1. Radiation Effects on Nb3Sn, copper and inorganic insulation
Al Zeller
NSCL/
MSU

2. Need to examine all components that go into a magnet:
Superconductor (Nb3Sn)
Insulation
Copper
Structural materials 3

3. Nb3Sn Unlike NbTi need to anneal at 700 C to regain critical current

4. 8

5. Possible problem with initial rise: If radiation field is not uniform over the whole conductor, get spatial   variation in Jc, which might affect field harmonics.   Note that radiation damage is like critical current in the peak field area: It is where coil will fail. 10

6. General limits for Nb3Sn:
5 X 108 Gy (500MGy) end of life
Tc goes to 5 K – X 1023 n/m2
Ic goes to 0.9 Ic0 at 14T – 1 X 1023 n/m2
Bc2 goes to 14T X 1022 n/m2
NOTE: En < 14 MeV
Damage increases as neutron energy increases 11

7. Radiation increases resistance
Copper
Radiation increases resistance 15

8. Quench protection becomes an issue – lower allowed current in the copper or higher temperatures during a quench   Can anneal out 80-90% of the increased resistance by going to 300K 16

9. From the Wiedemann-Franz-Lorenz law at a constant temperature λρ = constant   Thermal conductivity decreases   Minimum propagating zone decreases: Lmpz = ((Tc-To)/j2)   So Lmpz -> λ 17

10. Problem:
Gas evolution Ranges from 0.09 for Kapton to >1 cm3/g/MGy for other epoxies Gas is released upon heating to room temperature 19
  Can cause swelling, rupture of containment vessel or fracturing of epoxy

11. Ceramic slurry that is fired?
Warming to room temperature may be required to keep conductivity of copper high, but conflicts with gas evolution problems.   Would like space for helium, so strong porous material would be nice. 20
Ceramic slurry that is fired?
Differential contraction?

12. Structural materials
Crystal structure affect radiation sensitivity FCC materials (e.g. copper) less affected than BCC materials (e.g. iron)

13. Radiation causes dislocation pinning
Structural materials
Radiation causes dislocation pinning
Ø    Decreases thermal conductivity Increases ratio of yield-to-tensile strength (brittle)
Generally makes material harder
Ø Decreases density (swelling)

14. 22

15. What do we want from inorganic insulation?
Electrical insulation
Structural strength
Radiation resistance
Dimensional stability
Thermal conductivity (possibly)
Low radiation absorption
Flexible
Low cost
Thermal contraction matched to conductor

16. A few general points of organic vs inorganic:
Inorganics should be last resort in high rad areas
Inorganics not favored in areas where the major
radiation is not neutrons
Inorganics useful for high-temperature processes
Inorganics good in compression, poor in shear

17. Volume swelling of
MgO
1% at 1 x 1025
N/m2
At 5 x 1023 n/m2
Nb3Sn has Jc = 0
for reactor spectra
neutrons.

18. Aluminum oxide
swelling as a
function of fluence
1% at 2 x 1025
N/m2

19. Spinel has lower
expansion rate than
alumina.

20. Density change in
alumina as a function
of fluence.
Note 1024 n/m2 Nb3Sn
is resistive at 5 x 1023.

21. Dose rate for SLHC
Cos θ D1 calculated
by Mokhov
Resistance decreases
by a factor of 1000.

22. Neutron fluence:
6 x 1022 n/m2
At 4 K, thermal cond.
reduced by about a
factor of 250.

23. Big caution: Damage in inorganic materials
is temperature dependent.
Damage at 4 K, for some properties, is 100
times more than the same dose or fluence
absorbed at room temperature.
Since Nb3Sn has a useful fluence limit of
1023 n/m2, critical properties of inorganic
insulators should be stable to 1025 n/m2
at 4 K.
Note that electrical insulation properties are
10 times less sensitive than mechanical ones.

24. Volume changes after 1024 n/m2
Material ΔV/V (%) notes ΔV/V (%)crit
Al2O
MgO
SiO Vitreous
SiO Quartz
MgAl2O x
MgAl2O x 1026
ΔV/V (%)crit is the strain limit

25. Diamond: density decreases by 3.5%
Ceramics Exposure to ~ 1024 – 1025 n/m2 Alumina: λ decreases by a factor of 4, density increased by 6.8%   BeO: Linear expansion of ~0.13%, Young’s modulus decreases by 64% 24
Diamond: density decreases by 3.5%

26. Important Note   All of the radiation studies on Nb3Sn are years old and we have lots of new materials.

27. Need new studies But I may be able to help.
Have funding for HTS irradiation, so may be
able to irradiate Nb3Sn
Need place to test samples