  Energy levels, radiative transition wavelengths and probabilities have been
studied for the W$^{26+}$ ion using multiconfiguration Dirac-Fock and
Dirac-Fock-Slater methods. Corona and collisional-radiative models have been
applied to determine lines and corresponding configurations in a low-density
electron beam ion trap (EBIT) plasma. Correlation effects for the $4f^{2}$,
$4d^{9}4f^{3}$, $4f5l$ ($l=0,...,4$), $4fng$ ($n=5, 6, 7$) configurations have
been estimated by presenting configuration interaction strengths. It was
determined that correlation effects are important for the $4f5s \rightarrow
4f^{2}$ transitions corresponding to weak electric octupole transitions in a
single-configuration approach. Correlation effects influence the $4f5d
\rightarrow 4f^{2}$ transitions by increasing transition probabilities by an
order of magnitude. Identification of some lines observed in fusion plasma has
been proposed. Spectra modeling shows strong increase of lines originating from
the $4f5s \rightarrow 4f^{2}$ transitions. Other transitions from the $10-30$
nm region can be of interest for the EBIT plasma.
