  Plasma diagnostics in magnetic confinement fusion plasmas by using visible
spectrum strongly depends on the knowledge of fundamental atomic properties. A
detailed collisional-radiative model of W$^{26+}$ ions has been constructed by
considering radiative and electron excitation processes, in which the necessary
atomic data had been calculated by relativistic configuration interaction
method with the implementation of Flexible Atomic Code. The visible spectrum
observed at an electron beam ion trap (EBIT) in Shanghai in the range of 332 nm
to 392 nm was reproduced by present calculations. Some transition pairs of
which the intensity ratio are sensitive to the electron density were selected
as potential candidate of plasma diagnostics. Their electron density dependence
are theoretically evaluated for the cases of EBIT plasmas and magnetic
confinement fusion plasmas.
