# Ellipticity

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The ellipticity (also referred to as elongation^{[1]}) refers to the shape of the poloidal cross section of the Last Closed Flux surface or separatrix of a tokamak.

Assuming^{[1]}:

*R*is the maximum value of_{max}*R*along the LCFS or separatrix.*R*is the minimum value of_{min}*R*along the LCFS or separatrix.*Z*is the maximum value of_{max}*Z*along the LCFS or separatrix.*Z*is the minimum value of_{min}*Z*along the LCFS or separatrix.*a*is the minor radius of the plasma, defined as*(R*._{max}- R_{min})/2

The ellipticity is then defined as follows:

## See also

## References

- ↑
^{1.0}^{1.1}T.C. Luce, Plasma Phys. Control. Fusion**55**(2013) 095009