In the last experimental campaign of the JET tokamak in December 2023, long duration discharges in deuterium plasmas were performed to assess the sustainment of the plasma performance over many resistive time scales and to address plasma-wall interaction physics in a full metallic environment with the ITER-like wall (ILW), featuring a W divertor and a Be first wall (Matthews et al 2011 Phys. Scr. 2011 014001; Neu et al 2011 Plasma Phys. Control. Fusion53 124040). Two types of long duration discharges were developed: (i) a 30 s flat-top ELMy H-mode with combined 12–14 MW neutral beam injection (NBI) and 2 MW of ion-cyclotron resonance heating (ICRH) and (ii) a 60 s long pulse with 4–6 MW of NBI during the entire flat-top and 2 MW of ICRH for about 40 s. The pulses were stationary from the radiation point of view without sign of core impurity accumulation and featured regular type-I ELMs with roughly equilibrated ion and electron temperatures in most cases. The discharges required significant technical adjustments in many subsystems, ranging from plasma shape control, machine protection and diagnostic settings (King et al Technical and Engineering challenges for long pulses on JET ITER). The experiments achieved the maximum energy ever injected in a single pulse in JET (EIN= 450 MJ) and challenged the operational domain of the inertially cooled divertor limits. An overview of the main properties of these discharges in terms of plasma stationarity, ELM behavior, plasma-wall interaction and overall performance will be presented and the contribution of these unprecedented JET-ILW results to the multi-machine CICLOP (Coordination on International Challenges on Long duration Operation) database (Litaudon et al 2024 Nucl. Fusion64 015001) will be highlighted.
This paper describes long-duration high-performance plasma discharges achieved in the JET tokamak with an ITER-like metal wall. The experiments demonstrated the ability to sustain H-mode operation for up to 60 seconds, achieving a record energy injection of 450 MJ. The results provide valuable insights into plasma-wall interactions and operational challenges for future long-pulse fusion devices.