Abstract: In order to investigate the process of optically triggered discharge formation, a model of ion space-charge formation based on classical plane electrodes and revised for a characteristic hollow-cathode discharge (HCD) configuration is proposed in this paper. The primary modified factor in our model is the penetrating electric-field parameter, which influences the ionization of trigger electrons and is calculated via particle simulation. Optical-trigger experiments are carried out using different voltages and under different seed-electron conditions, provided by two different photocathodes, Cu and Mg. The ion-accumulation rates calculated by our model are compared to the discharge-formation time, which is deduced from optical-trigger experiments. The results demonstrate that the process of positive space-charge formation is dominant in the HCD formation process or trigger delay, which is highly dependent on the seeding-electron density and applied voltage, and can therefore be quantitatively described by our model. Additionally, electron-beam generation is investigated by optically triggered HCD experiments on Mg- and Cu-photocathode-based devices. The results show that a more efficient trigger device is capable of generating an electron beam with higher amplitude and density.