and with different Bt directions to investigate drift direction effects. We expect that in lower single null (LSN) plasmas with the magnetic field in the forward direction (Fwd Bt) the ratio of high field side (HFS) to low field side (LFS) fueling will increase with the injected torque due to changes in the near-SOL parallel flows. These experiments will shed light on important dependencies of neutral fueling and will inform pedestal modeling to predict and optimize future burning plasma experiments.

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