  An electron beam ion trap (EBIT) is used to measure extreme ultraviolet
spectra between 10 nm and 25 nm from highly-charged ions of tungsten with an
open 3d shell (W XLVIII through W LVI). We found that almost all strong lines
are due to the forbidden magnetic-dipole (M1) transitions within $3d^n$ ground
configurations. A total of 37 spectral lines are identified for the first time
using detailed collisional-radiative (CR) modeling of the EBIT spectra. A new
level-merging scheme for compactification of rate equations is described. The
CR simulations for Maxwellian plasmas show that several line ratios involving
these M1 lines can be used to reliably diagnose temperature and density in hot
fusion devices.
