pyFrost-GM Campaign 3: Nitrogen and Surface Chemistry

Part of the pyFrost-GM Verification & Validation

V&V Campaigns Hub

Key Objectives for Campaign 3

Nitrogen (N₂) Validation: Expand the code's validation coverage to N₂ discharges, benchmarking against established literature cases.
Surface Chemistry: Integrate and validate surface interaction models to capture wall effects more accurately.
Remaining oxygen items: the deviation at the lowest pressure and a like-for-like LoKI-GM reference run.

Proposed Next Steps

Status: planned. Campaign 2 brought the oxygen benchmark within a few percent of the paper and made pyFrost-GM faster than the LoKI-GM MATLAB reference. Campaign 3 widens the validation to nitrogen and to surface chemistry, and follows up the remaining oxygen differences below 1 Torr.

Core Objectives

1. Increasing Validation Coverage to N₂

Motivation: Oxygen (O₂) provided an excellent initial testbed, but Nitrogen (N₂) is a cornerstone of plasma processing and atmospheric applications. The heavy reliance on vibrational energy transfer in N₂ rigorously tests the electron energy distribution function (EEDF) coupling.
Approach: Benchmark pyFrost-GM against well-documented N₂ literature cases, comparing vibrational distributions, self-consistent E/N, and dominant neutral species densities.

2. Implementing Surface Chemistry

Motivation: Pure gas-phase kinetics are often insufficient for low-pressure discharges where wall recombination and quenching drive the global balance.
Approach: Introduce a robust boundary condition framework for species destruction and recombination at the surfaces. Validate the wall loss rates against both experimental surface loss probabilities and reference solvers.

3. Closing the Remaining Oxygen Items

Lowest pressure: at 0.19 Torr, O$_2(a^1\Delta_g)$ is 14 % below the paper and E/N 3.8 % above it, with LoKI-B and both MultiBolt runs alike, so the cause lies in the chemistry rather than the Boltzmann solver.
Like-for-like reference: rerun the LoKI-GM (MATLAB) baseline with the paper’s pressure-dependent wall recombination probability and flow, so that pyFrost-GM can be compared with it for densities as well as rates.
MultiBolt rotational losses: add the continuous approximation for rotations (CAR) that LoKI-B includes; at 1 Torr it changes the electron temperature by only 0.02 %, but it should be confirmed at 0.2 and 10 Torr.

Simulation & Development Plan

Phase	Focus Area	Key Deliverable
Phase 1	Remaining oxygen items	Explain the 0.19 Torr deviation; LoKI-GM baseline at the paper’s conditions.
Phase 2	N₂ Reaction Mechanisms	Successfully load and parse the complete N₂ vibrational scheme.
Phase 3	Surface Chemistry Integration	Implement wall sticking coefficients and surface recombination rules.
Phase 4	Full N₂ V&V Run	Compare fixed-point and self-consistent N₂ solutions with reference data.

Success criteria: the oxygen benchmark within 5 % at every pressure, successful alignment of N₂ state populations with reference models, and verified implementation of wall chemistry for key metastable species.

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