MHD threshold prior-art screen, version 2
Screen date: 5 October 2026

Decision
This bounded screen is complete for the specified leads at the access levels below. A full-text novelty review is NOT complete: the Riggins 2004, Macheret 2002 and Meyer 2005 journal full texts were not obtained. A public working note may describe the result as a transparent, reproducible accounting synthesis. Neither its conservation identity, dimensionless rescaling, ionization-cost criterion nor inlet-control concept is established as new physics. arXiv readiness must not be inferred from completion of this screen.

Candidate contribution to test
An openly reproducible, boundary-explicit dimensionless ledger linking an independently estimated inlet benefit to the round-trip energy penalty, with source-specific efficiency definitions, feasibility masking and uncertainty. This is a possible presentation/methods contribution, not an established scientific novelty claim. It would become stronger if it reproduced a matched inlet benchmark and quantified a previously unreported, robust limit.

Mathematical distinction (our derivation, not attributed to the sources)
For Delta = c - d + h*s*(g*d-e-a), d>0, let x=e/d, alpha=a/d, chi=c/d and R=g*h*s. Then Delta/d = chi-1+R-h*s*(x+alpha). If g>0, this equals chi-1+R*[1-(x+alpha)/g]. Thus an R-versus-x map still requires g (or h*s) and alpha; collapsing everything into R alone is not valid with loads subtracted from the electrical bus. Instead define ell=(e+a)/(g*d), so Delta/d=chi-1+R*(1-ell), with ell<=1 for a self-powered bus. The dimensional value 400 kJ/kg disappears, but boundary and efficiency assumptions do not.

Evidence matrix

1. Litchford et al., NASA/TP-2000-210387, Thermodynamic Cycle Analysis of Magnetohydrodynamic-Bypass Hypersonic Airbreathing Engines.
Primary full-text record: https://ntrs.nasa.gov/api/citations/20000095934/downloads/20000095934.pdf
Access: primary PDF text returned by search; targeted introduction/methods screen, not complete equation-by-equation review in this pass.
Overlap: ideal-gas cycle analysis already parameterizes energy extraction/addition, component isentropic efficiency and a fraction of generated power diverted to pre-ionization. It seeks closed-form performance trends and feasible component ranges. Therefore a parametric ionization/efficiency map by itself is not sufficient novelty. Our useful-energy conversion variables cannot be equated to its isentropic efficiencies without derivation.

2. Macheret, Shneider and Miles (2001), Potential Performance of Supersonic MHD Power Generators, DOI 10.2514/6.2001-795.
Primary institution record: https://collaborate.princeton.edu/en/publications/potential-performance-of-supersonic-mhd-power-generators
Author manuscript: https://www.researchgate.net/publication/228712456_Potential_performance_of_supersonic_MHD_power_generators
Access: institution abstract and author full text; targeted introduction, ionization balance, current closure and symbol definitions inspected.
Overlap: explicitly requires ionization consumption below electrical extraction and links this requirement to conductivity, strong fields, Hall effects and ion slip. Includes Mach/altitude performance calculations. Generator electrical surplus is not proof of positive whole-engine benefit. Claims that ionization affordability is a newly identified bottleneck are excluded.

3. Macheret, Shneider and Miles (2002), Magnetohydrodynamic Control of Hypersonic Flows and Scramjet Inlets Using Electron Beam Ionization, DOI 10.2514/2.1616.
Primary record: https://collaborate.princeton.edu/en/publications/magnetohydrodynamic-control-of-hypersonic-flows-and-scramjet-inle/
Access: institutional abstract only; full text unresolved.
Overlap: couples beam ionization, plasma kinetics, MHD and 2D inviscid flow to restore off-design shock position, discusses Hall fields and ionizer/extraction power. A reduced c(Mach, sigma, B) must be positioned as a simpler, explicitly limited reduction of an already studied coupling, not its discovery.

4. Shneider, Macheret and Miles (2004), Analysis of Magnetohydrodynamic Control of Scramjet Inlets, DOI 10.2514/1.3998.
Primary record: https://collaborate.princeton.edu/en/publications/analysis-of-magnetohydrodynamic-control-of-scramjet-inlets/
Author manuscript: https://www.researchgate.net/publication/228953902_Analysis_of_Magnetohydrodynamic_Control_of_Scramjet_Inlets
Access: institutional abstract and targeted full-text conclusion excerpts, not complete figure reproduction.
Overlap: Mach 5-10 inlet compression, mass capture, coupled plasma/flow equations and shock repositioning are already analyzed. The conclusion explicitly retains total-pressure and installation penalties and calls for system studies. An arbitrary positive inlet credit is not a substitute for this comparison. The new reduced model needs a declared reference inlet, pressure recovery, capture and energy boundary.

5. Riggins (2004), Analysis of the Magnetohydrodynamic Energy Bypass Engine for High-Speed Airbreathing Propulsion, DOI 10.2514/1.4980.
Primary record: https://scholarsmine.mst.edu/mec_aereng_facwork/3080/
Access: institutional abstract/citation only; linked publisher full text not obtained.
Overlap: total-pressure penalties, inverse-cycle losses, choking, cooling and realistic engine comparison already receive detailed treatment. The abstract reports lower MHD-bypass performance over Mach 8-12.2 in its simulations. This is important contrary prior art; it neither proves universal failure nor supplies calibration for our energy-credit model. Full-text comparison remains required before a novelty claim.

6. Murray et al. (2006), Magnetohydrodynamic Power Generation Using Externally Ionized, Cold, Supersonic Air as Working Fluid, DOI 10.2514/1.11611.
Primary record: https://collaborate.princeton.edu/en/publications/magnetohydrodynamic-power-generation-using-externally-ionized-col/
Author-uploaded full text: https://www.researchgate.net/publication/245425962_Magnetohydrodynamic_Power_Generation_Using_Externally_Ionized_Cold_Supersonic_Air_as_Working_Fluid
Access: full text inspected at ionization, current-closure and conductivity sections; uploaded by coauthor M. N. Shneider.
Overlap: experimentally extracts small electrical output from externally ionized Mach-3 cold air and models current. Sustaining ionization and tensor/effective conductivity are already central. High scalar conductivity can coexist with low effective transverse electron conductivity at large Hall parameter. Its low ionization fraction of flow enthalpy must not be confused with ionization fraction of generated power, and the experiment is not an integrated energy-bypass demonstration.

7. Meyer et al. (2005), Measurement of Flow Conductivity and Density Fluctuations in Supersonic Nonequilibrium Magnetohydrodynamic Flows, DOI 10.2514/1.13736.
Publisher metadata: https://doi.org/10.2514/1.13736
Author-record abstract: https://www.researchgate.net/publication/245426116_Measurement_of_Flow_Conductivity_and_Density_Fluctuations_in_Supersonic_Nonequilibrium_Magnetohydrodynamic_Flows
Access: publisher metadata and abstract copy; journal full text unresolved. Issue date is September 2005; publisher's 2012 online date is not its research year.
Abstract-level result: nitrogen-flow conductivity approximately 0.05 S/m is inferred from electrical measurements; approximately 0.1 S/m is extrapolated. These are not direct measurements between 1 and 130 S/m. They establish relevant diagnostic precedent, not a universally empty conductivity interval or matched wall-plug energy relation.

8. Nishihara (2006), Low-Temperature Supersonic Flow Control Using Repetitively Pulsed MHD Force, Ohio State dissertation.
Official PDF: https://etd.ohiolink.edu/acprod/odb_etd/ws/send_file/send?accession=osu1164748794&disposition=inline
Access: downloaded official full text; 136 pages; targeted abstract and printed pp.48-51 checked. Local file: prior-art-nishihara2006.pdf. SHA256 b22a74ae8da6a96939f6bc912158ccf29745564f6a70226346603aa2c9e40289.
Result: abstract reports scalar conductivity 0.073 S/m in nitrogen and 0.072 S/m in air. Printed pp.50-51 explain that systematic current-voltage and cathode-fall characterization improves the earlier RF measurement. This strengthens the need to separate scalar conductivity, effective current closure, electrode losses and measurement inference. It does not calibrate a hypersonic integrated cycle. This dissertation is a distinct follow-up source, not a substitute for the missing Meyer article.

9. Starikovskiy, Aleksandrov and Shneider (2023), Analysis of the Efficiency of MHD Cycle Supported by Nanosecond Pulsed Discharge Pre-ionization, DOI 10.1088/1361-6595/acc053.
Publisher: https://doi.org/10.1088/1361-6595/acc053
Publisher-supplied full text: https://www.researchgate.net/publication/368945962_Analysis_of_the_efficiency_of_MHD_cycle_supported_by_nanosecond_pulsed_discharge_pre-ionization
Access: full-text sections6-7, equations6-8 and figures13-15 screened; ResearchGate explicitly identifies IOP Publishing as supplier. Direct IOP fetch failed.
Overlap: explicitly compares sustaining-ionization expenditure with generator extraction, distinguishing segmented and continuous-electrode current closure. The approximately3% headline belongs to an ideal-generator estimate; the detailed energy example is CO2, and qualitative plasma-image agreement does not validate whole-cycle energetics. The 2022 precursor DOI10.2514/6.2022-0827 must be recognized as the same research line, not counted as independent confirmation. Direct close prior art to an ionization-cost map.

10. Lieu (2026), Reduced-Order Evaluation of Superconducting Magnetoplasma Propulsion in Aircraft and Rocket Flight, DOI10.1016/j.ast.2026.113752.
Primary publisher record: https://www.sciencedirect.com/science/article/pii/S1270963826021280
Access: publisher search-indexed abstract/highlights/limitations excerpts; direct full-text retrieval failed. Available online6 September2026, journal pre-proof.
Overlap: recent reduced-order conductivity/field/chemistry/system-penalty screening. It explicitly calls for finite-rate chemistry and current-closure upgrades. No quantitative result is imported into our model. Full text must be checked for closer overlap before asserting a new reduced-order screening methodology.

Search coverage and stopping rule
Targeted DOI/title queries for five assigned leads; followed their directly relevant inlet-control and generator-energy predecessors; searched combinations of MHD bypass, dimensionless, round-trip, efficiency, ionization cost, threshold and break-even; checked primary NASA, Princeton, Missouri S&T, publisher and OhioLINK records. Author/publisher-supplied manuscripts were used when publisher retrieval failed. Unrelated liquid-metal power plants, fusion, astrophysical MHD and generic indexes were excluded from substantive comparison. This is a bounded English-language screen, not a Scopus/Web of Science export, patent search, systematic review or guarantee of absence. No inference of novelty is made from failure of a keyword query to return an exact map.

Unresolved retrievals and publication gate
- Obtain full journal texts of10.2514/1.4980,10.2514/2.1616 and10.2514/1.13736; finish figure/equation comparison where presently only excerpts were inspected.
- Check full recent primary paper10.1016/j.ast.2026.113752 for model overlap.
- Secondary lead10.1016/j.cap.2026.08.018 remained unverifiable at its primary endpoint; no claims from it used.
- Before arXiv, fix the claim to the contribution actually demonstrated, validate reduced inlet credit against a declared benchmark or label it unvalidated, and obtain human author approval. Author metadata should not block these scientific tasks.

Suggested manuscript statement
Prior analyses already couple MHD inlet control, ionization expenditure and cycle losses. We present a reproducible normalization and evidence-boundary audit of a conditional energy ledger. Its purpose is to expose what independently demonstrated inlet benefit is needed to offset round-trip conversion and auxiliary losses; it is not a prediction of net installed thrust or a claim to have discovered MHD energy bypass.

Targeted retrieval closeout, same date
Macheret2001 symbol check: Gamma denotes particle flux (p.4; equations20-21). Beta denotes recombination coefficients (equations24-25,38); its Hall parameter is Omega_e. Equation1 compares sustaining-ionization power with extraction; equations5-8 address Hall/ion-slip constraints. The requested Gamma, beta_crit and B_controllable definitions were not located as such. Do not attribute newly chosen definitions to this paper.

Riggins alternative edition: NASA record20020073109 is a2002 JANNAF conference paper, not the2004 journal article. Fresh official API https://ntrs.nasa.gov/api/citations/20020073109 confirms downloads=[]; the conventional PDF endpoint returns404. It provides an additional primary abstract but no full text. Equivalence of equations/figures between editions is unverified.

Lieu2026 closeout: publisher page offers institutional access/purchase; direct PDF fetch returned403. Exact-title author-manuscript/arXiv searches found no accessible primary full text in this pass. No paywall or access control was bypassed.

Finite essential remaining actions before asserting scientific novelty
1. Obtain the Riggins2004 journal article (or2002 manuscript, while tracking edition differences), Macheret2002 article, Meyer2005 article and Lieu2026 article through lawful library or author access. These four access gaps are explicit; no repeated retrieval attempts are scheduled.
2. Compare the resulting equations, objective, normalization and claimed validity range with our completed reduced model. A missing full text is not evidence that it lacks the same result.
3. Identify the original source and exact definitions of the user's Gamma, beta_crit and B_controllable, or label our alternatives as newly defined screening quantities. The2001 symbol check does not resolve that provenance.
4. Demonstrate a bounded contribution beyond reparameterization; otherwise frame submission as a reproducible methodological/evidence note without claiming new propulsion physics.
The optional unverified2026 hybrid-plasma lead remains outside the evidence used and does not prevent writing the conditional note. Scientific development and author-metadata collection proceed independently.
