# FisMat2017 - Submission - View

**Abstract's title**: Hydrogen scattering from a cesiated surface model

**Affiliation**: CNR-NANOTEC (P.LAS.M.I. Lab)

**Affiliation Address**: Via G. Amendola 122/D, 70126 Bari

**Country**: Italy

In the last years, the interest for the negative ion production increased significantly for its application in several fields spanning from microelectronics [1] to magnetically confined fusion[2], from space propulsion[3] to injector for particles accelerators[4].

In low-pressure plasmas negative hydrogen ions can be produced via surface collisions, in this case the conversion yield depends on the work function of the surface. Since many years it is well know the high efficiency in the production of negative ions from the interaction of plasma particles with electrodes on which cesium has been adsorbed [5]

In this work, the interaction of hydrogen atom with a cesiated surface model was studied. First, we determine the work function of considered surface model using dipole correction method [6]. Then the dynamics of interaction was investigated *via* Molecular Dynamics (MD) calculations using a semiclassical collisional method [7]. We perform DFT calculations to determine the interaction potential for H atom interacting on the cesiated surface model. These calculations allow getting another important result of this work, i.e. the interaction potential for a hydrogen atom and the net charge transfer between the impinging species and the surface.

Then we propagated thousands of trajectories to determine the probabilities of surface processes and toget insights on the reaction mechanism and its dependence on the surface topology. The surface processes studied in MD calculations occurs on a time scale of fs, but applicative process occurs on longer time scale. Therefore, this work aims to shed light on the interaction mechanism of hydrogen atoms with a cesiated surface at atomic level and determine accurate collisional data needed as input for kinetic plasma models, used to describe on the real time scale the formation of negative ions.

[1] C. Thomas, Y. Tamura, T. Okada, A. Higo and S. Samukawa, Estimation of activation energy and surface reaction mechanism of chlorine, J. Phys.D: Appl. Phys. **47** (2014) 275201.

[2] U. Fantz, P. Franzen and D. Wunderlich, Development of negative hydrogen ion sources for fusion: Experiments and modeling, Chem. Phys. **398** (2012)7–16,.

[3] S. Mazouffre, Electric propulsion for satellites and spacecraft: established technologies and novel approaches, Plasma Sources Sci. Technol. **25** (2016) 033002.

[4] A. Ueno, H. Oguri, K. Ikegami, Y. Namekawa and K. Ohkoshi, Interesting experimental results in Japan Proton Accelerator Research Complex H^{-} ion-source development, Rev. Sci. Instrum. **81** (2010) 02A720.

[5] V. Dudnikov, Thirty years of surface plasma sources for efficient negative ion, Rev. Sci. Instrum. **73**, p. (2002) 992.

[6]L. Bengtsson , Dipole correction for surface supercell calculations, Phys. Rev. B **59** (1999) 12301-12304.

[7] G. D. Billing, Dynamics of Molecule Surface Interactions, JohnWiley & Sons, New-York, 2000.