pub fn calculate_vacuum_field(
grid: &Grid2D,
coils: &[CoilConfig],
mu0: f64,
) -> FusionResult<Array2<f64>>Expand description
Calculate vacuum magnetic flux from coils using the toroidal Green’s function.
For each coil at (Rc, Zc) with current I, the flux contribution is:
Ψ = (μ₀ I / 2π) · √((R + Rc)² + (Z - Zc)²) · ((2 - k²)K(k²) - 2E(k²)) / k²
where k² = 4 R Rc / ((R + Rc)² + (Z - Zc)²), clipped to [1e-9, 0.999999].
Returns Ψ_vacuum [nz, nr].