Background: Thorium, with its high melting point (3370 K) and neutron economy, emerges as a candidate for thermal protection systems (TPS) in hypersonic re-entry and impurity diagnostics in fusion plasmas. However, its actinide nature poses radiological, erosive, and electromagnetic risks, necessitating rigorous evaluation amid advancing non-LTE and MHD technologies. Purpose: This study assesses thorium's ionization behavior, ablation performance, risk-benefit trade-offs, and plasma sheath impacts to determine viability for hypersonic vehicles and plasma environments. Methods: Collisional-radiative modeling generated ionization fractions across T=2000–15000 K and ne=10¹⁸–10²³ m⁻³. CFD-ABL simulations quantified TPS recession under 2.5–5 MW/m² fluxes. Multi-attribute utility theory (MAUT) integrated risk-benefit metrics, while DSMC-FDTD couplings probed MHD efficiency and RF transmission for Th injections (0–30%). Findings: Neutral Th dominates cool edges (f=0.272), shifting to Th⁺ (0.971) in cores and Th²⁺ (0.615) at stagnation, with rates surging 10⁷-fold. TPS ablation escalated to 49M mm recession, 988k kg/m²/s mass loss, and 14.9/10 risk from aerosols (3.95×10¹⁷ Bq/m²). ThO₂ netted -0.286 (thermal 20.7/100 overshadowed by radiological 0.900), favoring ZrC (0.449). Th injection hiked ωp 20–50%, nullified RF transmission (0.0%), boosted MHD η=0.79 (+21%), but cratered stability -28.6%, with severity >0.9 in 80% domains. Conclusion: Thorium's thermal prowess fractures under radiological and blackout perils, rendering it suboptimal for operational deployment despite diagnostic utility. Recommendation: Pivot to ZrC TPS and non-actinide MHD seeding; confine Th to suborbital tests and spectroscopic proxies for 40% risk reduction.
Belay Sitotaw Goshu (Sat,) studied this question.