EFDA-JET-PR(05)17
A Parallel Transport Model of Tokamak Power Exhaust Transients
In many tokamak power exhaust transients, eg. Edge Localised Modes (ELMs), thermal quench of disruptions and intermittent SOL bursts (so called blobs), thermal energy is largely removed to divertor or limiter tiles by parallel transport in semi-collisionless plasma filaments. Such transient parallel losses are governed by the coupled Fokker-Planck and Maxwell's equations. While numerical simulations of this system are now becoming available, they are still computationally expensive (CPU time in days) and require specialist support. In this paper, two simplified parallel loss models are developed, one based on the kinetic, the other on the moment or fluid approach. The two models can be combined to form a kinetic-fluid hybrid, whose accuracy can be further improved by using fitting parameters to best match the available kinetic results. This contribution demonstrates that such simple models can capture most of the salient features of kinetic simulations at substantial savings in both cost and complexity (CPU time in seconds). They may be used either as stand alone interpretive tools or as modules in larger turbulence and/or transport codes. As shown here, the fluid model can successfully reproduce ELM filament densities and electron energies measured at the outer poloidal limiter on JET, as well as recent measurements of far-SOL ELM filament ion energies on JET. Taking confidence from this favourable comparison, it is then used to predict the ion impact energies in Type-I ELM filaments on ITER.