Application of diffusion theory to neutral atom transport in fusion plasmas

Abstract

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Multidimensional and Multifluid Plasma Edge Modelling: Status and New Directions

“…The outboard SOL (0 = 00) is to the rear of the figure. This is not a consistent plasma-neutral computation but simply illustrates the result of a neuual diffusion model for prescribcd plasma profiles determined from experimental data [61] to represent a 'typical' ohmic shot. The use of prescribed plasma profiles in the core region is recommended when modelling the edge plasma in order to allow neutral transport between the core and edge regions to evolve in a consistent fashion.…”

“…A fluid diffusion multigroup model was developed and applied to the case of a fixed plasma background in TEXTOR [60]. The model was shown to give accurate results (compared to SN transport) even in optically thin regions (corresponding to low plasma density) and near boundaries when Manhak boundary conditions are employed [61].…”

“…Disadvantages of the neutral diffusion approximation include: neutral momentum has no time dependence, there is no angular dependence for material surface reflection coefficients, and accuracy is less than achievable with MC methods. A general concensus is that it cannot be used for the near vacuum region in the pumping ducts, however, the demonstration of accuracy in optically thin limits [61], suggests that even in the ducts, a multigroup formulation with energy dependent wall reflection can be accurate. The neutral diffusion model has been developed previously [39] from the approach used in transport theory expressing velocity vectors in angular variables.…”

Application of diffusion theory to neutral atom transport in fusion plasmas

“…a At least three types of diffusion theories are available, namely, Isotropic Diffusion Theory (IDT) or the familiar Pj-diffusion theory [14][15][16][17], asymptotic diffusion theory!19], and flux-limited diffusion theoryf20J. Numerical comparisons reported in reference [21] show that IDT gives better accuracy for neutral transport compared to the other two. Likely reasons are that asymptotic diffusion theory solves for the asymptotic part of the total transport Figure 1 also shows the solution using tho 1-D slab geometry code SPUDNUT [6].…”

User's manual for FENAT: a two-dimensional multigroup diffusion theory Finite Element Neutral Atom Transport code

“…The code FENAT has been developed to meet this objective. It is based on the energy dependent diffusion theory which has been shown to provide very good accuracy for the transport of neutral atoms in fusion plasmas [3,4].…”