1. Fusion Experiment WENDELSTEIN 7-X
High geometric precision in the construction of the WENDELSTEIN 7-X fusion experiment
T. Bräuer
Max-Planck-Institut für Plasmaphysik
Unternehmung WENDELSTEIN 7-X
D Greifswald, Wendelsteinstraße 1
Content: Fusion basics and assembly strategy
Second order datum point system on components
Survey of first magnet half module
Conclusion, outlook

2. WENDELSTEIN 7-X is a fusion experiment !
WENDELSTEIN 7-X: fusion basics
WENDELSTEIN 7-X is a fusion experiment ! p + D e n 3 He g 4 2
Physical Aim:
Prove of the stellarator principle as a realistic concept for a future power plants
but no break even, no Tritium
Control of a plasma at very high temperatures of 100 Mio Kelvin
Quasi stationary operation
Technical aim:
Construction of the device under industrial like conditions
Very tight collaboration with manufacturers
Creation of a very strong, very precise magnet field with a relative accuracy of 1...2·10-4

3. Fivefold symmetry of torus Flip symmetry of a module
WENDELSTEIN 7-X: assembly strategy
Design scheme of W7-X
Main dimensions of W7-X
Main radius: 5.5m
High: 5.5m
Mass: 725t
50 non planar coils (NPC)
(Ø  3.0 m, m = 5 t)
20 planar coils (PLC)
(Ø  3.5 m, m = 2 t)
Coil support structure (CSS)
Plasma vessel (PV)
Outer vessel (OV)
Fivefold symmetry of torus
Flip symmetry of a module

4. Fivefold and flip symmetry:
WENDELSTEIN 7-X: assembly strategy
Fivefold and flip symmetry:
Fivefold symmetry:
5 identical modules with 10 NPC and 4 PLC, CSS, PV
Flip symmetry:
2 flip symmetric half modules per module
5 NPC und 2 PLC per half module
Flip symmetric half modules of CSS
Flip symmetric half modules of PV

5. Steps of half module assembly:
WENDELSTEIN 7-X: assembly strategy
Steps of half module assembly:
Adjustment of coils
Accuracy requirements: 0.5 … 1.5 mm
Adjustment of coil support structure
Accuracy requirements: 1.0 … 1.5 mm

6. Module and torus assembly:
WENDELSTEIN 7-X: assembly strategy
Module and torus assembly:
Two half modules are jointed together
Module is lowered in half shell of outer vessel and adjusted to final position

7. Adjustment of components: mainly done by Laser-Tracker (LTD)
WENDELSTEIN 7-X: assembly strategy
Adjustment of components:
mainly done by Laser-Tracker (LTD)
6 … 12 datum points per component
Adjustment residual: 0.5 … 1.5 mm
Survey accuracy: 0.2 … 0.3 mm
Final surveys and documentation:
Mainly done by photogrammetry
Short survey time
Flexible lines of sight and camera positions possible
Survey accuracy: 0.2 … 0.4 mm
Access to datum points becomes more and more difficult with progress of assembly due to using fitted holes for assembly purposes and blocking of lines of sight by components and staff folders
Creation of a second order datum point system with a high number of points is necessary !

8. WENDELSTEIN 7-X: second order datum points
Creation of a second order datum point system for photogrammetry on the components
Usually 12…20 original datum points per component
Installation of additional 200 second order points for photogrammetry
Half module of support structure:
Size [m]: 1,5 x 2,5 x 2,5; weight  5 t
Roughly 200…300 pictures necessary
Roughly 1day
Non planar coil: size [m]: 2,5 x1,5 x 3,5; weight  5.5 t

9. WENDELSTEIN 7-X: second order datum points
Creation of a second order datum point system for photogrammetry on a coil
sticky targets on the coil
Support P1
Stand foot 2
Stand foot 1
Support M1 a. 2
Aux. point 3
Coil support 1 a. 2
Ref. points
 3.5m
Usually 12…15 original datum points per coil
 200 new points per coil
Comparison of photogrammetry and Laser-Tracker at 15 datum points
Feature targets for using in fitted holes, i. e. original datum points
Coil with original datum points

10. Accuracy analysis of second order datum points:
WENDELSTEIN 7-X: second order datum points
Accuracy analysis of second order datum points:
Number of points: 15
RMS: 0.17 mm
Number of points: 221
Number of surveys: 6
Mean RMS: µm
68%
32%
Conditions:
No air condition
Different operators
For each survey a new set up of scale bars and coded targets
Removing and replacing targets of datum holes
LTD repeatability accuracy (σ): mm
Result:
Under real conditions the second order datum points show additional but acceptable uncertainties and can be used in later surveys

11. Situation for survey of magnet half module:
WENDELSTEIN 7-X: Survey of first magnet half module
Situation for survey of magnet half module:
Two assembly stands next to each other
Workflow in work shop is ongoing (crane, transport, …)
No air condition
Volume of half module x 5 x 4 m³
Max. high over ground: 6m
Lots of fixing structures, platforms …

12. Situation for survey of magnet half module:
WENDELSTEIN 7-X: Survey of first magnet half module
Situation for survey of magnet half module:
Access to the coils is blocked by:
Machine table at bottom
Support structure at inner side
Fixing structures at back, left and right

13. Results of photogrammetry survey: accessibility of datum points
WENDELSTEIN 7-X: Survey of first magnet half module
Results of photogrammetry survey: accessibility of datum points
5 independent surveys
Up to 750 pictures per survey
First order datum points:
Total number at all coils:
Accessible by photogrammetry: 53
Accessible by Laser-Tracker:
(only by using of T-Probe)
Second order points:
Total number at all coils:
Accessible

14. Actual coil positions meet the tolerance requirements
WENDELSTEIN 7-X: Survey of first magnet half module
Results of photogrammetry survey: comparison of actual and nominal coil position
AAB13
AAB22
AAB45
AAB51
AAC13
AAC51
AAB17
Required adjustment tolerance: mm
Maximum deviation: 1.3 mm
Est. repeatability accuracy of survey (68%): mm
Cross check with Laser- Tracker survey shows similar results (see below)
Actual coil positions meet the tolerance requirements

15. Repeatability accuracy analysis:
WENDELSTEIN 7-X: Survey of first magnet half module
Repeatability accuracy analysis:
Number of surveys: 5
Duration of all 5 surveys: 1d
2 operators
1 camera
In all surveys the same set up of scale bares and coded targets
No air condition
Ongoing workflow in workshop
Number of points: 1198
Mean RMS: mm
68%
32%

16. Cross check with Laser-Tracker:
WENDELSTEIN 7-X: Survey of first magnet half module
Cross check with Laser-Tracker:
One Laser-Tracker survey
(Laser-Tracker used with T-Probe)
Duration: 1d
Maximum deviation of a coil measured by Laser-Tracker: mm
Meets the tolerance requirement
Average of 5 photogrammetry surveys
Transformation of photogrammetry to Laser-Tracker survey
number of points:
Mean deviation: 0.22 mm
RMS: mm

17. The experiment WENDELSTEIN 7-X will go into
WENDELSTEIN 7-X: Conclusion, outlook
Conclusion, outlook :
Coils of fist magnet half module have been assembled inside required tolerance!
Assembly methods have been proofed and can be used for future modules
Assembly is feasible under industrial like conditions, especially under fast rate of construction
Photogrammetry has been proofed as a reliable and fast survey technique for final surveys
Accessibility can be improved by a second order datum point system for photogrammetry, especially for the next assembly steps: module assembly
assembly of torus
Second order datum points show an acceptable increase of uncertainty
New generation of cameras will be tested to reduce survey time and improve accuracy
The experiment WENDELSTEIN 7-X will go into
operation in 2014 !