A trapped distribution of low‐energy electrons was used to alleviate spherical aberration in a solenoidal magnetic lens. The space‐charge‐correction method has potential application to the focusing of heavy, negatively charged particles such as H- ions. In the geometry investigated, the field contributions from trapped electrons cancel net electric fields along magnetic flux surfaces. The lens magnetic fields therefore define equipotential surfaces. Experimental results were obtained using a 10‐keV electron beam as a nondestructive probe in a solenoid lens with 65‐G peak field. Annular distributions of trapped electrons were achieved that were stable against the diochotron instability. Deflections of the probe beam were consistent with theoretical predictions. The peak focused current density of the 10‐keV beam was improved twentyfold with the addition of trapped electrons in the lens.
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