The size of the beam is defined by slits. It can usefully be adjusted between 50 * 50 microns (horizontal * vertical) and 100* 100 microns (see under for specific beamline range). There are two pairs of slits in the slitbox. The first pair (furthest from the sample Slit1) are used to define the size of the beam. There are a second pair of slits which are used as guard slits (Slit2) and are used to clean the beam of any spurious x-rays which may cause low angle scatter in your images. These are usually set to slightly bigger than the first slits and their movements are related with the mouvements of Slit1.

Beamsize can be set easily in mxCuBE using the vertical and horizontal beam size input tab.

Apart for id14-3, the blue square displayed on the crystal image is dynamically adjusted for beam size and camera zoom level. Obviously, the flux measured at the sample position changes with the beamsize.

23-2 specific details

The options "vertical beam size" and "horizontal beam size" in mxCuBE are NOT appropriate on ID23-2 and have been replaced by "vertical cleaning slits" and "horizontal cleaning slits". Beam size is defined by the mirror focusing and not by the slits in the slitbox. It is better to leave s1v ("vertical beam size") and s1h ("horizontal beam size") more open (around 0.3 - 0.4 mm gap) than s2v and s2h and to close and use s2v and s2h (range from 0.05 to 0.5 mm with 0.3 or 0.2 being a good compromise between intensity and beam profile) as cleaning slits rather than as beam defining slits.

Id14-3 specific details

1. In the Microdiff GUI click on 'Beam location', open the fast shutter
2. Open the safety shutter
3. You should see a blue square
4. Using the microdiff GUI you are able to measure the beam size.
5. Set the beam size as you wish
6. Check that neither the aperture nor the beamstop cut the beam
7. In the Microdiff GUI click on 'Sample transfer'
8. In mxCuBE, click on QuickRealign