Laser Mégajoule (LMJ) is an experimental inertial confinement fusion (ICF) device being built in France by the French nuclear science directorate, CEA. Inertial confinement fusion ( ICF) is a process where Nuclear fusion reactions are initiated by heating and compressing a fuel target typically in the form of This article is about the country For a topic outline on this subject see List of basic France topics. The Commissariat à l’énergie atomique (Atomic Energy Commission or CEA, is a French “public establishment of an industrial and commercial character” whose Laser Mégajoule plans to deliver about 1. 8 MJ of laser power to its targets, making it about as powerful as its US counterpart, the National Ignition Facility (NIF). The National Ignition Facility, or NIF, is a Laser -based Inertial confinement fusion (ICF research device under construction at the Lawrence Laser Mégajoule is the the largest ICF experiment to be built outside the US, where ICF research has been strongly related to nuclear weapons research. A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. Likewise, one of Laser Mégajoule's primary tasks will be refining fusion calculations for France's own nuclear weapons industry. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus

Laser Mégajoule uses a series of 240 laser beamlines, grouped into eight groups of 30. Each beamline contains two main glass amplifiers, which are optically pumped using xenon flashlamps. Optical pumping is a process in which Light is used to raise (or "pump" Electrons from a lower Energy level in an Atom or Molecule A xenon flash lamp is an Electric glow discharge lamp designed to produce extremely intense incoherent, full-spectrum white light for very short durations A "feeder" laser beam is fed via optical fiber into each of the beamlines where it travels through the two amplifiers. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length In order to extract more power from the amplifiers, which are not particularly efficient in transmitting power to the beam, the laser pulse is sent through the amplifiers twice by an optical switch in front of a mirror. In Telecommunication, an optical switch is a Switch that enables signals in Optical fibers or Integrated optical circuits (IOCs to be selectively At the other end of the beamline a deformable mirror is used to remove imperfections in the wavefront.

The target chamber lies in a large experiment room in the middle of the building, with the beamlines arranged on either side. After being switched into the main room, the beams are first aimed towards the target chamber by mirrors, and then travel through an optical frequency multiplier to boost the frequency into the ultraviolet. This article is too short and requires more citations-- please add notices An optical frequency multiplier is a nonlinear optical device in which Photons Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The mirrors are arranged in order to have the pulse impinge in the middle of the chamber from all sides.

A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for frequency conversion on the LMJ. A single crystal, also called monocrystal, is a Crystalline Solid in which the Crystal lattice of the entire sample is continuous and unbroken Monopotassium phosphate (also potassium dihydrogen phosphate, KDP, or monobasic potassium phosphate, MKP) -- 24 -- Saint-Gobain SA ( is a French Multinational corporation, founded in 1665 in Paris and headquartered on the outskirts of Paris at La Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization

Like NIF, LMJ intends to use the "indirect drive" approach, where the laser light is used to heat a high-Z cylinder made of some heavy metal (often gold) known as a "hohlraum". Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 In Radiation Thermodynamics, a hohlraum (a German Loanword, originally a non-specific word for "hollow area" or "cavity" The hohlraum then gives off x-rays, which are used to heat a small fuel pellet containing a deuterium-tritium (DT) fusion fuel. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth Tritium (ˈtɹɪtiəm symbol or, also known as Hydrogen-3) is a radioactive Isotope of Hydrogen. Although considerable laser energy is lost to heating the hohlraum, x-rays are much more efficient at heating the fuel pellet, making the indirect drive method applicable to nuclear weapons research. The x-rays rapidly heat the outer layer of the pellet so quickly that it explodes outward, causing the remainder of the pellet to be forced inward and causes a shock wave to travel in through the pellet to the middle. When the shock wave converges from all directions and meets in the middle, the density and temperature briefly reach the Lawson criterion and start fusion reactions. In Nuclear fusion research the Lawson criterion, first derived by John D If the rate of reactions is high enough the heat generated by these reactions will be enough to cause surrounding fuel to fuse as well, this process continuing until the majority of the fuel in the pellet is consumed. This process is known as "ignition", and has long been a goal of fusion researchers.

Construction on the Laser Mégajoule started with a single set of eight beamlines known as the Ligne d'Integration Laser (Laser Integration Line), or LIL, powered by a 450 MJ energy bank. The Laser Integration Line is a sub-piece use in the Laser Mégajoule. When problems are worked out in the LIL, construction will continue with the construction of four more similar units and the installation of the additional beamlines. LIL was completed in 2002, and currently the entire LMJ system is expected to be completed in 2010 (originally 2008).

References

• Laser Mégajoule (in French)