2024 – Demonstrate core-edge solution for high performance plasma with high-beta hybrid core, small ELMs and divertor detachment

Demonstrate core-edge solution for high performance plasma with high-beta hybrid core, small ELMs and divertor detachment

2024 Research Campaign, Core-Edge Integration

Purpose of Experiment

A scenario with a high-performance core—high BN and high confinement factor—combined with a boundary solution that limits peak heat flux to the divertor is needed for ITER and future fusion pilot plants (FPP). Recent experiments have demonstrated two paths to achieving edge localized mode (ELM) mitigation in high performance scenarios: the grassy ELM regime accessed through low edge collisionality and the small ELM regime accessed through high edge collisionality. Both regimes show high frequency ELMs with 5-10% of the transient heat loads seen with large Type-I ELMs. This experiment seeks to further explore these regimes and examining their compatibility with a detached divertor, focusing on core-edge integration and the expansion of operation conditions relevant to FPP and ITER.

Experimental Approach

The first half of the experiment aims to: a) assess the compatibility of small/grassy ELMs with a detached divertor under enhanced divertor pumping conditions (Core-edge integration); b) access the FPP/ITER relevant condition, including higher heating power, lower safety factor (q95), and increased fusion gain factor (G); c) leverage strong shaping from Shape-Volume-Rise (SVR) for mitigating edge peeling-ballooning modes, thereby broadening the operational scope for low-collisionality grassy ELMs. The second half of the experiment seeks to perform similar studies with a high collisionality edge. Access to this regime should improve as the shape is modified to use the strong shaping available with the new SVR divertor. The previous experiment achieved high performance at high density but did not consistently access the high frequency ELM regime. In addition, divertor parameters were not well measured in the previous experiment so it is unknown whether the high frequency ELM regime effected divertor detachment. This experiment will explore the physics of divertor detachment in this high frequency ELM regime. An important aspect of this experiment is preserving the core performance during divertor detachment. Impurity injection in the divertor region with N2 or Ne will be used to achieve detachment.

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