الانصهار المتحكم به - الطاقة النووية .. الفيزياء

Controlled Fusion - Nuclear Energy .. Physics

Controlled Fusion

Despite the intensity of research conducted all over the world, man has not yet succeeded, to this day, in harnessing nuclear reactions (or thermonuclear reactions as they are sometimes called) for peaceful purposes. There are three main problems that still stand in the way of this path: reaching the ignition temperature, confining the reaction to a container (because all known materials evaporate at a few thousand degrees Celsius) and recovering the energy resulting from the reaction.

In 1963, scientists reached the ignition temperature necessary to fuse deuterium with trithium inside a special tube for a very short period (3 microseconds). This was done by passing a strong electrical pulse through a gas mixture at low pressure, which led to the creation of a magnetic field that was so strong that it prevented the plasma particles from touching the walls of the tube due to the field's ability to move the charged particles in spiral lines surrounding the coffee lines and converging as the field itself increases in intensity. Therefore, the particles can only move.

(Above) A schematic diagram of a fusion reactor.
(Middle) The three mediators in a fusion reaction.
(Bottom) Plasma confinement.

Plasma confinement in a baseball bat (left) and a magnetic confinement tube surrounded by magnetic mirrors (right).

Between the top and bottom of the tube, it cannot pass through at all. This contraction of the plasma by the magnetic field is called the disc effect and practically solves the problem of confining the reaction to a relatively small space. Unfortunately, the confined plasma is not stable, even for a short time, because it twists and is prone to contact with the walls of the tube. Therefore, most current research on fusion is directed towards designing devices that will make the magnetically confined plasma able to remain in a stable state long enough to extract the energy produced by the reaction itself.

The pulse required to create the plasma and raise its temperature to the ignition point requires a large amount of energy. In order for the reaction to produce a surplus of energy, the plasma must be confined for a period of time not exceeding a certain minimum that corresponds to a certain temperature and a certain density of matter. Lawson found that the product of the time of confinement of the plasma in the deuterium-trithium reaction by its density must be at least 1410 s × particles per cm3, for the substance to reach a state of decomposition in which the amount of thermal energy produced is sufficient to provide the pulse with the energy it needs. The drawing shows Lawson's criterion as a plane drawn over a variable temperature range ranging from the ignition temperature to 5 × 810 degrees.

So far, no device has been able to reach this plane, despite the possibility of achieving two of the three conditions of fusion (temperature, density, confinement time) separately.

Scientists have been able to reach a higher state of stability in some devices by introducing additional forms of electric current to the tube. The first device used for this purpose was composed of straight rods called Ioff rods, after their Russian inventor Ioff.

There are other forms that were used to create a magnetic well by means of rods similar to the grip of a baseball, which were later named after them.

It is worth noting that all research related to the designs of future fusion reactors was carried out with great enthusiasm, the aim of which was to investigate the best means of controlling this energy. The simplest model of these reactors is the reactor that uses the deuterium-tritium reaction and gives 80% of its energy in the form of fast neutrons. In this type, the coolant lithium liquid surrounding the reactor tube absorbs the energy of the neutrons. It is known that the possibility of using neutrons to produce fissionable fuel from 238 U is one of the advantages of this method.

As for fusion reactions that give most of their energy in the form of charged particles, such as the deuterium-tritium reaction, kinetic energy is converted into electrical energy in a direct manner. This is achieved by collecting particles on alternating charge paths to which appropriate voltages are applied, which increases the value of the energy conversion, which sometimes reaches 90%.

(A fusion reactor is used to generate electricity directly from the collection of charged particles).