Design studies for an advanced ECR ion source

Abstract

Magnet design codes, plasma dispersion solvers, and particle-in-cell (PIC) simulation codes have been used to arrive at the first step in the design of an advanced ion source based on electron cyclotron resonance (ECR) technology. The advanced concept design uses a minimum-B magnetic mirror geometry which consists of a multicusp magnetic field to assist in confining the plasma radially, a flat central field for tuning to the ECR resonant condition, and specially tailored mirror fields in the end zones to confine the plasma in the axial direction. The magnetic field is designed to achieve an axially symmetric plasma ‘‘volume’’ with constant mod-B, which extends over the length of the central field region. This design, which strongly contrasts with ‘‘surface’’ ECR zones characteristic of conventional ECR ion sources, results in dramatic increases in the absorption of rf power, thereby increasing the electron temperature and ‘‘hot’’ electron population within the ionization volume of the source. The creation of a volume rather than a surface ECR zone is, therefore, commensurate with the generation of higher beam intensities, higher charge states, and a higher degree of ionization. A summary of the results of these studies is presented in this report.