Ethan Peterson

This work describes a design study of a cyclotron-driven Fusion Prototypic Neutron Source (C-FPNS) target optimized to meet US specifications for a fusion materials irradiation target. The analysis supports the use of multiple compact deuterium cyclotron beams at a total current under 40 mA in the range of 35–60 MeV converging on a flowing annulus of lithium surrounding the sample target. The sample target region is modeled as miniaturized tensile and Charpy bend-bar specimens located within the central region of the annulus. A specific focus of this work is to provide a highly uniform flux trap of fusion-relevant neutrons maximizing the average neutron damage per unit of beam current. This design achieves the goals recently enumerated by the US community of sample volume (>50 cm ³ ) and damage (>10 dpa yr ⁻¹ ) metrics with damage gradient (<40%) within the sample target region.

Negative triangularity (NT) offers a potential solution to the high heat fluxes incident on the divertor of reactor-class tokamaks by blocking access to H-mode. An important step in assessing how NT may scale to a reactor is determining the behavior of existing current drive schemes in NT. Lower hybrid current drive (LHCD) is an attractive technology due to its high efficiency. The effect of triangularity on high field side (HFS) LHCD was evaluated with the ray-tracing/Fokker-Planck codes GENRAY/CQL3D using positive triangularity (PT) and NT equilibria with otherwise identical shaping parameters generated by the Grad-Shafranov solver TokaMaker. Two classes of devices were considered: DIII-D-class and ARC-class. Triangularity was found to significantly affect LHCD physics, with strong absorption being achieved for a wider variety of launcher configurations in NT than PT. Larger driven currents were predicted in PT than NT for some DIII-D-class cases and the majority of the ARC-class cases. The LH current density profiles were more narrow on average in NT than PT. Finally, the neutron flux incident on the launcher was considered for the ARC-class plasmas. Overall, HFS LHCD is expected to function well in NT.

Hydrogen isotope permeability in molten salts is commonly inferred from permeation experiments using one-dimensional interpretations, which may not capture the coupled transport pathways in realistic systems. In this work, a multidimensional, multi-material transport modeling framework implemented in FESTIM is applied to permeation measurements from the HYPERION experiment over 773K to 973K. The model resolves hydrogen isotope transport across molten salt, nickel structures, and external boundaries, with two limiting boundary conditions (ideal coating and uncoated conditions) bracketing the possible hydrogen exchange with the environment. A validation-informed inverse framework is used to infer the FLiBe permeability by matching simulated and measured steady-state permeation fluxes. The model reproduces the measured fluxes under both boundary-condition limits while revealing significant lateral transport and sidewall leakage pathways absent from one-dimensional interpretations. The inferred FLiBe permeability follows Arrhenius behavior but spans more than an order of magnitude across boundary-condition limits, demonstrating that one-dimensional formulations cannot reliably extract permeability from coupled-system permeation experiments. These results provide a physically grounded basis for interpreting permeation measurements and highlight the importance of multidimensional transport modeling for property inference in fusion-relevant molten-salt systems.

Achieving tritium self-sufficiency is a critical challenge for future fusion power plants. The BABY 1L experiment, part of the LIBRA project at MIT, aims to benchmark tritium breeding and release in molten salt breeder systems under deuterium-tritium (DT) neutron irradiation. Building on the initial \SI{100}{mL} campaign, BABY 1L introduces a tenfold increase in breeder volume, improved thermal and gas handling systems, and enhanced neutron diagnostics, including a proton recoil telescope. We report on results from four irradiation experiments using sealed-tube DT neutron generators, with tritium collected by water bubblers measured via liquid scintillation counting. Experimentally determined Tritium Breeding Ratios (TBRs) were compared to OpenMC neutronics simulations, showing very good agreement. The measured TBR values demonstrate a six-fold improvement over the \SI{100}{mL} experiments, largely attributed to the increased solid angle and improved measurement fidelity. We also investigate tritium release dynamics and identify diffusion-limited transport as the dominant regime in the salt volume in the temperature range 630-750 \si{\celsius}. Additionally, we observe that the introduction of hydrogen in the helium carrier gas significantly accelerates tritium release, consistent with an isotopic exchange mechanism. All analysis is conducted through the open-source \texttt{libra-toolbox} \cite{libra-toolbox}, which streamlines simulation, data processing, and validation across experimental campaigns. These results provide critical insights into the design and operation of future liquid breeder systems and demonstrate the maturity of the BABY platform as a testbed for tritium breeding studies.