Transport Simulation Workloads

Solving how particles, heat, and momentum move across the plasma to predict confinement and profiles for both machines.

Transport sets performance

Beyond equilibrium and stability lies transport: how particles, energy, and momentum diffuse and convect across the confining field. Transport determines the density and temperature profiles, and therefore the fusion power and confinement, of both machines. L0 runs transport solves to predict these profiles and to close the loop between heating, fueling, and performance.

The transport equations

Plasma transport is described by coupled continuity and energy-balance equations for each species, with fluxes driven by gradients through diffusivities and convective velocities. The central difficulty is that the transport coefficients are set by turbulence, so they are not simple constants but depend on the very gradients they redistribute.

# 1D flux-surface-averaged transport (per species):
# dn/dt = -1/V' d/drho( V' Gamma ) + S_n
# 3/2 d(nT)/dt = -1/V' d/drho( V' q ) + P_heat - P_loss
# Gamma = -D dn/drho + n v   ;  q = -n chi dT/drho
# D, chi, v from turbulence models / gyrokinetics

Where the coefficients come from

Kronos supplies transport coefficients either from reduced turbulence models or from first-principles gyrokinetic runs. The gyrokinetic route is expensive and lives among the heaviest L0 workloads; the reduced-model route is cheap enough to sweep. Both feed the same profile solver, trading fidelity against breadth.

• Breeder core profiles feeding 85.0 MW fusion power estimates
• Edge transport in the negative-triangularity ELM-free regime
• Burner central-cell profiles under mirror confinement
• Impurity and helium-ash transport

The two machines pose distinct transport questions. The breeder's negative triangularity changes edge transport and is a central reason for the delta -0.30 choice; the burner's open geometry couples transport to end losses and the ambipolar potential rather than to a closed-flux edge. The same solver framework handles both with different geometry and closures.

Transport results are the bridge from physics to performance. They set the profiles that feed neutronics source distributions, thermomechanical loads, and the twin's Power module, making transport the workload that ties the rest of the L0 chain to the numbers that define each machine.