Longitudinal Structure Functions ($F_{L}$) at an Electron-Ion Collider

Current knowledge of gluon distribution functions in nuclei is extremely limited in range in $x$ and $Q^{2}$, due to the energies available in fixed target experiments performed to date. An electron-ion collider (EIC) would greatly extend this range, into a region in the $x$ and $Q^{2}$ plane where saturation of gluons is expected to become the dominant mechanism determining the properties of nuclear matter. Measurements of longitudinal structure functions ($F_{L}$) directly probe gluon distributions, as $F_{L}$ is directly related to the gluon distribution at tree level. Projections for experimental measurement of $F_{L}$ will be presented, along with considerations driving experimental setups.