Connecting recent JET isotope L–H transition studies to H-mode access in new ITER scenarios

This paper reviews recent experimental advances in characterising the low-to-high confinement mode (L–H) transition in tokamaks, with a particular focus on ITER-relevant results from JET and metallic wall tokamaks. Achieving H-mode is critical for the success of ITER, and the robustness of the H-mode access in the recently revised ITER research plan is assessed in the present paper. Findings from JET and metallic wall machines are applied to ITER predictions for both the early and nuclear operational phases. Notably, a new multi-machine, metallic wall-specific scaling of the L–H power threshold is applied to ITER scenarios, revealing significant deviations from the widely used ITPA 2008 scaling derived primarily from C-wall machines. JET findings on the L–H transition dependence on plasma isotope mass are applied to ITER, which will first explore H-mode in Deuterium plasmas before progressing to deuterium–tritium plasmas. Achieving H-mode in Hydrogen plasmas is deemed unlikely under the available heating and current drive (H&CD) power and, therefore, not planned in the ITER strategy. In the nuclear phase, ITER will explore full-performance scenarios in D plasmas with increased H&CD power, including neutral beam injection (NBI). Shine-through NBI power limitations will not constrain the operational space for H-mode access. H-mode access might prove challenging at high plasma current and density in D plasmas, especially considering the recent metal wall L–H power threshold scaling. This timely analysis incorporates the latest experimental findings, providing valuable insights to support the successful and efficient exploitation of ITER.