Observation of Edge Harmonic Oscillations in JET-ILW Deuterium,Tritium and DT plasmas.

Long-lived EHOs that suppress ELMs have been reported in co-NBI plasmas in JET, with a Carbon wall [1,2]. Here we report on recent observations of transient EHOs in Deuterium, Tritium and DT plasmas in the JET-ILW, with Be walls and a W divertor. EHOs are observed in early phases of hybrid plasmas (co-NBI injection) and they delay the arrival of the 1st ELM, but are typically destroyed as gas is added to deliberately initiate an ELMy phase [3]. Modes are typically n=1, edge localised, with at least an n=2 harmonic, sometimes more. They are generally observed at low collisionality, as expected from the exfernal mode model [4]. Transient QH-modes with duration of up to 500 ms have also been reported in AUG with a full W wall, both with co and counter NBI [6]. In AUG EHOs appear in the low density, high temperature branch, with the pedestal close to the kink-peeling boundary. Future work in both JET and AUG aims at investigating access conditions, extending the QH-mode to stationarity, and determining whether it can be a viable operating regime for future fusion devices. [1] E. R. Solano et al, Phys. Rev. Lett. 104 185003 (2010) [2] E. R. Solano et al, 45th EPS Conf. on Plasma Physics, Prague, P4.1044 (2018) [3] C Challis et al, 48th EPS Conf. on Plasma Physics, Online (2022) Poster 287. [4] D. Brunetti et al., Phys. Rev. Lett. 122, 155003 (2019).[5] E. Viezzer et al, 47th EPS Conf. on Plasma Physics, Online, (2021) P1.1054