Improving extraction and transport simulations of the superconducting ECR ion source VENUS

Abstract

A plasma sheath extraction model has been added to the three-dimensional, particle-in-cell (PIC) code WARP in order to simulate the extraction and transport of ion beams from the superconducting ECR ion source VENUS. The WARP code is ideally suited to simulate ECR ion source transport systems since it can handle large particle numbers, multiple species, applied and self fields, and has a powerful PYTHON programming shell that allows the user to easily customize the simulation. The addition of an axially symmetric sheath extraction model for a multi species plasma allows for the simulation of the entire VENUS beam line including extraction. To benchmark this model against experiment we have produced axially symmetric beams from VENUS composed almost exclusively of one ion species. These axially symmetric beams are produced by operating the VENUS source without sextupoles, which confine the plasma radially. In addition we performed single species experiments with the sextupoles energized. These measurements confirm the expected triangular shape of the extracted beam. To simulate asymmetric plasma extraction, a simple approximation using the results of the symmetric extraction model is employed. Comparisons between simulation and experiment for both extraction cases at a beam profile diagnostic device (beam harp) after the extraction and at an emittance scanner after the analyzing magnet are presented. Good agreement in both the size and shape of the beam were found at the beam harp provided the beam is not overfocused to a waist before the harp. Simulation and experiment also show reasonable agreement in beam size and divergence angle when comparing emittance scanner measurements after the analyzing dipole. © 2008 Elsevier B.V. All rights reserved. PACS: 07.77.Ka; 29.25.Ni; 29.27.Ac; 29.27.Eg