1. The XAS beamline at the Australian Synchrotron
Principal Scientist - Chris Glover (PhD ANU, MAXLAB, AS since 1/2005)
Scientist – Bernt Johannessen (PhD ANU, Photon Factory, AS since 5/2009)
SSO – Lisa Giachini (PhD Bologna, AS since 9/2008)

2. Specification / Status
Source: 1.9T 40 pole wiggler
Si(111) and Si(311) crystals. Close to theoretical resolutions via use of collimating mirror.
Beamline operated in modes as per table. Limited ability to change modes in a single beamtime.
Transmission and Fluorescence EXAFS capability
100 Element detector commissioning (ROI mode)
Flux: > 5e12 photon/s for Si(111) in 0.1x0.5 mm FWHM
Focus variable 0.1x0.5 mm to 1 x 2 mm
Harmonic rejection managed by mirrors < 1e-5
Accepting general users via peer review proposal. Next call for proposals 10 Sept.
Mode
Energy Range (keV)
M1 Stripe
Incidence Angle
Max M1 Power (W)
Max DCM Power (W) 1
4 – 10 Si
~ 3.15
~ 1200
~ 250 2
9 - 20 Rh
~ 600
~ 700 3 Pt
~ 500 4
~ 2.15
~ 620 5
> 30 -
< 420

3. Main Beamline Components
Collimating Mirror
1.4m Si substrate
3 Cu fins in l-Ga slots
Si, Rh & Pt Stripes
SESO 4 bender
Accept 2.1 mrad (h)
2.1 – 3.15 mrad incid.
1kW max designed heat load
Accel cryocooled DCM
25mm fixed offset or pseudo channel cut
Si(111) and Si(311) pairs
5 – 40 deg Bragg => 3 – 43 keV
1st and 2nd crystals indirectly LN2 cooled
Max designed power load = 700W
Accel (Messer) cryocooler
RON 905 encoder on Bragg
160 x 80 x 80 mm first crystals rotating around downstream end.
0.5 mm In foil / Cu cooling sandwich.
Focussing Mirror
1.4m SiO2 substrate
2 cylinder toroid for different focus / angle of incidence
Rh & Pt Stripes
SESO U bender
100 x 500 um FWHM

4. Energy Resolution and Heat Load
Theoretical resolutions achieved from M1 bender via backscattering measurements
Power load stability superb - not an issue.

5. Effect of Heatload – repeated scans of Ag edge
energy scale is slightly different due to hutch slits (I think?)
Spec is 0.3 eV at Rh edge over 24 hrs – basically met.

6. Power loading tests - V Good
Conditions: LN2 4.5 L/min flow at 2.0 Bar = cryocooler 50 Hz.
First crystal warms up to 120 K max.
Its clear current cooling performance is > 30% better than needed !!!

7. Energy Stability Performance
Monochromator accuracy measured via metal foils to encoder (running in open loop). Repeatability better than 0.1 eV on Si(111) - maximum deviation from tabulated values 0.25 eV!
Stability and operation of Messer cryocooler superb - not an issue. No effect of cryocooler seen on beam.

8. Cryocooler stability
Messer cryocooler stability superb – 0.1% pressure stability – no influence of subcooler fill
Fully remote controllable – can cool down DCM from home!

9. Flux Stability Performance
DCM Vibration performance. Compare IC flux fully tuned vs 50% detuned. Tuned – 0.1 % sampled at 100 Hz stability. Detuned on the derivate edge of rocking curve – any motion translate into flux modulations

10. DCM Vibrations
FFT of beam positions – most motion in the vertical = between parallelism of 2 crystals.
Lots of work done on DCM already to reduce susceptibility to vibrations: internal clamping of LN2 lines, placing whole DCM on elastomeric damping pads (filtering 25 Hz) – effect has already been reduced by ~ 10x.
Clearly, source of vibration in beam related to first and second crystal motions.
Coupling of ground (the excitation source) to crystals was via internal LN2 cooling lines.
Operate crycooler > 50 Hz so as to not excite resonances.
Main remaining problems:
2nd crystal resonance at ~ 44 Hz
isolate from Hz band in floor

11. Focussing and Stability
Any vibrations translate into flux modulations – and also position.
At 12 keV on Si(111) 100 um vertical beam (FWHM) has 15 um vibration (FWHM). Use guard slit at experiment.
For Si(311) rocking curve much narrower – effect may be a concern for low noise fluorescence measurements at high energy.

12. Homogenous sample: Cu foil
Cu foil in transmission, 10 repeat scans out to k = 24 A-1.

13. Temperature dependence Cu foil and a-Ge

14. Problems with saturation of Ion Chambers
Oxford Danfysik ion chambers found to saturate at relatively low fluxes – now use OKEN ICs – much better linearity
Worse if gas is sealed. Currently flowing gas. (Cleaned, baked, re-sealed, difference HP gases tried).
For transmission experiments run with 0.5 x 1mm WBSL or with wiggler gap open to 50 mm to reduce flux and use typical gases (eg N, Ar etc). “Bend magnet mode”
For high fluxes need to flow He (~ 1/2 bottle a day critical flow). Surprisingly no degradation in performance vs sealed
Slow – of the order of 100’s Hz.

15. 100 Element Ge detector
100 element Ge PAD with XIA DXP electronics arrived July Final cost $1.8 M (AUD).
Will be controlled by EPICS (Mark Rivers).
Goal is to use XIA electronics in ‘mapping mode’ for on the fly energy scans.
Resolution at 5.9 keV, 0.5 uSec shaping time, 100 kcps.
226
221 c
213
220
253
224
229
237
240
235
238
219
230
225
232
234
231
242
233
218
216
227
223
228
247
210
217
243
205
222
212

16. Facilities First experimental hutch is a ‘standard XAFS’ setup
Second exp hutch is for non standard / long setup / user supplied equipment
100 Element Ge PAD with XIA DXP electronics delivered July 09.
10 Element Ge + 1 element Si drift detector
Harmonic rejection mirror for < 7 keV
Closed cycle He cryostat (15 – 300K)
Software controllable Keithley gains / sample temperature / motions
OKEN ion chambers with flowing gas linear at high fluxes
Easy to use scan GUI on top of EPICS subsystems.

17. Future upgrade Plans Complete fitout of second hutch:
High temperature furnace
High pressure cell
Q-EXAFS monochromator
IXS setup (RAMAN + RIXS)
Bent Laue analyzer setup
Radioactive sample ‘tent’
Medium energy XAS beamline on BM
Si – transition metal K edges
Any other suggestions?
Submission deadline 10 Oct 2009.