Experimental Study of H-L Transitions in JET

ITER operation scenarios foresee the access to H-mode with limited additional heating at low density, followed by an increase in density and power while remaining in H-mode to the required operating conditions. Such scheme is thus sensitive to the level of hysteresis in the H-mode power and to the competing evolution of input power, density and radiation losses from the bulk plasma. Whereas most studies focus on the access to H-mode, the H-L back transition is less explored. This work examines the evolution and properties of JET plasmas with the ITER-like wall at the H-L back transition in relation to the forward L-H transition. The influence of the wall composition (C versus Be/W), in particular on the density evolution, radiation losses and impurity composition, is also analysed, through direct comparison of forward and back transitions in JET-C and JET-ILW plasmas.
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EFDC130320 556.52 Kb