87 lines
2.5 KiB
Markdown
87 lines
2.5 KiB
Markdown
---
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title: MAGNETICDATA.TXT
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section: 5
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---
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# NAME
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magneticdata.txt --- MHD equilibrium data for **gray**(1)
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# FORMAT
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The MHD equilibrium data can be specified in two ways: as the free parameters
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of a simple analytical model, or as numerical data in the G-EQDSK format.
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## analytical equilibrium
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The format for the analytical magneticdata.txt file is as follows:
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R₀ z₀ a
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B₀
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q₀ q₁ α
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npoints
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R₁ z₁
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R₂ z₂
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...
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where:
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- *R₀, z₀* are the coordinates of the magnetic axis (m)
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- *a* is the plasma boundary minor radius (m)
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- *B₀* is the value of toroidal field on the magnetic axis (T)
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- *q₀, q₁, α* are the parameters of the safety factors (see below)
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- *npoints* is the number of points in the plasma limiter contour
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that followsAa
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- *R_i, z_i* are the coordinates of the points in contour (m)
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Note: When viewing the torus from above, a positive B₀ results in a
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counterclockwise toroidal field and the plasma current is
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clockwise if q and B₀ have opposite signs.
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### analytical model notes
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The model used in GRAY describes a plsma with circular cross section centered
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on the magnetic axis at a major radius *R₀* and extending up to the minor
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radius *a*, where the density is exactly zero.
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There is no X point nor separatrix.
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The flux surfaces are circular and the normalised toroidal radius is exactly:
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ρ_t(R, z) = √[(R - R₀)² + (z - z₀)²]/a
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The toroidal field is given explicitly by *B_t(R) = B₀ R/R₀*; the poloidal
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field is determined implicitly by the safety factor profile.
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The latter is parametrised as:
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q(ρ_p) = q₀ + (q₁ - q₀)ρ_p^α,
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where *ρ_p* is the normalised poloidal flux.
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## numerical equilibrium
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The format of the numerical equilibrium is the G-EQDSK informal standard
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(See the GRAY manual for the specification).
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The data strictly necessary to perform a GRAY simulation are limited to:
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poloidal flux, safety factor, poloidal current function, magnetic axis and
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plasma boundary.
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If a limiter contour is provided it will be used to compute reflections.
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# EXAMPLES
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1. An analytical magneticdata.txt
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2.96 0.0 1.25 ! R₀ z₀ a
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6 ! B₀
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3.5 10 2 ! q₀ q₁ α
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4 ! npoints
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1.61 -1.35 ! a simple square limiter
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1.61 +1.35
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4.31 +1.35
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4.31 -1.35
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2. An analytical magneticdata.txt without limiter
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2.96 0.0 1.25 ! R₀ z₀ a
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6 ! B₀
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3.5 10 2 ! q₀ q₁ α
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0 ! no limiter contour
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# SEE ALSO
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**gray**(1)
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