Laboratory measurements of Fe XXIV line emission: 3 -> 2 transitions near excitation threshold

Using the Electron Beam Ion Trap facility at Lawrence Livermore National La boratory, we have measured relative cross sections for Fe XXIV line emissio n at electron energies between 0.7 and 3.0 keV. The measurements include li ne formation by direct electron impact excitation (DE), radiative cascades, resonant excitation (RE), and dielectronic recombination (DR) satellites w ith captured electrons in n greater than or equal to 5 levels. Good agreeme nt with R-matrix and distorted wave calculations is found. In collisionally ionized plasmas, at temperatures near where the ion abundance peaks (kT(e) similar to 1.7 keV), the RE contributions are found to be less than or sim ilar to 5% of the line emission, while the DR satellites contribute less th an or similar to 10%. While good agreement with state-of-the-art atomic phy sics calculations is found, there is less good agreement with existing spec tral synthesis codes in common astrophysical use. For the Fe XXIV 3p(3/2) - -> 2s(1/2), 3p(1/2) --> 2s(1/2), and 3d(5/2) --> 2p(3/2) transitions, the s ynthesis code MEKAL underestimates the emissivity in coronal equilibrium by similar to 20% at temperatures near where the ion abundance peaks. In situ ations where the ionization balance is not solely determined by the electro n temperature, RE and DR satellites may contribute a considerable fraction of the line emission.