1. A Double Crystal Monochromator of Sagittal Focusing at SSRF J.H. He, S.J. Xia, Z.C. Hou, J.L. Gong, X.M. Jiang and Y. Zhao SSRF Project Team Shanghai Institute of Nuclear Research, Chinese Academy of Sciences, I. Introduction II. Design and Construction III. Preliminary Tests

2. I. Introduction Characteristics of sagittal focusing monochromator(SFM): –monochromatizing and focusing the beam simultaneously, useful for simplifying/optimizing the beamline optics –large horizontal acceptance – good focusing

3. Aim and task Why to make a SFM: – two beamlins at SSRF proposing to use SFM, which is commercially available, but expensive –developing the relevant techniques, a first try in China Major requirements: –a good focusing performance –bearable to the rather high heat load(~0.5W/mm 2 ), can be used at SSRF bending magnet beamline and BSRF wiggler beamline

4. II. Design and Construction Operating principles and modes: Design features Products

5. Operating principles and modes: when X = H/2sin  ， Y = H/2cos , fixed H; when H(max)=30mm ，  =5.5-25deg., required X,Y translation range: chosen X,Y range:  X = 150mm,  Y = 50mm Incident beam X Y H θ Exit beam 1 st crystal 2 nd crystal Schematic operating principles of the monochromator By controlling X and Y, the monochromator can work at different modes: a) fixed beam exit height; b) variable beam exit height; c) direct beam;

6. Design features : Main structure of the monochromator

7. Main features of the design: independent adjustment of crystal positions to facilitate the different operating modes direct water cooling to stand rather high heat-load accurate bending of the crystal, driven by the complex flexure hinge mechanism independent adjustment of crystal orientations by using the flexure hinge mechanism movable support of the main structure to facilitate the installation and maintenance

8. 1) 1 st crystal cooling system Similar to PF-monochromator (H. Oyanagi et al.), modified to be a) compatible to the silicon manufacturing technique available in China b) able to stand the required heat-load

9. Crystal shape and parameters

10. Photos of 1 st crystal

11. Crystal cooling system: Cooling water is fed into the crystal through the rotation axis

12. 2) 2 nd -crystal and crystal bender Tilt-table flexure hinge mechanism: driven symmetrically by two actuator with better than 0.1  m resolution 2 nd -crystal

13. 2 nd -crystal ： ribbed to resist the anticlastic distortion when bent 2 nd -crystal parameters ： w=0.6mm, e=1.4mm, h=10.0mm, t=0.8mm R s :1 ~ 10 m, R a ≥ 2200m, corresponding to 12 μ rad average slope error

14. Photo of crystal bender

15. 3) Crystal orientation adjustment Micro-actuator Balancing spring Right circular flexure hinge mechanism

16. maximal rotation angle ： beryllium bronze ： E=115GPa ，  =1.15GPa Required rotation angle ： >  0.5  Three adjustments for : 1 st crystal roll 2 nd crystal pitch 2 nd crystal yaw

17. 4) Movable support

18. Photo of main structure

19. III. Preliminary tests 1) Test of crystal orientation adjustment Resolution obtained ： 1 st crystal roll  0.16 , 2 nd crystal pitch  0.18 , 2 nd crystal yaw  0.48  optical auto-collimator DCM

20. Ideal focusing condition ： R=2F 1 F 2 sin  /( F 1 +F 2 ), F 1 :object distance ; F 2 :are and image distance The focusing image diffuses when bending curvature deviates from the Ideal R by  R crystal surface is not ideally cylindric with a spread of  R at the average radius of R image diffuseness:  W   F 1 /F 2  F 2 =  (F 1 +F 2 )(  R/R), 2) Test of focusing performance

21. Source width(H) : 1.2mm ， F 1 =17.5m ， F 2 =7m,  =11 , spot width ： 0.6mm ，  W=0.12mm,  W/W=25% ，  R/R  0.25%, R  2m F 1 =25m ， F 2 =14m,  =13 , spot width ： 0.9mm,  W=0.13mm,  W/W=19% ，  R/R  0.2%, R  4m Laser simulation test

22. 3) Test of cooling effect A particular testing apparatus: an electrical gun with maximum power of 800W is used to used to simulate the synchrotron radiation power distribution a specially designed interferometer is used to measure the surface profile of the crystal.

23. Distortion Crystal surface profile at different heat-load Conclusion: By prebending the crystal in an opposite direction, surface distortion due to the heat-load up to ~ 400W and 1w/mm 2 can be reduced to a tolerable a level (R>1000m). prebending

24. 4) Other Specifications Rotation(Bragg) angle Range: -2°- 30° Reproducibility: 1.8 〞 Resolution 0.18 〞 Acceptance Horizontal: >2.0 mrad Vertical: >0.25 mrad Vacuum < 5×10 -6 Torr

25. Summary a good performance of the adjusting mechanisms, the bending mechanism and the mechanical structure on-line test necessary

26. ACKNOWLEDGMENT We thank Mr. Sizhong Zhou and his group, Mr. Renkui Zhou, Fanghua Han and Shicuang Liu for their collaboration at the mechanical design and construction of the monochromator. We thank Dr. Freund and his group at ESRF for their kind help in making the focusing crystal and for their helpful discussions. We also thank Dr. Oyanagi for his helpful discussion on the crystal cooling techniques.