of 14 Alignment of beamlines using x-ray beam K. Klementiev, ALBA/CELLS is complement to mechanical alignment uses the optics components themselves + beam diagnostics is periodically done on every beamline Outline: Introduction Available tools for beamline alignment Ray tracing of misaligned beamline (XAS) Entangled misalignments Alignment strategy

of 14 Introduction What others have done? There are a very few papers and web-pages on the topic “Alignment of synchrotron beamlines”. Most of them are aimed at automatic alignment. There is The Automatic Beamline Alignment Project in ESRF (Olof Svensson et al). It is aimed at algorithms and software. What I intend to present? not an automatic procedure, but rather basic understanding of misaligned optics; to stress the importance of ray tracing for studying misalignments of various kind; to notice the usefulness of the monochromator as a kind of diagnostics device (never mentioned in literature, although some people use this); a (general) strategy for initial beamline alignment.

of 14 mask 1.5h×0.25v mrad 2 Available tools for beamline alignment 1)FSMs and/or BPMs 2)energy scan 3)rocking curve (piezo- or motor- actuated) 4)intensity monitors 5)slit scans 6)wave front analysis (pin-hole array) 7)secondary monochromator (x-ray emission spectrometer) low-E filters bent CM DCM piezo on 2 nd crystal bent toroid FM sample top MPW, 1m, period 80mm K=13, B=1.74T Ec=10.4 keV side Z, pitch, yaw, roll, R y x z y x z Z, X, pitch, yaw, roll, R Bragg Z, 2 rolls (miscuts) FSM 1) 2) 3) slit 5) intensity 4) intensity 4) pin-hole array 6) XES 7)

of 14 Fluorescence screen monitors roll d  pitch d  height dz screen view tilt = d   x ~ 2L·d  ·d   z ~ 2L·d  + 2dz FSMs are of limited usage for initial alignment because: To detect image tilts due to a roll of ~1 mrad, the screen resolution must be ~10 µm. In the initial alignment the screen itself has unknown  x and  z. Some misalignments give correlated shifts of the image, e.g. pitch and height here. All the upstream optic elements contribute to the image. Nevertheless, FSMs are useful for: localizing big misalignments, detecting relative shifts during energy changes, development of alignment strategy basing on the image shape, fine alignment basing on wave front analysis.

of 14 Fine pitch scan of the 2 nd crystal, ±0.01º (350 µrad): wide enough even at low energy 2.4 keV with Si(111). Two intensity monitors: Why two? If you have only one, you will only notice the asymmetry of the rocking curve, not the shift. Remember that the detuning of one of the crystals splits the energy band passed through the monochromator. If you detune the 2 nd crystal, one of the two sub-bands stays at the nominal energy, the other is shifted proportionally to the detuning angle ( see also [Schulte-Schrepping & Drube, NIMA 467–468 (2001) 396] ). For the same intensity drop this shift is stronger at higher energies when considered absolutely but stronger at lower energies when considered relative to the Darwin width, i.e. it is more visible at lower energies. Rocking curves a)to decouple intensity and position for the piezo-detuning feedback system; b)to detect the rocking curve shifts for alignment (see below). 1)right after the monochromator, 2)at the experiment. Si 111, 2.4 keVSi 111, 9 keV

of 14 Ray tracing of misaligned beamline (XAS) Collimating Mirror (OpticalAlignment-1-CM.ppt) DCM (OpticalAlignment-2-DCM.ppt) Focusing Mirror (OpticalAlignment-3-FM.ppt) Click the buttons below to invoke the corresponding presentations. Ray tracing was done at 4 different energies (see the 4 columns) For each energy (column) there are two animated beam images: 1)behind the detuned optical element; 2)at the sample position. All animations are synchronized, i.e. for the same detuning at a time. The rocking curves are recorded at the two positions: a)after the DCM, b)at the sample. The rocking curves are shown as i.two 3D surfaces (for “a” and “b” rocking curves) in order to see if there is a maximum over the detuning coordinate, ii.as usual 2D plots (in the lowest row) to mimic the real measurements of rocking curves; the “a” rocking curves are normalized to 1 and the “b” rocking curves are normalized to ½.

of 14 hardly distinguishable (next slide) fixed Ray tracing. Summary height pitch roll vert. defocusing; no maximum; image tilt → ~1 mrad small hor. defocusing; maximum → ~0.5 mm hor. defocusing; weak maximum → ~0.1 mrad low E yaw no defocusing; weak max at high E → ~1 mrad bending R vert. defocusing; no maximum; E-analysis → ~10% R 0 1 st or 2 nd Xtal height Collimating Mirror DCM Focusing Mirror similar but ~no defocusing and beam cut at small Bragg angles (high E) DCM height vert. defocusing; no maximum (if within exit slit aperture);  x  tan  ·d  energy dependent 1 st Xtal roll Xtal miscuts similar height ~no defocusing; maximum → ~0.5 mm low E roll vert. defocusing; no maximum; image tilt → ~1 mrad lateral same pitch yaw vert. defocusing; image tilt → ~1 mrad; defocusing, no maximum; similar to FM roll & lateral low E high E hor. defocusing; weak max → ~0.2 mrad bending R vert. defocusing; no maximum; defocusing no changes except beam cut at small Bragg angles (high E) asymmetric vertical intensity profile is not seen in the real white beam! low E: high E:

of 14 Correlated misalignments full beam 1.5h×0.25v mrad 2 vertically reduced beam 1.5h×0.025v mrad 2 horizontally reduced beam 0.15h×0.25v mrad 2 FM lateral = ±2 mm FM roll = ±25 mrad FM yaw = ±0.5 mrad FM R = ½ · R 0..2·R 0 R 0 =5.46 km CM R = ½ · R 0..2·R 0 R 0 =8.56 km

of 14 Alignment flow diagram 0 align beamline set nominal CM pitch set nominal DCM height and gap set nominal FM pitch and height set CM roll=0 set CM yaw=0 align CM height + FM height + FM pitch (flow diagram 1) align DCM rolls and miscuts (flow diagram 2) align DCM height (flow diagram 3) align FM roll + FM lateral + FM yaw + CM R + FM R (flow diagram 4) end low heat load high heat load: 750 W absorbed by 1 st Xtal

of 14 Alignment flow diagram 1 align CM height + FM height + FM pitch end measure rocking curves (RCs) at high E what do the RCs look like? low E high E align FM pitch by looking for symmetric and not shifted RCs at high E high E: symmetric low E align CM height by looking for symmetric RCs at low E high and low E: symmetric and not shifted high E: symmetric low E: symmetric and shifted align FM height by looking for intensity maximum measure RCs at low E

of 14 Alignment flow diagram 2 align DCM rolls (miscuts) end take “beam image” at the sample at high E what do the images look like? low Ehigh E do 2D scan  roll1   roll2  by looking for maximum intensity high and low E: same horizontal position reduce the vertical exit slit down to the high E image size take “beam image” at the sample at low E go to low E. Important! Use calibration curve “roll vs. 2 nd Xtal translation”  x = 2L·tan  ·d  E.g. if you have 30 µrad roll change when you translate the 2 nd Xtal and L=15m:  x~1mm.

of 14 Alignment flow diagram 3 align DCM height end go to high E (small Bragg angles) scan DCM height to find the two positions when the footprint is out of the Xtal surface (seen as decrease of intensity); take the middle of the two

of 14 Alignment flow diagram 4 align FM roll + FM lateral + FM yaw + CM R + FM R end set FM roll=0 take “beam image_full” at the sample at arb. E with widely open exit slit reduce vertical exit slit and take “beam image_hor” open vertical exit slit reduce horizontal exit slit and take “beam image_vert” which beam shape gives the stronger beam size reduction in vertical? no reduction optimize FM lateral1+ FM lateral2 by doing 2D scan and looking for max intensity optimize CM R and FM R by doing 2D scan and looking for max intensity make horizontal beam

of 14 Q&A What are the generalities for all beamlines ? Rocking curves are asymmetric under motion of mirrors and crystal into/out of the beam. E.g. if you have an intensity monitor upstream your KB system, you can easily decouple at least 2 of the N (=7? 8?) degrees of freedom. Miscut and roll misalignment in crystals lead to energy-dependent horizontal shifts. This presentation is about a hard x-ray beamline. What would differ for a soft one? Don’t know. How to repeat the ray tracing for another beamline? The Matlab scripts are freely available. Prepare Shadow projects for different energies in the way that the OE positions are fixed and coincide with the physical ones. Ask me for further help. Outlook Ray tracing with the pinhole array at defocusing/de-collimating conditions and thermal bumps. Programs for pinhole image analysis + inverse problem. May I have a student for this? Eventually, automatic beamline alignment based on the pinhole images Thanks to J.Nicolás for introduction into the analysis of the imaging properties by means of the path function. Using his approach (ask him for the article) and the tools like Mathematica one can analyze the images without ray tracing. I don’t know what is easier though.