Comparison of L-Mode Regimes with Enhanced Confinement by Impurity Seeding in JET and DIII-D
The use of non-intrinsic impurities in tokamaks can reduce peak heat fluxes to divertor components by reducing power flow across the last closed flux surface, which is desirable for fusion reactors. This reduced heat flow can also allow the discharge to remain below the L-H power threshold, further reducing transient heat pulses, i.e. ELMS, to plasma facing surfaces. An additional benefit of impurity seeding is that, under some conditions, enhanced confinement is also observed. Neon seeding has been injected into JET and DIII-D discharges, increasing confinement up to H97Y = 1.1, i.e. equivalent to ELMing H-mode, while maintaining an L-mode edge. The purpose of this work is to examine the similarities and differences in such discharges in both tokamaks, providing size scaling and leading to an understanding of the underlying physical mechanisms.