Inertial fusion

from Wikipedia, the free encyclopedia
Stations in the ignition of an inertial fusion reaction:
1. Laser or X-ray radiation heats the fusion target.
2. The fusion fuel is compressed by the inward implosion pressure of the outer layer.
3. The fuel reaches the density and temperature required for ignition.
4. Nuclear fusion processes take place, a multiple of the energy used is released.
Note: Blue arrows stand for inwardly directed radiation processes, orange for outwardly directed; Violet ones represent the thermal energy (shock wave) used for compression

As inertial confinement fusion methods are referred to appropriate for very short time conditions for thermonuclear reactions produce, namely the fusion of deuterium and tritium .

principle

In contrast to the magnetic confinement of the fusion plasma (see nuclear fusion reactor and fusion by means of magnetic confinement ), the Lawson criterion is fulfilled in the case of "inertial confinement" in that the fuel is extremely compressed and heated up by very fast, superficial energy input. The necessary containment time to "burn off" a large part of the fuel is then only nanoseconds . During this short time the inertia of the plasma itself is sufficient to hold it together; hence the name inertial fusion . Inertial fusion can claim that its functioning with energy gain has already been proven in practice, because the hydrogen bomb works according to this principle. The work on inertial fusion at the Lawrence Livermore National Laboratory resulted from efforts to miniaturize hydrogen bombs. Considerations about inertial fusion with lasers were first publicly presented in a 1972 Nature article by John Nuckolls and colleagues.

Procedure

A small amount of fusion fuel within a reactor vessel can be heated up very quickly by high-energy, sufficiently finely focusable light or particle beams (see driver ). These rays - at least two rays from opposite directions, but in most concepts far more - enter the target through small openings , a hollow body a few millimeters in size. Inside there is a small ball of a few milligrams of fusion fuel in solid form, such as a frozen deuterium-tritium mixture. The rays hit the inner wall of the target and heat it up so that the resulting plasma radiates thermally in the X-ray range . Radiation transport heats all surfaces evenly, including that of the fuel globule, see cavity radiation . The gas pressure of the plasma breaks off an outer layer, compressing the remaining fuel concentrically. In the center of the shock wave, the temperature is sufficient for the fusion reaction. This method of causing the fusion fuel to react by means of the intermediate hollow body is known as indirect drive .

Original hopes that the fuel ball encased with thin glass or metal could be compressed sufficiently evenly by means of the jets serving as drivers without the interposition of the hollow radiation body ( direct drive ), have proven to be unrealistic; the Rayleigh-Taylor instability exacerbates any unevenness.

Another method - which has not yet been tested in practice (2012) - is to bring about compression and ignition separately by using an additional high-intensity laser pulse ( fast ignitor ) to strongly heat the compressed plasma at one point.

Use

Experimental observations of the burning process in a fusion plasma of extremely high density are not possible with a hydrogen bomb , because its energy output is limited by the nuclear fission explosion necessary for ignition ; a reaction chamber and measuring devices would be destroyed. Inertial fusion, on the other hand, can be brought about and examined with very small (milligram) amounts of fuel in a reaction chamber.

These investigations - as a replacement for the nuclear weapons tests previously carried out by the nuclear powers - are primarily of military interest. The pilot plants NIF in the USA and LMJ in France (see below ) are operated or built for this purpose and financed mainly from military budgets. They are therefore not geared towards the development of inertial fusion power plants. The “sociology of weapons laboratories” was also cited as a secondary motive for the high level of investment, as these would need new projects to attract young scientists after the nuclear armament had been scaled back.

The crucial difference between these experiments, each with individual "shots" and a reactor that provides permanent useful energy, is that the targets in the reactor would have to be positioned and ignited in rapid succession (several per second). In addition, the achievement of a net energy gain - at least with laser drivers - has so far also failed because of the efficiency of the drivers.

driver

Theoretically, concepts with laser , light ion and heavy ion beams are examined . So far, only laser technology has been significantly developed experimentally.

Laser-driven test facilities

The older high-power laser NOVA at the Lawrence Livermore National Laboratory
View inside an A315 amplifier (second largest amplifier, free beam diameter 315 mm) of the NOVA system (USA) and the PHEBUS (France). The amplifier has been used in Germany as the main amplifier for the high-energy laser system PHELIX since 2003

The NIF ( National Ignition Facility ) is located at the Lawrence Livermore National Laboratory in Livermore, California. 192 high-power lasers were installed on an area of ​​20,000 m², the beams of which converge in a spherical reaction chamber 10 meters in diameter. The hollow body, which is a few millimeters in size, is placed in the middle of the chamber. The plant went into full operation in 2009. In October 2010, a full shot was coupled into a tritium-containing target for the first time. In July 2012, the laser pulse achieved a peak power of 423 terawatts, a world record for high-power lasers. In September and November 2013, two experiments in which all 192 lasers were used succeeded in generating more energy by nuclear fusion than the fuel had previously absorbed from the ablation layer of the fuel globule.

The French LMJ ( Laser Mégajoule ) has been developed near Bordeaux since 1994 and has been set up since 2004. The LIL (ligne d'intégration laser) is currently the first system for testing the technologies in operation. Here, 360 flash lamps are used on an area of ​​10,000 m² that convert 15 MJ (megajoules) of stored electrical energy. The planned LMJ system is to use 10,800 flash lamps and 440 MJ on 40,000 m². The project sponsor is the CEA 2 ( Commissariat à l'énergie atomique et aux énergies alternatives ), the French nuclear energy authority, which is also responsible for military research.

The planned European fusion test facility High Power laser Energy Research Facility (HiPER) is to use the fast ignitor technology.

Ion beam driver

High-performance laser drivers are not yet suitable for power plant purposes, i.e. net energy generation, because the efficiency and also the possible shot repetition frequency are still too low.

Heavy ion beams have a much higher energy density than laser beams and could - with essentially known technology - be generated with much better efficiency. Light ion beams (for example lithium ions ) also have different arguments in terms of physics and accelerator technology .

The ion-driven fusion for energy generation is currently (as of 2012) only discussed theoretically. Considered attempts in Germany with the ion accelerator of the GSI Helmholtz Center for Heavy Ion Research and their PHELIX high-energy laser system in combination will not be pursued further, as the expansion of the international accelerator center FAIR at GSI has priority.

literature

  • JJ Duderstadt, G. Moses: Inertial Confinement Fusion. Wiley, 1982.
  • G. Velarde, Y. Ronen, JM Martinez-Val (Eds.): Nuclear Fusion by Inertial Confinement. CRC Press, 1993, ISBN 0-8493-6926-6 .
  • AA Harms, KF Schoepf, GH Miley, DR Kingdon: Principles of Fusion Energy . World Scientific, Singapore 2000, ISBN 981-02-4335-9 .
  • S. Pfalzner: An Introduction to Inertial Confinement Fusion. CRC Press, 2006, ISBN 0-7503-0701-3 .

Individual evidence

  1. ^ J. Nuckolls, L. Wood, A. Thiessen, G. Zimmerman: Laser compression of matter to superhigh densities: thermonuclear applications . Nature , Vol. 239, 1972, pp. 139-142.
  2. ↑ Information from the German Physical Society on inertial fusion (as of 2011) .
  3. ↑ H. Darnbeck: US military wants to research nuclear fusion in small format. In: Spiegel-Online from March 25, 2008.
  4. ↑ photonics.com: 1st Successful Ignition Experiment at NIF , October 25, 2010, accessed March 24, 2011.
  5. ↑ Lawrence Livermore National Laboratory: Newsroom: In the News, NIF & Photon Science , 2012.
  6. ↑ Fuel gain exceeding unity in an inertially confined fusion implosion , in: Nature , February 12, 2014
  7. ↑ Will Dunham: US scientists achieve 'turning point' in fusion energy quest , Reuters , February 12, 2014.
  8. ↑ cea.fr: Le prototype de la LIL. ( Memento of December 30, 2008 in the Internet Archive ) accessed on March 30, 2009 (French).
  9. ↑ HiPER website
  10. ↑ Inertial fusion with heavy ion beams. (PDF; only accessible after accepting a security certificate).
  11. ^ Ingo Hofmann; Rudolf Bock: Heavy Ion Inertial Fusion . In: Reinhard Stock (Ed.): Encyclopedia of Nuclear Physics and its Applications . Wiley-VCH, Weinheim 2013, ISBN 978-3-527-40742-2 , chapter 24.
  12. ↑ see design of a reactor with light ion driver (PDF, in English; 31.08 MB).
  13. ↑ see article: Part I: The Energy that Drives the Stars Comes Closer to Earth of the LBNL

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