The Quasi-Continuous Exhaust (QCE) is a regime that is naturally free of type-I Edge Localised Modes (ELM). It combines the high density at the plasma edge needed for power exhaust with the high normalised energy confinement typical for H-mode operation. In the QCE regime large-scale ELMs are avoided and high-frequency, low-amplitude filaments are present leading to the name-giving quasi-continuous edge transport of particles and energy.
In a recently published, Nuclear Fusion Letter, Michael Faitsch (IPP, MPG) and Mike Dunne (IPP, MPG) and their colleagues reported that for the first time the QCE regime was successfully achieved in JET with a metal wall. Moreover, it was demonstrated in the last JET deuterium-tritium campaign DTE3 that the regime is compatible with D–T operation. Porting the QCE regime to JET strongly benefited from the experimental and modelling efforts at the medium sized tokamaks ASDEX Upgrade and TCV.
Using the physics picture developed from the ASDEX Upgrade experimental results, the route to the QCE regime in JET reported here is following closely the approach that was successful in ASDEX Upgrade. First, strong plasma shaping—large elongation and triangularity and the highly correlated closeness to double null—was developed. Benefiting from his deep knowledge of JET capabilities and his long experience as Session Leader, the contribution of Peter Lomas (UKAEA) was crucial to achieve this first step.
Second, sufficient fuelling to achieve high enough density at the pedestal foot, close to the separatrix, is applied. In addition, neon seeding proved to be very beneficial to avoid type-I ELMs when reducing the main ion fuelling. The data analysis and modelling of these discharges must continue in the coming years. It is particularly important to evaluate the particle and heat fluxes on the first wall and their impact on material sputtering to better predict the extrapolation to future devices like ITER. Actually, ITER Organisation is now considering this regime as a possible candidate to reach ITER targets and is calling for additional studies.
The original publication can be found here:
The quasi-continuous exhaust regime in JET, M. Faitsch et al 2025 Nucl. Fusion 65 024003, DOI 10.1088/1741-4326/adaa86 https://iopscience.iop.org/article/10.1088/1741-4326/adaa86