AN ADVANCED ECR ION-SOURCE WITH A LARGE UNIFORMLY DISTRIBUTED ECR PLASMA-VOLUME FOR MULTIPLY-CHARGED ION-BEAM GENERATION

A new ECR ion source geometry has been conceived which uses a minimum- B magnetic mirror geometry consisting of a multi-cusp, magnetic field, to assist in confining the plasma radially, a flat central field for tuning to the ECR resonant condition, and specially tailored mirror fi elds in the end zones for confining the plasma in the axial direction. The magnetic field, designed to achieve an axially symmetric plasma ' 'volume'' with constant mod-B, extends over the length of the central field region. This design, which strongly contrasts with ''surface'' E CR zones characteristic of conventional ECR ion sources, results in dr amatic increases in the adsorption of RF power, thereby increasing the electron temperature and ''hot'' electron population within the ioniz ation volume of the source. The ECR zone is concentrated symmetrically around the axis of symmetry and along the length of the plasma volume rather than in thin surface layers located off-axis as is the case in conventional ECR ion sources. The creation of a ''volume'' rather tha n a ''surface'' ECR zone and its distribution relative to the optical axis where the ions of interest are extracted is commensurate with the generation of higher beam intensities, higher charge states and a hig her degree of ionization. The new ECR ion source concept has been comp utationally designed through the use of magnet design codes, plasma-di spersion sources, and particle-in-cell (PIG) codes. A summary of the d esign attributes of the source is given in this report.