Experiments directed toward developing fusion power are invariably done with dedicated machines which can be classified according to the principles they use to confine the plasma fuel and keep it hot.
The major division is between magnetic confinement and inertial confinement. In magnetic confinement, the tendency of the hot plasma to expand is counteracted by the Lorenz force between currents in the plasma and magnetic fields produced by external coils. The particle densities tend to be in the range of 1018 to 1022 m-3 and the linear dimensions in the range of 0.1 to 10 m. The particle and energy confinement times may range from under a millisecond to over a second, but the configuration itself is often maintained through input of particles, energy, and current for times that are hundreds or thousands of times longer. Some concepts are capable of maintaining a plasma indefinitely.
In contrast, with inertial confinement, there is nothing to counteract the expansion of the plasma. The confinement time is simply the time it takes the plasma pressure to overcome the inertia of the particles, hence the name. The densities tend to be in the range of 1031 to 1033 m-3 and the plasma radius in the range of 1 to 100 micrometers. These conditions are obtained by irradiating a millimeter-sized solid pellet with a nanosecond laser or ion pulse. The outer layer of the pellet is ablated, providing a reaction force that compresses the central 10% of the fuel by a factor of 10 or 20 to 103 or 104 times solid density. These microplasmas disperse in a time measured in nanoseconds. For a reactor, a repetition rate of several per second will be needed.
Magnetic confinement
Within the field of magnetic confinement experiments, there is a basic division between toroidal and open magnetic field topologies. Generally speaking, it is easier to contain a plasma in the direction perpendicular to the field than parallel to it. Parallel confinement can be solved either by bending the field lines back on themselves into circles or, more commonly, toroidal surfaces, or by constricting the bundle of field lines at both ends, which causes some of the particles to be reflected by the mirror effect. The toroidal geometries can be further subdivided according to whether the machine itself has a toroidal geometry, i.e., a solid core through the center of the plasma. The alternative is to dispense with a solid core and rely on currents in the plasma to produce the toroidal field.
Mirror machines have advantages in a simpler geometry and a better potential for direct conversion of particle energy to electricity. They generally require higher magnetic fields than toroidal machines, but the biggest problem has turned out to be confinement. For good confinement there must be more particles moving perpendicular to the field than there are moving parallel to the field. Such a non-Maxwellian velocity distribution is, however, very difficult to maintain and energetically costly.
The mirrors' advantage of simple machine geometry is maintained in machines which produce compact toroids, but there are potential disadvantages for stability in not having a central conductor and there is generally less possibility to control (and thereby optimize) the magnetic geometry. Compact toroid concepts are generally less well developed than those of toroidal machines. While this does not necessarily mean that they cannot work better than mainstream concepts, the uncertainty involved is much greater.
Somewhat in a class by itself is the Z-pinch, which has circular field lines. This was one of the first concepts tried, but it did not prove very successful. Furthermore, there was never a convincing concept for turning the pulsed machine requiring electrodes into a practical reactor.
The dense plasma focus is a controversial and "non-mainstream" device that relies on currents in the plasma to produce a toroid. It is a pulsed device that depends on a plasma that is not in equilibrium and has the potential for direct conversion of particle energy to electricity. Experiments are ongoing to test relatively new theories to determine if the device has a future.
Toroidal machine
Toroidal machines can be axially symmetric, like the tokamak and the RFP, or asymmetric, like the stellarator. The additional degree of freedom gained by giving up toroidal symmetry might ultimately be usable to produce better confinement, but the cost is complexity in the engineering, the theory, and the experimental diagnostics. Stellarators typically have a periodicity, e.g. a fivefold rotational symmetry. The RFP, despite some theoretical advantages such as a low magnetic field at the coils, has not proven very successful.
* Alcator C-Mod, Massachusetts Institute of Technology, United States [1]
* ASDEX Upgrade (Axialsymmetrisches Divertorexperiment), Max-Planck-Institut für Plasmaphysik, Garching, Germany [2]
* DIII-D, General Atomics, United States [3]
* EAST, Anhui, People's Republic of China
* IGNITOR, Frascati, Italy [4]
* ITER, Cadarache, France [5] (to be constructed)
* JT-60, JAERI, Japan [6]
* JET (Joint European Torus), Culham, UK [7]
* KSTAR, National Fusion Research Institute, Republic of Korea [8]
* MAST (Mega-Ampere Spherical Tokamak), Culham, UK [9]
* NSTX (National Spherical Torus Experiment), Princeton Plasma Physics Laboratory, United States [10]
* PEGASUS Toroidal Experiment, University of Wisconsin–Madison, United States [11]
* SST-1 (Steady State Superconducting Tokamak), Institute for Plasma Research, India [12] (under construction)
* START (Small Tight Aspect Ratio Tokamak), Culham, UK [13] (1991-1998)
* TCV (Tokamak à Configuration Variable), École Polytechnique Fédérale de Lausanne, Switzerland [14]
* TEXTOR (Tokamak Experiment for Technology Oriented Research), Forschungszentrum Jülich, Germany [15]
* TFR (Tokamak de Fontenay-aux-Roses), Commissariat à l'énergie atomique, Fontenay-aux-Roses, France
* TFTR (Tokamak Fusion Test Reactor), Princeton Plasma Physics Laboratory, United States [16] (1982-1997)
* Tore Supra, Département de Recherches sur la Fusion Contrôlée, Cadarache, France
* NCSX (National Compact Stellarator Experiment), Princeton Plasma Physics Laboratory, United States [17] (phased out)
* Wendelstein-7AS, Max-Planck-Institut für Plasmaphysik, Garching, Germany [18] (1988-2002)
* Wendelstein 7-X, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany [19] (under construction)
* LHD (Large Helical Device), National Institute for Fusion Science, Japan [20]
* Helically Symmetric Experiment (HSX) University of Wisconsin–Madison, United States [21]
* H-1 Heliac, Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australia [22]
* TJ-II[23], National Fusion Laboratory, Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (Ciemat)[24], Spain
Reversed field pinch (RFP)
* RFX (Reversed-Field eXperiment), Consorzio RFX, Padova, Italy [25]
* MST (Madison Symmetric Torus), University of Wisconsin–Madison, United States [26]
* T2R, Royal Institute of Technology, Stockholm, Sweden
* TPE-RX, AIST, Tsukuba, Japan
Compact Toroid (CT)
* Sustained Spheromak Physics Experiment
Field-Reversed Configuration (FRC)
Open field lines
Levitated Dipole
* Levitated Dipole Experiment (LDX), MIT/Columbia University, United States [27]
Laser-driven
Current or under construction experimental facilities
Solid state lasers
* National Ignition Facility (NIF), United States [28]
* Commissariat à l'Énergie Atomique's Laser Mégajoule at Barp, Gironde (Bordeaux, France) (under construction)
* The Laboratory for Laser Energetics' OMEGA EL Laser in Rochester, US.
* The Gekko XII laser at the Institute for Laser Engineering in Osaka, Japan
* ISKRA-4 and ISKRA-5 Lasers at the Russian Federal Nuclear Center VNIIEF [29]
Le Laser Mégajoule (currently under construction)
* The Naval Research Laboratories' Pharos laser, 2 beam 1 Kj/pulse (IR) Nd:Glass laser
* Vulcan laser at the central Laser Facility, Rutherford Appleton Laboratory, 2.6 Kj/pulse (IR) Nd:glass laser
* Trident laser, at LANL; 3 beams total; 2 x 400 J beams, 100 ps - 1 us; 1 beam ~100 J, 600 fs - 2 ns.
Gas lasers
* The Naval Research Laboratories' NIKE laser. (Krypton Fluoride gas laser)
* PALS (Prague Asterix Laser System) formerly the "Asterix IV" laser at the Academy of Sciences of the Czech Republic. [30](1 kJ max. output iodine laser at 1.315 micrometre fundamental wavelength)
Dismantled experimental facilities
Solid-state lasers
* 4 pi laser built during the mid 1960s at Lawrence Livermore National Laboratory
* Long path laser built at LLNL in 1972
* The two beam Janus laser built at LLNL in 1975
* The two beam Cyclops laser built at LLNL in 1975
* The two beam Argus laser built at LLNL in 1976
* The 20 beam Shiva laser built at LLNL in 1977
* 24 beam OMEGA laser completed in 1980 at the University of Rochester's Laboratory for Laser Energetics
* The 10 beam Nova laser (dismantled) at LLNL. (First shot taken, December 1984 - final shot taken and dismantled in 1999)
Gas lasers
* "Single Beam System" or simply "67" after the building number it was housed in, a 1 Kj carbon dioxide laser at Los Alamos National Laboratory
* Gemini laser, 2 beams, 2.5 Kj carbon dioxide laser at LANL
* Helios laser, 8 beam, ~10 Kj carbon dioxide laser at LANL
* Antares laser (dismantled) at LANL. (40 kJ CO2 laser, largest ever built, production of hot electrons in target plasma due to long wavelength of laser resulted in poor laser/plasma energy coupling)
* Aurora laser 96 beam 1.3 Kj total krypton fluoride (KrF) laser at LANL
* Sprite laser few joules/pulse laser at the Central Laser Facility, Rutherford Appleton Laboratory
* Z machine
* ZEBRA device at the University of Nevada's Nevada Terawatt Facility. [31]
* Saturn accelerator at Sandia National Laboratory [32]
Inertial electrostatic confinement
* Fusor
* Polywell
Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License
