I. Introduction II. Design and Construction III. Preliminary Tests

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

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

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/mm2), can be used at SSRF bending magnet beamline and BSRF wiggler beamline

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

2nd crystal X Exit beam Y Incident beam H θ 1st crystal Operating principles and modes: when X = H/2sin，Y = H/2cos,fixedH; whenH(max)=30mm，=5.5-25deg., required X,Y translation range: chosen X,Y range: X = 150mm, Y = 50mm 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;

Design features : Main structure of the monochromator

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

1) 1st 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

Crystal shape and parameters

Photos of 1st crystal

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

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

2nd -crystal ：ribbed to resist the anticlastic distortion when bent Rs :1 ~ 10 m, Ra≥2200m, corresponding to 12μrad average slope error 2nd -crystal parameters： w=0.6mm, e=1.4mm, h=10.0mm, t=0.8mm

Photo of crystal bender

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

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

4) Movable support

Photo of main structure

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

2) Test of focusing performance • Ideal focusing condition： • R=2F1F2sin/( F1+F2), • F1:object distance ; F2 :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  F1/F2 F2=(F1+F2)(R/R),

Laser simulation test Source width(H) : 1.2mm，F1=17.5m，F2=7m, =11  , spot width：0.6mm， W=0.12mm, W/W=25%， R/R0.25%, R 2m F1=25m，F2=14m, =13 , spot width：0.9mm, W=0.13mm, W/W=19%， R/R0.2%, R 4m

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.

Crystal surface profile at different heat-load Distortion Conclusion: By prebending the crystal in an opposite direction, surface distortion due to the heat-load up to ~ 400W and 1w/mm2 can be reduced to a tolerable a level (R>1000m).

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

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

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. Thank you!

I. Introduction II. Design and Construction III. Preliminary Tests