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Inertial confinement fusion (ICF) is a fusion energy process that initiates nuclear fusion reactions by compressing and heating targets filled with thermonuclear fuel. In modern machines, the targets are small spherical pellets about the size of a pinhead typically containing a mixture of about 10 milligrams of
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
2H and tritium 3H. To compress and heat the fuel, energy is deposited in the outer layer of the target using high-energy beams of
photons A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alway ...
,
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...
s or
ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s, although almost all ICF devices used lasers. The beams heat the outer layer, which explodes outward. This produces a reaction force against the remainder of the target, which accelerates it inwards and compresses the fuel. This process also creates
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...
s that travel inward through the target. Sufficiently powerful shock waves can compress and heat the fuel at the center such that fusion occurs. ICF is one of two major branches of fusion energy research, the other is magnetic confinement fusion. When it was first publicly proposed in the early 1970s, ICF appeared to be a practical approach to power production and the field flourished. Experiments during the 1970s and '80s demonstrated that the efficiency of these devices was much lower than expected, and reaching
ignition Ignition may refer to: Science and technology * Firelighting, the human act of creating a fire for warmth, cooking and other uses * Combustion, an exothermic chemical reaction between a fuel and an oxidant * Fusion ignition, the point at which a ...
would not be easy. Throughout the 1980s and '90s, many experiments were conducted in order to understand the complex interaction of high-intensity laser light and
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
. These led to the design of newer machines, much larger, that would finally reach ignition energies. The largest operational ICF experiment is the
National Ignition Facility The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition wit ...
(NIF) in the US. In 2021, a test "shot" reached 70% of the energy put into it, slightly besting the best results for the magnetic machines set in the 1990s. On 13 December 2022, the
National Ignition Facility The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition wit ...
announced that they achieved fusion ignition for the first time, by delivering 2.05 megajoules (MJ) of energy to the target, resulting in 3.15 MJ of fusion energy output.


Description


Fusion basics

Fusion reactions join together smaller atoms to form larger ones. This occurs when two atoms (or ions, atoms stripped of their electrons) come close enough that the nuclear force pulls them together. Atomic nuclei are positively charged, and thus repel each other due to the electrostatic force. Overcoming this repulsion to bring the nuclei close enough requires an input of kinetic energy, known as the '' Coulomb barrier'' or ''fusion barrier energy''. Less energy is needed to cause lighter nuclei to fuse, as they have less electrical charge and thus a lower barrier energy. This means the barrier is lowest for hydrogen. Conversely, the nuclear force increases with the total number of nuclei, so the
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s of hydrogen with additional
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s further reduce the required energy. The easiest fuel to use for fusion production is the combination of
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
, 2H, and tritium, 3H. This combination is known as D-T. Even under ideal conditions, the chance that a D and T pair of ions will undergo fusion is very small; the chance is much higher that they will scatter instead. For this reason, the fuel must be held together for a period of time to give the ions many chances to approach other ions. Increasing the density of the fuel also helps, as it means the ions will have more encounters in a given time. Finally, the chance that the reaction will take place is not linear, this
cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...
is heavily dependent on individual ion energies. It is the combination of these three factors, energy (temperature), density and confinement time that is important. This combination is known as the
fusion triple product The Lawson criterion is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is ...
, and the value of the triple product needed to produce net energy is known as the
Lawson criterion The Lawson criterion is a figure of merit used in nuclear fusion research. It compares the rate of energy being generated by fusion reactions within the fusion fuel to the rate of energy losses to the environment. When the rate of production is ...
.


Thermonuclear devices

The first ICF devices were the
hydrogen bomb A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...
s invented in the early 1950s. A hydrogen bomb consists of two bombs in a single case. The first, the ''primary stage'', is a fission-powered device normally using
plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
. When it explodes it gives off a burst of thermal X-rays that fill the interior of the specially designed bomb casing. These X-rays are absorbed by a special material surrounding the ''secondary stage'', which consists mostly of the fusion fuel. The X-rays heat this material and cause it to explode outward. Due to
Newton's Third Law Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it. These laws can be paraphrased as follows: # A body remains at rest, or in motion ...
, this causes the fuel inside to be driven inward, compressing and heating it. This causes the fusion fuel to reach the temperature and density where fusion reactions begin. In the case of D-T fuel, most of the energy is released in the form of
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...
s and neutrons. Under normal conditions, an alpha can travel about 10 mm through the fuel, but in the ultra-dense conditions in the compressed fuel, they can travel about 0.01 mm before their electrical charge interacting with the surrounding plasma causes them to lose velocity. This means the majority of the energy released by the alphas will be deposited back in the fuel. This transfer of kinetic energy heats the surrounding particles to the energies they need to undergo fusion as well. This process causes the fusion fuel to burn outward from the center. The electrically neutral neutrons travel longer distances in the fuel mass and do not contribute to this self-heating process. In a bomb, they are instead used to either breed more tritium through reactions in a lithium-deuteride fuel, or are used to fission additional fissionable fuel surrounding the secondary stage, often part of the bomb casing. The requirement that the reaction has to be sparked by a fission bomb makes the method impractical for power generation. Not only would the fission triggers be expensive to produce, but the minimum size of such a bomb is large, defined roughly by the
critical mass In nuclear engineering, a critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fissi ...
of the
plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
fuel used. Generally, it seems difficult to build efficient nuclear devices much smaller than about 1 kiloton in yield, and the fusion secondary would add to this yield. This makes it a difficult engineering problem to extract power from the resulting explosions.
Project PACER Project PACER, carried out at Los Alamos National Laboratory (LANL) in the mid-1970s, explored the possibility of a fusion power system that would involve exploding small hydrogen bombs (fusion bombs)—or, as stated in a later proposal, fission bom ...
studied solutions to the engineering issues, but also demonstrated that it was not economically feasible. The cost of the bombs was far greater than the value of the resulting electricity.


ICF mechanism of action

The energy needed to overcome the Coulomb barrier corresponds to the energy of the average particle in a gas heated to 100 million
Kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
. The
specific heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...
of hydrogen is about 14
Joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
per gram-Kelvin, so considering a tiny amount of fusion fuel, 1 milligram for instance, the energy needed to raise the mass as a whole to this temperature is 1.4 million
Joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s, or ~1 megajoule (MJ). In the more widely developed
magnetic fusion energy Magnetic confinement fusion is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, along with i ...
(MFE) approach, confinement times are on the order of a second. This is not a physical limit, modern machines can maintain a plasma for minutes. In this case the confinement time represents the amount of time it takes for the energy from the reaction to be lost to the environment through a variety of mechanisms. For a one second confinement, the density needed to meet the Lawson criterion is about 1014 particles per cubic centimetre. For comparison, air at sea level has about 2.7 x 1019 particles per cubic centimetre, so the MFE approach has been described as "a good vacuum". Considering a 1 milligram drop of D-T fuel in liquid form, the size is about 1 mm and the density is about 4 x 1020. There is nothing holding the fuel together in this case, any heat created within it by fusion events will cause it to expand at the
speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...
, which leads to a confinement time around 2 x 10−10. At liquid density the required confinement time to reach the Lawson criterion is about 2 x 10−7. In this case only about 0.1 percent of the fuel will have fused before the drop is blown apart. The trick to ICF is that the rate of the fusion reactions is a function of density, and density can be improved through compression. If the drop is compressed from 1 mm to 0.1 mm in diameter, the confinement time drops by the same factor of 10 because the particles have less distance to go before they escape. At the same time the density, which is the cube of the dimensions, increases by 1,000 times. This means the overall rate of fusion increases 1,000 times while the confinement drops by 10 times, a 100-fold improvement. In this case 10% of the fuel undergoes fusion; 10% of 1 mg of fuel will produce about 30 MJ of energy, 30 times that of the energy needed to compress it to that density. The other key concept in ICF is that the entire fuel mass does not have to be raised to 100 million K. Recall that in a fusion bomb the reaction continues because the alpha particles released in the interior heat the fuel around it. At liquid density the alphas will travel about 10 mm and thus their energy will escape the 1 mm fuel. In the 0.1 mm compressed fuel, the alphas will have a range of about 0.016 mm, meaning that they will stop within the fuel and heat it. In this case a "propagating burn" can be caused by heating only the center of the fuel to the needed temperature. This requires far less energy; calculations suggested 1 kJ would be enough to reach the compression goal alone. Some method would be needed to heat the interior to fusion temperatures, and do so at the right time when the fuel was compressed and the density was high enough. In modern ICF devices, the density of the resulting fuel mixture is as much as one-thousand times the density of water, or one-hundred times that of lead, around 1000 g/cm3. Much of the work since the 1970s has been on ways to create the central hot-spot that starts off the burning, and dealing with the many practical problems that cropped up while trying to reach the desired densities.


Heating concepts

Early calculations suggested that the amount of energy needed to start the propagating burn would be very small; only a tiny amount of fuel had to be raised to the required temperature. This has proven difficult and new methods have emerged in an effort to make this process more efficient.


Central hot spot ignition

The initial solution to the heating problem involved the careful "shaping" of the energy delivery. The idea was to use an initial lower-energy pulse to vaporize the capsule and cause compression, and then a very short, very powerful pulse near the end of the compression cycle. The goal is to launch a
shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...
into the compressed fuel that travels inward to the center. When it reaches the center it meets the same wave travelling in from the other sides. This causes a brief period where the density in the center reaches much higher values, over 800 g/cm3. Known as "central hot spot ignition", the concept was the first to suggest ICF was not only a practical route to fusion, but relatively simple. This led to numerous efforts to build working systems in the early 1970s. These experiments revealed a number of unexpected loss mechanisms. Early calculations suggested about 4.5x107 J/g would be needed, but modern calculations place it closer to 108 J/g. Further control of the process on modern machines has led to complex shaping of the pulse into multiple sections in time.


Fast ignition

In the "fast ignition" approach, a separate laser is used to provide the additional energy directly to the center of the fuel. This can be arranged through mechanical means, often using a small metal cone that punctures the outer fuel pellet wall to allow the laser light access to the center. In tests, this approach has failed as the pulse of light has to reach the center at a precise time, when it is obscured by the debris and especially free electrons from the compression pulse. It also has the disadvantage of requiring a second laser pulse, which generally demands a completely separate laser.


Shock ignition

"Shock ignition" is similar in concept to the hot-spot technique, but instead of ignition being achieved via compression heating of the hotspot, a final powerful, shock is sent into the fuel at a late time to trigger ignition through a combination of compression and shock heating. This increases the efficiency of the process with an eye to lowering the overall amount of power required.


Direct vs. indirect drive

In the simplest method of inertial confinement, the fuel is arranged as a sphere. This allows it to be pushed inward uniformly from all sides. To produce the inward force, the fuel is placed within a thin capsule that absorbs energy from the driver beams, causing the capsule shell to explode outwards. The capsule shell is usually made of a lightweight plastic, and the fuel is deposited as a layer on the inside by injecting a gaseous fuel into the shell and then freezing it. Shining the driver beams directly onto the fuel capsule is known as "direct drive". In order for the fusion fuel to reach the required conditions, the implosion process must be extremely uniform in order to avoid significant asymmetry due to Rayleigh–Taylor instability and similar effects. For a beam energy of 1 MJ, the fuel capsule cannot be larger than about 2 mm before these effects disrupt the implosion symmetry. This limits the size of the beams to a narrow diameter that is difficult to achieve in practice. This difficulty has led to a method called "indirect drive", in which the beam does not shine on the fuel capsule directly. Instead, it shines into a small cylinder of heavy metal, often
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
or
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
, known as a "
hohlraum In radiation thermodynamics, a hohlraum (a non-specific German word for a "hollow space" or "cavity") is a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity. This idealized cavity can be approximated in pra ...
". The beams are arranged so they do not hit the fuel capsule suspended in the center. The beam energy heats the
hohlraum In radiation thermodynamics, a hohlraum (a non-specific German word for a "hollow space" or "cavity") is a cavity whose walls are in radiative equilibrium with the radiant energy within the cavity. This idealized cavity can be approximated in pra ...
until it emits
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10  picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
s. These X-rays fill the interior of the hohlraum and heat the capsule. The advantage of indirect drive is that the beams can be larger and less accurate, which greatly eases driver design. The disadvantage is that much of the delivered driver energy is used to heat the hohlraum until it is "X-ray hot", so the end-to-end energy efficiency is much lower than the direct drive method.


Challenges

The primary problems with increasing ICF performance are: * Improving the energy delivered to the target * Controlling symmetry of the imploding fuel * Preventing premature heating of the fuel before sufficient density is achieved * Preventing premature mixing of hot and cool fuel by
hydrodynamic In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and ...
instabilities * Formation of a 'tight' shockwave convergence at the fuel center. In order to focus the shock wave on the center of the target, the target must be made with great precision and sphericity with aberrations of no more than a few micrometres over its (inner and outer) surface. Likewise, the aiming of the laser beams must be precise in space and time. Beam timing is relatively simple and is solved by using delay lines in the beams' optical path to achieve
picosecond A picosecond (abbreviated as ps) is a unit of time in the International System of Units (SI) equal to 10−12 or (one trillionth) of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000  ...
timing accuracy. The other major problem plaguing the achievement of high symmetry and high temperatures/densities of the imploding target are so called "beam-beam" imbalance and beam anisotropy. These problems are, respectively, where the energy delivered by one beam may be higher or lower than other beams impinging on the target and of "hot spots" within a beam diameter hitting a target which induces uneven compression on the target surface, thereby forming Rayleigh-Taylor instabilities in the fuel, prematurely mixing it and reducing heating efficacy at the time of maximum compression. The Richtmyer-Meshkov instability is also formed during the process due to shock waves. All of these problems have been significantly mitigated by beam smoothing techniques and beam energy diagnostics to balance beam to beam energy; however, RT instability remains a major issue. Target design has improved tremendously. Modern
cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
hydrogen ice targets tend to freeze a thin layer of deuterium on the inside of the shell while irradiating it with a low power IR laser to smooth its inner surface and monitoring it with a
microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...
equipped
camera A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...
, thereby allowing the layer to be closely monitored ensuring its "smoothness". Cryogenic targets filled with D-T are "self-smoothing" due to the small amount of heat created by tritium decay. This is often referred to as "
beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
-layering". In the indirect drive approach, the absorption of thermal x-rays by the target is more efficient than the direct absorption of laser light. However, the hohlraums take up considerable energy to heat, significantly reducing the energy transfer efficiency. Most often, indirect drive hohlraum targets are used to simulate
thermonuclear weapons A thermonuclear weapon, fusion weapon or hydrogen bomb (H bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lowe ...
tests due to the fact that the fusion fuel in them is also imploded mainly by X-ray radiation. A variety of ICF drivers are evolving. Lasers have improved dramatically, scaling up from a few
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s and kilowatts to megajoules and hundreds of terawatts, using mostly frequency doubled or tripled light from neodymium glass amplifiers. Heavy ion beams are particularly interesting for commercial generation, as they are easy to create, control, and focus. However, it is difficult to achieve the energy densities required to implode a target efficiently, and most ion-beam systems require the use of a hohlraum surrounding the target to smooth out the irradiation.


History


Conception


United States

ICF history began as part of the " Atoms For Peace" conference in 1957. This was a large, international UN sponsored conference between the superpowers of the US and the
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
. Some thought was given to using a hydrogen bomb to heat a water-filled cavern. The resulting steam would then be used to power conventional generators, and thereby provide electrical power. This meeting led to the
Operation Plowshare Project Plowshare was the overall United States program for the development of techniques to use nuclear explosives for peaceful construction purposes. The program was organized in June 1957 as part of the worldwide Atoms for Peace efforts. As ...
efforts, formed in June 1957 and formally named in 1961. Three primary concepts were part of Plowshare; energy generation under Project PACER, the use of nuclear explosions for excavation, and for fracking in the
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
industry. PACER was directly tested in December 1961 when the 3 kt
Project Gnome Project Gnome was the first nuclear test of Project Plowshare and was the first continental nuclear weapon test since Trinity to be conducted outside of the Nevada Test Site, and the second test in the state of New Mexico after Trinity. It was t ...
device was detonated in bedded salt in New Mexico. While the press looked on, radioactive steam was released from the drill shaft, at some distance from the test site. Further studies led to engineered cavities replacing natural ones, but the Plowshare efforts turned from bad to worse, especially after the failure of 1962's Sedan which produced significant
fallout Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioac ...
. PACER continued to receive funding until 1975, when a 3rd party study demonstrated that the cost of electricity from PACER would be ten times the cost of conventional nuclear plants. Another outcome of the "Atoms For Peace" conference was to prompt Nuckolls to consider what happens on the fusion side of the bomb as the fuel mass is reduced. This work suggested that at very small sizes, on the order of milligrams, very little energy would be needed to ignite it, much less than a fission primary. He proposed building, in effect, tiny all-fusion explosives using a tiny drop of D-T fuel suspended in the center of a hohlraum. The shell provided the same effect as the bomb casing in an H-bomb, trapping x-rays inside to irradiate the fuel. The main difference is that the X-rays would not be supplied by a fission bomb, but by some sort of external device that heated the shell from the outside until it was glowing in the x-ray region. The power would be delivered by a then-unidentified pulsed power source he referred to, using bomb terminology, the "primary". The main advantage to this scheme is the efficiency of the fusion process at high densities. According to the Lawson criterion, the amount of energy needed to heat the D-T fuel to break-even conditions at ambient pressure is perhaps 100 times greater than the energy needed to compress it to a pressure that would deliver the same rate of fusion. So, in theory, the ICF approach could offer dramatically more gain. This can be understood by considering the energy losses in a conventional scenario where the fuel is slowly heated, as in the case of
magnetic fusion energy Magnetic confinement fusion is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, along with i ...
; the rate of energy loss to the environment is based on the temperature difference between the fuel and its surroundings, which continues to increase as the fuel temperature increases. In the ICF case, the entire hohlraum is filled with high-temperature radiation, limiting losses.


Germany

In 1956 a meeting was organized at the
Max Planck Institute Max or MAX may refer to: Animals * Max (dog) (1983–2013), at one time purported to be the world's oldest living dog * Max (English Springer Spaniel), the first pet dog to win the PDSA Order of Merit (animal equivalent of OBE) * Max (gorilla) (1 ...
in Germany by fusion pioneer Carl Friedrich von Weizsäcker. At this meeting
Friedwardt Winterberg Friedwardt Winterberg (born June 12, 1929) is a German-American theoretical physicist and was a research professor at the University of Nevada, Reno. He is known for his research in areas spanning general relativity, Planck scale physics, nucle ...
proposed the non-fission ignition of a thermonuclear micro-explosion by a convergent shock wave driven with high explosives. Further reference to Winterberg's work in Germany on nuclear micro explosions (mininukes) is contained in a declassified report of the former East German
Stasi The Ministry for State Security, commonly known as the (),An abbreviation of . was the Intelligence agency, state security service of the East Germany from 1950 to 1990. The Stasi's function was similar to the KGB, serving as a means of maint ...
(Staatsicherheitsdienst). In 1964 Winterberg proposed that ignition could be achieved by an intense beam of microparticles accelerated to a velocity of 1000 km/s. And in 1968, he proposed to use intense electron and ion beams, generated by
Marx generator A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are used in high-energy physics experiments, as well as to simulate ...
s, for the same purpose. The advantage of this proposal is that the generation of charged particle beams is not only less expensive than the generation of laser beams but can entrap the charged fusion reaction products due to the strong self-magnetic beam field, drastically reducing the compression requirements for beam ignited cylindrical targets.


USSR

In 1967, research fellow Gurgen Askaryan published an article proposing the use of focused laser beams in the fusion of
lithium deuteride Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...
or deuterium.


Early research

Through the late 1950s, Nuckolls and collaborators at
Lawrence Livermore National Laboratory Lawrence Livermore National Laboratory (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...
(LLNL) completed computer simulations of the ICF concept. In early 1960, they performed a full simulation of the implosion of 1 mg of D-T fuel inside a dense shell. The simulation suggested that a 5 MJ power input to the hohlraum would produce 50 MJ of fusion output, a gain of 10x. This was before the laser and a variety of other possible drivers were considered, including pulsed power machines, charged particle accelerators, plasma guns, and hypervelocity pellet guns. Two theoretical advances advanced the field. One came from new simulations that considered the timing of the energy delivered in the pulse, known as "pulse shaping", leading to better implosion. The second was to make the shell much larger and thinner, forming a thin shell as opposed to an almost solid ball. These two changes dramatically increased implosion efficiency and thereby greatly lowered the required compression energy. Using these improvements, it was calculated that a driver of about 1 MJ would be needed, a five-fold reduction. Over the next two years, other theoretical advancements were proposed, notably
Ray Kidder Ray E. Kidder () was an American physicist and nuclear weapons designer. He is best known for his outspoken views on nuclear weapons policy issues, including nuclear testing, stockpile management, and arms control. Kidder was a weapons physic ...
's development of an implosion system without a hohlraum, the so-called "direct drive" approach, and
Stirling Colgate Stirling Auchincloss Colgate (; November 14, 1925 – December 1, 2013) was an American physicist at Los Alamos National Laboratory and a professor emeritus of physics, past president at the New Mexico Institute of Mining and Technology (New Mexic ...
and Ron Zabawski's work on systems with as little as 1 μg of D-T fuel. The introduction of the laser in 1960 at Hughes Research Laboratories in California appeared to present a perfect driver mechanism. Starting in 1962, Livermore's director
John S. Foster, Jr. John Stuart Foster Jr. (born September 18, 1922) is an American physicist, best known as the fourth director of Lawrence Livermore National Laboratory and as Director, Defense Research and Engineering under four Secretaries of Defense and two Pre ...
and Edward Teller began a small ICF laser study. Even at this early stage the suitability of ICF for weapons research was well understood and was the primary reason for its funding. Over the next decade, LLNL made small experimental devices for basic laser-plasma interaction studies.


Development begins

In 1967 Kip Siegel started KMS Industries. In the early 1970s he formed KMS Fusion to begin development of a laser-based ICF system.Sean Johnston
"Interview with Dr. Larry Siebert"
American Institute of Physics, 4 September 2004
This development led to considerable opposition from the weapons labs, including LLNL, who put forth a variety of reasons that KMS should not be allowed to develop ICF in public. This opposition was funnelled through the Atomic Energy Commission, which demanded funding. Adding to the background noise were rumours of an aggressive Soviet ICF program, new higher-powered CO2 and glass lasers, the electron beam driver concept, and the energy crisis which added impetus to many energy projects. In 1972 Nuckolls wrote a paper introducing ICF and suggesting that testbed systems could be made to generate fusion with drivers in the kJ range, and high-gain systems with MJ drivers. In spite of limited resources and business problems, KMS Fusion successfully demonstrated fusion from the ICF process on 1 May 1974. However, this success was soon followed by Siegel's death, and the end of KMS fusion about a year later. By this point several weapons labs and universities had started their own programs, notably the solid-state lasers ( Nd:glass lasers) at LLNL and the
University of Rochester The University of Rochester (U of R, UR, or U of Rochester) is a private research university in Rochester, New York. The university grants undergraduate and graduate degrees, including doctoral and professional degrees. The University of Roc ...
, and
krypton fluoride Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often u ...
excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...
s systems at Los Alamos and the
Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...
.


"High-energy" ICF

High-energy ICF experiments (multi-hundred joules per shot) began in the early 1970s, when better lasers appeared. Nevertheless, funding for fusion research stimulated by energy crises produced rapid gains in performance, and inertial designs were soon reaching the same sort of "below break-even" conditions of the best magnetic systems. LLNL was, in particular, well funded and started a laser fusion development program. Their
Janus laser The Janus laser was a (then considered high power) two beam infrared neodymium doped silica glass laser built at Lawrence Livermore National Laboratory in 1974 for the study of inertial confinement fusion. Janus was built using about 100 pounds o ...
started operation in 1974, and validated the approach of using Nd:glass lasers for high power devices. Focusing problems were explored in the Long path and
Cyclops laser Cyclops was a high-power laser built at the Lawrence Livermore National Laboratory (LLNL) in 1975. It was the second laser constructed in the lab's ''Laser'' program, which aimed to study inertial confinement fusion (ICF). The Cyclops was a singl ...
s, which led to the larger
Argus laser Argus was a two-beam high power infrared neodymium doped silica glass laser with a output aperture built at Lawrence Livermore National Laboratory in 1976 for the study of inertial confinement fusion. Argus advanced the study of laser-target inte ...
. None of these were intended to be practical devices, but they increased confidence that the approach was valid. At the time it was believed that making a much larger device of the Cyclops type could both compress and heat targets, leading to ignition. This misconception was based on extrapolation of the fusion yields seen from experiments utilizing the so-called "exploding pusher" fuel capsule. During the late 1970s and early 1980s the estimates for laser energy on target needed to achieve ignition doubled almost yearly as plasma instabilities and laser-plasma energy coupling loss modes were increasingly understood. The realization that exploding pusher target designs and single-digit kilojoule (kJ) laser irradiation intensities would never scale to high yields led to the effort to increase laser energies to the 100 kJ level in the UV band and to the production of advanced ablator and cryogenic DT ice target designs.


Shiva and Nova

One of the earliest large scale attempts at an ICF driver design was the
Shiva laser The Shiva laser was a powerful 20-beam infrared neodymium glass (silica glass) laser built at Lawrence Livermore National Laboratory in 1977 for the study of inertial confinement fusion (ICF) and long-scale-length laser-plasma interactions. Presu ...
, a 20-beam neodymium doped glass laser system at LLNL that started operation in 1978. Shiva was a "proof of concept" design intended to demonstrate compression of fusion fuel capsules to many times the liquid density of hydrogen. In this, Shiva succeeded and compressed its pellets to 100 times the liquid density of deuterium. However, due to the laser's strong coupling with hot electrons, premature heating of the dense plasma (ions) was problematic and fusion yields were low. This failure by Shiva to efficiently heat the compressed plasma pointed to the use of
optical frequency multiplier An optical frequency multiplier is a nonlinear optical device in which photons interacting with a nonlinear material are effectively "combined" to form new photons with greater energy, and thus higher frequency (and shorter wavelength). Two types ...
s as a solution that would frequency triple the infrared light from the laser into the ultraviolet at 351 nm. Newly discovered schemes to efficiently triple the frequency of high intensity laser light discovered at the Laboratory for Laser Energetics in 1980 enabled this method of target irradiation to be experimented with in the 24 beam OMEGA laser and the
NOVETTE laser Novette was a two beam neodymium glass (phosphate glass) testbed laser built at Lawrence Livermore National Laboratory in about 15 months throughout 1981 and 1982 and was completed in January 1983. Novette was made using recycled parts from the dis ...
, which was followed by the
Nova laser Nova was a high-power laser built at the Lawrence Livermore National Laboratory (LLNL) in California, United States, in 1984 which conducted advanced inertial confinement fusion (ICF) experiments until its dismantling in 1999. Nova was the first ...
design with 10 times the energy of Shiva, the first design with the specific goal of reaching ignition conditions. Nova also failed, this time due to severe variation in laser intensity in its beams (and differences in intensity between beams) caused by filamentation that resulted in large non-uniformity in irradiation smoothness at the target and asymmetric implosion. The techniques pioneered earlier could not address these new issues. This failure led to a much greater understanding of the process of implosion, and the way forward again seemed clear, namely the increase in uniformity of irradiation, the reduction of hot-spots in the laser beams through beam smoothing techniques to reduce Rayleigh–Taylor instabilities imprinting on the target and increased laser energy on target by at least an order of magnitude. Funding for fusion research was severely constrained in the 1980s.


National Ignition Facility

The resulting design, dubbed the
National Ignition Facility The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition wit ...
, started construction at LLNL in 1997. NIF's main objective is to operate as the flagship experimental device of the so-called nuclear stewardship program, supporting LLNLs traditional bomb-making role. Completed in March 2009, NIF has now conducted experiments using all 192 beams, including experiments that set new records for power delivery by a laser. As of October 7, 2013, for the first time a fuel capsule gave off more energy than was applied to it. In June, 2018 the NIF announced attainment of a record production of 54kJ of fusion energy output. On August 8, 2021 the NIF made a significant advancement in production of 1.3MJ of fusion energy output, 25x higher than the 2018 result, generating 70% of the break-even definition of ignition - when energy out equals energy in.


Fast ignition

The concept of "fast ignition" may offer a way to directly heat fuel after compression, thus decoupling the heating and compression phases of the implosion. In this approach the target is first compressed "normally" using a laser system. When the implosion reaches maximum density (at the stagnation point or "bang time"), a second ultra-short pulse ultra-high power petawatt (PW) laser delivers a single pulse focused on one side of the core, dramatically heating it and starting ignition. The two types of fast ignition are the "plasma bore-through" method and the "cone-in-shell" method. In plasma bore-through, the second laser is expected to bore straight through the outer plasma of an imploding capsule and to impinge on and heat the dense core. In the cone-in-shell method, the capsule is mounted on the end of a small high-z (high
atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
) cone such that the tip of the cone projects into the core of the capsule. In this second method, when the capsule is imploded, the laser has a clear view straight to the high density core and does not have to waste energy boring through a 'corona' plasma. However, the presence of the cone affects the implosion process in significant ways that are not fully understood. Several projects are currently underway to explore the fast ignition approach, including upgrades to the
OMEGA laser The Laboratory for Laser Energetics (LLE) is a scientific research facility which is part of the University of Rochester's south campus, located in Brighton, New York. The lab was established in 1970 and its operations since then have been fund ...
at the University of Rochester, the
GEKKO XII The is a high-power, 12-beam, neodymium-doped glass laser at the Osaka University's Institute for Laser Engineering (大阪大学レーザーエネルギー学研究センター) completed in 1983, which is used for high energy density physics an ...
device in Japan.
HiPer The High Power laser Energy Research facility (HiPER), is a proposed experimental laser-driven inertial confinement fusion (ICF) device undergoing preliminary design for possible construction in the European Union. , the effort appears to be i ...
is a proposed £500 million facility in the
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
. Compared to NIF's 2 MJ UV beams, HiPER's driver was planned to be 200 kJ and heater 70 kJ, although the predicted fusion gains are higher than NIF. It was to employ diode lasers, which convert electricity into laser light with much higher efficiency and run cooler. This allows them to be operated at much higher frequencies. HiPER proposed to operate at 1 MJ at 1 Hz, or alternately 100 kJ at 10 Hz. The project last produced an update in 2014. It was expected to offer a higher ''Q'' with a 10x reduction in construction costs times.


Other projects

The French
Laser Mégajoule Laser Mégajoule (LMJ) is a large laser-based inertial confinement fusion (ICF) research device near Bordeaux, France, built by the French nuclear science directorate, Commissariat à l'Énergie Atomique (CEA). Laser Mégajoule plans to deliver ...
achieved its first experimental line in 2002, and its first target shots were conducted in 2014. The machine was roughly 75% complete as of 2016. Using a different approach entirely is the ''z''-pinch device. ''Z''-pinch uses massive electric currents switched into a cylinder comprising extremely fine wires. The wires vaporize to form an electrically conductive, high current plasma. The resulting circumferential magnetic field squeezes the plasma cylinder, imploding it, generating a high-power x-ray pulse that can be used to implode a fuel capsule. Challenges to this approach include relatively low drive temperatures, resulting in slow implosion velocities and potentially large instability growth, and preheat caused by high-energy x-rays. Shock ignition was proposed to address problems with fast ignition. Japan developed the KOYO-F design and laser inertial fusion test (LIFT) experimental reactor. In April 2017, clean energy startup Apollo Fusion began to develop a hybrid fusion-fission reactor technology. In Germany, technology company Marvel Fusion develops a novel approach to laser-initiated inertial confinement fusion. The startup adopted a short-pulsed high energy laser and the aneutronic fuel pB11. Founded in Munich 2019, Marvel Fusion aims to build and operate commercial fusion power plants of up to 1 GW by 2030. For this purposes, it startet to work together with Siemens Energy,
TRUMPF The TRUMPF Group is a German industrial machine manufacturing company. It is a family-owned company with its head office in Ditzingen near Stuttgart. TRUMPF is one of the world's biggest providers of machine tools. With more than 70 operative su ...
, and
Thales Thales of Miletus ( ; grc-gre, Θαλῆς; ) was a Greek mathematician, astronomer, statesman, and pre-Socratic philosopher from Miletus in Ionia, Asia Minor. He was one of the Seven Sages of Greece. Many, most notably Aristotle, regarded him ...
to develop the necessary components for a future power plant and the laser systems. The company entered a partnership with the
Ludwig Maximilian University of Munich The Ludwig Maximilian University of Munich (simply University of Munich or LMU; german: Ludwig-Maximilians-Universität München) is a public research university in Munich, Germany. It is Germany's sixth-oldest university in continuous operatio ...
in July 2022 to jointly research the company's approach. In March 2022, Australian company HB11 announced successful fusion using non-thermal laser fusion of hydrogen and boron-11, at a notably higher than predicted rate of alpha particle creation.


As an energy source

Practical power plants built using ICF have been studied since the late 1970s; they are known as inertial fusion energy (IFE) plants. These devices would deliver several targets per second into the reaction chamber, and capture the resulting heat and neutron radiation from their implosion and fusion to drive a conventional
steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...
.


Technical challenges

Even if the many technical challenges in reaching ignition were all to be solved, practical problems seem just as difficult to overcome. Laser-driven systems were initially believed to be able to generate commercially useful amounts of energy. However, as estimates of the energy required to reach ignition grew dramatically during the 1970s, these hopes were abandoned. Given the low efficiency of the laser amplification process, about 1 to 1.5%, and the losses in generation, steam-driven turbine systems are typically about 35% efficient, fusion gains would have to be on the order of 125-fold just to energetically break even. Fast ignition and similar approaches changed the situation. In this approach gains of 100-fold are predicted in the first experimental device, HiPER. Given a gain factor of about 100 and a laser efficiency of about 1%, HiPER produces about the same amount of ''fusion'' energy as electrical energy was needed to create it (and thus will require more gain to produce electricity after considering losses). It also appears that an order of magnitude improvement in laser efficiency may be possible through the use of newer designs that replace flash lamps with
laser diode file:Laser diode chip.jpg, The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a di ...
s that are tuned to produce most of their energy in a frequency range that is strongly absorbed. Initial experimental devices offer efficiencies of about 10%, and it is suggested that 20% is possible. With "classical" devices like NIF about 330 MJ of electrical power are used to produce the driver beams, producing an expected yield of about 20 MJ, with maximum credible yield of 45 MJ. HiPER requires about 270 kJ of laser energy, so assuming a first-generation diode laser driver operating at 10% the reactor would require about 3 MJ of electrical power. This is expected to produce about 30 MJ of fusion power. Even a poor conversion to electrical energy appears to offer real-world power output, and incremental improvements in yield and laser efficiency appear to be able to offer a commercially useful output.


Practical problems

ICF systems face some of the same secondary power extraction problems as magnetic systems in generating useful power. One of the primary concerns is how to successfully remove the heat generated from the reaction chamber without interfering with the targets and driver beams. Another concern is that the released
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s react with the reactor structure, causing it to become intensely radioactive, as well as mechanically weakening the construction metals. Fusion plants built of conventional metals like
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
would have a fairly short lifetime and the core containment vessels would have to be replaced frequently. Yet another concern is fusion afterdamp, which is debris left in the reaction chamber which could interfere with subsequent shots. The most obvious such debris is the helium ash produced by fusion, but there is also unburned hydrogen fuel and other non-fusible elements used in the composition of the fuel pellet. This potential problem is most troublesome with indirect drive systems using metal hohlraums. There is also the possibility of the driver energy not hitting the fuel pellet completely and striking the containment chamber, sputtering material that could foul the interaction region, or the lenses or focusing elements of the driver. One concept in dealing with these problems, as shown in the HYLIFE-II design, is to use a "waterfall" of FLiBe, a molten mix of
fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts typ ...
salts of
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
and
beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
, which both protect the chamber from neutrons and carry away heat. The FLiBe is then passed into a heat exchanger where it heats water for use in the turbines. The tritium produced by splitting lithium nuclei can be extracted in order to close the power plant's thermonuclear fuel cycle, a necessity for perpetual operation because tritium is rare and must be manufactured. Another concept, Sombrero, uses a reaction chamber built of carbon-fiber-reinforced polymer which has a low neutron
cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...
. Cooling is provided by a molten ceramic, chosen because of its ability to absorb the neutrons and its efficiency as a heat transfer agent.


Economic viability

Another factor working against IFE is the cost of the fuel. Even as Nuckolls was developing his earliest calculations, co-workers pointed out that if an IFE machine produces 50 MJ of fusion energy, one might expect that a shot could produce perhaps 10 MJ of power for export. Converted to better known units, this is the equivalent of 2.8 kWh of electrical power. Wholesale rates for electrical power on the grid were about 0.3 cents/kWh at the time, which meant the monetary value of the shot was perhaps one cent. In the intervening 50 years the price of power has remained about even with the rate of inflation, and the rate in 2012 in
Ontario, Canada Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...
was about 2.8 cents/kWh. Thus, in order for an IFE plant to be economically viable, fuel shots would have to cost considerably less than ten cents in 2012 dollars. Direct-drive systems avoid the use of a hohlraum and thereby may be less expensive in fuel terms. However, these systems still require an ablator, and the accuracy and geometrical considerations are critical. The direct-drive approach still may not be less expensive to operate.


Nuclear weapons program

The very hot and dense conditions encountered during an ICF experiment are similar to those created in a thermonuclear weapon, and have applications to nuclear weapons programs. ICF experiments might be used, for example, to help determine how warhead performance will degrade as it ages, or as part of a program of designing new weapons. Retaining knowledge and expertise inside the nuclear weapons program is another motivation for pursuing ICF. Funding for the NIF in the United States is sourced from the 'Nuclear Weapons Stockpile Stewardship' program, and the goals of the program are oriented accordingly. It has been argued that some aspects of ICF research may violate the
Comprehensive Test Ban Treaty The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty to ban nuclear weapons test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments. It was adopted by the United Nations ...
or the Nuclear Non-Proliferation Treaty. In the long term, despite the formidable technical hurdles, ICF research could lead to the creation of a "
pure fusion weapon A pure fusion weapon is a hypothetical hydrogen bomb design that does not need a fission "primary" explosive to ignite the fusion of deuterium and tritium, two heavy isotopes of hydrogen used in fission-fusion thermonuclear weapons. Such a weapon ...
".


Neutron source

Inertial confinement fusion has the potential to produce orders of magnitude more neutrons than
spallation Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary p ...
. Neutrons are capable of locating hydrogen atoms in molecules, resolving atomic thermal motion and studying collective excitations of photons more effectively than X-rays. Neutron scattering studies of molecular structures could resolve problems associated with
protein folding Protein folding is the physical process by which a protein chain is translated to its native three-dimensional structure, typically a "folded" conformation by which the protein becomes biologically functional. Via an expeditious and reproduci ...
, diffusion through membranes, proton transfer mechanisms, dynamics of
molecular motor Molecular motors are natural (biological) or artificial molecular machines that are the essential agents of movement in living organisms. In general terms, a motor is a device that consumes energy in one form and converts it into motion or mecha ...
s, etc. by modulating
thermal neutrons The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...
into beams of slow neutrons. In combination with fissile materials, neutrons produced by ICF can potentially be used in
Hybrid Nuclear Fusion Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...
designs to produce electric power.


See also

*
Magneto-inertial fusion Magneto-inertial fusion (MIF) describes a class of fusion devices which combine aspects of magnetic confinement fusion and inertial confinement fusion in an attempt to lower the cost of fusion devices. MIF uses magnetic fields to confine an initial ...
* Magnetized target fusion (MTF) * Magnetic confinement fusion *
Antimatter catalyzed nuclear pulse propulsion Antimatter-catalyzed nuclear pulse propulsion (also antiproton-catalyzed nuclear pulse propulsion) is a variation of nuclear pulse propulsion based upon the injection of antimatter into a mass of nuclear fuel to initiate a nuclear chain reaction fo ...
* Laboratory for Laser Energetics *
Leonardo Mascheroni Pedro Leonardo Mascheroni (born 1935) is a physicist who, according to the United States government, attempted to sell nuclear secrets to a Federal Bureau of Investigation (FBI) agent posing as a Venezuela Venezuela (; ), officially the Boli ...
, who proposed using
hydrogen fluoride laser The hydrogen fluoride laser is an infrared chemical laser. It is capable of delivering continuous output power in the megawatt range. Hydrogen fluoride lasers operate at the wavelength of 2.7-2.9  µm. This wavelength is absorbed by the atmos ...
s to achieve fusion. *
Bubble fusion Bubble fusion is the non-technical name for a nuclear fusion reaction hypothesized to occur inside extraordinarily large collapsing gas bubbles created in a liquid during Sonic cavitation, acoustic cavitation. The more technical name is sonofusion ...
, a phenomenon claimed – controversially – to provide an ''acoustic'' form of inertial confinement fusion. *
List of laser articles This is a list of laser topics. A * 3D printing, additive manufacturing * Abnormal reflection * Above-threshold ionization * Absorption spectroscopy * Accelerator physics * Acoustic microscopy * Acousto-optic deflector * Acousto-optic modul ...
* List of plasma physics articles * Pulsed power *
Laser Mégajoule Laser Mégajoule (LMJ) is a large laser-based inertial confinement fusion (ICF) research device near Bordeaux, France, built by the French nuclear science directorate, Commissariat à l'Énergie Atomique (CEA). Laser Mégajoule plans to deliver ...
*
Dense Plasma Focus A dense plasma focus (DPF) is a type of plasma generating system originally developed as a fusion power device starting in the early 1960s. The system demonstrated scaling laws that suggested it would not be useful in the commercial power role, and ...
* Proton-boron fusion


Notes


References


Bibliography

* * * * * *


External links


National Ignition Facility ProjectZpinch Home PageEurope plans laser-fusion facility
''(Physicsweb)''
Lasers point the way to clean energy
''(The Guardian)''
National Laser Fusion Energy Development PlanLaser Inertial-Confinement Fusion-Fission Energy
{{Nuclear fusion reactors Lawrence Livermore National Laboratory