  We provide a discussion of the density and photoexcitation sensitivity of the
X-ray spectra of Fe L-shell ions (Fe XVII-Fe XXIV) calculated with the
Livermore X-ray Spectral Synthesizer, a suite of IDL codes that calculates
spectral models of highly charged ions based primarily on HULLAC atomic data.
These models are applicable to collisionally ionized laboratory or cosmic
plasmas with electron temperatures T_e ~ 2-45 MK (0.2-4 keV) and electron
densities n_e > 1E11 cm^{-3}. Potentially useful density diagnostics are
identified for Fe XVII and Fe XIX-Fe XXIII, with the most straightforward being
the Fe XVII I(17.10 A)/I(17.05 A) line ratio and the Fe XXII I(11.92 A)/I(11.77
A) line ratio. Applying these models to the Chandra X-ray Observatory High
Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find
that the strength of all the Fe L-shell lines are consistent with electron
densities n_e > 1E14 cm^{-3}. Specifically, from the observed Fe XVII I(17.10
A)/I(17.05 A) line ratio, we infer an electron density n_e > 2E14 cm^{-3} at
the 3 sigma level, while from the observed Fe XXII I(11.92 A)/I(11.77 A) line
ratio, we infer n_e = 1.0^{+2.0}_{-0.5}E14 cm^{-3} at the 1 sigma level and n_e
> 2E13 cm^{-3} at the 3 sigma level.
