ORIGINAL PAPER Simulation of Electron Trajectories in the Multicusp Ion Source Using Geantn4 Monte Carlo Code Fatemeh Khodadadi Azadboni Æ Mahmood Sedaghatizade Published online: 25 September 2009 Ó Springer Science+Business Media, LLC 2009 Abstract To optimize the multicusp ion source, under- standing of transport properties of electrons is indispensable. Since the transport of electrons in the multicusp ion source is a three-dimensional problem, we use the 3D computer code Geant4, to model the particle trajectories. The goal is to study the effect of electron injection into a cylindrical gas chamber and the electron trajectories. The role of the mag- netic filter in contemporary negative ion sources is analyzed. The conditions in the magnetic filter adjacent to the plasma electrode optimum for the generation, formation, and extraction of an H - ion beam are found. The simulation results are in good agreement with the experimental data. Keywords Multicusp ion source  Electron trajectories  Magnetic filter  Low electron temperature  Geant4 code Introduction Multicusp ion source have used in many application, such as neutral beam injectors for fusion devices, particle accelera- tors, ion implantation systems, neutron tubes for oil well logging and proton therapy machines [1–9]. Magnetic mul- tipole plasma confinement geometries employing permanent magnet buckets are used extensively for a range of laboratory plasma applications. Magnetic multicusp confinement is used to confine hot electrons and source plasma particles. The ionization efficiency of hot electrons can be enhanced substantially and the plasma particles can diffuse freely in a volume with low magnetic fields [6–11]. The plasma source for a particular application must provide useful ion species with the needed current density, electron temperature, and plasma uniformity. It should also be compact, simple, flexible, reliable, and efficient. Thus, to optimize the negative ion source; understanding of transport properties of both hydrogen neutrals and negative ions is indispensable. The knowledge of electron trajecto- ries under the influence of electrostatic and magnetic fields in a plasma discharge helps in understanding and predict- ing various discharge characteristics. Many zero dimen- sional codes [12–15] for hydrogen plasma and neutrals have been developed and successfully applied for the analyses of H 2 sources up to now. However, a multidi- mensional simulation model that can take into account real geometry and profile effects is required for more detailed understanding of their transport processes. In the present article, we have used a Geant4 Monte Carlo simulation code for the study of electron trajectories in a multicusp ion source and operation of magnetic filters regarding their use for electron cooling in the sources of the negative hydrogen ion beams. The influence of various filter shapes and dif- ferent distance of extraction aperture on plasma discharge has been studied by tracing the primary electron trajecto- ries into plasma chamber and near the magnet filter. Modeling of Multicusp Ion Source The Geant4 code (v.8.2) was used to simulate the multicusp ion source configuration. The main features are briefly summarized as follows. The ion source is a cylindrical F. Khodadadi Azadboni  M. Sedaghatizade Department of Physics, K.N. Toosi University of Technology, 41, Shahid Kavian St., 15875-4416, Tehran, Iran F. Khodadadi Azadboni (&) Member of Young Researchers Club, Islamic Azad University, Sari Branch, 48161-194, Sari, Iran e-mail: fatemeh@sina.kntu.ac.ir; fatemeh.khodadadiazadboni8@gmail.com 123 J Fusion Energ (2010) 29:150–156 DOI 10.1007/s10894-009-9248-4