Undulator settings

Two complementary undulators are installed on ID29 - the U21 and the U35. The nominal energy range of the beamline after the optics is 5.2 - 20keV, however harder X-rays above 20keV are accessible if the toroidal mirror is removed from the beam path. The soft X-ray boundary is limited by the shape of the Si[111] monochromator crystal. The U21 is an in vacuum undulator which has been comissioned since January 2002. It delivers a high brilliance first harmonic X-ray beam in the range of 8.5 - 16.0keV, which is suitable for the most common MAD experiments (Se, Br, Hg, Pt, etc...). The U35 undulator supplies softer X-rays on the first harmonic from 9.5keV down to 4.2keV, although the harder X-rays on the third harmonic (12.6 - 19.5 keV) also allow access to the selenium K-edge and the uranium L₃-edge.

Do NOT use both undulators simultaneously, the heat load could damage the optics!

Undulator settings

Minimum undulator gaps

Maximum primary slit settings

Changing the undulator gaps

Table of undulator settings

Undulator settings

Please note before you start that the both undulators emit a very high power flux of X-rays which could damage the optical elements if used incorrectly. For this reason, the minimum gap and maximum primary slit settings should be checked before starting.

Undulator settings for all of the accessible absorption edges on ID29 are given in the table at the end of the section. A manual adjustment may be necessary to optimise the flux via the ID control panel of the Machine status window (Commands Menu / ID control ).

If the incident beam seems low, check the following:

• X-ray wavelength?
• primary slit size?
• secondary slit size?
• experimental slit size?
• attenuators?

Minimum undulator gaps

The minimum gap settings for the U21 and U35 undulators are given in the table below. Because of the high power emitted by both undulators, users are prohibitted to use both undulators simultaneously! In some special cases, beamline scientists may wish to use the undulators in tandem. Minimum permissible gap values are given when the other undulator is at its minimum gap. Do not go below the these values!

Maximum primary slit settings

As for the minimum gap settings, the primary slits should not be set larger than 3.0mm * 1.0mm (H*V). Primary slits are controlled via OPTICS, i.e.

  Changing the undulator gaps

Remember: DO NOT use both undulators simulataneously! Open the undulator gap in use before switching ot the other!

Changing the undulator gaps can be done two different ways:

1. via the ID control panel To open the ID control panel, select the Command menu of the Front End window. Click the mouse cursor in the small white window corresponding to the gap (NOT the taper window), and enter the desired undulator value...

Then hit the return key! And wait for the undulator gap to finish moving!

2. via bliss. If you moved the undulators through idappli do a sync_hard in bliss

Table of undulator settings

Theoretical undulator settings for all of the accessible absorption edges on ID29 are given in the table below. A manual adjustment may be necessary to optimise the flux via the ID control panel of the Machine status window (Commands Menu / ID control ).