2.4 GEM Apertures

GEM has 5 motorised beam-defining apertures which are controlled by the PLC. A final sixth aperture (closest to the sample) called the 'beam-scraper' is set by computer by using the LabView PC. The first 5 apertures can only be set symmetrically, whilst the beam-scraper can be set asymmetrically. The beam-scraper can also be removed from the beam if necessary. The motorised beam-scraper can be replaced by the old hand-adjusted beam-scraper if necessary. The apertures are at the following distances from the moderator:

Click here for a schematic of the GEM beamline.

The maximum beam size at the sample which can be set is 20mm wide and 40mm high.

The maximum area of the moderator which can be viewed is 84mm wide and 90mm high.

Last updated on 07 Mar 2003 by Alex Hannon (a.c.hannon@rl.ac.uk)