We are requesting the funding of an R&D program aiming at characterizing the use of an existing technology in high-energy physics (HEP), a time projection chamber (TPC), for a new application, the high-precision detection of high-energy photons, and in particular of their polarization fraction. The ultimate goal, on a longer term, is the launch of such a detector in space to study gamma photons from cosmic sources. We are developing a novel concept for a gamma-ray detector based on a TPC, which will be: - the first polarimeter for cosmic gamma rays in the energy range MeV-GeV, such as those emitted by active galaxy nuclei (AGN), gamma-ray bursts (GRB) and pulsars. Polarimetry is performed by the analysis of the angular properties of triplet conversion events (gamma e- -> e+e- e-), that are reconstructed in the TPC. - a telescope with an angular resolution improvement of one order of magnitude over previous telescopes in this energy range. This instrument allows to fill the sensitivity gap between energy ranges in which the Compton telescopes (0.01 - 5 MeV) and telescopes using pair conversion in a high-Z converter (> 0.1 GeV) are most sensitive. - A dead-time-free GRB detector, since it is based on a TPC. The realization of the proposed ground-based characterization is a prerequisite for a future spatial mission. In addition to the characterization of a prototype exposed to a linearly polarized gamma-ray beam from an accelerator, two important deliverables will be: - the first experimental validation of polarization asymmetries at low energy, the knowledge of which is needed for polarized gamma-ray astronomy but also to validate experimentally a number of assumptions made in the theoretical computations based on QED. - the implementation of an exact Monte Carlo (MC) generator of conversion events in the HEP simulation software Geant4, i.e. a generation of the full 5D probability density function (PDF).