The luminosity of the ring-ring version of the proposed electron-ion collider eRHIC is limited by the beam-beam effect on the electrons. Once the beam-beam limit is reached. the luminosity no longer increases linearly with the bunch intensity of the ion beam. but begins to saturate and even drops again if the beam-beam tuneshift is increased further. https://www.ealisboa.com/flash-grab-Hellfire-Sloe-Gin-special-find/