The effect of neutron and gamma
radiation on magnet components
Michael Eisterer, Rainer Prokopec, Reinhard K. Maix,
H. Fillunger, Thomas Baumgartner, Harald W. Weber
Vienna University of Technology
Atominstitut, Vienna, Austria
RESMM Workshop, Fermilab, 14 February 2012
LOW TEMPERATURE PHYSICS
ACKNOWLEDGEMENTS
Work on the superconductors started at ATI in 1977 and was done partly
at Argonne, Oak Ridge and Lawrence Livermore National Laboratories as
well as at FRM Garching.
Work on the insulators started in 1983 and in systematic form in 1990.
Many graduate students and post-doctoral fellows have been involved.
Substantial support by the European Fusion Programme (EFDA) and by
the ITER Organization (IO) is acknowledged.
The contributions of the ATI crew are gratefully acknowledged.
Senior scientists: H. Fillunger, K. Humer, R.K. Maix, F.M. Sauerzopf
Post-docs: K. Bittner-Rohrhofer, R. Fuger, F. Hengstberger, R. Prokopec,
M. Zehetmayer
PhD students: T. Baumgartner, M. Chudy, J. Emhofer
LOW TEMPERATURE PHYSICS
Outlook
• Radiation environment in a fission reactor
– Neutron and g - spectrum
• Damage production
– neutrons, g - radiation
• Scaling: Prediction of behavior in other radiation environments
• Superconductors: NbTi, Nb3Sn, MgB2, cuprates
– Transition temperature, critical current
• Insulators: epoxy resin, cyanate ester, bismaleimides
– Dielectric strength
– Mechanical properties
• Ultimate tensile strength, iterlaminar shear strength, fatigue behavior
– Gas evolution
• Conclusions
LOW TEMPERATURE PHYSICS
Fission of 235U
+ ~200 MeV
http://www.atomicarchive.com/Fission/Fission1.shtml
kinetic energy of fission products: ~165 MeV
prompt gamma rays: ~7 MeV
kinetic energy of the neutrons: ~6 MeV
energy from fission products (b-decay): ~7 MeV
gamma rays from fission products : ~6 MeV
anti-neutrinos from fission products : ~9 MeV
LOW TEMPERATURE PHYSICS
Neutron Energy Distribution
Rotating Target Neutron Source
Lawrence Livermore National Laboratory
Atominstitut, Vienna
Intense Pulsed Neutron Source, Argonne National Laboratory
LOW TEMPERATURE PHYSICS
Fission: prompt g emission
F.C. Maienschein
R.W. Peelle
W. Zobel
T. A. Love
Second United Nations
International
Conference on the
Peaceful Uses of Atomic
Energy 1958
Total: 1 MGy/h
7 photons/fission, 7 MeV/fission, ~100 keV to ~8 MeV, peak at 300 keV
In addition: radioactive decay, e--e+ annihilation (511 keV), n-capture, Bremsstrahlung
LOW TEMPERATURE PHYSICS
Damage Production: Neutrons
“Elastic” collision with lattice atoms:
(Hydrogen)
 En
4mL mn
Ep 
En
2
1
mL  mn 
4
En mL  1
mL
Minimum energy to displace one atom:
(epithermal and fast neutrons)
E p  EB ~4 eV C-H
Stable?
~few eV in metals
~5-40 eV in ionic crystals
E p   1 keV: Displacement cascades
Stable in HTS
Disintegrate at room temperature to small clouds of point defects in LTS
LOW TEMPERATURE PHYSICS
Damage Production: Neutrons
Nuclear reactions: (n,g), (n,b), (n,a) ,fission
Example:
10B
+ n → 7Li (1 MeV) + 4He (1.7 MeV)
Neutron caption cross sections are most often
largest at low neutron energies.
(n,g), (n,b): point defects
LOW TEMPERATURE PHYSICS
Damage Production: Gamma rays
Interaction via electronic system:
4 Eg2
Compton scattering:
Ep 
Photoelectric effect:
Ee  Eg
Pair production:
mc 2  2 Eg
Eg  1.022 MeV
Ionization!
• Breaks chemical bonds in organic molecules.
(plastic deteriorates in sunlight.)
• Little effect in crystalline materials (superconductors).
LOW TEMPERATURE PHYSICS
Damage Calculation: Neutrons
Fast neutron fluence: 4×1022 m−2 (E > 0.1 MeV)
Superconductors:
Insulators:
LOW TEMPERATURE PHYSICS
Other Radiation Environments?
Scaling
Superconductors:
T 
  ( E )T ( E )
dF
dE
dE
dF
 dE dE
ED  T Ft
(E)
T(E)
F(E)
t
displacement energy cross section
damage enegy
neutron cross section
primary recoil energy distribution
neutron flux density distribution
irradiation time in the neutron spectrum F(E)
Insulators:
Dose (total absorbed energy) [Gy]=[J/kg]
Prediction of property changes in other radiation environments (?)
LOW TEMPERATURE PHYSICS
Changes of Superconducting Properties
Transition Temperature Tc
- through disorder
Normal state resistivity rn
- through the introduction of additional scattering centers
Upper critical field Hc2
- through the same mechanism:
rn  1/l  k  Hc2
Critical current density Jc
- through the production of pinning centers
LOW TEMPERATURE PHYSICS
Changes in Transition Temperature
maximum fluence around
7-10 x 1023 m-2 (E>0.1 MeV)
Decrease at a fast fluence of1022 m-2:
NbTi: ~ 0.015 K
• A-15: ~ 0.3 K
• Cuprates: ~ 2 K
• MgB2: ~ 4 K (n,a)!
•
LOW TEMPERATURE PHYSICS
Changes of the Critical Current
NbTi, 4.2 K
IPNS (distr.)
RTNS (14 MeV)
Damage energy scaling:
H.W. Weber, Int. J. Mod. Phys. E 20 (2011) 1325
LOW TEMPERATURE PHYSICS
Changes of the Critical Current
NbTi, 4.2 K
Irradiation temperature is rather unimportant! (intermediate
warm-up)
H.W. Weber, Int. J. Mod. Phys. E 20 (2011) 1325
LOW TEMPERATURE PHYSICS
Changes of the Critical Current
Nb3Sn, 4.2 K
IC / IC0
EM Nb3Sn at µ0H = 12 T
RHQT Nb3Al at µ0H = 16 T
6T
-2
fast neutron fluence (m )
H.W. Weber, Adv. Cryog. Eng. 32 (1986) 853
LOW TEMPERATURE PHYSICS
J
JC
H
T
TC
HC2(T)
LOW TEMPERATURE PHYSICS
J
JC
H
T
TC
HC2(T)
LOW TEMPERATURE PHYSICS
Changes of the Critical Current
MgB2, 4.2 K
fast neutron fluence: 1022 m-2
9
MgB2 4.2 K
2
Jc(A/m )
10
8
10
unirradiated
22
-2
10 m
7
10
4
6
8
10
12
14
B (T)
Maximum at around 1-2×1022 m-2 depending on Tcunirr.
LOW TEMPERATURE PHYSICS
Changes of the Critical Current
Y-123
• Decrease of JC at low fields
• Increase of JC at higher field
• Start of (overall) degradation
depends on temperature
(1-2×1022 m-2 at 77 K)
Crossover field (mT)
2x1021 m-2
4x1021 m-2
1x1022 m-2
77 K
244
382
630
64 K
114
219
440
50 K
130
195
334
LOW TEMPERATURE PHYSICS
ITER TF coil design
Structures
Radial Plate (RP)
(60 tons)
Conductor (35 tons)
14 m
7 RP
9m
TF Coil (300 tons) Boeing 747:
~185 t
A380: ~280 t
Coil Case
(200 tons)
Winding
(7 double pancakes)
Insulation (glass and resin) ∼ 5 tons
LOW TEMPERATURE PHYSICS
Impregnation of TF Model Coil
LOW TEMPERATURE PHYSICS
-1
Dielectric Strength (kV mm )
Dielectric strength at 77 K after reactor irradiation
120
100
80
60
40
Laminate
20
Sandwich
0
0
21
10
10
-2
Neutron Fluence (m , E>0.1M eV)
22
ITER
LOW TEMPERATURE PHYSICS
Radiation effects on insulators
Neutrons directly deposited energy by the entire neutron spectrum
(via computer codes and damage parameters for
each constituent of resin, i.e. H, C, O, N, ...)
production of H, He → gas production
g-rays
Dose rate (Gy/h) times irradiation time (h)
 Total absorbed energy (Gy)
 Scaling quantity ?
LOW TEMPERATURE PHYSICS
Damage calculations
Examples:
ZI-003 (Epoxy Resin)
ZI-005 (Bismaleimide Triazine)
15 wt% H, 75 wt% C, 3 wt% N, 7 wt% O
5 wt% H, 73 wt% C, 10 wt% N, 12 wt% O
irradiated to 5x1022 m-2 (E>0.1 MeV) in:
irradiated to 7.8x1021 m-2 (E>0.1 MeV)
TRIGA Vienna:
IPNS Argonne:
ZI-003:
from neutrons:
from gamma rays:
186 MGy
(50 %)
182 MGy
(50 %)
-----------------------368 MGy (100%)
16.3 MGy
(39 %)
25.9 MGy
(61 %)
------------------------42.2 MGy
(100%)
ZI-005:
from neutrons:
from gamma rays:
76 MGy
(30 %)
182 MGy
(70 %)
-----------------------258 MGy (100%)
6.5 MGy
(20 %)
25.9 MGy
(80 %)
------------------------32.4 MGy
(100%)
LOW TEMPERATURE PHYSICS
Mechanical Tests
Tensile test specimen geometries
MTS 810 test facility
Fatigue measurements
1,00
 / max
0,75
 = 0.8 max
R=0.1
u
0,50
0,25
l=u*0.1
0,00
0,00
0,05
0,10
0,15
0,20
Time (s)
LOW TEMPERATURE PHYSICS
Influence of radiation environment and resin composition
TRIGA Vienna
2 MeV electrons
60-Co g-rays
IPNS Argonne
Irradiation at ~340 K
Tests at 77 K
Bismaleimide
Epoxy
Epoxy
Scaling works well!
LOW TEMPERATURE PHYSICS
Influence of irradiation temperature and of annealing to RT
Bismaleimide
Garching ~ 5 K
Ekaterinburg 77 K
ATI ~340 K
Tests at 77 K
Epoxy
Epoxy
LOW TEMPERATURE PHYSICS
Radiation Effects on Different Resins Tested
for ITER
110
O
100
O
O
N
H3C
90
H
H
80
Mechanical strength (%)
C
H
70
O
O
60
O
50
C
N
epoxy
cyanate ester
40
30
20
Cyanate ester
Cyanate ester/epoxy (40:60)
Epoxy
10
0
0
1x10
21
1x10
• Costs of CE up to 10 times higher than for
epoxies
• CE can be mixed with epoxies for reducing costs
 CE/epoxy blends
22
Neutron fluence (E>0.1 MeV)
LOW TEMPERATURE PHYSICS
Influence of CE content
ultimate tensile strength after irradiation @ 77 K
22
-2
22
-2
0°
1*10 m
2*10 m
DGEBF
Ansaldo (90°)
90°
286 MPa
DGEBA
Alstom (90°)
387 MPa
20 % CE
T10 (20) (90°)
265 MPa
30 % CE
T8 (30) (90°)
269 MPa
40 % CE
T2 (40) (90°)
313 MPa
100 % CE
T1 (100) (90°)
250 MPa
0
10
20
30
40
50
60
70
80
90
100
UTSirr/UTSunirr (%)
LOW TEMPERATURE PHYSICS
Influence of CE content
Interlaminar shear strength after irradiation @ 77 K
22
-2
22
-2
22
-2
0°
1*10 m
2*10 m
90°
4*10 m
Ansaldo (90°)
DGEBF
41 MPa
Ansaldo (0°)
45 MPa
Alstom (90°)
DGEBA
20 % CE
75 MPa
Alstom (0°)
81 MPa
T10 (20) (90°)
48 MPa
T10 (20) (0°)
62 MPa
T8 (30) (90°)
30 % CE
40 % CE
100 % CE
63 MPa
T8 (30) (0°)
74 MPa
T2 (40) (90°)
57 MPa
T2 (40) (0°)
77 MPa
T1 (100) (90°)
42 MPa
T1 (100) (0°)
59 MPa
0
10
20
30
40
50
60
70
80
90
100
ILSSirr/ILSSunirr (%)
LOW TEMPERATURE PHYSICS
Fatigue measurements @ 77 K
No significant influence of the irradiation!
LOW TEMPERATURE PHYSICS
Bonded Glass/Polyimide tapes
Delamination caused by weak bonding between resin and
polyimide
Radiation resistant bonding agent necessary!
LOW TEMPERATURE PHYSICS
Gas Evolution Rates
Material
Chemistry
Neutron Fluence
(E>0.1 MeV)
(1021 m-2)
Total absorbed
Dose
(MGy)
Gas Evolution
Mean ± Sdev
(mm3)
Gas Evolution Rate
Mean ± Sdev
(mm3g-1MGy-1)
CTD-422
Cyanate Ester/Epoxy
1
4.19
105 ± 0
68.9 ± 2.4
CTD-10x
Cyanate Ester/Epoxy/BMI
1
4.05
83 ± 11
57.1 ± 6.8
CTD-101K
Epoxy/Anhydride
1
4.14
165 ± 0
108.4 ± 1.9
CTD-7x
Cyanate Ester/Epoxy/PI
1
3.90
75 ± 0
48.2 ± 0.4
CTD-15x
Cyanate Ester/BMI
1
4.46
60 ± 0
38.9 ± 0.3
CTD-101
Epoxy/Anhydride
1
4.11
165 ± 21
114.3 ± 10.3
CTD-HR3
Cyanate Ester/PI
1
4.31
60 ± 0
33.9 ± 0.5
CTD-404
CTD-404
Cyanate Ester
1
5
4.04
20.18
68 ± 11
200 ± 9
47.0 ± 7.4
30.4 ± 1.1
ER Baseline
Epoxy/Anhydride
1
4.15
263 ± 11
176.2 ± 10.3
LOW TEMPERATURE PHYSICS
Conclusions
• Minor influence of irradiation temperature
• Superconductors
– Defects mainly caused by high energy neutrons (except MgB2)
– Decrease of transition temperature
– Critical current initially increases (except NbTi) then decreases
(1-2x1022 m-2)
– Scaling by damage energy
• Insulators
–
–
–
–
Defects caused by (nearly) all neutrons and g rays
Degradation of mechanical properties
Gas evolution
Scaling by total absorbed energy (dose)
LOW TEMPERATURE PHYSICS