LH Power Losses In Front of the JET Launcher

In recent JET experiments, Lower Hybrid (LH) power losses in the Scrape‐Off Layer (SOL) were characterized using infra‐red (IR) thermography. Hot spots were observed on objects intercepting the field lines passing in front of the LH launcher, i.e. on poloidal limiters and on dumplates located at the top of the tokamak; their locations being in good agreement with magnetic field line tracing using the EFIT equilibrium code. The dumplate temperature was monitored while scanning the launcher position so that the radial distance between field lines intercepting the hot spots and the launcher was increased up to 3.5 cm. The dissipation layer in front of the launcher was estimated to be at least 3.5 cm wide, in agreement with recent measurements on Tore‐Supra, but not with simple models that predict a dissipation layer in the mm range.