A study of the heating and current drive options and confinement requirements to access steady-state plasmas at Q ∼ 5 in ITER and associated operational scenario development

Access to steady-state (SS) plasma scenarios that can be potentially achieved in ITER by the exploitation of the neutral beam (NB) and electron cyclotron (EC) heating and current drive capabilities, including their foreseen upgrades, has been assessed and development of the Q similar to 5 ITER SS operation (SSO) scenario has been carried out by combining all the necessary physics and engineering components. A set of modelling codes including 0.5D/1.5D transport and source modelling suites (METIS, ASTRA and CORSICA) and ideal MHD stability analysis codes (KINX and MISHKA) are applied to combined analysis and scenario development. Operating the plasma with a moderate density peaking factor (n (e0)/ similar to 1.3) for sufficient fusion gain (Q up to 5) at a low density (f (GW) = 0.6-0.8) and the required current drive efficiency produced an internal inductance (l (i)(3) similar to 0.8-0 9) which improves the stability margin for low-n external ideal MHD modes. Based on this first observation, a combined operational space and ideal MHD stability analysis has recently identified Q similar to 5 ITER SS target plasmas (Polevoi et al 2020 Nucl. Fusion 60 096024), and then the CORSICA scenario modelling suite has been applied to study access to the target plasmas as well as to develop a candidate operation scenario. Ideal MHD stability analysis on the SS plasmas has been performed using DCON embedded in the CORSICA scenario modelling suite. The use of off-axis electron cyclotron current drive (ECCD) with a power level of 20-30 MW from the equatorial and upper launchers was essential for the tailoring of the current profile to maintain ideal MHD stability of SS plasmas in ITER. Upgrading the NBI power from the baseline 33 MW to 49.5 MW provided the necessary current drive capability to allow fully non-inductive Q similar to 5 operation with an energy confinement enhancement requirement (H (98) less than or similar to 1.6) similar to that achieved in some experiments in present tokamaks (Petty et al 2020 62nd Annual Meeting of the APS Division of Plasma Physics, Virtual Meeting (USA, 9-13 November 2020); Snyder et al 2019 Nucl. Fusion 59 086017; Solomon et al 2013 Nucl. Fusion 53 093033). The CORSICA simulations of the access to the Q similar to 5 ITER SS target plasmas show that, provided that the enhancement of the energy confinement (H (98) similar to 1.5-1.6) is achieved, it is possible for ITER to demonstrate the Q similar to 5 SSO with NB and EC heating and current drive within the limits of the ITER Central Solenoid (CS)/Poloidal Field (PF) coil systems.

Automated summary

Access to steady-state plasma scenarios potentially achievable in ITER through the use of neutral beam and electron cyclotron heating and current drive capabilities has been assessed. A Q similar to 5 ITER SS operation scenario has been developed, with the use of modeling codes and ideal MHD stability analysis. Operating the plasma with moderate density and low density conditions, along with necessary current drive efficiency, has been shown to improve stability, with upgrades to NBI power and off-axis ECCD essential for maintaining ideal MHD stability.