Materials processing and machine applications of bulk HTS

Abstract

We report a refrigeration system for rotating machines associated with the enhancement of the trapped magnetic flux of bulk high-temperature superconductor (HTS) field poles. A novel cryogenic system was designed and fabricated. It is composed of a low-loss rotary joint connecting the rotor and a closed-cycle thermosiphon under a GM cryocooler using a refrigerant. Condensed neon gas was adopted as a suitable cryogen for the operation of HTS rotating machines with field poles composed of RE-Ba-Cu-O family materials, where RE is a rare-earth metal. Regarding the materials processing of the bulks HTS, thanks to the addition of magnetic particles to GdBa 2 Cu 3 O 7−d (Gd123) bulk superconductors an increase of more than 20% in the trapped magnetic flux density was achieved at liquid nitrogen temperature. Field-pole Gd123 bulks up to 46 mm in diameter were synthesized with the addition of Fe-B alloy magnetic particles and assembled into the synchronous machine rotor to be tested. Successful cooling of the magnetized rotor field poles down to 35 K and low-output-power rotating operation was achieved up to 720 rpm in the test machine with eight field-pole bulks. The present results show a substantial basis for making a prototype system of rotating machinery of applied HTS bulks.

Trapped Flux and Levitation Properties of Multiseeded YBCO Bulks for HTS Magnetic Device Applications—Part II: Practical and Achievable Performance

“…Following, according to possible excitation methods for trapped-field magnet applications, we investigated the trapped-flux properties by pulsedfield magnetization (PFM) in LN2. Next, we further studied the trapped-flux capability and its relaxation properties by FCM at lower temperatures down to 30 K, which is an interesting temperature for the present HTS bulk rotating machines [15], [33]. After that, toward the levitation-device applications, we investigated the levitation performance of the multiseeded bulk samples above a permanent magnet guideway (PMG), which is involved in the HTS maglev vehicle system.…”

Relaxation Properties of the Trapped Flux of Bulk High-Temperature Superconductors at Different Magnetization Levels

“…Thus, the relaxation rate is another useful parameter to judge the saturation of the bulk magnet besides the peak trapped field. According to (4), the bulk with the saturated trapped flux also achieves the highest current density J . Before saturation, the relaxation rate of the trapped flux of bulk HTS is related to the excitation method, but at the saturation state, the relaxation rate would depend only on the critical current density J c .…”

“…Deng ( ) · K. Tsuzuki · M. Miki · B. Felder · S. Hara · M. Izumi Laboratory of Applied Physics, Department of Marine Electronics and Mechanical Engineering, Tokyo University of Marine Science and Technology, Tokyo 135-8533, Japan e-mail: zgdeng@gmail.com ing techniques have a very high current-carrying capability, typically with a critical current density J c around 10 5 A/cm 2 in self field at 77 K [1]. The large supercurrents circulating inside the bulk after excitation lead to two kinds of attractive applications: levitation force and trapped flux, which have been widely applied to the fields of magnetic levitation systems [2,3], electrical machines [4,5], strong magnetic field generators [6], and so on. However, both the macroscopic magnetic force and magnetic flux in operation observe a decay in time, resulting from the associated decay of supercurrents.…”

Improvement of Critical Current Density and Flux Trapping in Bulk High-Tc Superconductors

“…magnetization using a homemade large dc current source. A large pulsed current is momentary applied to armature copper windings by which a pulsed magnetic field is formed and applied to the bulk field poles [60][61][62][63]. Figure 14.…”