We have determined the absolute fluxes of various species injected from a dielectric surface into the surface-flashover-produced anode plasma in a magnetically insulated ion diode by observations of time-dependent line intensities and use of time-dependent collisional radiative calculations. Neutral particles, singly charged ions, and doubly charged ions produced on the dielectric surface were found to be continuously injected during the voltage pulse with the injection of neutral particles and singly charged ions continuing also after the main pulse. The determined fluxes explained the observed rise in the areal density of the plasma electrons. Using observed particle velocity distributions the particle flow in the plasma was calculated. It was found that mainly multiply charged ions and protons reach the plasma ion-emitting region. The flux ratio of doubly charged ions to protons produced by hydrogen ionization in the outer plasma region was found to rise towards the end of the pulse, consistent with the corresponding ratio in the extracted ion beam. The determined plasma composition allowed the electron-cooling processes to be evaluated. Such investigations can be used in plasma source design.