Isotope dependence of the H-mode pedestal in JET-ILW plasmas

In tokamak H-mode plasmas, the level of energy and particle transport at the plasma edge is reduced and a steep pressure gradient is formed, giving rise to an edge pressure "pedestal", which positively affects the global energy confinement. A positive isotope mass scaling of the thermal energy confinement time in H-mode plasmas has been observed in several tokamaks, however, this favourable isotope dependence has not yet been fully understood theoretically. This thesis examines the pedestal structure, edge transport, linear MHD stability and inter-ELM edge current evolution in a series of JET-ILW Hydrogen (H) and Deuterium (D) type I ELMy H-mode plasmas with the aim to better understand the isotope dependence of the pedestal and its contribution to the favourable isotope scaling. Simulations of the inter-ELM edge current evolution showed that current diffusion contributes little to the time evolution of the total edge current prior to the ELM crash. Therefore, current diffusion does not explain why JET-ILW type I ELMy pedestals at high gas rate and moderate to high plasma beta are found to be stable to Peeling-Ballooning modes. The pedestal pressure is typically higher in D than in H at the same input power and gas rate, with the difference mainly due to lower density in H than in D. Analysis of the pedestal structure and power balance, and results of interpretative 2D edge transport simulations with EDGE2D-EIRENE indicate that the difference in neutral penetration between H and D leads only to minor changes in the pedestal density and temperature profiles, and differences in heat and particle transport must also play a role in the favourable isotope scaling of the pedestal. The effect of the isotope mass on linear MHD pedestal stability is small, but an indirect isotope dependence through the separatrix temperature is qualitatively consistent with the reduced pedestal confinement in H and could play a role in JET-ILW H-mode plasmas at low gas rate.