2D analysis of tokamak divertor-plasma detachment-bifurcation with operational parameters and geometries
Year: 2024
Type: article
Abstract: UEDGE simulations with density scans for various input power, transport coefficients and outer poloidal leg length are performed to study the conditions for the existence of a bifurcation-like drop of T e at the outer strike point, commonly referred to as a detachment cliff, when transitioning to a detached plasma from an attached plasma in the outer divertor as the upstream density increases (McLean et al., 2015). The simulation results show that a detachment cliff tends to occur with a higher power input regardless of diffusivities and leg length. Further analysis of change of plasma profiles at a cliff indicate that, in addition to the sharp reduction of the E × B drift fluxes in the outer divertor studied in Jaervinen et al., (2018), the substantial change of the Mach number in the outer divertor and the decrease of the outer mid-plane T e due to the radiation front moving across the separatrix into the confinement region above the X-point consistently occur for all UEDGE density scans that have a detachment cliff. UEDGE time-dependent simulation of the evolution of a detachment cliff shows that the rapid increase of radiation above the X-point occurs in a time scale of ∼ 0 . 3 – 0 . 5 ms , which could possibly be the trigger for the formation of a detachment cliff, quicker than the Mach number change in a time scale of ∼ 1 ms and the drop of T e in a time scale of ∼ 2 – 3 ms in the outer divertor. • Extended operational parameter ranges are scanned using UEDGE to look for conditions for the formation of a detachment cliff. • At a detachment cliff the outer-strike-point Mach Number experienced a bifurcation-like decrease and the radiation front enters the last-closed-flux-surface (LCFS). • The radiation front moves across the LCFS in a time scale of 0.3–0.5 ms at a detachment cliff, which could be the trigger for the cliff.
Source: Nuclear Materials and Energy
Authors: M. Zhao, F. Scotti, T.D. Rognlien, A.G. McLean, G. Burke, A. Holm
Institution: Lawrence Livermore National Laboratory
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,840
OpenAlex ID: W4404733699