I. Introduction II. Design and Construction III. Preliminary Tests
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Transcript of I. Introduction II. Design and Construction III. Preliminary Tests
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 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 simplifyi
ng/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
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
YH
θ
Exit beam
1st crystal
2nd crystal
Schematic operating principles of the monochromator
mmX 121)sinθ
1
θsin
1(
2
H
maxmin mmY 48.1)
cosθ
1
θcos
1(
2
H
maxmin
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
Tilt-table flexure hinge mechanism:
driven symmetrically by two actuator with better than 0.1m resolution
2nd -crystal
2nd -crystal : ribbed to resist the anticlastic distortion when bent
2nd -crystal parameters :
w=0.6mm, e=1.4mm, h=10.0mm, t=0.8mm
2
3
111 t
h
e
w
R
R
s
a
Rs :1 ~ 10 m, Ra ≥2200m, corresponding to 12μrad average slope error
Photo of crystal bender
3) Crystal orientation adjustment
Micro-actuator
Balancing spring
Right circular flexure hinge mechanism
3.2/4
3 tR
E
maximal rotation angle :
beryllium bronze : E=115GPa , =1.15GPa
Required rotation angle : >0.5
Three adjustments for :
1st crystal roll
2nd crystal pitch
2nd crystal yaw
4) Movable support
Photo of main structure
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
optical auto-collimator
DCM
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),
2) Test of focusing performance
Source width(H) : 1.2mm , F1=17.5m , F2=7m, =11 , spot width : 0.6m
m , 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
Laser simulation test
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.
0 5 10 15 20 25 30 35 40 45 50 55 60
-0.3
-0.2
-0.1
0.0
0.1
3mmÁ¦±Û£¬10L/minÁ÷Á¿µÄ¾§Ìå ÐαäÇúÏß
76W,0.19W/mm2
152W,0.38W/mm2
228W,0.57W/mm2
304W,0.76W/mm2
380W,0.96W/mm2
456W,1.14W/mm2
532W,1.34W/mm2Ð
αäÁ
¿( m
)
X (mm)
Dis
tort
ion
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/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.