Power exhaust by SOL and pedestal radiation at ASDEX Upgrade and JET

TLDR

Future fusion reactors need a safe, steady‑state divertor, and detached divertor operation with high radiated power fractions offers a potential solution. The study aims to understand how impurity seeding affects plasma confinement and stability to predict the applicability of high‑radiation detached divertor scenarios in future devices. The authors increase radiation by seeding impurities—N for scrape‑off‑layer, Ne or Ar for SOL/pedestal, and Kr for core radiation. Experiments on ASDEX Upgrade and JET with N, Ne, or Kr seeding achieved high radiated power fractions and fully detached divertors, with the highest radiation originating near the X‑point for N and Ne, and impurity seeding altering pedestal transport and impacting confinement and stability.

Abstract

Future fusion reactors require a safe, steady state divertor operation. A possible solution for the power exhaust challenge is the detached divertor operation in scenarios with high radiated power fractions. The radiation can be increased by seeding impurities, such as N for dominant scrape-off-layer radiation, Ne or Ar for SOL and pedestal radiation and Kr for dominant core radiation. Recent experiments on two of the all-metal tokamaks, ASDEX Upgrade (AUG) and JET, demonstrate operation with high radiated power fractions and a fully-detached divertor by N, Ne or Kr seeding with a conventional divertor in a vertical target geometry. For both devices similar observations can be made. In the scenarios with the highest radiated power fraction, the dominant radiation originates from the confined region, in the case of N and Ne seeding concentrated in a region close to the X-point. Applying these seed impurities for highly radiative scenarios impacts local plasma parameters and alters the impurity transport in the pedestal region. Thus, plasma confinement and stability can be affected. A proper understanding of the effects by these impurities is required in order to predict the applicability of such scenarios for future devices.