1.4 Contents of This Book
9
the irreversibility in the flux pinning phenomena does not originate from the breaking
of time-reversal symmetry but from a special mechanism.
In Chap. 6, the longitudinal magnetic field effect is introduced as a peculiar electromagnetic phenomenon in a current-carrying superconductor in a parallel magnetic
field. It is well known that the force-free state, i.e., the state with zero Lorentz force
because the current and magnetic flux are parallel to each other, is established in
the superconductor. In this configuration of magnetic field and current, the critical
current density takes on a much larger value than in the usual transverse magnetic
field, and Josephson’s formula for electric field E = B × v does not hold, where B
and v are the magnetic flux density and velocity of the flux lines, respectively. The
flux line lattice has a characteristic distortion, i.e., the force-free strain, in the forcefree state, and it is speculated that the driving torque works on flux lines to release
the distortion in a similar way to the Lorentz force. The longitudinal magnetic field
effect is explained comprehensively from the balance between the driving torque
and the pinning torque that works to keep the distortion. The driving torque can be
derived from the energy that penetrates the superconductor when the force-free strain
is introduced. If we assume that the force-free torque does not exist, it results in a
violation of the principle of energy conservation. The important thing is that the flux
pinning plays an essential role in the longitudinal magnetic field effect. If there is no
pinning effect, the longitudinal magnetic field effect does not appear.
In Chap. 7, the essence of this book is summarized, and we look over the position
that electromagnetic phenomena in superconductors occupy in the present field of
electromagnetism. In addition, we also discuss what kind of progress is expected
in science in the future, based on the above argument. On the other hand, the most
attractive point of superconductivity is its technological applications. In this chapter
the present status and future possibility of applications in the medical, environmental,
traffic, and energy fields are briefly introduced.
Some topics are given in the “Coffee break” column at the end of each chapter.
Please enjoy it.
Coffee break (1)
Superconducting oxygen
Oxygen is a chemical element that occupies about 21% of the air on Earth. It is
also a common element of the third largest mass fraction in the universe following
hydrogen and helium. Oxygen also shows superconductivity. It is one of the most
difficult elements, however, to reach superconductivity. Oxygen is condensed to a
liquid at 90.2 K and becomes a bluish solid at 54.8 K. The crystalline oxygen has a
cubic structure and has a metallic sheen under the very high pressure of one million
atmospheres. The transition to the superconducting state is realized at the extremely
low temperature of 0.6 K under 1.25 million atmospheres.
9
the irreversibility in the flux pinning phenomena does not originate from the breaking
of time-reversal symmetry but from a special mechanism.
In Chap. 6, the longitudinal magnetic field effect is introduced as a peculiar electromagnetic phenomenon in a current-carrying superconductor in a parallel magnetic
field. It is well known that the force-free state, i.e., the state with zero Lorentz force
because the current and magnetic flux are parallel to each other, is established in
the superconductor. In this configuration of magnetic field and current, the critical
current density takes on a much larger value than in the usual transverse magnetic
field, and Josephson’s formula for electric field E = B × v does not hold, where B
and v are the magnetic flux density and velocity of the flux lines, respectively. The
flux line lattice has a characteristic distortion, i.e., the force-free strain, in the forcefree state, and it is speculated that the driving torque works on flux lines to release
the distortion in a similar way to the Lorentz force. The longitudinal magnetic field
effect is explained comprehensively from the balance between the driving torque
and the pinning torque that works to keep the distortion. The driving torque can be
derived from the energy that penetrates the superconductor when the force-free strain
is introduced. If we assume that the force-free torque does not exist, it results in a
violation of the principle of energy conservation. The important thing is that the flux
pinning plays an essential role in the longitudinal magnetic field effect. If there is no
pinning effect, the longitudinal magnetic field effect does not appear.
In Chap. 7, the essence of this book is summarized, and we look over the position
that electromagnetic phenomena in superconductors occupy in the present field of
electromagnetism. In addition, we also discuss what kind of progress is expected
in science in the future, based on the above argument. On the other hand, the most
attractive point of superconductivity is its technological applications. In this chapter
the present status and future possibility of applications in the medical, environmental,
traffic, and energy fields are briefly introduced.
Some topics are given in the “Coffee break” column at the end of each chapter.
Please enjoy it.
Coffee break (1)
Superconducting oxygen
Oxygen is a chemical element that occupies about 21% of the air on Earth. It is
also a common element of the third largest mass fraction in the universe following
hydrogen and helium. Oxygen also shows superconductivity. It is one of the most
difficult elements, however, to reach superconductivity. Oxygen is condensed to a
liquid at 90.2 K and becomes a bluish solid at 54.8 K. The crystalline oxygen has a
cubic structure and has a metallic sheen under the very high pressure of one million
atmospheres. The transition to the superconducting state is realized at the extremely
low temperature of 0.6 K under 1.25 million atmospheres.