Senior Multiphysics Modeling Engineer

About Helion We are a fusion power company based in Everett, WA, with the mission to build the world's first fusion power plant, enabling a future with unlimited clean electricity. Our vision is a world with clean, reliable, and affordable energy for everyone. Since Helion's founding in 2013, we have raised over $1 billion from long-time investors such as Sam Altman, Mithril, and Capricorn Investment Group as well as new investors SoftBank and Lightspeed to propel us forward. Our last prototype, Trenta, completed 10,000 high-power pulses and reached plasma temperatures of 100 million degrees Celsius (9 keV). We are now operating Polaris, our next prototype on the path to the world's first fusion power plant. This is a pivotal time to join Helion. You will tackle real-world challenges with a team that prizes urgency, rigor, ownership, and a commitment to delivering hard truths – values essential to achieving what no one has before. Together, we will change the future of energy, because the world can't wait. What You Will Be Doing: We are seeking a Senior Multiphysics Modeling Engineer to develop and validate coupled thermal–mechanical–fluid models for Helion's fusion hardware. You will bridge simulation and experimental data to inform material selection, component design, and operating limits in one of the most demanding engineered environments in the world. This role is highly cross-functional, partnering with materials scientists, test engineers, and mechanical designers to ensure modeling directly drives hardware decisions. You will report to our Materials Manager, onsite in Everett, WA. You Will: - Develop and maintain multiphysics models (primarily in MOOSE) for high-temperature ceramic and metallic components, plasma- and power-facing structures, and pulsed-load systems. - Simulate coupled thermal, structural, and electromagnetic behavior under rapid cyclic loading, high heat flux, and large temperature gradients, and implement and calibrate constitutive models for fatigue-dominated damage, fracture, and other relevant degradation mechanisms in extreme environments. - Execute rigorous verification and validation (V&V) by performing convergence studies, co-designing calibration and validation experiments with materials and test engineers, and systematically comparing model predictions to experimental results to quantify discrepancies and refine models, properties, and test plans to close the simulation–experiment gap. - Apply uncertainty quantification and sensitivity analysis to support life predictions, design margins, and operating envelope definition. - Translate modeling results into actionable design guidance for materials, joints, components, and inspection strategies. - Use simulation results to help establish material allowables and operating envelopes for high-temperature metallic and ceramic components. - Run large-scale simulations in HPC environments and build reproducible, version-controlled modeling workflows. - Help define a modeling roadmap and standards for key components and failure modes, including expectations for V&V, documentation, and workflow reproducibility as the modeling function grows. Required Skills: - PhD (or MS with significant experience) in Mechanical Engineering, Nuclear Engineering, Materials Science, Applied Physics, or related field with a computational focus. - 5+ years of experience in multiphysics finite element or finite volume modeling of coupled thermal–mechanical systems including experience with irradiated materials modeling and materials in severely degrading environments (e.g., plasma, fusion/fission, high-flux/high-dose environments, etc.) - Proficiency with at least one advanced multiphysics platform (e.g., MOOSE, Abaqus, COMSOL, ANSYS, BISON, OpenMC, MCNP), with willingness to work in MOOSE. - Demonstrated experience with verification and validation against experimental data. - Experience running simulations in HPC environments (parallel computing, job scheduling). - Prog