In-situ estimation of the thermal resistance of carbon deposits in the JET tokamak

• Heat flux and thermal resistance estimation done in non-linear unsteady conditions.
• In-situ estimation of the space distribution of the deposit thermal resistance.
• Correlation between the thermal resistance and the strike point location history.

The present paper deals with the heat flux estimation and the thermal characterization of the poorly attached Surface Carbon Layer (SCL) to the Plasma Facing Component (PFC) observed on the inner vertical tiles of the JET Tokamak. A nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to estimate the time variation of the heat flux necessary to characterize in situ the space and time variations of the thermal resistance Rth of the SCL. The method is applied on L mode power step plasma discharge (#58850). One embedded thermocouple (TC) is used to the heat flux estimation (another embedded TC is used for validate the estimation) and infrared (IR) measurements coming from the IR camera KL3 are used to estimate the SCL thermal resistance. The estimated SCL thermal resistance is compared to the history of the strike point location to highlight the correlation between the spatial distribution of the SCL thermal resistance and the location of the maximum heat flux.