Predictive multi-channel flux-driven modelling to optimise ICRH tungsten control and fusion performance in JET

Predictive multi-channel flux-driven modelling to optimise ICRH tungsten control and fusion performance in JET

Predictive multi-channel flux-driven modelling to optimise ICRH tungsten control and fusion performance in JET 150 150 UKAEA Opendata

The evolution of the JET high performance hybrid scenario, including central accumulation of the tungsten (W) impurity, is reproduced with predictive multi-channel integrated modelling over multiple confinement times using first-principle based models. 8 transport channels are modelled predictively, with self-consistent sources, radiation and magnetic equilibrium, yielding a system with multiple non-linearities which can produce a radiative temperature collapse after several confinement times. W is transported inward by neoclassical convection driven by the main ion density gradients and enhanced by poloidal asymmetries due to centrifugal acceleration. The slow evolution of the bulk density profile sets the timescale for W accumulation. Prediction of this phenomenon requires a turbulent transport model capable of accurately predicting particle and momentum transport (QuaLiKiz) and a neoclassical transport model including the effects of poloidal asymmetries (NEO) coupled to an integrated plasma simulator (JINTRAC). The modelling capability is applied to optimise the available actuators to prevent W accumulation, and to extrapolate in power and pulse length. Central NBI heating is preferred for high performance, but comes at the price of central deposition of particles and torque which pose the risk of W accumulation. The primary mechanisms for ICRH to control W in JET are via its impact on the bulk profiles and turbulent diffusion. High power ICRH near the axis can sensitively mitigate against W accumulation, and ion heating (He-3 minority) is predicted to provide more resilience to W accumulation than electron heating (H minority) in the JET hybrid. Extrapolation to DT plasmas finds 17.5MW of fusion power and improved confinement compared to DD, due to reduced ion-electron energy exchange, and increased Ti/Te stabilisation of ITG instabilities. The turbulence reduction in DT increases density peaking and accelerates the arrival of W on axis; this may be mitigated by reducing the penetration of the beam particle source with an increased pedestal density.

Collection:
Journals
Journal:
Nuclear Fusion
Publisher:
IOP (Institute of Physics)
Published date:
18/04/2021