Thermonuclear Power Energy
In nuclear physics and nuclear chemistry, nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus.
It is accompanied by the release or absorption of energy, which allows matter to enter a plasma state.
The fusion of two nuclei with lower mass 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; vice-versa for the reverse process, nuclear fission.
In the simplest case of hydrogen fusion, two protons have to be brought close enough for their mutual electric repulsion to be overcome by the nuclear force and the subsequent release of energy.
Nuclear fusion occurs naturally in stars.
Artificial fusion in human enterprises has also been achieved, although has not yet been completely controlled.
Building upon the nuclear transmutation experiments of Ernest Rutherford done a few years earlier, fusion of light nuclei (hydrogen isotopes) was first observed by Mark Oliphant in 1932; the steps of the main cycle of nuclear fusion in stars were subsequently worked out by Hans Bethe throughout the remainder of that decade.
Research into fusion for military purposes began in the early 1940s as part of the Manhattan Project, but was not successful until 1952.
Research into controlled fusion for civilian purposes began in the 1950s, and continues to this day.
Fusion reactions power the stars and produce all but the lightest elements in a process called nucleosynthesis.
Although the fusion of lighter elements in stars releases energy, production of the heavier elements absorbs energy.
When the fusion reaction is a sustained uncontrolled chain, it can result in a thermonuclear explosion, such as that generated by a hydrogen bomb.
Reactions which are not self-sustaining can still release considerable energy, as well as large numbers of neutrons.
Research into controlled fusion, with the aim of producing fusion power for the production of electricity, has been conducted for over 50 years.
It has been accompanied by extreme scientific and technological difficulties, but has resulted in progress.
At present, break-even (self-sustaining) controlled fusion reactions have not been demonstrated in the few tokamak-type reactors around the world.
Workable designs for a reactor which will theoretically deliver ten times more fusion energy than the amount needed to heat up plasma to required temperatures (see ITER) are scheduled to be operational in 2018.
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 electromagnetic 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 a free neutron, generally releases more energy than it takes to force the nuclei together; this is an exothermic process that can produce self-sustaining reactions.
The energy released in most nuclear reactions is much larger than that in chemical reactions, because the binding energy that holds a nucleus together is far greater than the energy that holds electrons to a nucleus.
Fusion reactions have an energy density many times greater than nuclear fission; i.e., 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 collision of matter and antimatter, is more energetic per unit of mass than nuclear fusion.
A tokamak is a machine producing a toroidal magnetic field for confining a plasma.
It is one of several types of magnetic confinement devices, and it is one of the most-researched candidates for producing controlled thermonuclear fusion power.
The term tokamak is a transliteration of the Russian word токамак which itself is an acronym made from the Russian words: "тороидальная камера с магнитными катушками" (toroidal'naya kamera c magnitnymi katushkami) — toroidal chamber with magnetic coils (possibly tochamac).
It was invented in the 1950s by Soviet physicists Igor Tamm and Andrei Sakharov (who had been inspired by an original idea from Oleg Lavrentyev).
The tokamak is characterized by azimuthal (rotational) symmetry and the use of the plasma-borne electric current to generate the helical component of the magnetic field necessary for stable equilibrium.
Although nuclear fusion research began soon after World War II, the programs were initially classified.
It was not until after the 1955 United Nations International Conference on the Peaceful Uses of Atomic Energy in Geneva that programs were declassified and international scientific collaboration could take place.
Experimental research of tokamak systems started in 1956 in Kurchatov Institute, Moscow by a group of Soviet scientists led by Lev Artsimovich.
The group constructed the first tokamaks, the most successful of them being T-3 and its larger version T-4. T-4 was tested in 1968 in Novosibirsk, conducting the first ever quasistationary thermonuclear fusion reaction.
In 1968, at the third IAEA International Conference on Plasma Physics and Controlled Nuclear Fusion Research at Novosibirsk, Soviet scientists announced that they had achieved electron temperatures of over 1000 eV in a tokamak device.
The National Ignition Facility, or NIF, is a laser-based inertial confinement fusion (ICF) research device located at the Lawrence Livermore National Laboratory in Livermore, California.
NIF uses powerful lasers to heat and compress a small amount of hydrogen fuel to the point where nuclear fusion reactions take place.
NIF is the largest and most energetic ICF device built to date, and the first that is expected to reach the long-sought goal of "ignition", producing more energy than was put in to start the reaction.
Construction began in 1997 but was fraught with problems and ran into a series of delays that greatly slowed progress into the early 2000s.
Progress since then has been much smoother, but compared to initial estimates, NIF is five years behind schedule and almost four times more expensive than budgeted.
The construction of the National Ignition Facility was certified complete on 31 March 2009 by the U.S. Department of Energy, and a dedication ceremony took place on 29 May 2009.
The first large-scale laser target experiments were performed in June 2009 and ignition experiments are expected to begin in 2010.