On the Genesis of Closed Current Filaments in the Edge of JET

Experimental observations show that ELMs lead to the ejection of a number of current carrying filamentary structures into the Scrape-Off Layer (SOL). ELMs generate structures with excess energy and density and it can be conjectured that they leave corresponding holes behind. In contrast to blobs/filaments, holes are usually quickly filled by parallel motion along the magnetic field and therefore exhibit a restricted lifetime. If such a hole, however, is in the vicinity of a resonant surface it closes on itself and increases its lifetime. We suppose that the Palm Tree Mode (PTM) is a signature of such an event and therefore a current hole in contrast to e.g. outer modes. The PTM is an ELM post-cursor, which was until now only detected in JET type-I ELMy H-mode plasmas as long as the rational q = 3 surface is close to the edge pedestal. Understanding PTMs enhances thus our knowledge of ELM and edge physics and contributes to the refinement of ELM models.
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