Preface S. Degenkolb, P. Geltenbort, T. Jenke, M. Jentschel, V.V. Nesvizhevsky, S. Roccia, T. Soldner, O. Zimmer, D. Rebreyend and A. Stutz EPJ Web Conf., 219 (2019) 00001 Published online: 12 December 2019 DOI: 10.1051/epjconf/201921900001