H. Tsutsui

R." Shimada

S. "Nomura

S. Tsuji-Iio

T. Hagita

Y. Ohata

National Institute for Fusion Science (NIFS-Repository)

§ 16. Design of a 7-T Force-Balanced Hel ical Coil Nomura, S., Ohata, Y., Hagita, T., Tsutsui, H., Tsuji-Iio, S., Shimada, R. A strong electromagnetic force caused by high mag-netic fields and coil current is a serious problem in mag-netically confined fusion devices and Superconducting Magnetic Energy Storage (SMES) systems. To cope with this problem, the concept of Force-Balanced Coil (FBC) has been developed. The FBC is a helically wound hy-brid coil of toroidal field coils (TFCs) and a solenoid [1[. The FEe call minimize working stresses by selecting an optimal number of poloidal turns [2[. In order to demon-strate the feasibility of the FBC concept for high field su-perconducting magnets, a 7-T Force-Balanced Coil (7-T FBC) was designed. Fig. 1 shows a schematic illustration of the 7-T Force-Balanced Coil (7-T FBC). The darker hatch indi-cates one complete helical winding_ The outer diameter of this coil is 530 mm. This si"e was decided by the size of the available cryostat in the case of an experiment with pool boiling liquid helium cooling. The design param-eters of the 7-T FBC are summari"ed in Table 1. The winding of the FBC is 6 poloidal turns with an aspect ratio of 4. This coil is a hand-made coil using NbTi su-perconductor with a diameter of 1.17 mm. The critical current of the NhTi stra.nd is 570 A at 7 T and 4.2 K. The rated coil current of the 7-T FBC is 535 A with 6% margin of the critical current. This FBC will have 270-kJ stored magnetic energy at maximum magnetic field of 7.0 T. The winding form is made of aluminum alloy and slots are cut on its surface with the shape of the helical winding with a numerically controlled (NC) lathe. The dimension of the slots is 30 mm x 30 mm as shown in 130 mm 270mm 530mm Force-balanced coil (NbTi) Figure 1: Schematic illustration of the 7-T force-balanced coil. Table 1: Design Parameters of the 7-T Force-Balanced Coil. Major radius Ro (mm) Minor radius aD (mm) Aspect ratio a: Helical windings 200 50 4 6 poloidal turns x 3 coils Total number of poloidal turns Maximum maguetic field (T) Coil current (A) 10800 7.0 535 1.9 270 Self inductance (H) Stored magnetic energy (kJ) E E g Outer module 24 turns x 11 layer Inner module 24 turns x 14 layer Figure 2: Schematic cross section of the 7-T force-balanced coil winding. Fig. 2. The winding is composed of two winding modules with 24 turns per layer. The inner winding module with 14 layers and the outer winding module with 11 layers are connected in series. The 7- 'I' FBC is designed within an allowable coil dimension of which maximum working stress within an allowable stress of the stabilizer of the NbTi strand. Al-though this size of the coil can't be realized with toroidal field coils and a solenoid due to the induced electromag-netic forces, the 7-T FBC can be excited up to the rated magnetic field without reinforcing materials for the NbTi strand. Then the winding of the 7-T FBC will be carried out without reinforcing materials for the NbTi strand. The experiments will be conducted with pool boil-ing liquid helium cooling in order to measure the quench properties of the 7-'I' FBC and evaluate the working stresses in the helical windings. References [11 Y. Miura, M. Sakota, R. Shimada: Force-Free Coil Principle Applied to Helical Winding, IEEE Trans. Magn. 30(4) (1994) 2573-2576. [21 H. Tsutsui, S. Nomura, R. Shimada: Optimiza-tion of SMES Coil by Using Virial Theorem, IEEE Trans. Appl. Superconduct. 12(1) (2002) 800-803. 115 

Design of a 7-T Force-Balanced Helical Coil

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)