Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions

Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions

The development of present-day technologies and materials for creating permanent magnets (in particular, at NSC KIPT), and increasing demands for devices in which these materials are used for physics and technology of intense (10 to 40 MeV) electron beam forming have motivated the comprehensive stud...

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Datum:1999
Hauptverfasser: Dovbnya, A.N., Tolstoy, A.E., Bovda, A.M., Utva, O.M., Uvarov, V.L., Krasnogolovets, M.A.
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Sprache:English
Veröffentlicht: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 1999
Schriftenreihe:Вопросы атомной науки и техники
Online Zugang:http://dspace.nbuv.gov.ua/handle/123456789/81367
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Назва журналу:Digital Library of Periodicals of National Academy of Sciences of Ukraine
Zitieren:Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions / A.N. Dovbnya, A.E. Tolstoy, A.M. Bovda, O.M. Utva, V.L. Uvarov, M.A. Krasnogolovets // Вопросы атомной науки и техники. — 1999. — № 3. — С. 48-49. — Бібліогр.: 2 назв. — англ.

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spelling irk-123456789-813672015-05-15T03:01:55Z Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions Dovbnya, A.N. Tolstoy, A.E. Bovda, A.M. Utva, O.M. Uvarov, V.L. Krasnogolovets, M.A. The development of present-day technologies and materials for creating permanent magnets (in particular, at NSC KIPT), and increasing demands for devices in which these materials are used for physics and technology of intense (10 to 40 MeV) electron beam forming have motivated the comprehensive study on characteristics of these materials under extreme conditions of their use. 1999 Article Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions / A.N. Dovbnya, A.E. Tolstoy, A.M. Bovda, O.M. Utva, V.L. Uvarov, M.A. Krasnogolovets // Вопросы атомной науки и техники. — 1999. — № 3. — С. 48-49. — Бібліогр.: 2 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81367 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
description The development of present-day technologies and materials for creating permanent magnets (in particular, at NSC KIPT), and increasing demands for devices in which these materials are used for physics and technology of intense (10 to 40 MeV) electron beam forming have motivated the comprehensive study on characteristics of these materials under extreme conditions of their use.
format Article
author Dovbnya, A.N.
Tolstoy, A.E.
Bovda, A.M.
Utva, O.M.
Uvarov, V.L.
Krasnogolovets, M.A.
spellingShingle Dovbnya, A.N.
Tolstoy, A.E.
Bovda, A.M.
Utva, O.M.
Uvarov, V.L.
Krasnogolovets, M.A.
Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions
Вопросы атомной науки и техники
author_facet Dovbnya, A.N.
Tolstoy, A.E.
Bovda, A.M.
Utva, O.M.
Uvarov, V.L.
Krasnogolovets, M.A.
author_sort Dovbnya, A.N.
title Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions
title_short Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions
title_full Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions
title_fullStr Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions
title_full_unstemmed Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions
title_sort study on radiation resistence of permanent ndfeb-base magnets under continuons radiation conditions
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
publishDate 1999
url http://dspace.nbuv.gov.ua/handle/123456789/81367
citation_txt Study on radiation resistence of permanent NdFeB-base magnets under continuons radiation conditions / A.N. Dovbnya, A.E. Tolstoy, A.M. Bovda, O.M. Utva, V.L. Uvarov, M.A. Krasnogolovets // Вопросы атомной науки и техники. — 1999. — № 3. — С. 48-49. — Бібліогр.: 2 назв. — англ.
series Вопросы атомной науки и техники
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fulltext STUDY ON RADIATION RESISTANCE OF PERMANENT NDFEB-BASE MAGNETS UNDER CONTINUOUS RADIATION CONDITIONS A.N.Dovbnya, A.E. Tolstoy, A.M. Bovda, O.M. Utva, V.L. Uvarov, M.A. Krasnogolovets* NSC KIPT, Kharkov, Ukraine; *Kharkov Technical University for Radioelectronics, Kharkov, Ukraine The development of present-day technologies and materials for creating permanent magnets (in particular, at NSC KIPT), and increasing demands for devices in which these materials are used for physics and technology of intense (10 to 40 MeV) electron beam forming have motivated the comprehensive study on characteristics of these materials under extreme conditions of their use. The decisive advantages of permanent-magnet (PM) systems are their small dimensions, the absence of electric power supply, the simplicity of design, the possibility of creating periodic structures directly in the vacuum chamber of the basic facility (e.g., undulators and wigglers in free electron lasers). On the other hand, with the magnetic structure brought closer to a high- power electron beam there arises a danger of radiation action on the magnet material causing changes in its characteristics and even failure. So, concurrent with planned programs performed at newly created and operating today nearly continuously the facilities of the R & D “Accelerator” Complex, experiments are conducted to investigate magnet specimens based on the NdFeB alloy. The alloys for rare-earth PMs were produced by combined induction smelting of metal components in a crucible and subsequent molding. The 34% Nd-1.1% B- 4.9% Fe ingots were manufactured in the induction vacuum furnace with an alundum crucible using the powder mixture Nd-NM3, ferroboron FB20, Fe - EhP335. The pouring was made in such a way as to ensure quick cooling of the melt in order to minimize its oxidation. After that, the alloy was processed by the conventional powder metallurgy technique; i.e., first it underwent grinding to particles, 400 ... 600 µm in size, and, then, wet milling in alcohol down to < 10 µm particles with the use of a vibratory ball mill. The aim of milling is to produce the particles that can be considered as tiny single crystals which comprise no grain boundaries. In this case, each particle has one axis of easy magnetization and this provides nearly a total particle orientation. On the other hand, the sintering requires that the particle surface be sufficiently large in order to ensure a high rate of the reaction during sintering. The milling is finished after the optimum granulometric composition is attained. The anisotropic properties of the material produced are formed in the oriented magnetic field following which the powder is compacted in the mold. The direction of pressing is coincident in this case with the direction of magnetization. The press capacity should be sufficient enough for the billet to keep its strength in subsequent operations, but at the same time it should not be too great lest the disorientation of C- axes of powder particles take place. At the end of the compaction cycle, for demagnetization purposes, the field equal in magnitude and opposite in direction as compared to the initial field is applied to the billet. The compacted material is sintered in vacuum resistance furnaces at a temperature between 1050 and 1100°C. After cooling down, the specimens were selectively examined for their magnetic properties, mass and geometrical shape; then the specimens were subjected to mechanical treatment (abrasion) and were checked for their magnetic properties again. The subsequent two-step heat treatment is carried out at a temperature between 250 and 300°C for 1.5 hour. The process is completed by grinding the products to obtain the required shapes and dimensions, and also by final magnetization in the ORIENTIR facility (NSC KIPT design), the field intensity being ≥ 3000 kA at τ ≥5 ms. The radiation tests of magnet specimens were carried out in the field of bremstrahlung from one of accelerators of the Technological Complex [1]. The upper boundary of energy spectrum from bremsstrahlung photons (Em) was estimated to be 11 MeV. The value of dose absorbed in the process of specimen irradiation was measured with the process dosimeter DRD-4/40 detectors mounted directly on the object under irradiation. The specimens were irradiated over certain time periods ∆t which correspond to the operation interval of the absorbed dose of the detector (15 ... 35kGy). The dose value in the specimen was calculated by t D dtdD d Md dM ∆ ⋅ ⋅ ⋅ = ρµ ρµ / , where µm, µd are the linear energy attenuation coefficients of photons in the specimen material under study and in the detector, respectively, at an effective photon energy Eeff = Em/2; ρm and ρd are the densities of the specimen and the detector; Dd is the dose measured by the detector. Simultaneously, the electron beam charge ∆Q corresponding to the irradiation time ∆t was measured. The ∆Q value was calculated by the method of computer integration of beam current pulse train. As a result, the dose received by specimens during the irradiation run was calculated by Q Q D D d Md dM ⋅ ∆ ⋅ ⋅ ⋅ = ρµ ρµ , where Q is the beam charge in one irradiation run. Six rectangular (6×8×16 mm3) plate-type magnet specimens prepared by the above-described technique ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3. Серия: Ядерно-физические исследования. (34), с. 48-49. 48 were taken for tests in the radiation field. The specimens were numbered 1, 2, ...6, and their opposite planes were arbitrarily called as “top” and “bottom”(see the tables) that corresponded to the magnetic poles N - S. The direction of the magnetization vector was easily determined with the Hall detector (type Sh1-8 device); the same device was used to measure the magnetization value. Table 1 characterizes the initial stage of experiments. The upper line gives the initial magnetization values (zero dose); the following three lines correspond to the irradiation doses given on the right. Table 1 Specimen number Dose 1 2 3 4 5 6 T B 2585 2925 2605 2920 2650 2950 2800 2850 2640 2510 2370 2485 D = 0 (initial magnetization values, Oe) T B 2620 2990 2420 2890 2600 2950 2820 2770 2630 2560 2290 1860 D1 = 350 Mrad T B 2570 2810 2230 2840 2620 2910 2820 2770 2610 2570 2080 1880 D2 = 450 Mrad T B 2550 2700 2425 2840 2360 2840 2810 2760 2600 2580 1940 1820 D3 = 450 Mrad A cursory analysis of the data has shown that the extreme specimens, i.e., the 1st and the 6th, exhibit most noticeable changes in magnetization. It was assumed that all six specimens “stuck” together into a single packet might screen each other in the radiation field and only the extreme specimens remained unprotected. Besides, this package may display the “effect of contact with a ferromagnetic body” which reduces the PM flux [2]. To minimize the mentioned phenomena in the next series of irradiation runs, the specimens were placed into an aluminum specimen holder, providing their spatial separation and excluding direct contacts. Table 2. Specimen number Dose 1 2 3 4 5 6 T B 2420 2640 2400 2835 2480 2820 2750 2720 2510 2580 1630 1740 D4 = 700 Mrad T B 2560 2210 2470 2880 2550 2900 2870 2750 2550 2610 1450 1720 D5 = 500 Mrad T B 2545 1930 2160 2830 2485 2880 2790 2690 2500 2540 1310 1660 D6 = 700 Mrad T B 2210 1850 2310 2740 2420 2810 2720 2620 2370 2390 1280 1425 D7 = 700 Mrad The results of the first tests of NdFeB-base PM specimens, the manufacturing process of which has been mastered at NSC KIPT, suggest the following conclusions and recommendations The initial residual magnetization can reach 3 kOε Irradiation in the gamma-radiation field to doses of 350 to 700 Mrad at intervals of 2 to 4 weeks leads to a gradual reduction in magnetization with an obvious anisotropy along the technological package of specimens At a total dose D ≅ 4 Grad the reduction in magnetization can reach about 3% in the middle of the assembly and nearly 45% at its edges. Improvement and refinement of geometry and technique of irradiation experiment are required On developing particular PM-based devices, it is recommended that the scale model device should be tested at real radiation conditions in order to predict the final parameters. REFERENCES 1. N.I. Aizatsky, Ju.I. Akchurin et al., Proc. of XVI Part. Accel. Workshop, Protvino, Oct. 1994, v.4, pp. 259-263. 2. A.G. Slivinskaya, A.V. Gordon, Permanent magnets (in Russian). Ehnergiya publ., M.-L., 1965, p.53. ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3. Серия: Ядерно-физические исследования. (34), с. 48-49. 48 Specimen number Dose Specimen number Dose References

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