Verification and validation of plasma burn-through simulations in preparation for ITER First Plasma

The development of tokamak start-up operation scenario often relies on operator's experiences, rather than more robust approach based on numerical modelling. Such a trial-and-error approach has fortunately worked to find start-up recipes in small or medium size devices, but increases the risk of delays to experiments. Moreover, it would not be appropriate anymore for a large superconducting tokamak like ITER. First plasma operation in ITER is planned in 2025, and it is of crucial importance to ensure robust successful start-up. However, ITER has a risk of failure in full ionization of the prefilled gas (i.e. plasma burn-through), which is an essential condition for the start-up operation, because the toroidal electric field available is limited to 0.33V/m, much lower than the value typically used in now-a-days tokamaks i.e. 1 V/m. In order to assist the heating power in the plasma burn-through phase, a few MW of ECH power is planned for ITER First Plasma, but there still is a large uncertainty as the ECH absorption efficiency is very low (~ a few %) due to the low Te during the plasma burn-through phase. Therefore, it is now important and timely to develop a reliable plasma burn-through modelling tool including ECH to further optimize the operation scenario for ITER First Plasma. This paper presents the summary of the code benchmark of plasma burn-through modelling codes, which was a joint modelling activity in ITPA-IOS for 2018 ~ 2020. For the first time, there was an extensive comparison between the plasma burn-through modelling codes presently available - DYON 1 [2] [3] [4], SCENPLINT [5] [6] [7], and BKD0 [8] [9] [10]. The benchmark activities were done in three steps, adding more complexities to the modelling in each step.