Driving our rapid iterations

Our simulation tools underpin First Light’s research efforts and the long-term business strategy. We develop two multi-physics codes used for the end-to-end design of our fusion systems. These core capabilities are supported by theoretical models, modern machine learning, data science, processing tools, and emphasis on software verification and validation. Large-scale simulation studies, and our comprehensive test suites, are enabled by our own High-Performance Computing (HPC) facilities.


Lines of code


SW quality assurance tests


In-house HPC core count

Software quality assurance

We consider software engineering best practises, quality control and assurance, and verification and validation driven development essential to our approach. Our experiments operate in extreme parameter spaces and it is not feasible to make validation measurements of all aspects. Nevertheless, the software must perform reliably. Algorithms must precisely represent the mathematical model and its solution, simulations must be reproducible, and the impact of changes must be tracked. Proper software quality is essential to proper scientific quality.

  • Hytrac unit tests 3600
  • Hytrac verification and validation tests 900
  • Other software CI tests 12000
  • Principal code repositories 20
  • Continuous integration build plans >100
  • Simulations in typical target design campaign >10000

Model specifications

Both of our flagship codes, Hytrac and B2, solve compressible two-temperature fluid dynamic equations. Additional physics, such as collisional and radiative transport, are included. Both codes model an arbitrary number of materials and use common microscale models and equation of state.

Hytrac is a 2D radiation hydrodynamic front-tracking code. The modelling of the material interfaces impact the predicted performance of our targets, and sensitivity to numerical choices can be greater than the sensitivity to thermophysical models. Hytrac aims for high interface fidelity and high-accuracy compressible flow solvers.

B2 is a 3D resistive magnetohydrodynamic code. B2 is newer than Hytrac and was developed, initially as a skunkworks project, to model our electromagnetically launched projectiles. It is now also used to model target performance.

We believe there is a big advantage to having two in-house codes. We are able to learn from cross-code comparisons where we would otherwise be developing models in isolation.

Simulation papers

Browse our Science Hub for papers, posters and publications about our simulations

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