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Recent progress in L-H transition studies at JET: Tritium, Helium, Hydrogen and Deuterium...

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Nuclear Fusion
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We present an overview of results from a series of L-H transition experiments undertaken at JET since the installation of the ITER-like-wall (JET-ILW), with Beryllium wall tiles and a Tungsten divertor. Tritium, Helium and Deuterium plasmas have been investigated. Initial results in Tritium show ohmic L-H transitions at low density and the power threshold for the L-H transition (PLH) is lower in Tritium plasmas than in Deuterium ones at low densities,while we still lack contrasted data to provide a scaling at high densities. In Helium plasmas there is a notable shift of the density at which the power threshold is minimum (ne,min) to higher values relative to Deuterium and Hydrogen references. Above ne,min(He) the L-H power threshold at high densities is similar for D and He plasmas. Transport modelling in slab geometry shows that in Helium neoclassical transport competes with interchange-driven transport, unlike in Hydrogen isotopes. Measurements of the radial electric field in Deuterium plasmas show that Er shear is not a good indicator of proximity to the L-H transition. Transport analysis of ion heat flux in Deuterium plasmas show a non-linearity as density is decreased below ne,min. Lastly, a regression of the JET-ILW Deuterium data is compared to the 2008 ITPA scaling law.