Development of an Electromagnet for a Compact High-Current Betatron
Abstract Generated abstract
This paper describes the design of an electromagnet for a compact high-current betatron intended to reduce installation weight and dimensions while limiting electron charge losses during acceleration. Drawing on studies of pole profiles that produce a monotonic radial increase in the field index and on the principle of more uniform magnetic-circuit loading, the authors present a hexagonal two-half electromagnet with profiled laminated poles, a central pole section, excitation windings, cooling, and provisions for using high-saturation alloy in selected regions. The design, developed during manufacture of a 9 MeV model of a 25 MeV betatron, reportedly reduced the betatron weight to 40 percent of the original design and allowed adjustment of the central air gap for tuning. Main parameters of the completed and commissioned 9 MeV model are provided, including a 140 kg electromagnet, 6 cm equilibrium orbit radius, and calculated bremsstrahlung dose rate of 4.8 R/min at 1 m.
Full Text
Proceedings of the Tomsk Polytechnic Institute
of the Order of the October Revolution and the Order of the Red Banner of Labor
named after S. M. Kirov
Volume 232 1975
DEVELOPMENT OF AN ELECTROMAGNET FOR A COMPACT HIGH-CURRENT BETATRON
V. A. Moskalev, V. L. Nikolaev, G. I. Sergeev
(Presented by the scientific seminar of the accelerator-development sector for low and medium energies, Research Institute of Nuclear Physics, Electronics, and Automation)
At present, the widely known Ш-shaped designs of high-current betatrons, which possess high radiation intensity, require further refinement in order to reduce the weight and dimensions of the installation, to obtain a more compact design, and also to reduce losses of electron charge during acceleration [1].
Studies carried out at Tomsk Polytechnic Institute have shown that, in high-current betatrons, from the standpoint of increasing the accelerated charge it is most expedient to use poles with a profile that ensures a monotonic increase of \(n\) with radius; in this case the magnitude of the accelerated charge is considerably greater (almost by an order of magnitude) than the charge accelerated in a betatron with \(n(r) \cong \mathrm{const}\) [2].
The idea of uniformly loading the steel of the betatron magnetic circuit appears promising for high-current betatrons.
In this connection, a design of the electromagnet was developed that takes into account all of the above and made it possible to reduce the weight of the high-current betatron to 40% of the original.
Figure 1 shows a cross section of the installation. The electromagnet consists of two symmetrical hexagonal halves, a central part, exciting and magnetizing windings, and a cooling system.
The profiled part of the pole, the yoke, and the uprights are assembled from solid-stamped sheets of transformer steel E-330, 0.35 mm thick, arranged in parallel. The central part of the pole is assembled from radially arranged plates. In the developed design of the betatron electromagnet, provision is made for the possibility of using a new electrical-engineering material with a higher saturation induction, of the “permendur” type, which makes it possible to increase the energy of the betatron by 30%.
Taking into account the high cost of the alloy (30–40 rubles/kg), this alloy was used in the design of the magnetic circuit only in the central part of the poles. The question of using the alloy is resolved specifically for each magnetic-circuit design, since the manufacturing technology for cores made from this alloy differs greatly from the technology adopted for silicon steels; i.e., simple replacement of the core material may not only fail to produce a positive effect, but may also significantly worsen the previous electrical-engineering parameters of the betatron electromagnet [3, 4, 5].
The designed fastening of the central part eliminates deformation of the plates of the central part, which makes it possible to preserve the magnetic properties of the alloy and provides adjustment of the central air gap of the interpole space, thereby facilitating tuning of the betatron electromagnet.
The cavities in the poles of the electromagnet can usefully be employed for placing the fan and electronic control circuits.
It is possible to use the vacuum chamber either as a soldered chamber or with continuous pumping [6].
The article uses materials obtained in the manufacture of a 9 MeV model of a 25 MeV high-current betatron.
Fig. 1. Design of the electromagnet: 1—rack; 2—yoke; 3—central part of the pole; 4—vacuum chamber; 5—winding; 6—fan.
Main Parameters of the 9 MeV Betatron Model
- Maximum energy of accelerated electrons — 9 MeV.
- Radius of the equilibrium orbit — 6.0 cm.
- Maximum magnetic-flux density at the equilibrium orbit — 5230 G.
- Logarithmic gradient of the magnetic field — 0.6.
- Weight of the electromagnet — 140 kg.
- Overall dimensions of the electromagnet —
height — 29.6 cm.
diameter — 47.7 cm. - Power supply capacity of the installation — 5.25 kW.
- Frequency of the current feeding the electromagnet windings — 50 Hz.
- Voltage on the primary winding — 380 V.
- Voltage on the secondary winding — 3150 V.
- Capacitance of the capacitor bank — 27.7 μF.
- Calculated dose rate of bremsstrahlung radiation (at a distance of 1 m from the target) — 4.8 R/min.
At present, the 9 MeV betatron model has been manufactured and put into operation.
LITERATURE
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A. A. Vorob’ev, V. A. Moskalev, High-Current Betatron and Stereobetatron. Moscow, Atomizdat, 1961.
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V. G. Shestakov. Investigation of Electrons from the Equilibrium Orbit in High-Current Betatrons. Candidate’s dissertation. TPI, Tomsk, 1969.
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G. Reinbot. Technology and Application of Magnetic Materials. GEI, Moscow–Leningrad, 1963.
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I. Gusev, Magnetic Materials. Moscow, 1961.
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A. A. Preobrazhenskii. Magnetic Materials. Moscow, “Vysshaya shkola,” 1965.
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L. M. Anan’ev, A. V. Vorob’ev, V. I. Gorbunov. Electron Induction Accelerator—Betatron. Moscow, Gosatomizdat, 1961, p. 98.