The backstop is made of 300 microns thick Tungsten carbide with a G ring shape. It is mounted on two motorised translation stage (bstopz and bstopy, vertical and horizontal respectively). A prealignment is performed by fitting accurately the metal pin on the backstop support right at the centre of the V shape by a strong magnet. The collimator aperture is 300 microns diameter. The alignment of the backstop is performed remotely by moving bstopy and bstopz and also manually if needed with the yaw and tilt screws on the backstop support (don't forget the locking screw buried below the backstop in the aluminium support!).

Note - If the beamstop is broken outside working hours then go to bed, as there are no spares on the beamline. These are kept in a safe place as they cost 1500 Euros!




How to align the beamstop

BeamStop image

Image of the YAG screen with the EH4 detector diode in. The scatter rings come from the beamstop, and are only at low resolution (~2.54A, ~2.18A, ~1.93A and others).

  • Adjust the bstopz motor in exes (+/- 10 microns) and take another image. Remember to set 'bstopz' motor to 0 in spec before taking another image as the data collection procedure will move the beamstop to zero first!