On the relative roles of neutral transport and plasma transport in the formation of the density pedestal in magnetically confined plasmas
Bibliographic record
Abstract
Currently, a much discussed question regarding the characteristic features of the plasma density radial profile—the ‘pedestal’—existing at or just inside the magnetic separatrix in tokamaks—is whether the neutral or plasma transport in that region is more controlling. In actual tokamak conditions, the neutral transport is generally quite complicated geometrically, making it difficult to understand the relative roles of plasma and neutral transport. Here, therefore, we consider a quite simplified configuration—one-dimensional slab geometry—in order to elucidate the essential aspects of the problem. It is found here, for the assumption of diffusive cross-field plasma transport, that simple quasi-one-dimensional modelling indicates that the spatial distribution of ionization of the recycling hydrogen neutral particles in the pedestal region, i.e. neutral transport, plays a strong role. It is also found, however, that the influence of plasma transport—specifically the effect of a ‘transport barrier’ just inside the separatrix where D ⊥ ( r ) varies rapidly—can also play a significant role. It is found that a third—and roughly equally important—influence on the shape of the density profile inside the separatrix is the value of the density decay length outside the separatrix, λ SOL , which enters as an important boundary condition of the problem; it is therefore important to know the relationship, e.g. from experiment, between λ SOL and the pedestal density, n ped , and to include that in the analysis. This paper ends with a discussion of what is required to analyse an actual tokamak plasma configuration. When undertaking the full three-dimensional interpretive analysis of a specific discharge condition in a specific tokamak, if the neutral transport—i.e. the spatial distribution of the ionization—can be accurately modelled in detail, and if the boundary condition information is available as input from the experimental data, then it should be possible to extract information on D ⊥ and its spatial variation near the separatrix from detailed particle-balance analysis of the density profile.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".