TOTAL CORRECTION OF PARASITIC SEXTUPOLE COMPONENTS IN MAGNETIC QUADRUPOLE LENSES

The presence of parasitic sextupole components in magnetic quadrupole lenses is a serious limitation to nuclear microprobe resolution. Earlier measurements of the parasitic sextupole component and the correction to below 0.15% of the quadrupole field strength using the rotating coil technique was initially limited by interference from the quadrupole component. An improvement of the technique has now been devised and used to reduce the parasitic sextupole component to 0.02%. The reduction has been confirmed using the shadow image technique, and improved resolution has been measured with the sextupole fields reduced.