ABSTRACT
“Electron Cyclotron Resonance Ion Sources are now in use at about 40 laboratories world-wide for highly charged ion injection into accelerators for physics research[1]. Using this type of ion source, heavy ions with charge as high as 39+ have been injected directly into cyclotrons at intensities of a few hundred nanoamperes[2], as well as nearly fully-stripped light ions at intensities of a few hundred microamperes for cyclotron or synchrotron injection[3]. When compared to H− and H+ beam transport systems, these are not ion beam intensities normally considered to be space charge dominated, and so a careful measurement of the initial beam properties should be sufficient to specify the beam transport system design and accelerator matching conditions. However, experimentally it is observed that both extremes- highly charged ions at low intensities and low charge ions at high intensities, exhibit sharp non-linear emittance growth in beam transport systems. This is true even in beam transport systems presumably having substantially higher designed acceptance than the initial beam emittance. In extreme cases, the overall beam transmission has actually been observed to decrease sharply with increasing beam intensity[4]. This mis-match has either been ignored or interpreted to imply that the initial beam characteristics were not well known. A correct interpretation of this emittance growth, as being a direct consequence of a non-linear growth in the beam envelope due to space charge forces, will be demonstrated using theory, simulations and experimental measurements. For proper matching of ECR ion source beams to accelerators, an aberration-free maximum beam intensity must be built into the beam transport system.”
