Multidimensional and Multifluid Plasma Edge Modelling: Status and New Directions

Abstract

The plasma boundary in magnetic confinement devices is observed in experiments and in computations to contain radial and poloidal variations in plasma potential, strong radial elecmc fields and large poloidd drift flows in addition to the parallel flow toward the plasma sheath boundaries and the panicle recycling from the walls. The global power balence is largely influenced by impurity radiation and thus by impurity m s p o n in the edge region. The behavior of the edge region is related to global confinement in ways not yet fully known and motivates further improvements in edge plasma modelling.General multifluid transport quations arc reviewed in the context of the c m n t status of plasma edge modelling. It is assumed that the macroscopic transport in the plasma edge region is suitable for a moments description, or fluid model. Progress is well established in computational treatments of the standard paradigm including classical parallel and anomalous cross-field flux coupled to neutrals in analytic or Monte Carlo steady state computations. Formulation of momentum diffusivities and curvature drift in toroidal coordinates are considered. New directions include defining the dominant influence of drifts and non-ambipolar flows, improving coupled plasma-neutral transport calculations, and mating impurity flow in full multifluid models.Calculation of the plasma potential driving the E x B drift in the scrape-off layer can be extended inside the last closed flux surface by conserving the divergence of the plasma cuments. Coupled plasma-neutral fluids using a neutral diffusion approximation show promise for recycling calculations. Impurity transport based on full multifluid treatment along the field lines has shown good agreement with divertor experiments.Advanced topics for the near future include. plasma core-edge transport coupling and eventually the direct solution of coupled mmentum equations rather than the presently assumed cross-field 'anomalous' flux functions. In the edge region, plasma sheath boundary conditions are a significant sink for plasma particles and heat; a small coupling between the momentum components in the plasma edge can be sufficient to drive an 'anomalously' large efflux from the core plasma.

Tokamak edge profile analysis employing Bayesian statistics

“…The standard edge physics model equations as implemented in advanced 2-D tokamak edge codes [8] are extremely complex, and their solution requires excessive computer time. For demonstration of the fitting algorithm, however, it seems reasonable to use only a small subset of these equations as a first approximation.…”

Challenges in plasma edge fluid modelling

“…Since about 1990 the list of physics to be included in such packages was agreed on [23][24][25][26][27][28][29] and step-by-step introduced:…”

Fluid Description of Edge Plasma Transport in a Non‐Orthogonal Coordinate System

“…As was pointed out earlier, the plasma fluid motion in the tokamak edge region requires a generalized coordinate system because SOL and divertor geometry cannot be described by an analytic metric [1,2]. Moreover, the non-orthogonal boundary of the target (due to the angle between the target and the magnetic surfaces) requires a non-orthogonal coordinate system.…”