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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, BNL N. Mokhov, FNAL Feb 14, 2012. Outline. Insertion Devices and Permanent Magnet Demagnetization Concerns

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  1. 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, BNL N. Mokhov, FNAL Feb 14, 2012

  2. Outline Insertion Devices and Permanent Magnet Demagnetization Concerns Irradiation of NdFeB magnets (APS) Demagnetization results and annealing Radioactivity measurements and assessment Future plans

  3. At Issue: De-magnetization of Insertion Devices 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) e± γ n e- n γ γ e± e± RESMM-2012, FNAL, Feb 13-15

  4. At Issue: De-magnetization of Insertion Devices 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 Spike Recoil atoms generates heat above Curie temperature over a very small volume forming tracks e± n γ e- γ n e± e± RESMM-2012, FNAL, Feb 13-15

  5. Experience 280 Mrad (1 Mrad = 10 kGy) absorbed dose from bending magnet X-rays 700 Mrad 60Co gamma rays  Changes within experimental uncertainties Fast Neutrons Fluence: 1.61 1014 n/cm2 Thermal Neutrons Fluence: 2.94 1012 n/cm2 APS Nd2Fe14B magnet demagnetization (after P.K. Job et al) RESMM-2012, FNAL, Feb 13-15

  6. Experience Irradiation Temperature Effect on Nd2Fe14B Demagnetization Damage Hierarchy: p> n> e> γ Also believed: HE p > LE p NEOMAX-50BH without thermal treatment (after Bizen et al) (after Bizen) Observed Effect of irradiating species (after Zeller) RESMM-2012, FNAL, Feb 13-15

  7. Nd2Fe14B Magnet Demagnetization using Fast Neutron, Photon and Electron Shower at BNL BLIP RESMM-2012, FNAL, Feb 13-15

  8. MARS 15 Analysis (N. Mokhov) <E> (MeV) Flux (cm-2 s-1) p: 23 8.6e5 n: 9 1.9e9 g: 1 3.2e9 e: 1 7.1e6 Here protons include those from neutron-induced reactions (recoils etc) Contributions to absorbed dose are not very different! RESMM-2012, FNAL, Feb 13-15

  9. Ni plated NdFeB 5cm x 4.75cm x 0.7cm RESMM-2012, FNAL, Feb 13-15

  10. RESMM-2012, FNAL, Feb 13-15

  11. RESMM-2012, FNAL, Feb 13-15

  12. 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

  13. Hall Probe in the hot cell  Magnetic field strength following irradiation RESMM-2012, FNAL, Feb 13-15

  14. 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

  15. RADIOACTIVITY STUDIES Irradiation COMPLETED June 2007 Dose Measurements, Feb 2012 11A (1.8 Grad) 50 mRem/hr gamma @ 1ft 1000 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 Curies Mn54 1.7e-04 Curies RESMM-2012, FNAL, Feb 13-15

  16. 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

  17. 27Co60 1173.2/1332.4 KeV 5.27y Mn54 (from Fe54(n,p) charge-exchange) 834.8 KeV 313d RESMM-2012, FNAL, Feb 13-15

  18. Mn54 60Nd147 531.0 (KeV) 511 KeV ? RESMM-2012, FNAL, Feb 13-15

  19. Path Forward • Decay 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 coercivity • Delineate between direct proton irradiation and combined field (at same dose) RESMM-2012, FNAL, Feb 13-15

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