Global Gyrokinetic Codes
Global gyrokinetic codes simulate turbulence across a macroscopic plasma volume, retaining profile variation and long-wavelength transport that flux-tube codes omit.
Beyond the flux tube
A global gyrokinetic code simulates a full radial extent of the plasma, or the whole cross-section, keeping the real variation of density, temperature, and geometry across the domain. Unlike a local code it does not assume constant gradients, so it captures profile shearing, avalanche-like transport events, and turbulence spreading between regions of different drive.
This realism is essential when the ion orbit width is a non-negligible fraction of the minor radius, which is the case in spherical tokamaks and in the edge of any device. The cost is large: global runs resolve many more modes and require far more grid points and particles.
Particle-in-cell vs continuum
Global codes come in two numerical families. Particle-in-cell codes represent the distribution by marker particles pushed along characteristics with fields solved on a grid. Continuum (Eulerian) codes discretize the distribution on a fixed phase-space grid. Each has trade-offs in noise, resolution, and conservation, and cross-verification between them builds confidence.
Electromagnetic and multiscale effects
At higher plasma pressure, magnetic fluctuations matter, so electromagnetic global runs are needed. Resolving electron and ion scales together is a multiscale challenge that pushes these codes to the largest available HPC systems.
Design relevance
For the low-aspect-ratio Hyperion breeder, global gyrokinetics is the more trustworthy turbulence tool because the flux-tube assumption is weak there. Simulations map transport across the profile to test predicted confinement, all as design study before the Q2 2027 construction start.
- Simulates a macroscopic plasma volume
- Retains profile variation and turbulence spreading
- PIC or continuum numerics
- Preferred at low aspect ratio despite high cost