Development of Prototype MGB ₂ Superconducting Solenoid Magnet for High-Efficiency Klystron Applications

Abstract

A wind-and-react MgB2 solenoid magnet for klystrons has been developed. While the current normal-conducting (Cu) magnet consumes 20 kW per magnet, this MgB2 magnet consumes less than 3 kW in refrigerator power. The conduction-cooled half coil of the magnet is 337 mm in inner diameter; the winding pack, 19.4 mm wide × 136.6 mm high, uses 2.7 km of 10 filament circular conductor, which is insulated with glass 0.83 mm in diameter, and is reacted after being wound onto a stainless steel bobbin. The coil has Cu plates of 0.2 mm in thickness between each coil layer and on the inner and outer sides. The magnet has two coils and produces 0.8 T in the center and its stored energy is 11.8 kJ. Together with the above-mentioned coil structure, these coils can consume stored energy in itself at quench without a special quench protection system. A performance test of the magnet was successful.

Performance of MgB2 Superconductor Developed for High-Efficiency Klystron Applications

“…The method of measuring T cs is written in the reference [11] and can be summarized as follows. First, achieve a steady state by bringing the coil winding to a certain temperature at a certain operating current I op .…”

“…The inner diameter of the coil: 337 mm; the coil length: 136.6 mm; the number of turns in a coil: 2432, and the number of coils: 2. Details of these specifications are also written in reference [11].…”

“…According to the design of the klystron magnet using Wire-C and Wire-D, the rated operational current is 57.1 A, and the maximum magnetic field of the coil winding is 1.06 T [11]. Fig.…”

“…7, there is a 9 K or larger temperature margin at the rated I op = 57.1 A, if the magnet is operated at 20 K as the temperature of the coil winding. According to the results of the quench tests, this temperature margin may be reduced [11]. Therefore, the magnet can be used at higher operational temperature, e.g., 25 K.…”

“…In the design of the MgB 2 prototype solenoid magnet, to achieve high efficiency, it is important to reduce heat penetration from room temperature to low temperature (superconducting coils) and to make the current leads of the magnet finer [11]. We chose the outer diameter of the MgB 2 wire to be 0.67 mm, thinking about workability of the coil winding.…”