A Scrape‐off Layer Based Density Limit for JET ELMy H‐modes

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Abstract
During a density ramp‐up JET ELMy H‐modes typically show a saturation of the core density which may even be followed by a decrease (density limit). At the limit the discharge detaches between ELMs and a recently proposed edge based detachment limit for the separatrix density applies. In this paper a simple picture is proposed for the relation between separatrix and core density which allows us to derive the corresponding limit for the core density. The empirical evidence from JET is discussed and compared with the model predictions. It is shown that the resulting limit for the line averaged density coincides in size and scaling with the empirical Greenwald limit.