Effect of Plasma Density on High Current Beam Extracted from a MEVVA Ion Source

Summary form only given. The MEVVA ion source has been intensively used to provide high current metallic ion beams for film deposition and material modification over the last two decades. At GSI it is using to produce a high particle current to fill up the heavy ion synchrotron SIS to its space charge limit. Many efforts have been made at GSI, to increase the beam brightness, to enhance the fraction of charge state 4⁺ for the design ion, to reduce the beam noise, and to improve the beam stability. To deliver the desired ion beam, a multi-aperture triode extraction system is used due to high mass to charge ratio of the design ion. In this paper, a fully three dimensional and interactive code KOBRA3-INP was used to investigate the behavior of the ion beam extracted from a high current MEVVA ion source and the effects of plasma density on extracted high current beam. The beam trajectory and space charge map in the extraction system are presented. Simulation shows that there exists a minimum divergence for the extracted ion beam at the plasma density of about 190 mA/cm², which corresponds to the perveance matched condition. Furthermore, as the plasma density increases, the intensity of the extracted ion beam increases. If the experimental data with an extracted current of about 135-140 mA are used, the experimental data can be reproduced in the simulation with the longitudinal ion energy of 188 eV, the transverse ion energy of 100 eV, and the plasma density of 165 mA/cm² under the assumption of the full space charge compensation.