1. SQXF Mirror QXFSM1 Strain Gauges
R. Bossert, G Chlachdize, S. Stoynev

2. Outline Strain gauge types and positions Values during construction
Prior analysis of coil cross section
Strain gauges during testing
Azimuthal coil full bridge
Axial coil full bridge
End preload “bullets”
Gauges bonded directly to coil
Summary

3. SQXF Mirror Strain Gauge Positions
Bolt on skin
Coil Protective Shell
Coil Midplane shim
Yoke (EDM’d blocks)
Aluminum Side Clamp
Full bridges on titanium
*Note: T stands for “transition” side and NT stands for “non-transition” side. The transition side is the side in which the cable transitions from the inner to the outer layer.
Coil Midplane Gauges
(side designated as T or NT)*
Coil Pole Gauges
(side designated as T or NT)*

4. Strain Gauges Strain gauge system, standard for short mirror:
1 set of full bridges on inner titanium pole, one azimuthal bridge, one longitudinal bridge.
4 quarter bridges bonded to inside surface of inner coil, used during construction only.
Gauges bonded to coil

5. Strain Gauges Strain gauges bonded to end preload bolts.
Array of gauges on skin at 60 and 90 degrees from midplane (HQ shell shown).
Strain gauges bonded to end preload bolts.

6. Side View
Bolt-on skin is 2 meters long, while coil is 1.6 meters long. Coil is placed with Lead End at one end of structure, allowing leads to be terminated in a conventional way. Remainder of structure to be filled with filler packs.
End Load
Similar to HQ mirrors. 2 preload bolts on each end, each applying 7 kN (1500 pounds) of force from the 50mm thick end plate, for a total of 14 kN (3000 pounds) at each end.

7. Assembly Steps – Planned and Actual
Press to 80 Mpa azimuthal stress in press without skin or clamps.
Actual – 79 MPa azimuthal
480 µS longitudinal
Drive in side clamps, increasing azimuthal preload to 90 Mpa
Actual – 89 MPa
530 µS longitudinal

8. Assembly Steps
3. Remove press pressure, clamps deflect, azimuthal preload is 50 MPa.
Actual – 66 MPa azimuthal
460 µS longitudinal
Install skin, return to press, press to azimuthal preload of 90 MPa.
Actual – 89 MPa azimuthal
310 µS longitudinal
Bolt skin and release press. Final average azimuthal coil preload of 70 MPa.
Actual – 77 MPa azimuthal
270 µS longitudinal

9. FEA at 300K
300K
Glued
Saz, Pa
Radial Shim=0.1mm

10. FEA at 4K 4K
Glued
Saz, Pa
At quench current the azimuthal Lorentz force in the mirror is ~30% lower than in the quadrupole model => lower coil prestress needed.

11. FEA at 18kA
4K 11.9T 18kA
Glued
Saz, Pa
Radial Shim=0.1mm

12. Azimuthal full bridge readings during cooldown
Reading from azimuthal full bridge on titanium, (strain x MOE)

13. Azimuthal full bridge readings during excitation
Reading from azimuthal full bridge on titanium, (strain x MOE)

14. Azimuthal full bridge readings during excitation
Readings from azimuthal full bridge on titanium, (strain x MOE)
At 290K before testing: MPa
At 4.5K before excitation:
At 1.9K before excitation:
Increase with current: MPa
At 290K after testing: MPa
Azimuthal full bridge summary:

15. Axial full bridge readings during cooldown
Reading from axial full bridge on titanium from 290K to 4.5K.

16. Axial Full Bridge readings during excitation
Reading from axial full bridge on titanium.

17. Axial Full Bridge readings during excitation
At 290K before testing: uS
At 4.5K before excitation: uS
At 1.9K before excitation: uS
Increase with current: uS
At 290K after testing: uS
Axial full bridge summary:

18. Strain gauge readings during cooldown – end preload
The “cold” readings are at 4.5K

19. Strain gauge readings during excitation
These readings are at 1.9K

20. Strain gauge readings during excitation
These readings are at 1.9K

21. Bullet reading summary

23. Quarter bridges bonded to coil during cooldown.

24. Quarter bridges bonded to coil during cooldown.

25. Quarter bridges bonded to coil during cooldown.

26. Quarter bridges bonded to coil during cooldown.

27. Summary
Azimuthal full bridges – large positive change in strain with cooldown. Typical of some other mirrors. Possibly due to bending of coil. Increase with current of about 50 MPa.
Axial full bridges – strain from +250 µS to -250 µS with cooldown. Slight tensile strain increase with current, returning at quench. Typical of axial bridges.
End load “bullets” - Value change with cooldown unclear. Increase in compressive load with current, between 2-7 kN, slightly higher values on Return End than Lead End.
Coil gauges – Uncalibrated. Cooldown data shown only. Some sign of bending of coil?
Shell gauges still not be analyzed
Coil gauges with excitation not analyzed