Ionization of Atomic Hydrogen by Low Energy Antiprotons

Ionization is an important process in astrophysical and technological plasmas and in the dissociation of molecules in the Earth's atmosphere. Technological plasmas are increasingly used in industrial processing of materials, particularly to affect their surface properties, and are widely used in the semiconductor industry. Energy from controlled plasma fusion of hydrogen isotopes presents us with the possibility of a 'clean' energy source to replace fossil fuels and to alleviate global warming resulting from carbon dioxide emissions from current generation power stations.The cross section for electron removal or ionization of the simplest atom (hydrogen, or its isotope deuterium) by antiprotons is currently of considerable interest. This is the simplest collision system for testing theory with only one active electron and, since the antiproton cannot capture an electron, the detection of a hydrogen ion in coincidence with an antiproton after the collision is a signature of the ionization process. We will measure the cross sections for ionization of atomic hydrogen by antiproton impact at low energies, in a range never before accessed experimentally. Our understanding of the ionization mechanism in such a simple three-body system should enable an important step forward in current theoretical models.A firm theoretical understanding of ionization is important to the applications mentioned above, as theory is often used to provide input to simulations and in the interpretation of observations in physical situations where dedicated experiments are difficult, or even impossible...

The main impact of this work will be on the academic community studying few-body Coulomb physics, particularly as involved in ionization. The results are eagerly awaited by the atomic collisions theory community and we anticipate that some serious long-standing discrepancies will be resolved and that the Fermi-Teller theory will be tested for the first time. Since accurate modelling of the ionization process has applications in laboratory (including industrial) fusion and astrophysical plasmas, a knock-on effect will be felt in these communities via the development of improved theoretical models and diagnostics. The study will impact on the growing antihydrogen community who will benefit from the data obtained in the proposed work via the development of a more complete understanding of very low energy antiproton collisions.