High temperature superconductivity

General scientific debates. Presentations of new technologies (not directly related to renewable energies or biofuels or other themes developed in other sub-sectors) forums).
actinium89
I learn econologic
I learn econologic
posts: 24
Registration: 02/10/17, 12:39
x 2

High temperature superconductivity




by actinium89 » 10/10/17, 16:50

In 1956, Leon Cooper showed that a very weak attraction between the electrons in a metal can create a stable state of pairs of electrons whose energy is lower than the energy of Fermi (corresponding to the minimum energy of the electrons conduction in a metal).

Although Cooper pairing is a phenomenon of quantum origin, it can also be explained in a simplified manner in the context of classical mechanics.
An electron in a metal behaves like a free particle (free electron gas). It is repelled by other electrons due to its negative charge, but it is attracted to the positive ions constituting the rigid crystal network of the metal.
This attraction creates vibrations in the network of positive ions (associated with quanta of energy called phonons) which slightly move the ions towards the electrons (electron-phonon interactions), thus increasing the local density of positive charge of the ions, attracting other electrons.
At long distance, this interaction between electrons due to the displaced ions can overcome the electronic repulsion, and allow them to pair.

The energy of the pairing interaction is quite low, of the order of 0.001 eV, and the thermal energy can therefore easily lead to the separation of the pairs, which implies that the system is cooled to very low temperature ( below -200 ° C).
The electrons of a pair are not necessarily spatially close; since the interaction is long-range, the paired electrons can be several hundred nanometers (billionths of a meter) apart.
Since the distance is usually greater than the average inter-electronic distance, a large number of Cooper pairs can occupy the same space without violating the Pauli exclusion principle.
Since the electrons have a spin of 1/2, the Cooper pairs therefore constitute composite bosons whose total spin has an integer value: 0 (anti-parallel spins) or 1 (parallel spins).
The property of bosons to condense in the same fundamental quantum state (Bose-Einstein condensation) is responsible for the specific properties characterizing superconductivity: zero internal magnetic field and electrical resistance.

The electrical resistance of a metal can be explained by the collisions that the conduction electrons undergo with the metal ions when crossing the conductor under the action of a potential difference.
The more regular the crystal lattice, the less resistance there is to the passage of an electric current.
The electrical resistance therefore increases with the temperature which causes random vibrations of the crystal lattice (increasing the risk of collision of an electron with an ion) and depends on the presence of impurities in the metal.

To obtain superconductivity at high temperature, it would therefore be necessary to increase the interaction energy of the pairs of electrons to increase their stability with temperature.

The pairing energy being linked to the attraction of the electron with the charge density of the ions of the crystal lattice, if one increases the amplitude of the oscillations of charge of the ions, one reinforces the attraction of the pairs of electrons (by increasing the local density of positive charge of the ions).

One solution could be to use a pulsating direct electric current in a magnetostrictive material at resonance, which would make it possible to obtain synchronized charge oscillations (interacting weakly with the pairs of electrons and therefore with less electrical resistance) of great amplitude capable of producing a maximum attraction effect of the pairs of electrons (which would move coherently) with the crystal lattice.

The problem is that at the same time, the magnetostrictive effect increases the heat dissipation.

To solve the problem, the system would have to be able to absorb the excess heat produced by reducing its overall energy and its entropy.

One can also imagine the existence of other superconduction mechanisms involving, for example, spin-phonon interactions to reduce electronic repulsion.
0 x
izentrop
Econologue expert
Econologue expert
posts: 13644
Registration: 17/03/14, 23:42
Location: picardie
x 1502
Contact :

Re: High temperature superconductivity




by izentrop » 10/10/17, 20:24

Hello,
High temperatures, it's - 165 ° and it tramples http://www.supraconductivite.fr/fr/inde ... -materiaux

I do not think that one day we arrive at superconductivity at room temperature, because we never had anything without nothing.

The energy it takes to operate the LHC is staggering, for example : Shock: https://home.cern/fr/about/engineering/ ... erformance
0 x
actinium89
I learn econologic
I learn econologic
posts: 24
Registration: 02/10/17, 12:39
x 2

Re: High temperature superconductivity




by actinium89 » 11/10/17, 00:01

Indeed, unless new materials with revolutionary properties are discovered, it is to be feared that there is still a long way to go to reach superconductivity at ambient temperature.

CERN, with a gigantic magnet generating a magnetic field of more than 16 teslas, intended to equip its future accelerators, holds the power record for superconductive dipole magnets (cf. https://home.cern/fr/about/updates/2015/11/test-racetrack-dipole-magnet-produces-record-16-tesla-field)

Superconducting at room temperature would make it possible to store larger quantities of electricity in light superconducting rings with a small footprint and thus replace the heavy batteries with low autonomy which equip current electric vehicles. But one problem remains: that of recharging the batteries. It is difficult to see how the current electrical network could cope with consumption peaks when, between 18 p.m. and 20 p.m., people who return from work, would all plug their electric vehicle into their personal charging station.
Should we build new nuclear power plants, considerably increase the capacity of wind farms and photovoltaics?
The democratization of electric vehicles, advocated by many to solve the problems of air pollution, is it likely to pose problems for the energy transition?
0 x
izentrop
Econologue expert
Econologue expert
posts: 13644
Registration: 17/03/14, 23:42
Location: picardie
x 1502
Contact :

Re: High temperature superconductivity




by izentrop » 11/10/17, 08:26

actinium89 wrote: It is difficult to see how the current electrical network could cope with consumption peaks when, between 18 p.m. and 20 p.m., people who return from work, would all plug their electric vehicle into their personal charging station.
It is no longer the same subject.

It is not insurmountable ... If at the same time the photovoltaic goes up in power, it will be necessary adapted incentive tariffs and charging stations near the work places.
0 x

Back to "Science and Technology"

Who is online ?

Users browsing this forum : No registered users and 105 guests