gray/doc/man/magneticdata.txt.5.md

title	section
MAGNETICDATA.TXT	5

NAME

magneticdata.txt --- MHD equilibrium data for gray(1)

FORMAT

The MHD equilibrium data can be specified in two ways: as the free parameters of a simple analytical model, or as numerical data in the G-EQDSK format.

analytical equilibrium

The format for the analytical magneticdata.txt file is as follows:

R₀ z₀ a
B₀
q₀ q₁ α
npoints
R₁ z₁
R₂ z₂
...

where:

• R₀, z₀ are the coordinates of the magnetic axis (m)
• a is the plasma boundary minor radius (m)
• B₀ is the value of toroidal field on the magnetic axis (T)
• q₀, q₁, α are the parameters of the safety factors (see below)
• npoints is the number of points in the plasma limiter contour that followsAa
• R_i, z_i are the coordinates of the points in contour (m)

Note: When viewing the torus from above, a positive B₀ results in a counterclockwise toroidal field and the plasma current is clockwise if q and B₀ have opposite signs.

analytical model notes

The model used in GRAY describes a plsma with circular cross section centered on the magnetic axis at a major radius R₀ and extending up to the minor radius a, where the density is exactly zero. There is no X point nor separatrix.

The flux surfaces are circular and the normalised toroidal radius is exactly:

ρ_t(R, z) = √[(R - R₀)² + (z - z₀)²]/a

The toroidal field is given explicitly by B_t(R) = B₀ R/R₀; the poloidal field is determined implicitly by the safety factor profile. The latter is parametrised as:

q(ρ_p) = q₀ + (q₁ - q₀)ρ_p^α,

where ρ_p is the normalised poloidal flux.

numerical equilibrium

The format of the numerical equilibrium is the G-EQDSK informal standard (See the GRAY manual for the specification).

The data strictly necessary to perform a GRAY simulation are limited to: poloidal flux, safety factor, poloidal current function, magnetic axis and plasma boundary. If a limiter contour is provided it will be used to compute reflections.

EXAMPLES

1. An analytical magneticdata.txt

    2.96 0.0 1.25  ! R₀ z₀ a
    6              ! B₀
    3.5 10 2       ! q₀ q₁ α
    4              ! npoints
    1.61  -1.35    ! a simple square limiter
    1.61  +1.35
    4.31  +1.35
    4.31  -1.35
   

2. An analytical magneticdata.txt without limiter

    2.96 0.0 1.25  ! R₀ z₀ a
    6              ! B₀
    3.5 10 2       ! q₀ q₁ α
    0              ! no limiter contour
   

SEE ALSO

gray(1)