# Presentation: 569770

## Hard X-ray Undulator Beamlines

J.P. Hill

EFAC Oct 20th 2006

- Hard X-ray Undulator Beamlines
- J.P. Hill
- EFAC Oct 20th 2006

## Outline

- Optics and Heat Load Issues
- Some example beamlines
- Inelastic X-ray Scattering
- Hard X-ray Nanoprobe
- Hard X-ray Coherent Scattering

## Heat Load Calculations

- Thermal load calculations performed for worst case of 2m SCU:

- Ex: Cryo-cooled Si monochromator at 30m

- 3mm x 1.5mm aperture
-             700 W, survivable (but large distortions).

- Sharma, Ravindranath (NSLS-II)_

- Power density is > 100 W mm-2

- Unapertured beam melts the crystal!

- (cf APS= 450 W)

**Notes:**
(Note, APS power is 450 W). Model used is modified “hockey puck” design from APS. In original APS design top surface was thin to allow most of the power through. This won’t work at NSLSII where the power is at lower energies, so thicker crystal is used in this model. The unapertured beam actually melted the crystal, this is a 3mm x 1.5 mm slit. Still to consider use of filter to remove 1st harmonic and use of diamond as options. Problems with orig APS design – that Pedro was part of, and is in use at CMC – include difficulty in polishing thin surface and resultant problems with speckle, difficulty in making the cryoseal and difficult to seal the LN2 manifold to the crystal; needed alwaysseveral tries before success; didn't survive pressure rise after poweroutage3. clamping forces in Bragg-parallel direction and the LN2 lines yankingon the plates clamped to the crystal4. beam passing though the undercut part of the crystal smashes into theend plates creating scatter.

## Diamond Window

- Possible coherence-preserving optic:

- Water-cooled diamond crystal

- diamond

- beam

- Maximum displacement in central spot is < 1nm
-          Gives only small optical phase shifts.

- Displacement map

**Notes:**
Separates SR vacuum from BL vacuum. NB windowless modes also possible.
Maximum displacement is 100nm. Water-cooled. Held fixed at 20C

## Results

- Maximum temperature = 126 K

- Gap closed, 8.9 keV 5th harmonic

- Incident Beam Filtered with 100 m Diamond window:

- 6 rad

- c.f. Darwin width = 31 rad

- Si(111)

- 343 W in 4 beam

- (c.f. zero thermal expansion at 125K)

-  Si(111) can handle central cone of U14 device
-  Negligible impact on flux thru-put and wavelength spread.
-  Slope errors would blur the beam spot. May need to adaptively correct with mirrors.

**Notes:**
w/o diamond window, power in same aperture goes up to 407 W and temperature rise is something like 140K. Thermal distortion is on the order of 10 microrads.

## Mirrors

- Performance of mirrors will be critical in ultimate performance of undulator beamlines:

- R+D Effort proposed to develop metrology and explore new polishing techniques to achieve these levels (P. Takacs)

## Inelastic X-ray Scattering

- FOE

- 0.1 meV

- 1 meV

- 50 meV

- Y. Shvyd’ko, A. Baron, J.P. Hill

## Importance of Flux

- Figure of merit: Flux per meV

## High vs. Low Energy X-rays for IXS

- We are proposing  0.1 meV at low energies.

## 0.1 meV IXS Layout

- _0.1 meV Spectrometer_

- Y.Shvyd’ko (unpublished)

-  Novel design featuring asymmetric backscattering optics
-  Operates at 9 keV, near the peak of the undulator spectrum

- Requires R+D, proposed for NSLS-II (Shvyd’ko)

## 0.1 meV Spectrometer

- Features
-  Temperature scanning of energy transfer.
-  Horizontal diffraction plane
-  Micron-sized spot.
-  Extremely clean resolution function.

- backscattering

- Asymmetric backscattering

- Y. Shvyd’ko
- S. Coburn

- NSLS-II, 3m U19   	>1 x 109 phs-1 at 0.1 meV
- APS        5m U33	1 x 109 phs-1 at 1 meV
- Spring-8 4.5m U35	5 x 109 phs-1 at 1 meV

## 50 meV Spectrometer

- Spectrometer features:
-  Vertical and horizontal scattering planes.
-  Multiple analysers.
-  Position sensitive detectors.

- More conventional optics:

- 4- bounce mono gives constant bandpass

## Position Sensitive Detector

- S. Huotari *et. al. *(2005)

- Improves energy resolution *and *thruput

## Nano-probe Beamline

- NSLS-II goal: 1nm spatial resolution

- T. Gog, K. Evans-Lutterodt

## Layout

- High Resolution Mono

- Undulator

- Detector

- Focusing Optics

- Sample

- Detector

- Detector

- Focusing Optics

-  Primarily used in scanning probe mode
-  Limited full-field capability (10m x 10m)

## Possible Configurations

- _1) “Direct” mode_

- _2) “Waveguide” mode_

- _Advantages_:
- Least optics to affect coherence
- _Disadvantages_
- Need long beamline for long working distance

- _Advantages_:
- Waveguide acts as secondary, coherent source, decoupled from upstream vibrations. Offers large working distance for short beamline.
- _Disadvantages_
- Overall efficiency. Potential issues with waveguide.

## Monochromaticity

- Diffractive optics, such as MLLs, require monochromatic beam to achieve desired focus:

- (N.B. Similar situation for refractive optics)

- For given working distance (straight line), desired monochromaticity lies below that line. Diamond (nnn) reflections shown for comparison.
- The 1nm constraint is extremely stringent in this regard.

- This constraint pushes design to use shorter working distances to increase flux, and to use higher operating energies

## Coherent Scattering Beamline

- FOE

- SOE

- SAXS/XPCS

- Wide-angle XPCS
- Coherent Diffraction

- A. Sandy, I. Robinson and S. Mochrie

## Coherent Scattering Layout

- High Resolution Mono

- Undulator

- Detector

- Focusing Mirror

- Sample

- NSLS II
- Experimental floor

- Outside NSLS II
- Experimental floor

- Sample

- Detector

- Focusing Mirror

- High Resolution Mono

- Shutter

- Water Cooled Mirrors

- Aperture

- Slit

- Diamond Window

- Water-cooled mirrors allow simultaneous operation of two endstations:
- XPCS (and SAXS)
- Coherent diffraction (and XPCS).

- Desire for 2) to be “long” to minimize radiation damage issues and for “demag” reasons.

## Long Beamlines

- Heavy access door

- Utilities tray

- Optical pipe

- X-ray beamline

- Airlock

- X-ray enclosure

- Cost = $162 k for 350 SF building

- Vibration issues still to be studied.

## Summary

- Undulator heat issues at NSLS-II appear tractable
- As examples, three possible undulator beamlines would each provide world-leading capabilities in
- Inelastic x-ray scattering (0.1 meV)
- Nanoprobe (1nm)
- Coherent Scattering
- Each raise a number of issues that need to be addressed in an R+D program (optics and detectors)
- User groups (BATs) would be expected to define the mission of such beamlines, and carry out detailed design, construction and operation.