LOW CARBON AND SILICON STEEL QUADRUPOLE MAGNETS

Transcription

1 LOW CARBON AND SILICON STEEL QUADRUPOLE MAGNETS H. Fukuma, N. Kumagai, Y. Takeuchi, K. Endo, M. Komatsubara To cite this version: H. Fukuma, N. Kumagai, Y. Takeuchi, K. Endo, M. Komatsubara. LOW CARBON AND SILICON STEEL QUADRUPOLE MAGNETS. Journal de Physique Colloques, 1984, 45 (C1), pp.c1-301-c < /jphyscol: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1984 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 JOURNAL DE PHYSIQUE Colloque C1, suppl6ment au no I, Tome 45, janvier 1984 page Cl-301 LOW CARBON AND SILICON STEEL QUADRUPOLE MAGNETS H. Fukuma, N. Kumagai, Y. Takeuchi, K. Endo and M. ~omatsubara* National Laboratory for High Energy Physics, Oho-machi, Ts'sukuba-gun, Ibaraki-ken, 305, Japan *~awasaki SteeZ Corporation, Kawasaki-cho, Chiba-shi, 260, Japan Resum6 - L'acier bas carbone d6velopp6 pour les circuits magnetiques est compar6 a l'acier au silicium du point de vue des performances d'un aimant quadrupol e. Abstract - The low carbon steel developped for the magnet core material is compared with the in regard to the performance of the quadrupole magnet. A large accelerator needs a large amount of iron with good magnetic and mechanical properties for the construction of the magnets. All magnets must have the uniform field properties to confine the charged particles, such as proton and electron, stable in the air gaps of the magnets a1 igned along an orbit. Several hundreds of magnets are made of several thousand tons of iron. As the magnet has a large weight on the accelerator cost, it is important to reduce the magnet cost in both sides of fabrication and material. Usually iron for the magnet has been selected mainly from the quality itself. The and the decarbonized steel are the candidates, but they are rather expensive. Recently the cheaper low carbon steel is used frequently to economize the expenses. However, the low carbon steel which is available commercially is made for the structural iron which does not require the magnetic properties but requires the workabi 1 i ty. Its magnetic properties obtained by the Epstein method on a small scale correspond to the low grade and lack in the uniformity. As for the, one can choose the magnetic properties which are different depending on the silicon content and their fluctuation can be made small by selecting the steel with the specified quality. This selection is possible because the silicon steel is widely used to the electrical machines and produced in large quantities. Therefore, the aims of this work are summarized as follows, - quality improvement of the low carbon steel by the slight modification of the production process, - possibility of the large scale production of the low carbon steel with the uniform qua1 i ty, and - sufficient mechanical strength required to the stamping process. After many trials on the chemical contents of elements and impurities and on the heat treatment, the low carbon steel having the similar magnetic properties to the middle class was obtained. I - LOW CARBON STEEL From the accelerator view points, we impose the specifications on the magnet core material such as hardness (or mechanical strength), permeabilities (v) at the specified flux densities, coercive force(hc), uniformities of the permeability and coercive force, etc. These specifications are required from both the fabrication process and the tolerance of the magnet performance. Their relations are - hardness -workability under the punching die, mechanical strength - permeability - iron saturation, magnet dimensions - coercive force - remanent field strength - uniformity - shuffling of laminations. Article published online by EDP Sciences and available at

3 CI-302 JOURNAL DE PHYSIQUE Another property to be considered is the magnetic after effect of the steel. If the after effect continues for a long time, it is required to wait or adjust the excitation current to establish the magnetic field corresponding to the energy of the particles circulating in the accelerator. This phenomenon is metallurgically explained as the migration of the nitrogen atoms in the steel and can be suppressed by removing the nitrogen impurity or by adding another elements such as aluminum to suppress the migration. The typical magnetic and mechanical properties of the low carbon steel compared with the are given in Table 1. The magnetic properties depend greatly on the lamination thickness. The best choice is around 0.5 mm. Initially the thickness was aimed more than 1 mm. However, the better properties were obtained for the thinner one. The 0.5 mm thick low carbon steel was tested further in regard to the reproducibility at the mass production stage. These trials gave the satisfactory results as shown in Table 2. Table 1 Mgnet?c and mchamcal propertier af steels Th>cknerr Uc at dm) Inn1 (Oel. 8 = 1 T 8 = 1.5T - - 8". Table 2 Repraduelbility runs at the mrr production stage Law carbon rteel LOW carbon HC at 1.5 T u(eou1 El steel (Oe) H I * :: 8 ; 1 T B = 1.8 T Hv HZ ill HZ r c 4233.r 1121 R % * B 0.96 x % x * 113 Silicon rteel high grade x ZOO middle grade x 145 Average low grade At the mass production stage, better results were obtained than at the laboratory stage. The high permeability at the high magnetic field is suitable for the core material of the quadrupole magnets for the colliding accelerator, because the operation at higher field gradient will be frequently required to attain higher luminosity. I1 - PERFORMANCE 06 QUADRUPOLE MAGNETS The quadrupole magnet with the dimensions of Fig. 1 was made of the low carbon steel with the properties of Table 2. Parameters of the magnet are given in Table 3. The shape of the magnet was designed to use the middle grade (S23 grade of the Japanese Industrial Standards) for the TRISTAN accumulation ring /I/. Two quadrupole magnets made of the different steels were investtgated to compare their performances. The B-H curves of both steels are shown in Fig. 2. Almost the same characteristics wi 11 promise the sirni 1 ar performances.

4 G(x)/G(o) 16- I = 800A I.O I xkm) 06-0 tow carbon steel s~l~con steel (S23 grade lowcarbonsteel(i0wgrade) Fig. 3 Radial distributions of the 1 field gradient, the sextupolar o -."....*..- * "" "" ' ' ' "";04 asymmetry was corrected. 10 lo3 lo' H h/m) Fig. 2 B-H curves. Field properties The two dimensional distributions of the field gradients were measured with the flip twin coils at the magnet center (Fig.3). Both curves hold up to 1200 A without any field deterioration. As expected from the B-H curves, the magnet saturation is larger for the than the low carbon steel above 2000 A/m. Fig. 4 shows the difference of the excitation curves of both magnets. An abscissa gives the excitation current and an ordinate the field gradient normalized at 400 A. A small improvement is seen above 1100 A (17 T/m). (+I* 1 (+)400fi Hysteresis One of the important problems to the colliding type of accelerator is the hysteresis of the steel. In the accelerator operation, the fine adjustment is frequently required and the hysteretic operation tracing a minor loop is usually encountered. By this operation the initial condition is not reproducible after returning to the initial current. 0,90t Fiq. 5 c 8 show the results of the deviations of-the field gradients when the magnet experienced three successive minor loops. The extent of the minor loops is given by the change of the excitation current in percent at the abscissa. The initial current was 938 A (14.6 T/m) for all cases. Both upward and downward changes of the current were applied. Three successive measurements under the same minor loops were made after the initializing operation of the magnet, which means three large loop excitations from 0 to 1330 A (20 T/m) to eliminate the memory of the steel of the pr a rn I eceding run. The change of the field gradient after tracing a minor loop is given in the Excitation current (A) ordinate in percent. Each deviation after the successive minor loop operations differs, but approaches to the final value. The hysteretic Fig. 4 Excitation curves.

5 C1-304 JOURNAL DE PHYSIQUE 0.5 I I. = 938A A Fig. 7 I - I0 (%I I0 I. O \ I- I (W Fig. 5 Hysteretic effect tracing 3 successive minor loops. I, - 938A 2.0 A I. = 938A 1.01 A I - I 0 (%I I0 Fig. 6 Fig. 8 effect of the low carbon steel is about 1.5 times larger than that of the silicon steel. This is also expected from the close correlation between the coercive force and the hysteretic loss. Authors acknowledge the discussions of Professors T. Nishikawa and Y. Kimura on the steel properties. They are also grateful to Messrs. Y. Ito and T. Sekita of Kawasaki Steel Corp. for their active interest to the new steel. Reference 1) K. Endo, H. kukuma, A. Kabe, Ta. Kubo, To. Kubo, N. Kumagai and Y. Takeuchi, KEK Internal (1982).