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Two design advances distinguish MARS from prior magnetic recoil spectrometers. First, redesigned ion optics reduce the focal-plane length to a size compatible with a silicon strip detector, making MARS the first inertial confinement fusion magnetic recoil neutron spectrometer with an electronic readout, enabling real-time data analysis and per-channel time-gating. Second, a dual-foil geometry (half CH2, half CD2) enables simultaneous spectral measurements of recoil protons and deuterons in a single shot, expanding neutron energy coverage to \u223c6\u201320\u00a0MeV. The conceptual design of the instrument, synthetic modeling framework, and shielding strategy are described. Monte Carlo transport and ion optics simulations show signal-to-background \u226b10 across the spectrum except for the alpha knock-on tail, with per-channel electronic time-gating providing additional background suppression. The open-source simulation framework additionally serves as a synthetic diagnostic for forward fits of parametric plasma models, showing good agreement with the true parameters.<\/jats:p>","DOI":"10.1063\/5.0347401","type":"journal-article","created":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T12:42:21Z","timestamp":1789994541000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["The next-generation magnetic recoil spectrometer for measurements of the absolute neutron spectrum at Pacific Fusion\u2019s demonstration system"],"prefix":"10.1063","volume":"97","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9684-6435","authenticated-orcid":false,"given":"N. 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