To create an eternal energy source on the Earth. Does it sound like utopian idea? It is not so.

Nuclear fusion shall allow to obtain the so-called free energy just from the water, at this the production waste will be absolutely safe hydrogen and helium.

And this process is not a human invention. The universe actively and globally uses fusion reactors. The nearest to us fusion reactor is the Sun.

The main problem is that scientists have not yet been able to create such fusion reactor for the energy released as a result of fusion reaction to exceed the energy required for the reaction itself.

 From the physics: what is nuclear fusion?

Before proceeding to the main part of our material and understanding why there is so much talks about nuclear fusion, let us refresh in memory the lessons on physics for the 11th form, but if there is nothing to refresh (it happens) then read on.

We already know how the humanity receives the energy by means of controlled nuclear reaction. Currently operated nuclear reactors use nuclear fission during which the atomic nuclei are split into 2 or 3 smaller nuclei. On the contrary, nuclear fusion does envisage the fission but the union of atoms. In other words, nuclear fusion envisages receiving of heavy nuclei from lighter ones.

How does it work?

Atomic nuclei consist of two types of nucleons — protons and neutrons. They are bound together by the so-called strong interaction force. At the same time, binding force of each nucleon depends on the total number of nucleons in the nucleus. In light nuclei one can observe the increase of binding energy with the number of nucleons and in heavy nuclei – the decrease. If nucleons are bind to light nuclei or split from heavy atoms, the binding energy difference shall be denoted as the difference between reaction energy and kinetic energy of released particles.

Change of nucleus structure is called nuclear transformation or nuclear reaction. Nuclear reaction with the increase of a number of nucleons in the nucleus is called nuclear reaction or nuclear fusion. Controlled nuclear fusion process is based on fusion of light atomic nuclei to form heavier nuclei with energy release.

Nuclear fusion for deuterium and tritium

Nucleus protons have electric charge which means that they undergo coulomb repulsion. In the nucleus this repulsion is compensated by strong interaction that holds the nucleons together. But strong interaction range is much less than of coulomb repulsion. That is why, to combine two nuclei into one they must first be brought close enough together to overcome the coulomb repulsion. Several methods are known: in stellar interior — gravitational forces, in accelerators — kinetic energy of accelerated nuclei or elementary particles, in nuclear reactors and nuclear weapon — thermal motion energy of nuclei.

A little bit of history

In compliance with abovementioned data, fusion is not a human invention. In 1934 George Gamow, Ukrainian-born American physicist, observing the sky of stars proposed a hypothesis that burning of stars takes place due nuclear fusion reactions inside them.

His assumption was developed four years later by Hans Bethe, American nuclear physicist. Bethe assumed that in the center of the Sun the hydrogen nuclei collide transforming into isotopes and then into other elements. The difference between their mass numbers lights up the stella body.

In the 1940s, one of the participants of the Manhattan Project (development of nuclear weapon) proposed to the colleagues to create not fission but fusion bomb (hydrogen bomb).

Stanislaw Ulam, mathematician, described possible fusion algorithm and started the research. In 1951, six years after nuclear testing, the United States conducted preliminary and a year later — full-scale testing of fusion charge. It consisted of liquid hydrogen isotopes which were replaced by a mixture of 40% lithium deuteride and 60% lithium deuteride-7 to increase power.

Soviet physicist Oleg Lavrentiev purposed the idea to use nuclear fusion for industrial purposes. Soon enough, simultaneously with the Americans, Igor Tamm and Andriy Sakharov revised Lavrentiev’s concept and proposed to confine plasma in copper doughnut–shaped (toroidal) vacuum chamber (so called tokamak) isolated with magnetic plates. That is how appeared the idea of tokamak facility constructed in 1954. By the way, the first fusion reactor — stellarator was constructed in 1951 by Lyman Spitzer, astrophysicist, in the framework of implementation of secret Matterhorn Project.

However, tokamak technology is currently considered to be the most advanced since we have accumulated great knowledge about it. That is why, it was chosen as the basis for the design of the  International Thermonuclear Experimental Reactor (ITER) but we shall talk about this later.

Formally, stellarators are considered to be more advanced in comparison to tokamaks. There are several reasons for this. First, in stellarators the plasma is heated up and confined only by external currents and coils. In tokamaks heating takes place due to electric current in plasma which, at the same time, creates additional magnetic field. Due to this, free electrons and ions with their own magnetic fields, which seek to destroy the main field and decrease the temperature and spoil everything at all, appear in the doughnut-shaped tokamak.

Second, stellarator chambers are not just doughnut-shaped but they have the form of flat doughnut: unlike tokamaks they do not have azimuthal symmetry. At the same time, flat doughnut-shaped coils of stellarators have helical form (tokamaks` coils are straight and parallel to each other), they spin the filed lines, in other words, cause rotational transformation. It also stabilizes plasma and shifts theoretical limit for optimal pressure inside the chamber. The higher is the pressure, the faster is the reaction.

Comparison of the tokamak structure (at the left) and the stellarator (at the right)

The Sun but on the Earth

In the south of France, near Aix-en-Provence city, 35 countries collaborate for construction of the International Thermonuclear Experimental Reactor (ITER). The button enabling the device which weight makes 23 thousand tons shall be pushed in 5 years. The construction of the world’s first fusion reactor lasts for more than 30 years.

“Our device is like the Sun but on the Earth” that is how the developers describe their project.

Construction. ITER image

ITER is the first-of-its-kind machine and unique scientific device. This is the final experiment to prove that humanity has technology, materials and knowledge to take the next step and build fusion power plant.

Project implementation started in November 1985 at the Geneva Summit when Mykhaylo Gorbachev, USSR General Secretary, proposed to Ronald Reagan, President of the United States of America, the idea of implementation of joint international project related to the development of fusion energy for peaceful purposes.

Negotiations lasted for a year and then an agreement was reached, European Union (Euratom), Japan, Soviet Union and the United States joined the project. The conceptual design development started in 1988 and then was followed by technical design development. In 2001, member states approved the final ITER project.

In 2003, People’s Republic of China, Republic of Korea and then India joined the project. The site selection for ITER construction was also a long-term process which terminated in 2005.

In compliance with the abovementioned data, ITER design is based on tokamak. This technology was chosen entirely due to the collected knowledge on tokamak.

There is a verity of fusion technologies such as stellarators (Wendelstein-7X), laser induced synthesis (Laser Megajoule і National Ignition Facility), proton-boron fusion (Tri-Alpha energy), etc. But scientific community believes that tokamak concept is the best way to achieve pure fusion energy.

Tokomak sectional drawing

Safety is perhaps the most important advantage of fusion reactor. And as it was explained earlier, uncontrolled chain reaction that causes core melting is impossible in ITER. After all, it is very difficult to create fusion reaction and sustain it. But whatever happens, in case when heating, cooling or fuel supply is out of control, the heat inside the vacuum chamber will disappear naturally. It’s almost like a gas jet goes out when you cut off the gas supply. The nuclear fusion process is safe by its nature. There is no gas explosion or gas escape hazard.

Preliminary safety analysis report of ITER contains the analysis of the risks and events that can cause site accidents. During normal operation, ITER radiological impact on the most at-risk population groups is thousand times less than impact of natural background radiation. And at worst-case scenarios, such as fire at tritium plant, evacuation or other population protective measures shall not be necessary.

And now, let us discredit the myth of free energy. Fusion energy shall never be for free. It is called free because it is clean and safe for future generations.

ITER shall produce 500 MW of fusion power. This amount is enough to study plasma combustion, a state which has never been achieved before on Earth in controlled environment.

It is expected that commercial fusion reactor power will exceed 500 MW for more than 10-15 times. For example, 2000 MW fusion power plant will be able to supply electricity to 2 million buildings. The scientists predict that industrial fusion plants may be commissioned in 2040. The exact date depends on public demand level and political will manifested in financial investment since it is not to come cheap.

The initial cost of 2000 MW fusion power plant is about $ 10 billion. These capital expenses are reimbursed by extremely low maintenance and fuel costs and rare component replacement during facility 60-year lifetime.

It should be noted that ITER is an experimental facility it is not designed to generate electricity. All the produced energy shall be converted into steam and released through the cooling towers.

And what about Ukraine?

Taras Shevchenko National University of Kyiv, Kyiv Institute of Physics and Kharkov Institute of Physics and Technology as well as some private laboratories study nuclear fusion in Ukraine. Although Ukraine is not a member of ITER international project, our physicists also participate in this project by means of cooperation with European experts. Such cooperation became possible due to the fact that since 2017 Ukraine is a full member of the European Physical Society for fusion research.

In his interview Anatoly Zagorodny, Ukrainian physicist, President of the National Academy of Sciences of Ukraine, said the following about ITER: “Among the wide range of tasks the issue, which relates to the improvement of the strength of the reactor internal wall contacting with thick and hot plasma, is of top importance for the increase of reactor power. Ukrainian physicists actively participate in corresponding research. Other tasks that our scientists are working at are improvement of diagnostics and development of theoretical models of plasma processes. The construction of commercial fusion reactor turned out to be much more complicated task than it seemed at first. However, the most of the way has been covered, this project shall bring us closer to new more powerful and environmentally safe source of energy”.

ITER official information was used at preparation of this material.