Centre de recherche sur les Ions, les MAtériaux et la Photonique (UMR 6252)

We study the transport of ions through dielectric capillaries to support experimentalists from the AMA team, to help to understand and to optimize the ion transmission through conical insulating micro-capillaries (see PELIICEAN project and AMA group). We profited from our experience in the modeling of charged micro-droplets deformation to propose a new model and write a numerical code dedicated to ion beam transmission through micro-capillaries.
While the ion guiding through glass capillaries due to charged patches is qualitatively understood, the complex nature of the electric conduction in such insulators makes quantitative predictions still a challenging task. Indeed, the guiding is determined by the discharge dynamics of the charge patches at the surface, which in turn depend (i) on the electrical properties of insulators under ion beam irradiation and (ii) on the position and nature of grounded electrodes. A realistic description of the surface and bulk conductivity of insulating capillaries has thus to be included in a theoretical model.
Previous simulations by other authors run quite slow, implying harsh simplifications in the theoretical model of the charge dynamics. We wrote a CPU efficient code, which afford a rather realistic description of the charge dynamics at the capillary interfaces, and which allows us to generate quantitative meaningful results. In a first attempt, we introduced surface charge dynamics along the inner surface. In the case of a conical insulating capillary, our numerical results show that a stable ion transmission could be achieved, where the incoming beam is sufficiently compressed to be focused outside the capillary into a small spot, similar to an electrostatic lens. However, comparison with experimental data still showed some discrepancies, asking for a more refined model.
We focus now on the modeling of charge transport in irradiated insulators. While the electric properties of neutral insulators have been extensively studied over decades, investigation of the electric properties of charged insulators under beam irradiation is a challenging task. Our goal is to identify the mechanism that play a major role in the charging up and discharge process of irradiated insulators and to model those mechanisms. At the same time, we will continue to optimize the algorithms so that systematic studies continue to be achievable. We will be guided by former experimental measurements as well as future measurements that will be realized by our collaborators.