Yinsen: A low power density HTS tokamak fusion reactor for marine and off-grid applications
Yinsen is a high-temperature-superconducting (HTS) tokamak reactor concept for off-grid applications such as maritime propulsion, remote power, and industrial energy. Rather than pursuing grid-scale power density, the design is anchored to a materials-limited fusion power density of $P_f/S_b=0.7~\mathrm{MW/m^2}$, obtained from a 35 DPA structural limit, a 20-year plant lifetime, 40% utilization, and a geometric damage-peaking correction. The resulting device has a V-4Cr-4Ti vacuum-vessel lifetime of $1040~\mathrm{MW\cdot yr}$, pointing to a minimum useful fusion power of $130~\mathrm{MW}$ and more than $25~\mathrm{MWe}$ net output. Integrated FUSE modeling refines the design into a self-consistent high-field baseline with a shaped 9.29 T, 9.67 MA plasma, while ASTRA transport analysis corroborates a broader operating window above the minimum design point. Divertor power handling is addressed with UEDGE modeling, showing that impurity-seeded detached operation is attainable with neon seeding, reducing peak heat fluxes well below $10~\mathrm{MW/m^2}$. OpenMC neutronics calculations with a double-layered WC/W$_2$B$_5$ shield show that the vacuum vessel is the lifetime-limiting solid structure, while the HTS magnets remain lifetime components: at the 130 MW baseline, total TF nuclear heating is 7.4 kW at 20 K, and the TF fast-neutron limit corresponds to roughly sixteen vacuum-vessel lifetimes. The same neutronics analysis gives $TBR\approx1.1$ with 30% $^6\mathrm{Li}$ enrichment and no dedicated neutron multiplier. Plant-level studies detail a supercritical CO$_2$ balance of plant and pulsed-power operation using a 34 kV medium-voltage backbone and local energy storage. Taken together, these results suggest that a low-power-density HTS tokamak offers a near-term path for relevant FOAK fusion reactors where many remaining challenges between $Q>1$ and economic grid operation are alleviated.