Briareus.jl

Briareus computes laser deposition, view-factor radiation transport and drive symmetry for laser-driven high-energy-density experiments: indirect-drive hohlraums, backlighter foils and other laser-irradiated targets. It covers the calculations a view-factor code such as VisRad is used for, and it adds gradient-based optimization of pointing, defocus, power balance and wavelength detuning, reduced laser–plasma corrections (backscatter, cross-beam energy transfer), and shot-review checks of beam clearance and unconverted light.

The model in brief

• Targets are assembled from meshed surfaces: cylinders, annuli, spheres, rectangles, frusta. Each patch side that radiates is an element of the radiation model. Laser entrance holes are transparent apertures that record the flux escaping through them.
• Beams enter from facility ports with elliptical super-Gaussian phase-plate spots, an f-number cone, pointing and defocus. A precomputed quadrature makes deposition a smooth function of those parameters, so derivatives come from automatic differentiation. An energy-conserving ray trace is the reference.
• Radiation is gray and diffuse. View factors account for occlusion, and a radiosity solve gives the incident flux on every element. Wall albedo can depend on time and on the local radiation temperature. Because the system is linear in the laser source, the response of the capsule flux to deposition is computed once and reused by optimizers.
• Symmetry is measured by Legendre and real spherical-harmonic moments, integrated exactly over each facet.

Units are mm, ns, TW (TW·ns = kJ), TW/mm² for flux (to_Wcm2 multiplies by 10¹⁴) and eV for temperature. Port angles are in degrees: polar angle from +z, azimuth counterclockwise from +x, which on NIF points to Switchyard 1.

Choose a path

• Learn by running a calculation. Laser spot on a foil checks deposition and defocus against exact results. Integrating sphere checks the radiation model against the sphere-multiplier formula. Freeing a bundle for radiography chooses a NIF bundle to drive a backlighter and restores the drive symmetry it costs, within worst-case beam clearance.
• Understand what the checks establish. Verification and validation separates the activities the tutorials and tests carry out.
• Look up exact behavior. The reference pages document every exported name.

Facility data and physics defaults are sourced in reference/research-notes.md in the repository, with a confidence level for each number.