On the polytropic coefficient of negative ions for modeling the sheath and presheath of electronegative plasmas
Bibliographic record
Abstract
The fluid description is widely used for the multi-dimensional modeling of low temperature plasmas with complex chemistries due to their relative low computational cost. It relies, however, on a series of simplifying assumptions and some truncation of the moment equations for describing the non-equilibrium between the electrons, positive ions, negative ions, and the neutrals. In this paper, the classical assumption of isothermal negative ions is revisited for electronegative plasmas and, more particularly, for the fluid modeling of the transition between the plasma and its sheath. To do so, and in contrast to previous studies, the energy balance equation for the negative ions is also computed, and it allows us to derive the polytropic coefficient γ of the negative ions in addition to one of the positive ions. Strong variations in the sheath and presheath of the negative ions temperature and their polytropic coefficient are observed. The polytropic coefficient is shown to be a strongly varying function of space having for consequence that the negative ions are isothermal only in a very narrow extension of the presheath. For the case considered in this paper, both positive and negative ion flows are nearly adiabatic at the sheath-edge and become adiabatic inside the sheath. This paper shows that classical fluid modeling assumptions need to be verified for each system under consideration, most particularly while modeling the transition from plasma to a wall.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".