Electron cyclotron resonance ion sources – physics, technology and future challenges O. Tarvainen, T. Kalvas, H. Koivisto, V. Skalyga, I. Izotov and D. Mansfeld EPJ Web Conf., 149 (2017) 01003 Published online: 04 August 2017 DOI: 10.1051/epjconf/201714901003