The indomitable plasma is ITER

Since the time of Soviet childhood, I have learned that a controlled thermonuclear synthesis will solve the energy problems of mankind. Thermonuclear energy will be cheap and environmentally friendly, you only need to overcome a number of technical problems. Overcoming, however, dragged on for more than half a century, and still there. Along the way, it turned out that the controlled thermal unit is not the most effective energy production technology [1]. It is unlikely to become profitable. Unless the cost of other energy sources will go off the way.

Nevertheless, it is important for scientists in practice to show that the thermonuclear reactor can produce more energy than to spend. That is why the international community in 2006 decided to build the largest ITER research reactor in the south of France, in Kadarash. This is a very expensive long -term project. Its budget is about $ 20 billion, and the first plasma will be received in 2025. Now there is a manufacture and installation of parts of the Tokamak, a vacuum camera is ready. And scientists are still looking for solutions to problems, without which the project will not completely take place. They were discussed at the 43rd conference on plasma physics, held in July in Belgium under the auspices of the European Physical Society [2].

Plasma breakdown

ITER is a large toroidal chamber where gaseous fuel enters - a mixture of deater with tritium. The fuel is heated to the ionization temperature with a gas discharge, and it turns into plasma. Then the plasma is heated to a high temperature, and a thermonuclear reaction begins. The fast neutrons resulting from the reaction freely leave the plasma and fall into special modules (forms) located on the walls of the chamber, in which water circulates. In the thick layer of water, neutrons are inhibited and heat it. This hot water serves as a source of energy. TEP and nuclear power plants also work - they also heat the water.

The problem of Tokamaks is that the plasma processes are not yet fully controlled. The most dangerous thing is when the plasma is suddenly cooled and touches the wall of the reactor. This is the so -called breakdown. The breakdown of the plasma threatens to stop the reactor for several months and large financial expenses.

In Tokamak, plasma will heat up to 100 million ° C. This is several times greater than the temperature in the sun. And the higher the temperature, the higher the rate of particles in the plasma. Moreover, there are always particles that move at speeds an order of magnitude higher than the average speed. The clashes of these fast particles with others due to their speed do not last long, and energy is transmitted ineffectively. During the breakdown, that is, the sharp cooling of the plasma, its conductivity falls, and the ring current of the plasma also seeks to decrease, but due to a large amount of iron around, induced currents occur in different parts of the installation. They induce a vortex electric field, preventing a decrease in plasma current. This vortex field is much more powerful than the constant electric plasma field. Thanks to the vortex field, fast electrons accelerate to sub -light speeds and can transfer the most plasma current. They are called - running electrons. If they get on the wall of the reactor, then they will instantly burn it. In addition, the part of the plasma current transferred to them will subside too quickly, which will cause mechanical overloads in the elements of the Tokamak that can destroy it. And the repair of the blanket and cameras is a long and expensive.

In principle, physicists can predict plasma breakdowns and take some measures, but what to do with running electrons is still unclear. It is apparently impossible to prevent their appearance. Is it possible to prevent their contact with the wall? One of the proposals is to use the reactor windings in order to hold the current of running electrons until it himself fades. But, according to estimates, the possibilities of windings may not be enough for this. Another option is to put inert gas, argon or neon into the camera to slow down the runaway electrons. However, gas, meeting with plasma, does not penetrate into it well and may not reach the runaway electrons. In any case, the problem of disruption of plasma has to be solved in the course of the construction of ITER.

Problem tritius

Another problem is where to get tritius for fuel. Now it is being developed in ordinary nuclear reactors or damping reactors. Only a few kilograms of tritium in the world are produced per year. Due to the small period of half-life, the storage of tritium is difficult-the reserves quickly decrease naturally.

In the first stages, ITER will work without tritium and a thermonuclear reaction. Experiments will begin with hydrogen, then go to deeria, and after a few years, if there are no emergency situations, they will add tritius. It will allow a thermonuclear reaction and getting more energy than it is spent on plasma heating.

It is unprofitable to develop and store tritius. Scientists think about the way to obtain it inside the reactor. Tritius is formed in reactions with the participation of a lithium isotope. If you place lithiums on the first wall of the camera, then proton and neutrons flying from plasma will react with it and produce the right amount of tritium. To launch ITER, you will need about 3 kg of tritius.

It is much easier to develop lithium, since its main source is sea water. You can put installations on the ocean and produce lithiums there. Again, deores can be extracted from sea water. The question in this case is the price of such a technology.

Suppose a problem with tritius solved. Further, in a thermonuclear reaction, deer-tri-trious fuel is burned out with the formation of helium. Helium accumulates in the center of plasma. In ITER, the discharge for plasma ignition will last only 300 seconds. You can roughly compare the operation of the installation with a kettle that boiled water and turned off. That is, until Tokamak has switched to work in stationary mode, the accumulation of helium in plasma does not represent a problem. Otherwise, helium will have to be removed from plasma.

The Helia charge is equal to two, which means that it radiates more than hydrogen, that is, additionally cools the plasma. In addition, due to helium, plasma pressure is growing, therefore, the fuel supply will have to be limited. In the end, helium will completely displace the fuel from the chamber, then the thermonuclear reaction will fade. In order to prevent this, scientists came up with special lodges of helium and impurities of other particles - saboteurs. They will be placed on the wall of the reactor so that the particles knocked out of the wall fly there before getting into plasma, as well as the nucleus of helium from the plasma itself.

Due to tritius, another problem arises-the induced radioactivity of the reactor wall. Tritius is well captured by a solid substance. It will clog into the wall of the camera, also worsening its strength and thermal conductivity, reassign in the cracks and gaps. Radioactivity will increase, and during a Tokamak stop, a person will no longer be able to go inside the camera to repair something. It will be necessary to either use robots-manipulators, or invent a way to knock tritius from the wall-this process is called air conditioning. For example, light a smoldering discharge next to the wall that would heat it and release tritius. And the vacuum pump would pump it near the wall.

Radioactivity in Tokamak will also be subject to neutrons during fuel burning. They react with the nuclei of the elements that make up the wall of the blanket, as a result of which radioactive isotopes are formed. The radioactivity in Tokamak, of course, will not be comparable to the one that exists in the active zone of nuclear power plants, but is still significant for the maintenance personnel. In any case, if we want ITR to work with tritium, we need to solve the problem of its synthesis and air conditioning.

And there, you see, it is time to build the industrial Tokamak DEMO, which works on a continuous category. Its implementation is assigned to the 2040s [3].

Tatyana Pichugina

1. Dmitry Dyakonov . There will be no “pure” thermonuclear energy // TRV-hunger, No. 38 of September 29, 2009.

2. Https://kuleuvencongres.be/eps2016

3. Http://scientification.ru/articles/megaproekt-veka-eto-tolko-nachalo