L-H TRANSITION STUDIES AT JET: TRITIUM, HELIUM AND DEUTERIUM

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 RF-heated Tritium show an unexpectedly high threshold when compared to Deuterium, to be investigated further. 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, and a drop in threshold at high densities. Transport modelling in slab geometry shows that in Helium neoclassical transport competes with interchange-driven transport, unlike in Hydrogenic 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.