The impact of neon seeding on pedestal performance and stability of JET-ILW deuterium H-mode discharges

This work presents a systematic study of the impact of neon seeding on pedestal performance and stability in JET-ITER baseline scenario discharges in deuterium at high input power extending the previous JET impurity seeding experiments. A neon-seeding scan of the JET-ITER baseline at I p = 2.5 MA, B T = 2.7 T, q 95 = 3.2 with high triangularity is being studied with the neon pedestal concentration up to 1.7 % at the pedestal top. As is typical in these discharges, the global confinement is increased approaching unity and the β N parameter reaches up to 2.3, with the increased radiation fraction. Detailed pedestal profile analysis showed that neon seeding reduces the pedestal density while substantially increasing both electron and ion pedestal temperatures, resulting in an overall ∼ 50 % increase of pedestal pressure compared to unseeded plasmas. Simultaneously, the total pressure pedestal width broadens mostly due to the increased T e width (n e broadening has negligible impact on total pressure width). The total pressure gradient develops in a way that stabilizes the pedestal against ideal peeling-ballooning (PB) modes. Ideal MHD stability calculations confirm that unseeded pedestals lie close to the PB boundary, while neon-seeded cases move deep into the PB stable domain, consistent with the observed transition to small/no-ELM operation. Comparison with Europed predictions exhibit good qualitative agreement in pedestal height trends, though systematic offsets and underestimation of pedestal widths highlight limitations of the current model.