  Rich soft X-ray emission lines of highly charged silicon ions (Si VI--Si XII)
were observed by irradiating an ultra-intense laser pulse with width of 200 fs
and energy of $\sim$90 mJ on the solid silicon target. The high resolution
spectra of highly charged silicon ions with full-width at half maximum (FWHM)
of $\sim$0.3--0.4\AA is analyzed in wavelength range of 40--90 \AA . The
wavelengths of 53 prominent lines are determined with statistical uncertainties
being up to 0.005 \AA . Collisional-radiative models were constructed for Si VI
-- Si XII ions, which satisfactorily reproduces the experimental spectra, and
helps the line identification. Calculations at different electron densities
reveal that the spectra of dense plasmas are more complicate than the spectra
of thin plasmas. A comparison with the Kelly database reveals a good agreement
for most peak intensities, and differences for a few emission lines.

Astrophysics