Equilibrium Magnetic Field
The equilibrium magnetic field is written [5,14] [see Equation (2.130)]
where is a convenient scale magnetic fieldstrength,
and

(14.18) 
is the safetyfactor profile. [See Equation (2.128).]
Here, and are dimensionless functions.
It follows from Equations (14.1)–(14.5), (14.17), and (14.18) that
The equilibrium poloidal magnetic flux (divided by ),
, satisfies,

(14.25) 
where, by convention,
. [Note that
is equivalent to the quantity defined in Equation (2.130).] The normalized poloidal magnetic
flux,
, is defined such that

(14.26) 
Hence,
and
. In general,
. Finally, if
then
. Thus, is the safetyfactor of the magnetic fluxsurface that encloses 95% of the poloidal magnetic flux enclosed by
the last closed magnetic fluxsurface.