Nuclear fusion is the process by which two or more atomic nuclei join
together, or "fuse", to form a single heavier nucleus. During this
process, matter is not conserved because some of the mass of the fusing
nuclei is converted to energy which is released. The binding energy of
the resulting nucleus is greater than the binding energy of each of the
nuclei that fused to produce it. Fusion is the process that powers
active stars.
There are many experiments examining the possibility of fusion power
for electrical generation. Nuclear fusion has great potential as a
sustainable energy source. This is due to the abundance of hydrogen on
the planet and the inert nature of helium (the nucleus which would
result from the nuclear fusion of hydrogen atoms). Unfortunately, a
controlled nuclear fusion reaction has not yet been achieved, due to the
temperatures required to sustain one.
Some fusion techniques can be employed in the design of atomic weaponry
and although more generally, it is fission and not fusion, that is
associated with the making of the atomic bomb. It is worth noting that
fusion can also have a role to play in the design of the hydrogen bomb.
The fusion of two nuclei with lower masses than iron (which, along with
nickel, has the largest binding energy per nucleon) generally releases
energy, while the fusion of nuclei heavier than iron absorbs energy. The
opposite is true for the reverse process, nuclear fission. This means
that fusion generally occurs for lighter elements only, and likewise,
that fission normally occurs only for heavier elements. There are
extreme astrophysical events that can lead to short periods of fusion
with heavier nuclei. This is the process that gives rise to
nucleosynthesis, the creation of the heavy elements during events such
as supernovae.
Creating the required conditions for fusion on Earth is very difficult,
to the point that it has not been accomplished at any scale for
protium, the common light isotope of hydrogen that undergoes natural
fusion in stars. In nuclear weapons, some of the energy released by an
atomic bomb (fission bomb) is used for compressing and heating a fusion
fuel containing heavier isotopes of hydrogen, and also sometimes
lithium, to the point of "ignition". At this point, the energy released
in the fusion reactions is enough to briefly maintain the reaction.
Fusion-based nuclear power experiments attempt to create similar
conditions using far lesser means, although to date these experiments
have failed to maintain conditions needed for ignition long enough for
fusion to be a viable commercial power source.
Building upon the nuclear transmutation experiments by Ernest
Rutherford, carried out several years earlier, the laboratory fusion of
heavy hydrogen isotopes was first accomplished by Mark Oliphant in 1932.
During the remainder of that decade the steps of the main cycle of
nuclear fusion in stars were worked out by Hans Bethe. Research into
fusion for military purposes began in the early 1940s as part of the
Manhattan Project, but this was not accomplished until 1951 (see the
Greenhouse Item nuclear test), and nuclear fusion on a large scale in an
explosion was first carried out on November 1, 1952, in the Ivy Mike
hydrogen bomb test.
Research into developing controlled thermonuclear fusion for civil
purposes also began in earnest in the 1950s, and it continues to this
day. Two projects, the National Ignition Facility and ITER are in the
process of reaching breakeven after 60 years of design improvements
developed from previous experiments.
The best results were obtained with the Tokamak-type installations (see the Figure below).


ITER: the world's largest Tokamak

ITER is based on the 'tokamak' concept of magnetic confinement, in
which the plasma is contained in a doughnut-shaped vacuum vessel. The
fuel—a mixture of deuterium and tritium, two isotopes of hydrogen—is
heated to temperatures in excess of 150 million°C, forming a hot plasma.
Strong magnetic fields are used to keep the plasma away from the walls;
these are produced by superconducting coils surrounding the vessel, and
by an electrical current driven through the plasma.
The origin of the energy released in fusion of light elements is due to
an interplay of two opposing forces, the nuclear force which draws
together protons and neutrons, and the Coulomb force which causes
protons to repel each other. The protons are positively charged and
repel each other but they nonetheless stick together, portraying the
existence of another force referred to as a nuclear attraction. The
strong nuclear force, that overcomes electric repulsion in a very close
range. The effect of this force is not observed outside the nucleus.
Hence the force has a strong dependence on distance making it a short
range force. The same force also pulls the neutrons together, or
neutrons and protons together. Because the nuclear force is stronger
than the Coulomb force for atomic nuclei smaller than iron and nickel,
building up these nuclei from lighter nuclei by fusion releases the
extra energy from the net attraction of these particles. For larger
nuclei, however, no energy is released, since the nuclear force is
short-range and cannot continue to act across still larger atomic
nuclei. Thus, energy is no longer released when such nuclei are made by
fusion (instead, energy is absorbed in such processes).
Fusion reactions of light elements power the stars and produce
virtually all elements in a process called nucleosynthesis. The fusion
of lighter elements in stars releases energy (and the mass that always
accompanies it). For example, in the fusion of two hydrogen nuclei to
form helium, seven-tenths of 1 percent of the mass is carried away from
the system in the form of kinetic energy or other forms of energy (such
as electromagnetic radiation). However, the production of elements
heavier than iron absorbs energy.
Research into controlled fusion, with the aim of producing fusion power
for the production of electricity, has been conducted for over 60
years. It has been accompanied by extreme scientific and technological
difficulties, but has resulted in progress. At present, controlled
fusion reactions have been unable to produce break-even
(self-sustaining) controlled fusion reactions. Workable designs for a
reactor that theoretically will deliver ten times more fusion energy
than the amount needed to heat up plasma to required temperatures (see
ITER) were originally scheduled to be operational in 2018, however this
has been delayed and a new date has not been stated.
It takes considerable energy to force nuclei to fuse, even those of the
lightest element, hydrogen. This is because all nuclei have a positive
charge (due to their protons), and as like charges repel, nuclei
strongly resist being put too close together. Accelerated to high speeds
(that is, heated to thermonuclear temperatures), they can overcome this
electrostatic repulsion and get close enough for the attractive nuclear
force to be sufficiently strong to achieve fusion. The fusion of
lighter nuclei, which creates a heavier nucleus and often a free neutron
or proton, generally releases more energy than it takes to force the
nuclei together; this is an exothermic process that can produce
self-sustaining reactions. The US National Ignition Facility, which uses
laser-driven inertial confinement fusion, is thought to be capable of
break-even fusion.
Energy released in most nuclear reactions is much larger than in
chemical reactions, because the binding energy that holds a nucleus
together is far greater than the energy that holds electrons to a
nucleus. For example, the ionization energy gained by adding an electron
to a hydrogen nucleus is 13.6 eV—less than one-millionth of the 17 MeV
released in the deuterium–tritium (D–T) reaction shown in the diagram to
the right. Fusion reactions have an energy density many times greater
than nuclear fission; the reactions produce far greater energies per
unit of mass even though individual fission reactions are generally much
more energetic than individual fusion ones, which are themselves
millions of times more energetic than chemical reactions. Only direct
conversion of mass into energy, such as that caused by the annihilation
collision of matter and antimatter, is more energetic per unit of mass
than nuclear fusion.
A substantial energy barrier of electrostatic forces must be overcome
before fusion can occur. At large distances two naked nuclei repel one
another because of the repulsive electrostatic force between their
positively charged protons. If two nuclei can be brought close enough
together, however, the electrostatic repulsion can be overcome by the
attractive nuclear force, which is stronger at close distances.
When a nucleon such as a proton or neutron is added to a nucleus, the
nuclear force attracts it to other nucleons, but primarily to its
immediate neighbours due to the short range of the force. The nucleons
in the interior of a nucleus have more neighboring nucleons than those
on the surface. Since smaller nuclei have a larger surface
area-to-volume ratio, the binding energy per nucleon due to the nuclear
force generally increases with the size of the nucleus but approaches a
limiting value corresponding to that of a nucleus with a diameter of
about four nucleons. It is important to keep in mind that the above
picture is a toy model because nucleons are quantum objects, and so, for
example, since two neutrons in a nucleus are identical to each other,
distinguishing one from the other, such as which one is in the interior
and which is on the surface, is in fact meaningless, and the inclusion
of quantum mechanics is necessary for proper calculations.
The electrostatic force, on the other hand, is an inverse-square force,
so a proton added to a nucleus will feel an electrostatic repulsion
from all the other protons in the nucleus. The electrostatic energy per
nucleon due to the electrostatic force thus increases without limit as
nuclei get larger.
With the help of powerful lasers one can create a dense and highly
ionized plasma. We need a highly ionized dense plasma to achieve nuclear
fusion (cold or hot).
Since 1989, it talks about achieving nuclear fusion hot and cold.
Another two decades have passed and humanity still does not benefit from
nuclear fusion energy. What actually happens? Is it an unattainable
myth? It was also circulated by the media that has been achieved nuclear
fusion heat. Since 1989 there are all sorts of scientists with all
kinds of crafted devices, which declare that they can produce nuclear
power obtained by cold fusion (using cold plasma). May be that these
devices works, but their yield is probably too small, or at an enlarged
scale these give not the expected results. This is the real reason why
we can't use yet the survival fuel (the deuterium).
Unfortunately today the dominant processes that produce energy are
combustion (reaction) chemical combination of carbon with oxygen.
Thermal energy released from such reactions is conventionally valued at
about 7000 calories per gram.
Only the early 20th century physicists have succeeded in producing,
other energy than by traditional methods. Energy release per unit mass
was enormous compared with that obtained by conventional procedures. The
Kilowatt based on nuclear fission of uranium nuclei has today a
significant share in global energy balance. Unfortunately, the nuclear
power plants burn the fuel uranium, already considered conventional and
on extinct.
The current nuclear power is considered a transition way, to the energy thermonuclear, based on fusion of light nuclei.
The main particularity of synthesis reaction (fusion) is the high
prevalence of the used fuel (primary), deuterium. It can be obtained
relatively simply from ordinary water.
Deuterium was extracted from water for the first time by Harold Urey in
1931. Even at that time, small linear electrostatic accelerators, have
indicated that D-D reaction (fusion of two deuterium nuclei) is
exothermic.
Today we know that not only the first isotope of hydrogen (deuterium)
produces fusion energy, but and the second (heavy) isotope of hydrogen
(tritium) can produce energy by nuclear fusion.
The first reaction is possible between two nuclei of deuterium, from
which can be obtained, either a tritium nucleus plus a proton and
energy, or an isotope of helium with a neutron and energy.

Observations: a deuterium nucleus has a proton and a neutron; a tritium nucleus has a proton and two neutrons.
Fusion can occur between a nucleus of deuterium and one of tritium.

Another fusion reaction can be produced between a nucleus of deuterium and an isotope of helium.

For these reactions to occur, should that the deuterium nuclei have
enough kinetic energy to overcome the electrostatic forces of rejection
due to the positive tasks of protons in the nuclei.
For deuterium, for average kinetic energy are required tens of keV.
For 1 keV are needed about 10 million degrees temperature. For this
reason hot fusion requires a temperature of hundreds of millions of
degrees.
The huge temperature is done with high power lasers acting hot plasma.
Electromagnetic fields are arranged so that it can maintain hot plasma.
The best results were obtained with the Tokamak-type installations.
ITER: the world's largest Tokamak
ITER is based on the 'tokamak' concept of magnetic confinement, in
which the plasma is contained in a doughnut-shaped vacuum vessel. The
fuel—a mixture of deuterium and tritium, two isotopes of hydrogen—is
heated to temperatures in excess of 150 million°C, forming a hot plasma.
Strong magnetic fields are used to keep the plasma away from the walls;
these are produced by superconducting coils surrounding the vessel, and
by an electrical current driven through the plasma.
Deuterium fuel is delivered in heavy water, D2O.
Tritium is obtained in the laboratory by the following reaction.

Lithium, the third element in Mendeleev's table, is found in nature in sufficient quantities.
The accelerated neutrons which produce the last presented reaction with
lithium, appear from the second and the third presented reaction.
Raw materials for fusion are deuterium and lithium.
All fusion reactions shown produce finally energy and He. He is a (gas)
inert element. Because of this, fusion reaction is clean, and far
superior to nuclear fission.
Hot fusion works with very high temperatures.
In cold fusion, it must accelerate the deuterium nucleus, in linear or
circular accelerators. Final energy of accelerated deuterium nuclei
should be well calibrated for a positive final yield of fusion reactions
(more mergers, than fission).
Electromagnetic fields which maintain the plasma (cold and especially
the warm), should be and constrictors (especially at cold fusion), for
to press, and more close together the nuclei.
The potential energy with that two protons reject each other, be calculated with the following relationship.

At a keV is necessary a temperature of 10 million 0C.
At 360 keV is necessary a temperature of 3600 million 0C.
In hot fusion it need a temperature of 3600 million degrees.
Without a minimum of 3000 million degrees we can't make the hot fusion reaction, to obtain the nuclear power.
Today we have just 150 million degrees made.
To replace the lack of necessary temperature, it uses various tricks.
In cold fusion one must accelerate the deuterium nuclei at an energy of
360 [keV], and then collide them with the cold fusion fuel (heavy water
and lithium).
Because obtaining the necessary huge temperature for hot fusion is
still difficult, it is time to focus us on cold nuclear fusion.
We need to bomb the fuel with accelerated deuterium nuclei.
The fuel will be made from heavy water and lithium.
The optimal proportion of lithium will be tested.
It would be preferable to keep fuel in the plasma state.
Much success!
The Author
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