Demagnetization of Nd₂Fe₁₄B, Pr₂Fe₁₄B, and Sm₂Co₁₇ Permanent Magnets in Spallation Irradiation Fields

Journal Article · 27 February 2018 · IEEE Transactions on Magnetics

DOI: https://doi.org/10.1109/TMAG.2017.2769040 · OSTI ID:1454811

Simos, Nikolaos  ^[1]; Ozaki, S. ^[1]; Mokhov, N. ^[2]; Zeller, A.  ^[3]; Mittig, W. ^[3]; Pellemoine, F. ^[3]

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1. Brookhaven National Lab. (BNL), Upton, NY (United States)
2. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
3. Michigan State Univ., East Lansing, MI (United States)

Prompted by the need for radiation-resistant permanent magnets for insertion devices (IDs) of high-brilliance next-generation synchrotrons such as the National Synchrotron Light Source II, the demagnetization of Nd₂Fe₁₄B and Pr₂Fe₁₄B was studied after exposure to a mixed irradiating field. Degradation and damage of the permanent magnetic material by components of electromagnetic showers induced in magnets by intense high-energy electron beams will alter the magnetic field structure of the IDs. Plate-like Nd₂Fe₁₄B magnets were irradiated to 1.8 Grad dose and were evaluated against Pr₂Fe₁₄B magnets irradiated to a lower dose of 20 Mrad. In addition, annular Sm₂Co₁₇ and Nd₂Fe₁₄B magnets integrated within a ferrofluidic feedthrough (FFFT) rotary seal were also irradiated to dose levels of 2 Grad for Sm₂Co₁₇ and 20 Mrad for Nd₂Fe₁₄B. Post-irradiation measurements of the magnetic intensity revealed that severe demagnetization exceeding 85% occurs in Nd₂Fe₁₄B magnets after only 50 Mrad dose and over 87% for Pr₂Fe₁₄B after 10 Mrad dose. The annular-shaped Sm₂Co₁₇ magnets of the FFFTs were almost insensitive to irradiation up to a dose of 2 Grad. Annular-shaped Nd₂Fe₁₄B magnets also showed resistance to demagnetization, a direct consequence of the annular shape which is characterized by the removal of the stronger demagnetizing field present at the center of a disk-like magnet. As a result, the sensitivity of boron-based permanent magnets to neutron energy (thermal versus fast) was also assessed via specifically designed experiments and discussed.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States); Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: SC0012704
• OSTI ID: 1454811
• Report Number(s): BNL-205752-2018-JAAM; TRN: US1901153
• Journal Information: IEEE Transactions on Magnetics, Vol. 54, Issue 5; ISSN 0018-9464
• Publisher: Institute of Electrical and Electronics Engineers. Magnetics GroupCopyright Statement
• Country of Publication: United States
• Language: English