This paper discusses biomagnetic effects and their possible applications that are unfamiliar to cryogenic and superconducting engineers. Biomagnetism is exotic applied magnetics and a transdisciplinary research target. There are two types of research methodology, physical and epidemiological. They are quite different. Both methodologies should be harmonized. The author proposes how to work in this transdisciplinary field. Finally, suggestions of guidelines for studing exotic phenomena are presented.
The cylindrical bulk current lead was fabricated using Pb-free Bi system superconductors in a solid-state reaction. The current lead attained a high transport critical-current density (Jc) of about 320A/cm2 at 77K, 0T and more than 1, 200A/cm2 at 40K, 2T. The Pb-free current lead was composed of both Bi-2223 and Bi-2212 phases judging from the AC susceptibility curve and X-ray diffraction pattern. The heat leakage and mechanical strength of the Pb-free cylindrical bulk current lead were approximately similar to those of a Pb-dope current lead consisting of the Bi-2223 phase only. The Pb-free bulk lead particularly showed a high Jc property at low temperatures and high magnetic field. The Pb-free current lead had the characteristics of both Bi-2212 and Bi-2223 phases. The application of the bulk current lead for a cryocooled superconducting magnet was investigated.
An austenitic steel used as a structural material of a superconducting magnet shows creep deformation and stress relaxation even at medium and low temperatures. Small plastic and creep strains in eight austenitic steels and a low-alloy steel were measured in a temperature range from 4 to 573K. Every steel including the low-alloy steel showed logarithmic creep strain at temperatures when stress was high enough to produce plastic strain. Although the creep strain rate in SUS316L at 293K was proportional to about the 7th power of stress when it was around 0.2% plastic-offset stress, the order of power decreased to 1 under lower stresses. The ratio of creep strain at 105s and plastic strain was 1-3 at 293K and 0.5-2 at 77K for the steels, though precipitate-hardened steel SUH660 showed a lower value. When creep strain at 105s in the steels was 0.02% at 77K, the stress levels were from 0.7 to 0.85 of 0.2% plastic-offset stress. Because creep strains were small compared to plastic strains at lower and higher temperatures, the ratios of 0.02% proof stresses for 105s creep and plastic strains were as high as 1.5 both at 4 and 573K. They were steadily lower values, 0.9-1.0, between 77 and 450K. Creep deformation in a component can be prevented by pre-straining with a plastic pre-strain larger than an estimated inelastic (plastic+creep) strain during operation. The pre-straining effect holds even when operation and pre-straining temperatures are different.