Positively charged antihydrogen ions can be efficiently cooled to cryogenic temperature. After removing the extra positron from the ion using a laser beam, direct measurement of the gravitational acceleration will be possible by observing the free fall of the neutral atom. To create the antimatter ions, antiprotons should be injected into a sufficiently dense ortho-positronium (o-Ps) cloud. To achieve the o-Ps density needed, thin mesoporous silica films are suggested as efficient converter systems which produce low-energy o-Ps with high efficiency upon irradiation with positrons at keV energy. The optimization of the growth parameters and the characterization of the films are discussed using 3 gamma annihilation franction, ortho-positronium lifetime and time-of-flight spectroscopy. A method for the determination of the precise vacuum ortho-positron escape yield, based on the correct measurement of the full o-Ps lifetime distribution, is presented. A positron source, presently under construction at CEA Saclay (France), is described. It is based on a dedicated linear electron accelerator and can serve as a test device for a future generation of self-containing, high-intensity positron sources that are free from radioactive isotopes.