Ray-Tracing Heating Codes
Ray-tracing codes follow electromagnetic wave beams through the plasma along the geometric-optics path, computing where heating and current-drive power deposit.
Geometric optics for waves
Radio-frequency and microwave heating launches electromagnetic waves that propagate into the plasma and deposit energy where they are absorbed. When the wavelength is short compared with the plasma gradients, the wave behaves like a ray. Ray-tracing codes integrate the geometric-optics equations, advancing a ray's position and wavevector through the inhomogeneous, magnetized, dispersive plasma.
Along the ray the code evaluates the local dispersion relation and the absorption coefficient, depositing power where damping is strong, typically at cyclotron resonances or their harmonics. The output is a deposition profile that feeds transport solvers as a heat and current source.
Which schemes it serves
Ray tracing is the standard tool for electron cyclotron and lower-hybrid systems, where the geometric-optics assumption holds well. For ion cyclotron waves the wavelength is longer and full-wave methods are often needed instead.
Coupling to Fokker-Planck
Absorption and current drive depend on the electron distribution, which the waves themselves distort. Accurate current-drive prediction couples the ray tracer to a Fokker-Planck solver so the quasilinear diffusion from the waves and the distortion of the distribution are computed self-consistently.
Design relevance
For the Hyperion breeder, ray tracing predicts where electron-cyclotron power lands, which matters for heating, for driving current to sustain the equilibrium, and for suppressing neoclassical tearing modes by depositing on rational surfaces. These are simulation studies preceding construction.
- Follows wave beams as geometric-optics rays
- Deposits power at resonances
- Standard for EC and LH systems
- Coupled to Fokker-Planck for current drive