Laser Mégajoule (LMJ) is a large laser-based inertial confinement
fusion (ICF) research device being built near Bordeaux, in
the French nuclear science directorate, CEA.
Laser Mégajoule plans to
deliver about 1.8 MJ of laser energy to its targets, making it
about as energetic as its US counterpart, the National Ignition
Laser Mégajoule is the largest ICF experiment to be
built outside the US, where ICF research has been strongly related to
nuclear weapons research. Likewise,
Laser Mégajoule's primary tasks
will be refining fusion calculations for France's own nuclear
Laser Mégajoule uses a series of 176 laser beamlines. Each beamline
contains two main glass amplifiers, which are optically pumped using
xenon flashlamps. A "feeder" laser beam is fed via optical fiber into
each of the beamlines where it travels through the two amplifiers. 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. 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. 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
Saint-Gobain for frequency conversion on the LMJ.
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". The hohlraum then gives off
x-rays, which are used to heat a small fuel pellet containing a
deuterium-tritium (DT) fusion fuel. 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. 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'Intégration
Integration Line), or LIL, powered by a 450 MJ energy bank. 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. The first laser
beam shots were planned for the beginning of 2014, but commencement
of operations was later postponed until December of that year.
Laser Mégajoule". CEA - Direction des Applications Militaires.
Retrieved 12 June 2012.
^ Charles Crespya; Denis Villate; Olivier Lobios (2013). "Study of
laser megajoule calorimeter's thermal behaviour for energy measurement
uncertainty optimisation". Review of Scientific Instruments. 81 (1).
Archived from the original on 2013-07-11.
^ Hélène Arzeno (11 January 2014). "Premier tir le 2 décembre au
Laser Megajoule". Sud Ouest. Retrieved 25 October 2014.
Optical systems in the LMJ
Laser Mégajoule (in French)
Laser Mégajoule (in English)
Fusion experimental devices by confinement method
Asia and Australia
Asia and Australia
Dense plasma focus
Laser Inertial Fusion Energy
Asterix IV (PALS)
International Fusion Materials Irradiation Facility
Coordinates: 44°38′30.88″N 0°47′15.91″W /
44.6419111°N 0.7877528°W / 44.6419111