162-541: 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 with high energy gain . It achieved the first instance of scientific breakeven controlled fusion in an experiment on December 5, 2022, with an energy gain factor of 1.5. It supports nuclear weapon maintenance and design by studying
324-519: A gain medium , a mechanism to energize it, and something to provide optical feedback . The gain medium is a material with properties that allow it to amplify light by way of stimulated emission. Light of a specific wavelength that passes through the gain medium is amplified (power increases). Feedback enables stimulated emission to amplify predominantly the optical frequency at the peak of the gain-frequency curve. As stimulated emission grows, eventually one frequency dominates over all others, meaning that
486-471: A lens system, as is always included, for instance, in a laser pointer whose light originates from a laser diode . That is possible due to the light being of a single spatial mode. This unique property of laser light, spatial coherence , cannot be replicated using standard light sources (except by discarding most of the light) as can be appreciated by comparing the beam from a flashlight (torch) or spotlight to that of almost any laser. A laser beam profiler
648-454: A particle identical to a helium-4 nucleus . They are generally produced in the process of alpha decay but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet , α . The symbol for the alpha particle is α or α . Because they are identical to helium nuclei, they are also sometimes written as He or 2 He indicating a helium ion with
810-419: A +2 charge (missing its two electrons ). Once the ion gains electrons from its environment, the alpha particle becomes a normal (electrically neutral) helium atom 2 He . Alpha particles have a net spin of zero. When produced in standard alpha radioactive decay , alpha particles generally have a kinetic energy of about 5 MeV and a velocity in the vicinity of 4% of the speed of light . They are
972-517: A 10 MJ system. Nevertheless, the authors noted, "Indeed, if it did turn out that a 100 MJ driver were required for ignition and gain, one would have to rethink the entire approach to, and rationale for, ICF". As of 1992, the Laboratory Microfusion Facility was estimated to cost about $ 1 billion. LLNL initially submitted a design with a 5 MJ 350 nm (UV) driver that would be able to reach about 200 MJ yield, which
1134-466: A bomb could be made that would still generate net positive power. A typical hydrogen bomb has two parts: a plutonium-based fission bomb known as the primary , and a cylindrical arrangement of fusion fuels known as the secondary . The primary releases x-rays, which are trapped within the bomb casing. They heat and compress the secondary until it ignites. The secondary consists of lithium deuteride (LiD) fuel, which requires an external neutron source. This
1296-464: A broad spectrum of light or emit different wavelengths of light simultaneously. Certain lasers are not single spatial mode and have light beams that diverge more than is required by the diffraction limit . All such devices are classified as "lasers" based on the method of producing light by stimulated emission. Lasers are employed where light of the required spatial or temporal coherence can not be produced using simpler technologies. A laser consists of
1458-504: A chain reaction. The materials chosen for lasers are the ones that have metastable states , which stay excited for a relatively long time. In laser physics , such a material is called an active laser medium . Combined with an energy source that continues to "pump" energy into the material, it is possible to have enough atoms or molecules in an excited state for a chain reaction to develop. Lasers are distinguished from other light sources by their coherence . Spatial (or transverse) coherence
1620-481: A charge of 1 e , and that helium has an atomic weight of 4. Nobody knew exactly how many electrons were in an atom. Protons and neutrons had not yet been discovered. Rutherford decided the second explanation was the most plausible because it is the simplest and sizeable deposits of helium were commonly found underground next to deposits of radioactive elements. His explanation was that as alpha particles are emitted by underground radioactive elements, they become trapped in
1782-436: A coherent beam has been formed. The process of stimulated emission is analogous to that of an audio oscillator with positive feedback which can occur, for example, when the speaker in a public-address system is placed in proximity to the microphone. The screech one hears is audio oscillation at the peak of the gain-frequency curve for the amplifier. For the gain medium to amplify light, it needs to be supplied with energy in
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#17328454040081944-419: A device lacks the spatial and temporal coherence achievable with lasers. Such a device cannot be described as an oscillator but rather as a high-gain optical amplifier that amplifies its spontaneous emission. The same mechanism describes so-called astrophysical masers /lasers. The optical resonator is sometimes referred to as an "optical cavity", but this is a misnomer: lasers use open resonators as opposed to
2106-473: A few centimetres in air. They can be absorbed by tissue paper or by the outer layers of human skin. They typically penetrate skin about 40 micrometres , equivalent to a few cells deep. Due to the short range of absorption and inability to penetrate the outer layers of skin, alpha particles are not, in general, dangerous to life unless the source is ingested or inhaled. Because of this high mass and strong absorption, if alpha-emitting radionuclides do enter
2268-501: A few layers of foil, and what was left was a second component that could penetrate the foils more easily, and he dubbed the latter " beta radiation ". In 1900, Marie Curie noticed that the absorption coefficient of alpha rays seemed to increase the thicker the barrier she placed in their path. This suggested that alpha radiation is not a form of light but made of particles that lose kinetic energy as they pass through barriers. In 1902, Rutherford found that he could deflect alpha rays with
2430-797: A form of radioactive decay. In both induced and spontaneous fission, the higher energies available in heavy nuclei result in long range alphas of higher energy than those from alpha decay. Energetic helium nuclei (helium ions) may be produced by cyclotrons , synchrotrons , and other particle accelerators . Convention is that they are not normally referred to as "alpha particles". Helium nuclei may participate in nuclear reactions in stars, and occasionally and historically these have been referred to as alpha reactions (see triple-alpha process and alpha process ). In addition, extremely high energy helium nuclei sometimes referred to as alpha particles make up about 10 to 12% of cosmic rays . The mechanisms of cosmic ray production continue to be debated. The energy of
2592-508: A gain medium must have a gain bandwidth sufficiently broad to amplify those frequencies. An example of a suitable material is titanium -doped, artificially grown sapphire ( Ti:sapphire ), which has a very wide gain bandwidth and can thus produce pulses of only a few femtoseconds duration. Such mode-locked lasers are a most versatile tool for researching processes occurring on extremely short time scales (known as femtosecond physics, femtosecond chemistry and ultrafast science ), for maximizing
2754-480: A given pulse energy, this requires creating pulses of the shortest possible duration utilizing techniques such as Q-switching . The optical bandwidth of a pulse cannot be narrower than the reciprocal of the pulse width. In the case of extremely short pulses, that implies lasing over a considerable bandwidth, quite contrary to the very narrow bandwidths typical of CW lasers. The lasing medium in some dye lasers and vibronic solid-state lasers produces optical gain over
2916-399: A higher energy level with energy difference ΔE, it will not stay that way forever. Eventually, a photon will be spontaneously created from the vacuum having energy ΔE. Conserving energy, the electron transitions to a lower energy level that is not occupied, with transitions to different levels having different time constants. This process is called spontaneous emission . Spontaneous emission is
3078-468: A highly ionizing form of particle radiation , with low penetration depth (stopped by a few centimetres of air , or by the skin ). However, so-called long-range alpha particles from ternary fission are three times as energetic and penetrate three times as far. The helium nuclei that form 10–12% of cosmic rays are also usually of much higher energy than those produced by nuclear decay processes, and thus may be highly penetrating and able to traverse
3240-471: A laser beam, it is highly collimated : the wavefronts are planar, normal to the direction of propagation, with no beam divergence at that point. However, due to diffraction , that can only remain true well within the Rayleigh range . The beam of a single transverse mode (gaussian beam) laser eventually diverges at an angle that varies inversely with the beam diameter, as required by diffraction theory. Thus,
3402-471: A laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above. This material can be of any state : gas, liquid, solid, or plasma . The gain medium absorbs pump energy, which raises some electrons into higher energy (" excited ") quantum states . Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In
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#17328454040083564-435: A laser of this power; Leonardo Mascheroni and Claude Phipps designed a new type of hydrogen fluoride laser pumped by high-energy electrons and reach the 100 MJ threshold. Others used the same data and new versions of their computer simulations to suggest that careful shaping of the laser pulse and more beams spread more evenly could achieve ignition with a laser powered between 5 and 10 MJ. These results prompted
3726-457: A laser pulse that has a flat temporal shape, but the temporal shape needed for ignition varies significantly over the duration of the pulse. The actual conversion process is about 50 percent efficient, reducing delivered energy to a nominal 1.8 MJ. As of 2010, one important aspect of any ICF research project was ensuring that experiments could be carried out on a timely basis. Previous devices generally had to cool down for many hours to allow
3888-401: A laser to be focused to a tight spot, enabling applications such as optical communication, laser cutting , and lithography . It also allows a laser beam to stay narrow over great distances ( collimation ), a feature used in applications such as laser pointers , lidar , and free-space optical communication . Lasers can also have high temporal coherence , which permits them to emit light with
4050-423: A layer of frozen deuterium–tritium (DT) fuel. The hollow interior contains a small amount of DT gas. In a typical experiment, the laser generates 3 MJ of infrared laser energy of a possible 4. About 1.5 MJ remains after conversion to UV, and another 15 percent is lost in the hohlraum. About 15 percent of the resulting x-rays, about 150 kJ, are absorbed by the target's outer layers. The coupling between
4212-458: A low-power flash of 1053-nanometer (nm) infrared light generated in an ytterbium -doped optical fiber laser termed Master Oscillator. Its light is split and directed into 48 Preamplifier Modules (PAMs). Each PAM conducts a two-stage amplification process via xenon flash lamps . The first stage is a regenerative amplifier in which the pulse circulates 30 to 60 times, increasing its energy from nanojoules to tens of millijoules. The second stage sends
4374-414: A magnetic field and an electric field, showing that alpha radiation is composed of positively charged particles. In 1906, Rutherford made some more precise measurements of the charge-to-mass ratio of alpha particles. Firstly, he found that the ratio was more or less the same whether the source was radium or actinium , showing that alpha particles are the same regardless of the source. Secondly, he found
4536-405: A minimum-size atomic nucleus that can support it. The smallest nuclei that have to date been found to be capable of alpha emission are beryllium-8 and tellurium-104 , not counting beta-delayed alpha emission of some lighter elements. The alpha decay sometimes leaves the parent nucleus in an excited state; the emission of a gamma ray then removes the excess energy . In contrast to beta decay ,
4698-418: A multi-level system as a method for obtaining the population inversion, later a main method of laser pumping. Townes reports that several eminent physicists—among them Niels Bohr , John von Neumann , and Llewellyn Thomas —argued the maser violated Heisenberg's uncertainty principle and hence could not work. Others such as Isidor Rabi and Polykarp Kusch expected that it would be impractical and not worth
4860-429: A net fusion energy gain, denoted Q , of about 5–8 (fusion energy out/UV laser energy in). Due to the design of the target chamber, the baseline design limited the maximum possible fusion energy release to 45 MJ, equivalent to about 11 kg of TNT exploding. When NIF was built and used in 2011, the fusion energy was far lower than expected – less than 1 kJ. Performance was gradually improved until, as of 2024,
5022-468: A plastic form with a layer of sputtered beryllium or beryllium–copper alloy, and then oxidizing the plastic out of the center. Beryllium targets offer higher implosion efficiencies from x-ray inputs. Although NIF was primarily designed as an indirect drive device, the energy in the laser as of 2008 was high enough to be used as a direct drive system, where the laser shines directly on the target without conversion to x-rays. The power delivered by NIF UV rays
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5184-441: A process called pumping . The energy is typically supplied as an electric current or as light at a different wavelength. Pump light may be provided by a flash lamp or by another laser. The most common type of laser uses feedback from an optical cavity —a pair of mirrors on either end of the gain medium. Light bounces back and forth between the mirrors, passing through the gain medium and being amplified each time. Typically one of
5346-462: A quantum-mechanical effect and a direct physical manifestation of the Heisenberg uncertainty principle . The emitted photon has a random direction, but its wavelength matches the absorption wavelength of the transition. This is the mechanism of fluorescence and thermal emission . A photon with the correct wavelength to be absorbed by a transition can also cause an electron to drop from the higher to
5508-432: A seminar on this idea, and Charles H. Townes asked him for a copy of the paper. In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first microwave amplifier, a device operating on similar principles to the laser, but amplifying microwave radiation rather than infrared or visible radiation. Townes's maser was incapable of continuous output. Meanwhile, in
5670-464: A single 500 terawatt (TW) peak flash of light that reaches the target from numerous directions within a few picoseconds . The design uses 192 beamlines in a parallel system of flashlamp-pumped, neodymium-doped phosphate glass lasers. To ensure that the output of the beamlines is uniform, the laser is amplified from a single source in the Injection Laser System (ILS). This starts with
5832-401: A small amount of air. He placed some uranium on the bottom electrode, and the radiation from the uranium ionized the air between the electrodes, creating a current. Rutherford then placed an aluminium foil (5 micrometers thick) over the uranium and noticed that the current dropped a bit, indicating that the foil was absorbing some of the uranium's radiation. Rutherford placed a few more foils over
5994-431: A small volume of material at the surface of a workpiece can be evaporated if it is heated in a very short time, while supplying the energy gradually would allow for the heat to be absorbed into the bulk of the piece, never attaining a sufficiently high temperature at a particular point. Other applications rely on the peak pulse power (rather than the energy in the pulse), especially to obtain nonlinear optical effects. For
6156-405: A source of radiation inserted directly into solid tumors (radium-224), and as an attachment to an tumor-targeting molecule, such as an antibody to a tumor-associated antigen. Radium-223 is an alpha emitter that is naturally attracted to the bone because it is a calcium mimetic. Radium-223 (as radium-223 dichloride) can be infused into a cancer patient's veins, after which it migrates to parts of
6318-497: A staff of theorists and experimentalists" and that while some of the experimental data would prove useful for weapons design, differences in the experimental setup limit their relevance. "Some of the physics is the same; but the details, 'wherein the devil lies,' are quite different. It would therefore also be wrong to assume that NIF will be able to support for the long term a staff of weapons designers and engineers with detailed design competence comparable to that of those now working at
6480-453: A typical kinetic energy of 5 MeV; the speed of emitted alpha particles is 15,000 km/s, which is 5% of the speed of light. This energy is a substantial amount of energy for a single particle, but their high mass means alpha particles have a lower speed than any other common type of radiation, e.g. β particles , neutrons . Because of their charge and large mass, alpha particles are easily absorbed by materials, and they can travel only
6642-646: A very narrow frequency spectrum . Temporal coherence can also be used to produce ultrashort pulses of light with a broad spectrum but durations as short as an attosecond . Lasers are used in optical disc drives , laser printers , barcode scanners , DNA sequencing instruments , fiber-optic and free-space optical communications, semiconductor chip manufacturing ( photolithography , etching ), laser surgery and skin treatments, cutting and welding materials, military and law enforcement devices for marking targets and measuring range and speed, and in laser lighting displays for entertainment. Semiconductor lasers in
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6804-430: A wide bandwidth, making a laser possible that can thus generate pulses of light as short as a few femtoseconds (10 s). In a Q-switched laser, the population inversion is allowed to build up by introducing loss inside the resonator which exceeds the gain of the medium; this can also be described as a reduction of the quality factor or 'Q' of the cavity. Then, after the pump energy stored in the laser medium has approached
6966-492: A wide range of technologies addressing many different motivations. Some lasers are pulsed simply because they cannot be run in continuous mode. In other cases, the application requires the production of pulses having as large an energy as possible. Since the pulse energy is equal to the average power divided by the repetition rate, this goal can sometimes be satisfied by lowering the rate of pulses so that more energy can be built up between pulses. In laser ablation , for example,
7128-408: Is a small spherical pellet containing a few milligrams of fusion fuel, typically a mix of deuterium (D) and tritium (T), as this composition has the lowest ignition temperature. The lasers can either heat the surface of the fuel pellet directly – known as direct drive – or heat the inner surface of a hollow metal cylinder around the pellet – known as indirect drive . In the indirect drive case,
7290-404: Is a transition between energy levels that match the energy carried by the photon or phonon. For light, this means that any given transition will only absorb one particular wavelength of light. Photons with the correct wavelength can cause an electron to jump from the lower to the higher energy level. The photon is consumed in this process. When an electron is excited from one state to that at
7452-477: Is also required for three-level lasers in which the lower energy level rapidly becomes highly populated, preventing further lasing until those atoms relax to the ground state. These lasers, such as the excimer laser and the copper vapor laser, can never be operated in CW mode. In 1917, Albert Einstein established the theoretical foundations for the laser and the maser in the paper " Zur Quantentheorie der Strahlung " ("On
7614-406: Is an anacronym that originated as an acronym for light amplification by stimulated emission of radiation . The first laser was built in 1960 by Theodore Maiman at Hughes Research Laboratories , based on theoretical work by Charles H. Townes and Arthur Leonard Schawlow . A laser differs from other sources of light in that it emits light that is coherent . Spatial coherence allows
7776-413: Is called an optical amplifier . When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser. For lasing media with extremely high gain, so-called superluminescence , light can be sufficiently amplified in a single pass through the gain medium without requiring a resonator. Although often referred to as a laser (see, for example, nitrogen laser ), the light output from such
7938-462: Is emitted by stimulated emission is identical to the photon that triggered its emission, and both photons can go on to trigger stimulated emission in other atoms, creating the possibility of a chain reaction . For this to happen, many of the atoms or molecules must be in the proper excited state so that the photons can trigger them. In most materials, atoms or molecules drop out of excited states fairly rapidly, making it difficult or impossible to produce
8100-421: Is formed by single-frequency quantum photon states distributed according to a Poisson distribution . As a result, the arrival rate of photons in a laser beam is described by Poisson statistics. Many lasers produce a beam that can be approximated as a Gaussian beam ; such beams have the minimum divergence possible for a given beam diameter. Some lasers, particularly high-power ones, produce multimode beams, with
8262-443: Is frequently used in the field, meaning "to give off coherent light," especially about the gain medium of a laser; when a laser is operating, it is said to be " lasing ". The terms laser and maser are also used for naturally occurring coherent emissions, as in astrophysical maser and atom laser . A laser that produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by
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#17328454040088424-421: Is impossible. In some other lasers, it would require pumping the laser at a very high continuous power level, which would be impractical, or destroying the laser by producing excessive heat. Such lasers cannot be run in CW mode. The pulsed operation of lasers refers to any laser not classified as a continuous wave so that the optical power appears in pulses of some duration at some repetition rate. This encompasses
8586-460: Is normally in the form of a small plutonium "spark plug" in the center of the fuel. Nuckolls's idea was to explore how small the secondary could be made, and what effects this would have on the energy needed from the primary to cause ignition. The simplest change is to replace the LiD fuel with DT gas, removing the need for the spark plug. This allows secondaries of any size – as the secondary shrinks, so does
8748-405: Is not the result of random thermal processes. Instead, the release of a photon is triggered by the nearby passage of another photon. This is called stimulated emission . For this process to work, the passing photon must be similar in energy, and thus wavelength, to the one that could be released by the atom or molecule, and the atom or molecule must be in the suitable excited state. The photon that
8910-405: Is the origin of terrestrial helium gas. The best-known source of alpha particles is alpha decay of heavier (mass number of at least 104) atoms. When an atom emits an alpha particle in alpha decay, the atom's mass number decreases by four due to the loss of the four nucleons in the alpha particle. The atomic number of the atom goes down by two, as a result of the loss of two protons –
9072-448: Is to convert the infrared (IR) light at 1053 nm into the ultraviolet (UV) at 351 nm in a device known as a frequency converter . These are made of thin sheets (about 1 cm thick) cut from a single crystal of potassium dihydrogen phosphate . When the 1053 nm (IR) light passes through the first of two of these sheets, frequency addition converts a large fraction of the light into 527 nm light (green). On passing through
9234-489: Is to heat an object; some of the thermal energy being applied to the object will cause the molecules and electrons within the object to gain energy, which is then lost through thermal radiation , that we see as light. This is the process that causes a candle flame to give off light. Thermal radiation is a random process, and thus the photons emitted have a range of different wavelengths , travel in different directions, and are released at different times. The energy within
9396-504: Is to pump the laser material with a source that is itself pulsed, either through electronic charging in the case of flash lamps, or another laser that is already pulsed. Pulsed pumping was historically used with dye lasers where the inverted population lifetime of a dye molecule was so short that a high-energy, fast pump was needed. The way to overcome this problem was to charge up large capacitors which are then switched to discharge through flashlamps, producing an intense flash. Pulsed pumping
9558-441: Is typically expressed through the output being a narrow beam, which is diffraction-limited . Laser beams can be focused to very tiny spots, achieving a very high irradiance , or they can have a very low divergence to concentrate their power at a great distance. Temporal (or longitudinal) coherence implies a polarized wave at a single frequency, whose phase is correlated over a relatively great distance (the coherence length ) along
9720-430: Is used to measure the intensity profile, width, and divergence of laser beams. Diffuse reflection of a laser beam from a matte surface produces a speckle pattern with interesting properties. The mechanism of producing radiation in a laser relies on stimulated emission , where energy is extracted from a transition in an atom or molecule. This is a quantum phenomenon that was predicted by Albert Einstein , who derived
9882-406: The behavior of matter under the conditions found within nuclear explosions. NIF is the largest and most powerful ICF device built to date. The basic ICF concept is to squeeze a small amount of fuel to reach pressure and temperature necessary for fusion. NIF hosts the world's most energetic laser . The laser indirectly heats the outer layer of a small sphere. The energy is so intense that it causes
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#173284540400810044-457: The fundamental interactions responsible for alpha decay are a balance between the electromagnetic force and nuclear force . Alpha decay results from the Coulomb repulsion between the alpha particle and the rest of the nucleus, which both have a positive electric charge , but which is kept in check by the nuclear force . In classical physics , alpha particles do not have enough energy to escape
10206-410: The phase of the emitted light is 90 degrees in lead of the stimulating light. This, combined with the filtering effect of the optical resonator gives laser light its characteristic coherence, and may give it uniform polarization and monochromaticity, depending on the resonator's design. The fundamental laser linewidth of light emitted from the lasing resonator can be orders of magnitude narrower than
10368-438: The potential well from the strong force inside the nucleus (this well involves escaping the strong force to go up one side of the well, which is followed by the electromagnetic force causing a repulsive push-off down the other side). However, the quantum tunnelling effect allows alphas to escape even though they do not have enough energy to overcome the nuclear force . This is allowed by the wave nature of matter, which allows
10530-421: The transverse modes often approximated using Hermite – Gaussian or Laguerre -Gaussian functions. Some high-power lasers use a flat-topped profile known as a " tophat beam ". Unstable laser resonators (not used in most lasers) produce fractal-shaped beams. Specialized optical systems can produce more complex beam geometries, such as Bessel beams and optical vortexes . Near the "waist" (or focal region ) of
10692-497: The "pencil beam" directly generated by a common helium–neon laser would spread out to a size of perhaps 500 kilometers when shone on the Moon (from the distance of the Earth). On the other hand, the light from a semiconductor laser typically exits the tiny crystal with a large divergence: up to 50°. However even such a divergent beam can be transformed into a similarly collimated beam employing
10854-551: The DOE to request a custom military ICF facility named the "Laboratory Microfusion Facility" (LMF). LMF would use a driver on the order of 10 MJ, delivering fusion yields of between 100 and 1,000 MJ. A 1989–1990 review of this concept by the National Academy of Sciences suggested that LMF was too ambitious, and that fundamental physics needed to be further explored. They recommended further experiments before attempting to move to
11016-550: The NIF beamline layout. As of 2005, other targets, called saturn targets, were specifically designed to reduce the anisotropy and improve the implosion. They feature a small plastic ring around the "equator" of the target, which becomes a plasma when hit by the laser. Some of the laser light is refracted through this plasma back towards the equator of the target, evening out the heating. NIF ignition with gains of just over 35 times are thought to be possible, producing results almost as good as
11178-531: The National Ignition Campaign, with the goal of reaching ignition just after the laser reached full power, some time in the second half of 2012. The campaign officially ended in September 2012, at about 1 ⁄ 10 the conditions needed for ignition. Thereafter NIF has been used primarily for materials science and weapons research. In 2021, after improvements in fuel target design, NIF produced 70% of
11340-670: The Quantum Theory of Radiation") via a re-derivation of Max Planck 's law of radiation, conceptually based upon probability coefficients ( Einstein coefficients ) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation. In 1928, Rudolf W. Ladenburg confirmed the existence of the phenomena of stimulated emission and negative absorption. In 1939, Valentin A. Fabrikant predicted using stimulated emission to amplify "short" waves. In 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and effected
11502-503: The Soviet Union, Nikolay Basov and Aleksandr Prokhorov were independently working on the quantum oscillator and solved the problem of continuous-output systems by using more than two energy levels. These gain media could release stimulated emissions between an excited state and a lower excited state, not the ground state, facilitating the maintenance of a population inversion . In 1955, Prokhorov and Basov suggested optical pumping of
11664-614: The acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation", would have been more correct. With the widespread use of the original acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers . Modern physics describes light and other forms of electromagnetic radiation as the group behavior of fundamental particles known as photons . Photons are released and absorbed through electromagnetic interactions with other fundamental particles that carry electric charge . A common way to release photons
11826-489: The adjacent Shiva facility. The resulting system would be much lower power than the LMF concept, with a driver of about 1 MJ. The new design included features that advanced the state of the art in the driver section, including multi-pass in the main amplifiers, and 18 beamlines (up from 10) that were split into 288 "beamlets" as they entered the target area. The plans called for the installation of two main banks of beamlines, one in
11988-745: The alpha particle emitted in alpha decay is mildly dependent on the half-life for the emission process, with many orders of magnitude differences in half-life being associated with energy changes of less than 50%, shown by the Geiger–Nuttall law . The energy of alpha particles emitted varies, with higher energy alpha particles being emitted from larger nuclei, but most alpha particles have energies of between 3 and 7 MeV (mega-electron-volts), corresponding to extremely long and extremely short half-lives of alpha-emitting nuclides, respectively. The energies and ratios are often distinct and can be used to identify specific nuclides as in alpha spectrometry . With
12150-485: The alpha particle to spend some of its time in a region so far from the nucleus that the potential from the repulsive electromagnetic force has fully compensated for the attraction of the nuclear force. From this point, alpha particles can escape. Especially energetic alpha particles deriving from a nuclear process are produced in the relatively rare (one in a few hundred) nuclear fission process of ternary fission . In this process, three charged particles are produced from
12312-450: The amount of energy needed for ignition. At the milligram level, the energy levels started to approach those available through several known devices. By the early 1960s, Nuckolls and several other weapons designers had developed ICF's outlines. The DT fuel would be placed in a small capsule, designed to rapidly ablate when heated and thereby maximize compression and shock wave formation. This capsule would be placed within an engineered shell,
12474-515: The arrival of the X-rays and the subsequent blast. This saved the reentry vehicle (RV) from blast damage and allowed them to be inspected. ICF tests used the same system, replacing the RVs by hohlraums. Each test simultaneously illuminated many targets, each at a different distance from the bomb to test the effect of varying of illumination. Another question was how large the fuel assembly had to be in order for
12636-565: The atmosphere gave off bursts of X-rays that could damage an enemy warhead at long range. To test the effectiveness of this system, and to develop countermeasures to protect US warheads, the Defense Atomic Support Agency (now the Defense Threat Reduction Agency) developed a system that placed the targets at the end of long tunnels behind fast-shutting doors. The doors were timed to shut in the brief period between
12798-409: The atom becomes a new element. Examples of this sort of nuclear transmutation by alpha decay are the decay of uranium to thorium , and that of radium to radon . Alpha particles are commonly emitted by all of the larger radioactive nuclei such as uranium , thorium , actinium , and radium , as well as the transuranic elements. Unlike other types of decay, alpha decay as a process must have
12960-417: The average being set at 20 times. A study of European nuclear workers exposed internally to alpha radiation from plutonium and uranium found that when relative biological effectiveness is considered to be 20, the carcinogenic potential (in terms of lung cancer) of alpha radiation appears to be consistent with that reported for doses of external gamma radiation i.e. a given dose of alpha-particles inhaled presents
13122-476: The beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase that vary randomly with respect to time and position, thus having a short coherence length. Lasers are characterized according to their wavelength in a vacuum . Most "single wavelength" lasers produce radiation in several modes with slightly different wavelengths. Although temporal coherence implies some degree of monochromaticity , some lasers emit
13284-439: The beamlines. Before firing, the amplifiers are first optically pumped by a total of 7,680 flash lamps. The lamps are powered by a capacitor bank that stores 400 MJ (110 kWh). When the wavefront passes through them, the amplifiers release some of the energy stored in them into the beam. The beams are sent through the main amplifier four times, using an optical switch located in a mirrored cavity. These amplifiers boost
13446-419: The behavior of matter and the transfer of energy and radiation under these conditions is key to understanding the basic physics of nuclear weapons and predicting their performance without underground nuclear testing." In 1998, two JASON panels, composed of scientific and technical experts, stated that NIF is the most scientifically valuable of all programs proposed for science-based stockpile stewardship. Despite
13608-425: The blue to near-UV have also been used in place of light-emitting diodes (LEDs) to excite fluorescence as a white light source; this permits a much smaller emitting area due to the much greater radiance of a laser and avoids the droop suffered by LEDs; such devices are already used in some car headlamps . The first device using amplification by stimulated emission operated at microwave frequencies, and
13770-509: The body (upon being inhaled, ingested, or injected, as with the use of Thorotrast for high-quality X-ray images prior to the 1950s), alpha radiation is the most destructive form of ionizing radiation . It is the most strongly ionizing, and with large enough doses can cause any or all of the symptoms of radiation poisoning . It is estimated that chromosome damage from alpha particles is anywhere from 10 to 1000 times greater than that caused by an equivalent amount of gamma or beta radiation, with
13932-505: The bomb tests. This data suggested that about 10 MJ of X-ray energy would be needed to reach ignition, far beyond what had earlier been calculated. If those X-rays are created by beaming an IR laser to a hohlraum, as in Nova or NIF, then dramatically more laser energy would be required, on the order of 100 MJ. This triggered a debate in the ICF community. One group suggested an attempt to build
14094-437: The bone where there is rapid turnover of cells due to the presence of metastasized tumors. Once within the bone, Ra-223 emits alpha radiation that can destroy tumor cells within a 100-micron distance. This approach has been in use since 2013 to treat prostate cancer which has metastasized to the bone. Radionuclides infused into the circulation are able to reach sites that are accessible to blood vessels. This means, however, that
14256-464: The capsule and the x-rays is lossy, and ultimately only about 10 to 14 kJ of energy is deposited in the fuel. The fuels in the center of the target are compressed to a density of about 1000 g/cm For comparison, lead has a density of about 11 g/cm). The pressure is the equivalent of 300 billion atmospheres . Before NIF was constructed, it was expected based on simulations that 10–15 MJ of fusion energy would be released, resulting in
14418-422: The charge-to-mass ratio of alpha particles to be half that of the hydrogen ion. Rutherford proposed three explanations: 1) an alpha particle is a hydrogen molecule (H 2 ) with a charge of 1 e ; 2) an alpha particle is an atom of helium with a charge of 2 e ; 3) an alpha particle is half a helium atom with a charge of 1 e . At that time in history, scientists knew that hydrogen ions have an atomic weight of 1 and
14580-403: The cylinder, called a hohlraum (German for 'hollow room' or 'cavity'), becomes hot enough to re-emit the energy as even higher frequency X-rays . These X-rays, which are more symmetrically distributed than the original laser light, heat the surface of pellet. In either case, the material on the outside of the pellet is turned into a plasma , which explodes away from the surface. The rest of
14742-561: The effect of nonlinearity in optical materials (e.g. in second-harmonic generation , parametric down-conversion , optical parametric oscillators and the like). Unlike the giant pulse of a Q-switched laser, consecutive pulses from a mode-locked laser are phase-coherent; that is, the pulses (and not just their envelopes ) are identical and perfectly periodic. For this reason, and the extremely large peak powers attained by such short pulses, such lasers are invaluable in certain areas of research. Another method of achieving pulsed laser operation
14904-535: The effort. In 1964, Charles H. Townes, Nikolay Basov, and Aleksandr Prokhorov shared the Nobel Prize in Physics , "for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser–laser principle". Alpha particle Alpha particles , also called alpha rays or alpha radiation , consist of two protons and two neutrons bound together into
15066-561: The ending of the Cold War led to dramatic changes in defense funding and priorities. The political support for nuclear weapons declined and arms agreements led to a reduction in warhead count and less design work. The US was faced with the prospect of losing a generation of nuclear weapon designers able to maintain existing stockpiles, or design new weapons. At the same time, the Comprehensive Nuclear-Test-Ban Treaty (CTBT)
15228-454: The energy of the laser, beating the record set in 1997 by the JET reactor at 67% and achieving a burning plasma . On December 5, 2022, after further technical improvements, NIF reached "ignition", or scientific breakeven , for the first time, achieving a 154% energy yield compared to the input energy. However, while this was scientifically a success, the experiment in practice produced less than 1% of
15390-492: The energy the facility used to create it: while 3.15 MJ of energy was yielded from 2.05 MJ input, the lasers delivering the 2.05 MJ of energy took about 300 MJ to produce in the facility. Inertial confinement fusion (ICF) devices use intense energy to rapidly heat the outer layers of a target in order to compress it. Nuclear fission provides the energy source for thermonuclear warheads, while sources such as laser beams and particle beams are used in non-weapon devices. The target
15552-548: The event instead of the normal two, with the smallest of the charged particles most probably (90% probability) being an alpha particle. Such alpha particles are termed "long range alphas" since at their typical energy of 16 MeV, they are at far higher energy than is ever produced by alpha decay. Ternary fission happens in both neutron-induced fission (the nuclear reaction that happens in a nuclear reactor), and also when fissionable and fissile actinides nuclides (i.e., heavy atoms capable of fission) undergo spontaneous fission as
15714-477: The existing Nova beamline room, and the other in the older Shiva building next door, extending through its laser bay and target area into an upgraded Nova target area. The lasers would deliver about 500 TW in a 4 ns pulse. The upgrades were expected to produce fusion yields of between 2 and 10 MJ. The initial estimates from 1992 estimated construction costs around $ 400 million, with construction taking place from 1995 to 1999. Throughout this period,
15876-595: The first demonstration of stimulated emission. In 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping , which was experimentally demonstrated two years later by Brossel, Kastler, and Winter. In 1951, Joseph Weber submitted a paper on using stimulated emissions to make a microwave amplifier to the June 1952 Institute of Radio Engineers Vacuum Tube Research Conference in Ottawa , Ontario, Canada. After this presentation, RCA asked Weber to give
16038-434: The flashlamps and laser glass to regain their shapes after firing (due to thermal expansion), limiting their use to one or fewer firings per day. One of the goals for NIF has been to reduce this time to less than four hours, in order to allow 700 firings a year. NIF is also exploring new types of targets. Previous experiments generally used plastic ablators , typically polystyrene (CH). NIF targets are constructed by coating
16200-491: The focal point. The filters ensure that the beam image is extremely uniform. Spatial filters were a major step forward. They were introduced in the Cyclops laser , an earlier LLNL experiment. The end-to-end length of the path the laser beam travels, including switches, is about 1,500 metres (4,900 ft). The various optical elements in the beamlines are generally packaged into Line Replaceable Units (LRUs), standardized boxes about
16362-452: The form of the 20-beam 200 kJ Nova laser . During the construction phase, Nuckolls found an error in his calculations, and an October 1979 review chaired by former LLNL director John S. Foster Jr. confirmed that Nova would not reach ignition. It was modified into a smaller 10-beam design that converted the light to 351 nm and increase coupling efficiency. Nova was able to deliver about 30 kJ of UV laser energy, about half of what
16524-538: The fuel explodes outward. Construction on the NIF began in 1997. NIF was completed five years behind schedule and cost almost four times its original budget. Construction was certified complete on March 31, 2009, by the U.S. Department of Energy . The first large-scale experiments were performed in June 2009 and the first "integrated ignition experiments" (which tested the laser's power) were declared completed in October 2010. From 2009 to 2012 experiments were conducted under
16686-411: The fuel symmetrically. The reactions release high-energy particles, some of which, primarily alpha particles , collide with unfused fuel and heat it further, potentially triggering additional fusion. At the same time, the fuel is also losing heat through x-ray losses and hot electrons leaving the fuel area. Thus the rate of alpha heating must be greater than the loss rate, termed bootstrapping . Given
16848-479: The fuel to self-heat from the fusion reactions and thus reach ignition. Initial data were available by mid-1984, and the testing ceased in 1988. Ignition was achieved for the first time during these tests. The amount of energy and the size of the fuel targets needed to reach ignition was far higher than predicted. During this same period, experiments began on Nova using similar targets to understand their behavior under laser illumination, allowing direct comparison against
17010-545: The fully symmetric direct drive approach. The history of ICF at Lawrence Livermore National Laboratory in Livermore, California , started with physicist John Nuckolls , who started considering the problem after a 1957 meeting arranged by Edward Teller there. During these meetings, the idea later known as PACER emerged. PACER envisioned the explosion of small hydrogen bombs in large caverns to generate steam that would be converted into electrical power. After identifying problems with this approach, Nuckolls wondered how small
17172-543: The fusion energy routinely exceeded 2 MJ. To be useful for energy production, a fusion facility must produce fusion output at least an order of magnitude more than the energy used to power the laser amplifiers – 400 MJ in the case of NIF. Commercial laser fusion systems would use much more efficient diode-pumped solid state lasers , where wall-plug efficiencies of 10 percent have been demonstrated, and efficiencies 16–18 percent were expected with advanced concepts under development in 1996. As of 2010 NIF aimed to create
17334-616: The half-life is long enough to allow for handling and shipping the seeds to a cancer treatment center at any location across the globe. Targeted alpha therapy for solid tumors involves attaching an alpha-particle-emitting radionuclide to a tumor-targeting molecule such as an antibody, that can be delivered by intravenous administration to a cancer patient. In computer technology, dynamic random access memory (DRAM) " soft errors " were linked to alpha particles in 1978 in Intel 's DRAM chips. The discovery led to strict control of radioactive elements in
17496-481: The hohlraum, which acts like the bomb casing. The hohlraum did not have to be heated by x-rays; any source of energy could be used as long as it delivered enough energy to heat the hohlraum and produce x-rays. Ideally the energy source would be located some distance away, to mechanically isolate both ends of the reaction. A small atomic bomb could be used as the energy source, as in a hydrogen bomb, but ideally smaller energy sources would be used. Using computer simulations,
17658-476: The human body and also many metres of dense solid shielding, depending on their energy. To a lesser extent, this is also true of very high-energy helium nuclei produced by particle accelerators. The term "alpha particle" was coined by Ernest Rutherford in reporting his studies of the properties of uranium radiation. The radiation appeared to have two different characters, the first he called " α {\displaystyle \alpha } radiation" and
17820-501: The indirect drive method of operation, in which the laser heats a small metal cylinder surrounding the capsule inside it, which then emits X-rays that heat the fuel pellet. Experimental systems, including the OMEGA and Nova lasers , validated this approach. The NIF's high power supports a much larger target than OMEGA or Nova; the baseline pellet design is about 2 mm in diameter. It is chilled to about 18 kelvin (−255 °C) and lined with
17982-575: The initial criticism, Sandia, as well as Los Alamos, supported the development of many NIF technologies, and both laboratories later became partners with NIF in the National Ignition Campaign. Work on the NIF started with a single beamline demonstrator, Beamlet. Beamlet successfully operated between 1994 and 1997. It was then sent to Sandia National Laboratories as a light source in their Z machine . A full-sized demonstrator then followed, in AMPLAB, which started operations in 1997. The official groundbreaking on
18144-530: The interior of a large tumor that is not vascularized (i.e. is not well penetrated by blood vessels) may not be effectively eradicated by the radioactivity. Radium-224 is a radioactive atom that is utilized as a source of alpha radiation in a cancer treatment device called DaRT ( diffusing alpha emitters radiation therapy ). Each radium-224 atom undergoes a decay process producing 6 daughter atoms. During this process, 4 alpha particles are emitted. The range of an alpha particle—up to 100 microns—is insufficient to cover
18306-770: The international STAR collaboration using the Relativistic Heavy Ion Collider at the U.S. Department of Energy 's Brookhaven National Laboratory to detect the antimatter partner of the helium-4 nucleus. Like the Rutherford scattering experiments , the antimatter experiment used gold. This time the gold ions ions moving at nearly the speed of light and colliding head on to produce the antiparticle, also dubbed "anti-alpha" particle. Alpha-emitting radionuclides are presently being used in three different ways to eradicate cancerous tumors: as an infusible radioactive treatment targeted to specific tissues (radium-223), as
18468-659: The labs to divide up SSMP efforts. An important part of this would be confirmation of computer models using low-yield ICF experiments. The Nova Upgrade was too small to use for these experiments. A redesign matured into NIF in 1994. The estimated cost of the project remained almost $ 1 billion, with completion in 2002. In spite of the agreement, the large project cost combined with the ending of similar projects at other labs resulted in critical comments by scientists at other labs, Sandia National Laboratories in particular. In May 1997, Sandia fusion scientist Rick Spielman publicly stated that NIF had "virtually no internal peer review on
18630-422: The laser power inside the cavity; this equilibrium determines the operating point of the laser. If the applied pump power is too small, the gain will never be sufficient to overcome the cavity losses, and laser light will not be produced. The minimum pump power needed to begin laser action is called the lasing threshold . The gain medium will amplify any photons passing through it, regardless of direction; but only
18792-426: The laser system from vibration, the foundation of each laser bay was made independent of the rest of the structure. Three-foot-thick, 420-foot-long and 80-foot-wide slabs required continuous concrete pours to achieve their specifications. Laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation . The word laser
18954-501: The lasing medium or pumping mechanism, then it is still classified as a "modulated" or "pulsed" continuous wave laser. Most laser diodes used in communication systems fall into that category. Some applications of lasers depend on a beam whose output power is constant over time. Such a laser is known as a continuous-wave ( CW ) laser. Many types of lasers can be made to operate in continuous-wave mode to satisfy such an application. Many of these lasers lase in several longitudinal modes at
19116-414: The latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved. In this state, the rate of stimulated emission is larger than the rate of absorption of light in the medium, and therefore the light is amplified. A system with this property
19278-485: The light four times through a circuit containing a neodymium glass amplifier similar to (but much smaller than) the ones used in the main beamlines, boosting the millijoules to about 6 joules. According to LLNL, designing the PAMs was one of the major challenges. Subsequent improvements allowed them to surpass their initial design goals. The main amplification takes place in a series of glass amplifiers located at one end of
19440-462: The light is reflected off mirrors in the switchyard and target area in order to hit the target from different directions. Since the path length from the Master Oscillator to the target is different for each beamline, optics are used to delay the light in order to ensure that they all reach the center within a few picoseconds of each other. One of the last steps before reaching the target chamber
19602-450: The linewidth of light emitted from the passive resonator. Some lasers use a separate injection seeder to start the process off with a beam that is already highly coherent. This can produce beams with a narrower spectrum than would otherwise be possible. In 1963, Roy J. Glauber showed that coherent states are formed from combinations of photon number states, for which he was awarded the Nobel Prize in physics . A coherent beam of light
19764-402: The literal cavity that would be employed at microwave frequencies in a maser . The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption. If the gain (amplification) in
19926-522: The lower level, emitting a new photon. The emitted photon exactly matches the original photon in wavelength, phase, and direction. This process is called stimulated emission. The gain medium is put into an excited state by an external source of energy. In most lasers, this medium consists of a population of atoms that have been excited into such a state using an outside light source, or an electrical field that supplies energy for atoms to absorb and be transformed into their excited states. The gain medium of
20088-407: The main NIF site was on May 29, 1997. At the time, the DOE was estimating that the NIF would cost approximately $ 1.1 billion and another $ 1 billion for related research, and would be complete as early as 2002. Later in 1997 the DOE approved an additional $ 100 million in funding and pushed the operational date back to 2004. As late as 1998 LLNL's public documents stated the overall price
20250-412: The maximum possible level, the introduced loss mechanism (often an electro- or acousto-optical element) is rapidly removed (or that occurs by itself in a passive device), allowing lasing to begin which rapidly obtains the stored energy in the gain medium. This results in a short pulse incorporating that energy, and thus a high peak power. A mode-locked laser is capable of emitting extremely short pulses on
20412-498: The medium is larger than the resonator losses, then the power of the recirculating light can rise exponentially . But each stimulated emission event returns an atom from its excited state to the ground state, reducing the gain of the medium. With increasing beam power, the net gain (gain minus loss) reduces to unity and the gain medium is said to be saturated. In a continuous wave (CW) laser, the balance of pump power against gain saturation and cavity losses produces an equilibrium value of
20574-443: The more penetrating one he called " β {\displaystyle \beta } radiation". After five years of additional experimental work, Rutherford and Hans Geiger determined that "the alpha particle, after it has lost its positive charge, is a Helium atom". Alpha radiation consists of particles equivalent to doubly-ionized helium nuclei (He ) which can gain electrons from passing through matter. This mechanism
20736-516: The nuclear charge in an atom and thus the number of electrons in an atom is equal to its atomic number . In 1920, Rutherford deduced the existence of the proton as the source of positive charge in the atom. In 1932, James Chadwick discovered the neutron . Thereafter it was known that an alpha particle is an agglomeration of two protons and two neutrons, essentially a helium atom with no electrons. While anti-matter equivalents for helium-3 have been known since 1970, it took until 2010 for members of
20898-404: The object is not random, however: it is stored by atoms and molecules in " excited states ", which release photons with distinct wavelengths. This gives rise to the science of spectroscopy , which allows materials to be determined through the specific wavelengths that they emit. The underlying physical process creating photons in a laser is the same as in thermal radiation, but the actual emission
21060-451: The order of tens of picoseconds down to less than 10 femtoseconds . These pulses repeat at the round-trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator. Due to the Fourier limit (also known as energy–time uncertainty ), a pulse of such short temporal length has a spectrum spread over a considerable bandwidth. Thus such
21222-432: The original 6 J to a nominal 4 MJ. Given the time scale of a few nanoseconds, the peak UV power delivered to the target reaches 500 TW. Near the center of each beamline, and taking up the majority of the total length, are spatial filters . These consist of long tubes with small telescopes at the end that focus the beam to a tiny point in the center of the tube, where a mask cuts off any stray light outside
21384-422: The pellet is driven inward on all sides, into a small volume of extremely high density. The surface explosion creates shock waves that travel inward. At the center of the fuel, a small volume is further heated and compressed. When the temperature and density are high enough, fusion reactions occur. The energy must be delivered quickly and spread extremely evenly across the target's outer surface in order to compress
21546-418: The photons in a spatial mode supported by the resonator will pass more than once through the medium and receive substantial amplification. In most lasers, lasing begins with spontaneous emission into the lasing mode. This initial light is then amplified by stimulated emission in the gain medium. Stimulated emission produces light that matches the input signal in direction, wavelength, and polarization, whereas
21708-409: The power output is essentially continuous over time or whether its output takes the form of pulses of light on one or another time scale. Of course, even a laser whose output is normally continuous can be intentionally turned on and off at some rate to create pulses of light. When the modulation rate is on time scales much slower than the cavity lifetime and the period over which energy can be stored in
21870-662: The properties of the emitted light, such as the polarization, wavelength, and shape of the beam. Electrons and how they interact with electromagnetic fields are important in our understanding of chemistry and physics . In the classical view , the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom . However, quantum mechanical effects force electrons to take on discrete positions in orbitals . Thus, electrons are found in specific energy levels of an atom, two of which are shown below: An electron in an atom can absorb energy from light ( photons ) or heat ( phonons ) only if there
22032-456: The reaction to a 2-dimensional approximation, which was all that was possible with the available computing power. LASNEX estimated that laser drivers in the kJ range could reach low gain, which was just within the state of the art. This led to the Shiva laser project which was completed in 1977. Shiva fell far short of its goals. The densities reached were thousands of times smaller than predicted. This
22194-457: The relationship between the A coefficient , describing spontaneous emission, and the B coefficient which applies to absorption and stimulated emission. In the case of the free electron laser , atomic energy levels are not involved; it appears that the operation of this rather exotic device can be explained without reference to quantum mechanics . A laser can be classified as operating in either continuous or pulsed mode, depending on whether
22356-426: The right conditions—high enough density, temperature, and duration—bootstrapping results in a chain reaction , burning outward from the center. This is known as ignition , which fuses a significant portion of the fuel and releases large amounts of energy. As of 1998, most ICF experiments had used laser drivers. Other drivers have been examined, such as heavy ions driven by particle accelerators . NIF primarily uses
22518-410: The rock strata and acquire electrons, becoming helium atoms. Therefore an alpha particle is essentially a helium atom stripped of two electrons. In 1909, Ernest Rutherford and Thomas Royds finally proved that alpha particles were indeed helium ions. To do this they collected and purified the gas emitted by radium, a known alpha particle emitter, in a glass tube. An electric spark discharge inside
22680-650: The same risk as a 20-times higher dose of gamma radiation. The powerful alpha emitter polonium-210 (a milligram of Po emits as many alpha particles per second as 4.215 grams of Ra ) is suspected of playing a role in lung cancer and bladder cancer related to tobacco smoking . Po was used to kill Russian dissident and ex- FSB officer Alexander V. Litvinenko in 2006. In 1896, Henri Becquerel discovered that uranium emits an invisible radiation that can leave marks on photographic plates, and this mystery radiation wasn't phosphorescence . Marie Curie showed that this phenomenon, which she called "radioactivity",
22842-410: The same time, and beats between the slightly different optical frequencies of those oscillations will produce amplitude variations on time scales shorter than the round-trip time (the reciprocal of the frequency spacing between modes), typically a few nanoseconds or less. In most cases, these lasers are still termed "continuous-wave" as their output power is steady when averaged over longer periods, with
23004-426: The second sheet, frequency combination converts much of the 527 nm light and the remaining 1053 nm light into 351 nm (UV) light. Infrared (IR) light is much less effective than UV at heating the targets, because IR couples more strongly with hot electrons that absorb a considerable amount of energy and interfere with compression. The conversion process can reach peak efficiencies of about 80 percent for
23166-414: The size of a vending machine that can be dropped out of the beamline for replacement from below. After amplification is complete the light is switched back into the beamline, where it runs to the far end of the building to the target chamber. The target chamber is a 10-metre-diameter (33 ft) multi-piece steel sphere weighing 130,000 kilograms (290,000 lb). Just before reaching the target chamber,
23328-418: The sphere to implode, squeezing the fuel inside. The implosion reaches a peak speed of 350 km/s (0.35 mm/ns), raising the fuel density from about that of water to about 100 times that of lead . The delivery of energy and the adiabatic process during implosion raises the temperature of the fuel to hundreds of millions of degrees. At these temperatures, fusion processes occur in the tiny interval before
23490-469: The teams estimated that about 5 MJ of energy would be needed from the primary, generating a 1 MJ beam. To put this in perspective, a small (0.5 kt ) fission primary releases 2 TJ. While Nuckolls and LLNL were working on hohlraum-based concepts, UCSD physicist Keith Brueckner was independently working on direct drive. In the early 1970s, Brueckner formed KMS Fusion to commercialize this concept. This sparked an intense rivalry between KMS and
23652-414: The technical issues" and that "Livermore essentially picked the panel to review themselves". A retired Sandia manager, Bob Puerifoy, was even more blunt than Spielman: "NIF is worthless ... it can't be used to maintain the stockpile, period". Ray Kidder , one of the original developers of the ICF concept at LLNL, was also highly critical. He stated in 1997 that its primary purpose was to "recruit and maintain
23814-400: The tube produced light. Subsequent study of the spectra of this light showed that the gas was helium and thus the alpha particles were indeed the helium ions. In 1911, Rutherford used alpha particle scattering data to argue that the positive charge of an atom is concentrated in a tiny nucleus. In 1913, Antonius van den Broek suggested that anomalies in the periodic table would be reduced if
23976-425: The two mirrors, the output coupler , is partially transparent. Some of the light escapes through this mirror. Depending on the design of the cavity (whether the mirrors are flat or curved ), the light coming out of the laser may spread out or form a narrow beam . In analogy to electronic oscillators , this device is sometimes called a laser oscillator . Most practical lasers contain additional elements that affect
24138-406: The uranium and found that, for the first four foils, the current steadily decreased at a geometric rate. However, after the fourth layer of foil over the uranium, the current didn't drop much and remained more or less level for up to twelve layers of foil. This result indicated that uranium radiation has two components. Rutherford dubbed one component "alpha radiation" which was fully absorbed by just
24300-410: The very high-frequency power variations having little or no impact on the intended application. (However, the term is not applied to mode-locked lasers, where the intention is to create very short pulses at the rate of the round-trip time.) For continuous-wave operation, the population inversion of the gain medium needs to be continually replenished by a steady pump source. In some lasing media, this
24462-417: The weapons design laboratories." In 1997, Victor Reis, assistant secretary for Defense Programs within DOE and SSMP chief architect defended the program telling the U.S. House Armed Services Committee that NIF was "designed to produce, for the first time in a laboratory setting, conditions of temperature and density of matter close to those that occur in the detonation of nuclear weapons. The ability to study
24624-470: The weapons labs. Formerly ignored, ICF became a hot topic and most of the labs started ICF work. LLNL decided to concentrate on glass lasers, while other facilities studied gas lasers using carbon dioxide (e.g. ANTARES, Los Alamos National Laboratory ) or KrF (e.g. Nike laser , Naval Research Laboratory ). Throughout these early stages, much of the understanding of the fusion process was the result of computer simulations, primarily LASNEX . LASNEX simplified
24786-408: The width of many tumors. However, radium-224's daughter atoms can diffuse up to 2–3 mm in the tissue, thus creating a "kill region" with enough radiation to potentially destroy an entire tumor, if the seeds are placed appropriately. Radium-224's half-life is short enough at 3.6 days to produce a rapid clinical effect while avoiding the risk of radiation damage due to overexposure. At the same time,
24948-515: Was $ 1.2 billion, with the first eight lasers coming online in 2001 and full completion in 2003. The facility's physical scale alone made the construction project challenging. By the time the "conventional facility" (the shell for the laser) was complete in 2001, more than 210,000 cubic yards of soil had been excavated, more than 73,000 cubic yards of concrete had been poured, 7,600 tons of reinforcing steel rebar had been placed, and more than 5,000 tons of structural steel had been erected. To isolate
25110-598: Was called a maser , for "microwave amplification by stimulated emission of radiation". When similar optical devices were developed they were first called optical masers , until "microwave" was replaced by "light" in the acronym, to become laser . Today, all such devices operating at frequencies higher than microwaves (approximately above 300 GHz ) are called lasers (e.g. infrared lasers , ultraviolet lasers , X-ray lasers , gamma-ray lasers ), whereas devices operating at microwave or lower radio frequencies are called masers. The back-formed verb " to lase "
25272-551: Was enough to attain the majority of the LMF goals.That program was estimated to cost about $ 600 million FY 1989 dollars. An additional $ 250 million would pay to upgrade it to a full 1,000 MJ. The total would surpass $ 1 billion to meet all of the goals requested by the DOE. The NAS review led to a reevaluation of these plans, and in July 1990, LLNL responded with the Nova Upgrade, which would reuse most of Nova, along with
25434-459: Was estimated to be more than enough to cause ignition, allowing fusion energy gains of about 40x, somewhat higher than the indirect drive system. As of 2005, scaled implosions on the OMEGA laser and computer simulations showed NIF to be capable of ignition using a polar direct drive (PDD) configuration where the target was irradiated directly by the laser only from the top and bottom, without changes to
25596-412: Was expected, primarily due to optical damage to the final focusing optics. Even at those levels, it was clear that the predictions for fusion production were wrong; even at the limited powers available, fusion yields were far below predictions. Each experiment showed that the energy needed to reach ignition continued to be underestimated. The Department of Energy (DOE) decided that direct experimentation
25758-409: Was not unique to uranium and a consequence of individual atoms. Ernest Rutherford studied uranium radiation and discovered that it could create ions , electrically charged particles in gas (thus we now call it ionizing radiation ). In 1899, Rutherford discovered that uranium radiation is a mixture of two types of radiation. He performed an experiment which involved two electrodes separated by
25920-516: Was signed in 1996, which would ban all criticality testing and made the development of newer generations of nuclear weapons more difficult. Out of these changes came the Stockpile Stewardship and Management Program (SSMP), which, among other things, included funds for the development of methods to design and build nuclear weapons without having to test them explosively. In a series of meetings that started in 1995, an agreement formed between
26082-469: Was the best way to settle the issue, and in 1978 they started a series of underground experiments at the Nevada Test Site that used small nuclear bombs to illuminate ICF targets. The tests were known as Halite (LLNL) and Centurion (LANL). The basic concept behind the tests had been developed in the 1960s as a way to develop anti-ballistic missile warheads. It was found that bombs that exploded outside
26244-424: Was traced to issues with the way the laser delivered heat to the target. Most of its energy energized electrons rather than the entire fuel mass. Further experiments and simulations demonstrated that this process could be dramatically improved by using shorter wavelengths. Further upgrades to the simulation programs, accounting for these effects, predicted that a different design would reach ignition. This system took
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