Optics

Optics and Detectors

First Optics Hutch, OH1

• The principal elements along the direct beam are in OH1: prepumping vessel primary slits, attenuator, secondary slits, three diamond monochromators, beamshutter and then in OH2: attenuator, secondary slits, monochromator, toroidal mirror, secondary slits and beamshutter. The elements on the sidebranches are: Ge(220) crystal and multilayer or toroidal mirror and beamshutter.

• The X-ray beams for the side stations are provided by transparent diamond monochromators. These monochromators use the (111) reflection in Laue or in Bragg mode from thin (0.05 - 0.15 mm) diamonds inserted into the white beam. A second crystal (for ID14-1: a sagitally focusing Ge (220) crystal and for ID14-2 and ID14-3 a plane Ge (220) crystal), will restore the beam direction parallel to the main beam. A third optical element (for ID14-1: a bent multilayer and for ID14-2 and ID14-3: a toroidal mirror), will focus the beam in the horizontal direction and reject higher harmonics.

Second Optics Hutch, OH2

• Since the diamond monochromators are essentially transparent, the optics used in this hutch must withstand the very high power load from the undulators. In order to avoid heat load and lifetime problems with the mirror, the first optical element is the monochromator. This monochromator has been designed to allow multiple crystals to be mounted in parallel (i.e. Si(111) and Si(311) crystals). The monochromator is cryogenically cooled. Focusing of the X-ray beam is achieved using a toroidal mirror situated at 47 m from the source: the toroid has been chosen to provide the optimal focus at the sample position in EH4, at a distance of 67 m.

ID14-1

This is a schematic showing the different optical elements as well as the vacuum sections (between beryllium windows) and fluorescent screens for X-ray beam diagnostics.

Compound Refractive Lenses

ID14-1 now (16-Jun-2006) has beryllium compound refractive lenses inserted after the diamond monochromator between the Pt foil and the first fluorescent screen. There are 3 lenses held in a box currently under primary vacuum. The box has a small hole for the beam to pass through where the lenses are and another, larger hole for alignment purposes. Current values observed for beam intensity on diode i0 (in experimental hutch at ~190mA uniform mode, undulators optimised for max flux on side stations) are ~2000 through alignment hole and ~3200 when lenses are in place - a 50% increase in beam intensity. The crl lenses are now incorporated into the realignment of the beam in MXCuBe.

If you are worried that there is a problem with the X-ray beam there are several things you can look at. Firstly open up an optics spec session on hpcc12 - type mono_eh1

• pon ; wa ; poff - for a print out of current motor positions.
• pjackout - ensures that the Pt foil is not in the beam.
• flin1 - puts in fluorescent screen 1 after lens box. Do you see beam (don't forget to turn on the monitors and oxford control boxes in control cabin
• flout1 - removes fluorescent screen 1 - this will stop your beam reaching the exp hutch if you leave it in.
• flin2 - puts in 2nd screen - this is after the conventional optics and just before the safety shutter - do you have beam here?
• flout2 - removes 2nd screen.

  You can scan the motors of the crl box to see if you are sitting at the maximum. To do this close up the experimental hutch and open the safety shutter. Make sure the fluorescent screens on mono_eh1 spec session are out. Then in eh1:

• dscan crltilt -0.5 0.5 20 1 - scans vertical tilt of crls - move to peak - peak should be at 0.
• dscan crlrot -0.5 0.5 20 1 - scans horizontal rotation of crls - move to peak - peak should be at 0.
• dscan crlz -0.5 0.5 20 1 - scans vertical translation of crls - move to peak - peak should be at 0.
• dscan crly -0.5 0.5 20 1 - scans horizontal translation of crls - move to peak - peak should be at 0.

  If still have no beam try larger scans (say -1 1 or -2 2) or move the box to the alignment hole. In theory this should be at crly -11. Type in mono_eh1:

• mv crly -11

  You can now repeat the above dscans to optimise the alignment of the box and then do a realign of the beam with MXCuBe.

  If you are unsure about this since it is new ring Dave Hall.