Numerical simulations of space charge effects and plasma dynamics for FEBIAD ion sources

Abstract

The FEBIAD (“forced electron beam induced arc discharge”) ion sources are used for the production of radioactive ion beams for a wide range of chemical elements. Their small volume and high operating temperature provide good confinement times and ionization efficiencies.The extracted ion current from a FEBIAD ion source depends on the parameters of the plasma created inside (density, temperature, potential), parameters which are themselves dependent on the input gas pressure and composition.Within the framework of the HIGHINT Marie Curie and the EURISOL DS programs, investigations are ongoing for high power direct targets, which can accommodate up to 100kW incoming proton beam power. For such systems, the quantity of impurities entering the ion source will increase, thus leading to a change of the plasma characteristics. The gas flow coming from the target will exceed the buffer gas flow, and the ionization of the trace elements will be controlled by the gas composition released from the target.An insight on the complex phenomena taking place in the ion source can be achieved using a Particle-In-Cell code (VORPAL, “versatile, object-oriented, relativistic, plasma analysis code with lasers”), which can simulate the dynamics of neutral and charged particles inside the plasma: ionization, recombination and charge exchange phenomena, secondary emissions and sputtering.