RF Alpha-Channeling in a D–³He Tandem-Mirror Burner: Raising the Recoverable Charged-Particle Fraction from 8% Toward 80%

Abstract

In a deuterium–helium-3 (D–^3He) tandem-mirror burner the fusion-born 14.68 MeV proton and 3.67 MeV alpha carry the overwhelming majority of the released power as fast, mirror-trapped ions. Left to thermalise, that energy is shared between electron drag and a broadly heated ion background whose confined, usefully recoverable share is small; the rest exits the loss cone as heat and inflates the recirculating power that sets the burner's engineering gain Q_E. RF alpha-channeling—a resonant wave that extracts perpendicular energy from a fusion product, hands it to the fuel ions, and simultaneously diffuses the spent ash toward the loss boundary—converts this loss into a directed gain. We formalise the mechanism as a bounce-averaged Fokker–Planck problem closed by a quasilinear cyclotron-resonant diffusion operator, derive the Fisch–Rax energy–position coupling E/=/n that makes channeling a bounded lever rather than a closure mechanism, and evaluate it at the frozen M-45 burner operating point (T_i=90 keV, n_e=2.6×10^20 m^-3, x_^3He=0.30, mirror-throat field B_m=17 T, central-cell field B_0c=5.50 T, effective mirror ratio R_mc=4.61). A reduced two-dimensional velocity-space kinetic solve, cross-checked against ray-tracing and particle-in-cell codes on the NVIDIA GPU HPC campaign, raises the recoverable charged fraction from a collisional baseline near 8% to about 80% and recovers up to 195 MW into the confined fuel ions—enough to cover the 40–110 MW plug-localised warm-fill RF cost with margin, while a full-volume warm fill (3.7 GW, 85% of P_ fus) is energetically precluded. We are explicit that this closes only under plug localisation (channeled power confined to 1–3% of the central-cell volume) and that the plant gain remains gated by the plug potential, not by channeling: the design-point Q_E=1.318 is untouched. Every headline quantity is a frozen anchor in the Kronos de-risking register.Key results (frozen anchors): n_e = 2.6 ×10^20; Frec = 8 %; f_n = 5.44 %.Live verification: 11 gate validator(s) with live-recompute cards (9 reproduced, 2 revised). See the Verification section and data/verification.csv.Related: Paper page · De-risking register · 3D model · Learn more about KronosPart of the 2026 Kronos publication series; independently re-run and stamped in the Kronos de-risking register (DOI 10.5281/zenodo.22645689).All numerical values are frozen design-point anchors; see the register.Public research artifact. No proprietary, financial, or supply-chain information is included.Note (REPLACE): This record replaces and supersedes DOI 10.5281/zenodo.22132168; please cite this version.