（様式 ３）

学氏名

高橋位論

文要旨圭太論 文 名Realization of superconducting bulk magnets with higher magnetic field gradient to provide a quasi-zero gravity space onearth
学位論文要旨Bulk superconductors such as (RE)BaCuO (RE: rare earth elements or Y) can be utilized as a so-called trapped fieldmagnets (TFM) that can “trap” the magnetic fields over several Tesla by exploiting the flux pinning effect of Type-Ⅱ
superconductors. The trapped field can be sustained inside the bulk with its induced supercurrent quasi-permanently once it
is magnetized and kept at a constant temperature; hence, can replace conventional magnets as a compact and strong magnet
for potential applications. It is noteworthy that there is a limit in the trapped field enhancement according to the tripartite
relation between Electromagnetic field, Temperature, and Mechanical stress as the brittle ceramic nature. For more practicaldesign, it is also desirable for the magnetic source to provide such a strong magnetic field even in an open space outside thevacuum chamber other than to be lightweight and mobile as a desktop-type apparatus. In this sense, the author newly
developed two hybrid-type TFMs called as a hybrid TFM lens (HTFML) which can generate a concentrated field higher than
the trapped field, and a high gradient-type TFM (HG-TFM) which can provide a higher magnetic force with its refined field
gradient product, Bz·dBz/dz. Including the introduction in chapter 1 and the conclusion in the last chapter 8, this Ph.D thesis
summarizes six papers published since 2018 to 2021, relating to the development of the HTFML in chapter 2 to chapter 5, its
applicational aspect for the magnetic separation in chapter 6, and another new concept of the HG-TFM in chapter 7. The
concepts of such hybrid-type TFMs were first considered using a numerical simulation in an efficient way, and then theexperimental validation was performed.
In chapters 4 and 5, the HTFML was validated experimentally. This exploits the “vortex pinning effect” of an outer bulk
cylinder and the “diamagnetic shielding effect” of an inner bulk magnetic lens to generate a concentrated magnetic field higher
than the trapped field from the outer TFM. This requires that, during the magnetizing process, the outer TFM cylinder is in thenormal state (T > superconducting transition temperature, Tc) and the inner magnetic lens is in the superconducting state (T <Tc) when the external magnetizing field is applied, followed by cooling to an appropriate operating temperature, then removing
the external field. This is explored for two potential cases: 1) exploiting the difference in Tc of two different bulk materials(“case-1”), e.g., MgB2 (Tc = 39 K) and GdBaCuO (Tc = 92 K) or 2) using the same material for the whole HTFML, e.g.,
GdBaCuO, but utilizing the same cryostat with different cooling loops that keep the outer bulk cylinder at a temperature above
Tc. As a result, the HTFML could reliably generate a concentrated magnetic field Bc = 3.55 T with an external magnetizing
field Bapp = 2 T in the “case-1”, and a higher Bc = 9.8 T with higher Bapp = 7 T in the “case-2,” respectively. Theseexperimental results were consistent well with the numerical estimation results in chapter 2 and 3.
In chapter 6, it was predicted by numerical simulation that the HTFML device after the magnetization process with anapplied field, Bapp = 10 T, can generate the maximum of Bc = 11.4 T, as well as an ultra-high Bz·dBz/dz over 3000 T2/m, which
can fulfill the requirement of the magnetic levitation of water drop as high as 1400 T2/m.
In chapter 7, state-of-the-art numerical simulations were used to investigate the magnetic properties of the proposed HGTFM in detail. In the modelling, slit ring bulks (slit-TFMs) are tightly stacked with TFM cylinders (full-TFMs), which isuseful to improve the magnetic field gradient with its inverse field through the slits. A maximum Bz·dBz/dz = 6040 T2/m waspredicted even by using the simpler conventional field-cooled magnetization (FCM) with Bapp = 10 T at 40 K, which should be
the highest value ever reported compared to any other magnetic sources. The HG-TFM has an advantage on the versatility,e.g., a wider open space and its simple operation at one constant temperature.
These devices deserve to be unique that its superior magnetic properties and the versatility come from the refinement of
the magnetizing method in contrast to conventional approaches that depend on the superconducting properties of the bulk
itself. Now, since the prototype can be installed even in a laboratory scale and can provide the quasi-zero gravity space in an
open space inside/outside the vacuum chamber, further applicational studies would be explored in a more practical setup
towards the new industrial application such as protein crystallization and cell culture.