Changing the beam size

Overview                    Changing the beam size in MxCube                    Changing the beam size manually

The beam size at the sample position is determined by 2 pairs of sample slits in the slitbox just upstream of the collimator. These are routinely set at 200 microns and are referred to as s1 and s2 (s1 = first pair of slits, s2 = second pair of slits i.e. those closest to crystal). The motors controlling the aperture size in the horizontal and vertical directions are: s1H (horizontal slits) s1V (vertical slits) s2H (2nd horizontal slits) and s2V (2nd vertical slits), respectively. The beam size is usually defined by s1 while s2 acts as a scatter guard.

Note: the minimum recommended beam size is 70 microns.

Setting the beam size in MxCube

The easiest way to change the beam size is by adjusting the horizontal and vertical values given in the Beamsize boxes in the MxCube GUI. A message will be piped to the GUI to confirm that the beam size has been changed sucessfully - please check for the confirmation message each time you change the beam size.

Remember: its a good idea to do a QuickAlignment each time you change the beam size!

Setting the beam size manually

The slit aperture size can also be adjusted in SPEC by clicking on the PX window and following the steps in the examples below.

Example 1:  to set the slits to 0.2 by 0.2 mm, use the following command:

PX> gap_slits 0.2

This macro will select the s1 slits as the beam defining aperture and wil set these slits to 0.2 by 02. It will also automatically set the s2 slits to a slightly larger value to act as a scatter guard which reduces the background on the detector.

Alternatively if you want to use an asymmetric beam you can manually set the slit size by using the mv command in the SPEC PX window.

Example 2: to set the beam size to 0.2 mm horizontally by 0.1 mm vertically use the following command:

PX> mv s1H 0.2 s1V 0.1 s2H 0.22 s2V 0.12

To check the syntax of a SPEC command you can just type the command and hit return.

PX> mv <motor name> <value>

For more infromation on SPEC commands check out the technical pages...