Assessing wall heat fluxes in the quasi-continuous exhaust regime at ASDEX Upgrade

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Abstract
The 3D fluid edge code EMC3-EIRENE has been used to simulate three ASDEX Upgrade discharges with the same equilibrium but different upstream collisionality ν ∗ . In this scan, the plasma transits from an ELMy state at low collisionality to being in the quasi-continuous exhaust regime (QCE) at high ν ∗ . Particular attention was devoted to matching the experimental plasma profiles in front of the ion cyclotron resonance heating (ICRH) limiter, aiming to obtain a reliable estimation of the ICRH limiter peak heat flux in the QCE regime discharge. As a result, we observed that while moving from ELMy to QCE, the limiter peak heat flux increases, reaching values in the order of the MW m − 2 for a limiter-separatrix distance of 6 cm . These values were compared with those at the outer divertor, measured by infrared thermography, revealing that the heat flux perpendicular to the limiter surface can reach up to 90% of the one impinging onto the outer target. Finally, an attempt was made to extend the obtained results towards ITER. This simple analysis suggests that a large wall clearance and a small incidence angle of the magnetic field line, not only on the divertor target but also on ITER’s first wall, might have a crucial role in preventing wall damage during QCE discharges.
Funding Information
  • EUROfusion (101052200)

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