Damage of NdFeB Permanent Magnets under Neutron Irradiation at the Brookhaven Linear Isotope Producer
N. Simos, P.K. Job, T. Tanabe, S. Ozaki, J O Conor and A. Aronson, BNLN. Mokhov, FNAL
Feb 14, 2012
OutlineOutline
Insertion Devices and Permanent Magnet Demagnetization Concerns
Irradiation of NdFeB magnets (APS)
Demagnetization results and annealing
Radioactivity measurements and assessment
Future plans
RESMM-2012, FNAL, Feb 13-15
At Issue: De-magnetization of Insertion Devices
e-γ
γγ
e±
e±
e±
nn
High brilliance in next generation light sources (i.e. 3 GeV NSLS II) is obtained from the high magnetic fields in insertion devices (ID)
The beam lifetime is limited to 3h by Coulomb scattering in the bunch
Effect occurs everywhere around the circumference leading to unavoidable beam loss in the adjacent low-aperture insertion devices (undulators and wigglers)
RESMM-2012, FNAL, Feb 13-15
At Issue: De-magnetization of Insertion Devices
e- γ
γ
e±e±
e±
n
n
Nd2Fe14B: 26.7% Nd by atomic weight, Fe 72.3%, Boron 1%
Boron only 1 % BUT various models/studies point at it being the dominant demagnetization factor
2 stable isotopes with 5B10 very large neutron capture cross section of 3.8 kb (compare to Co59 with 36.6 b
Curie Temp Tc exceedance Sm2CO17 (800o)> SmCO5(700o) >Nd2-xFe14B (300o)x = substitute of other rare earths
Thermal SpikeRecoil atoms generates heat above Curie temperature over a very small volume forming tracks
RESMM-2012, FNAL, Feb 13-15
Experience
APS Nd2Fe14B magnet demagnetization(after P.K. Job et al)
280 Mrad (1 Mrad = 10 kGy) absorbed dose from bending magnet X-rays700 Mrad 60Co gamma rays Changes within experimental uncertainties
Fast Neutrons Fluence: 1.61 1014 n/cm2
Thermal Neutrons Fluence: 2.94 1012 n/cm2
RESMM-2012, FNAL, Feb 13-15
Experience
NEOMAX-50BH without thermal treatment (after Bizen et al)
Irradiation Temperature Effect on Nd2Fe14B Demagnetization
(after Zeller)
(after Bizen)
Observed Effect of irradiating species
Damage Hierarchy: p> n> e> γ
Also believed: HE p > LE p
RESMM-2012, FNAL, Feb 13-15
Nd2Fe14B Magnet Demagnetization using Fast Neutron, Photon and Electron Shower at BNL BLIP
RESMM-2012, FNAL, Feb 13-15
MARS 15 Analysis (N. Mokhov)
<E> (MeV) Flux (cm-2 s-
1)
p: 23 8.6e5 n: 9 1.9e9: 1 3.2e9 e: 1 7.1e6
Here protons include thosefrom neutron-inducedreactions (recoils etc)
Contributions to absorbeddose are not very different!
RESMM-2012, FNAL, Feb 13-15
Ni plated NdFeB5cm x 4.75cm x 0.7cm
RESMM-2012, FNAL, Feb 13-15
n_spectra at Invar target and NdFeBgraph is for normalized p flux of 10^12 p/s
1.E+06
1.E+07
1.E+08
1.E+09
0.001 0.01 0.1 1 10 100
MeV
1/cm
2-s
n_NdFeB (with water moderator)
n_Invar
Normalized Gamma Spectra (proton flux = 10^12 p/s)
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
1.E+10
0.1 1 10 100
MeV
1/c
m2
-s
gamma_Invar
gamma_NdFeB
RESMM-2012, FNAL, Feb 13-15
Normalized e-spectra (flux = 10^12 p/s)
1.E-01
1.E+01
1.E+03
1.E+05
1.E+07
1.E+09
1.E+11
0.1 1 10 100
MeV
1/cm
2-s
e_Invar
e_NdFeB
Secondary proton spectra
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
0.1 1 10 100MeV
1/cm
2-s
RESMM-2012, FNAL, Feb 13-15
Neutron FLUX at magnet location = 1.4825 e+11 n/cm2-s
Neutron Fluence (11A/1.8 Grad) = 4.38 e+17 n/cm2
Neutron Fluence (6A/50 Mrad) = 1.29 e+16 n/cm2
ADD to the neutron fluence on the magnet electron and gamma fluences
RESMM-2012, FNAL, Feb 13-15
Hall Probe in the hot cell Magnetic field strength following irradiation
RESMM-2012, FNAL, Feb 13-15
Hall Probe in the hot cell Magnetic field strength following irradiation
Observation:
Non-uniformity of field of un-irradiated magnets
Same holds true at reduced levels following irradiation
RESMM-2012, FNAL, Feb 13-15
RADIOACTIVITY STUDIES
Irradiation COMPLETED June 2007
Dose Measurements, Feb 2012
11A (1.8 Grad) 50 mRem/hr gamma @ 1ft1000 mRem/hr @ contact
3A (1.2 Grad)
30/500 meR/hr gamma
ESTIMATION of TOTAL Activity (using MicroShield 7.0)
3A Co60 2.3e-03 Curies (8.51e+07 Becquerel) Mn54 1.9e-04 Curies (7.03e+06 Becquerel)
11A Co60 3.8e-03 CuriesMn54 1.7e-04 Curies
RESMM-2012, FNAL, Feb 13-15
NdFeB Irradiated at BLIP
10
100
1000
10000
100000
1000000
10000000
0 200 400 600 800 1000 1200 1400
Energy (KeV)
Co
un
ts
0.001
0.01
0.1
1
10
Flu
enc
e &
Co
un
t R
atio
s (3
A/1
1A
)
1.8 Grad (Magnet 11A)
1.2 Grad (Magnet 3A)
Counts Ratio (3A/11A)
Fluence Ratio (3A/11A)
RADIOACTIVITY STUDIES
Note: 3A saw neutrons that were not moderated.
That is a possible explanation of the difference between the
fluence ratio and the counts ratio
RESMM-2012, FNAL, Feb 13-15
NdFeB Irradiated at BLIP with Neutron Spectra
10
100
1000
10000
100000
1000000
0 500 1000 1500 2000Energy (KeV)
Co
un
ts
1.8 Grad (Magnet 11A)
1.2 Grad (Magnet 3A)No neutron moderation
Mn54 (from Fe54(n,p) charge-exchange)
27Co60 1173.2/1332.4 KeV
834.8 KeV
5.27y
313d
RESMM-2012, FNAL, Feb 13-15
NdFeB Irradiated at BLIP with Neutron Spectra
2000
4000
6000
8000
10000
12000
14000
16000
0 100 200 300 400 500 600 700 800 900 1000
Energy (KeV)
Co
un
ts
1.8 Grad (Magnet 11A)
1.2 Grad (Magnet 3A)No neutron moderation
60Nd147 531.0 (KeV)
?
Mn54
511 KeV
RESMM-2012, FNAL, Feb 13-15
Path ForwardDecay process monitoring for radioactivity assessment => handling for remagnetization
Benchmarking of MCNPX, CINDER-90 and/or ORIGEN codes against the decaying magnet photon spectra to be used in estimating service/handling of actual insertion device (ID) magnets
Explore re-magnetization procedures of the already irradiated NdFeB magnets (suggestions welcomed)
Expose and evaluate the radiation resistance of other ID magnets (i.e. SmxCoy) to similar complex spectra (energies and species).
Sm-Co have exhibited greater resistance to mono-energetic radiation
Test doping with other elements or substitution of Nd that tend to enhance intrinsic coercivityDelineate between direct proton irradiation and combined field (at same dose)
