Plasma Edge Fluid Codes
Edge fluid codes solve Braginskii transport equations on a field-aligned mesh coupled to a Monte Carlo neutral model to predict divertor and scrape-off-layer plasma.
The fluid edge approach
The most widely used edge tools are coupled plasma-fluid and neutral-kinetic packages. The plasma side solves Braginskii fluid equations, conservation of particles, parallel momentum, and electron and ion energy, on a two-dimensional mesh aligned with the magnetic field in the poloidal plane. The neutral side is handled by a separate Monte Carlo module that tracks atoms and molecules through the same geometry.
The two are iterated: the plasma ionizes and heats neutrals, the neutrals recycle from surfaces and provide particle and momentum sources back to the plasma. This coupling is what makes the codes predictive for recycling-dominated divertors.
Grid and geometry
A field-aligned quadrilateral mesh spans from a few centimeters inside the separatrix out into the SOL and private-flux region and down to the divertor targets. Building this grid from an equilibrium is itself a specialized mesh-generation task, since the geometry near the X-point is singular.
Cross-field transport as input
Cross-field transport coefficients are not solved self-consistently; they are prescribed, often tuned to match experimental profiles. This is the main limitation of the fluid approach and a reason kinetic and turbulence codes are used to inform the coefficients.
Design use
Edge fluid codes are the workhorse for divertor design. For the Hyperion breeder they estimate target heat flux, detachment thresholds, and impurity seeding requirements in simulation. Results carry the caveat that prescribed transport coefficients embed assumptions that only operation can confirm.
- Braginskii fluid plasma plus Monte Carlo neutrals
- Field-aligned 2D poloidal mesh
- Cross-field transport is prescribed, not solved
- Standard tool for divertor and detachment design