X23A2 Howto: Setting the Harmonic Rejection Mirror

Motor names

• HOS-z : Vertical translation

• HOS-rot: Rotation angle

• HOS stands for "Harmonic Order Sorter" (yeah ... I know ... )

Setting the mirror

1. To translate the mirror entirely out of the beam, drop it by 10 mm (i.e. 10 mm in the negative direction.

2. To bring the mirror into the beam, return it to 0.

3. To level the mirror (i.e. make it flat), use the bubble level from the tool box. That's good enough for this chore.

4. Set the entrance slits to about 1 mm vertically (unless at a very high energy and very steep mirror angle)

5. Adjust HOS-rot to cut off about half the beam

6. Scan HOS-rot from 0 to about 0.5 to find the critical angle. Move to that angle.

7. Once you find an angle you like, tweak the mirror up and down by a couple hundred microns to verify that the beam is centered on the mirror. The signal on I₀ will drop if you walk the beam off the mirror. You are looking for a range of HOS-z that is constant in I₀

8. The ion chambers must be physically raised to meet the exit angle of the beam.

9. If you change energies and mirror angle, remember that you will need to adjust the height of your sample to accommodate the new exit angle from the mirror.