Characterisation of local ICRF heat loads on the JET ILW

TL;DR

This study characterizes heat loads on JET ICRF antennas with the new ITER-Like-Wall, revealing heat-flux intensities and how different strap phasings affect power deposition and heat flux distribution.

Contribution

It provides the first detailed measurements of local heat fluxes on JET ICRF antennas with the ITER-Like-Wall, using IR thermography and thermal modeling.

Findings

Maximum heat flux ~4.5 MW/m2 at specific phasing and power levels

Dipole phasing reduces heat flux compared to +/-π/2 phasing

2-20% of ICRF power deposited on antenna components

Abstract

When using Ion Cyclotron Range of Frequency (ICRF) heating, enhanced heat-fluxes are commonly observed on some plasma facing components close to the antennas. Experiments have recently been carried out on JET with the new ITER-Like-Wall (ILW) to characterize the heat flux to the JET ICRF antennas. Using Infra-Red thermography and thermal models of the tiles, heat-fluxes were evaluated from the surface temperature increase during the RF phase of L-mode plasmas. The maximum observed heat-flux intensity was ~ 4.5 MW/m2 when operating with -{\pi}/2 current drive strap phasing at power level of 2MW per antenna and with a 4 cm distance between the plasma and the outer limiters. Heat-fluxes are reduced when using dipole strap phasing. The fraction of ICRF power deposited on the antenna limiters or septa was in the range 2-10% for dipole phasing and 10-20% with +/-{\pi}/2 phasing.