National Ignition Facility

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Cross-section through the NIF. The laser pulse is generated in the space to the right of the center and directed into the beam guides (blue) and on to the amplifiers (violet). After passing through the amplifier several times, the light is cleaned by filters (blue) and directed into the "switching field" (red), which guides it further into the target chamber (silver). The assembly hall for optical glasses can be found in the upper left corner.
The target in the target holder on the transport arm. The two triangular shells enclose the target gas-tight during transport and keep it cold. They are only opened shortly before the laser shot.
Entrance area of ​​the NIF hall

The National Ignition Facility ( NIF ) is a facility of the Lawrence Livermore National Laboratory (LLNL) in Livermore , California , United States and is overseen by the National Nuclear Security Administration (NNSA). In this facility, which was completed in 2009, experiments on inertial fusion take place. The purpose is to simulate nuclear weapon explosions in order to ensure the functional reliability of American nuclear weapons without surface or underground nuclear weapon tests. Initially it was announced that inertial fusion as a civilian energy source was also the goal.

The first directly aimed at ignition of nuclear fusion experiment in the NIF in September 2010. The imposed by the US Congress appointment ignition ( Ignition ) of thermonuclear fusion to be reached by the end of September 2012 could not be met; the target could only be compressed to half the calculated density. The goal of a fusion reactor is no longer mentioned in 2012.

The lead scientist is John Lindl .

Layout and function

The most powerful laser in the world is located in the NIF . The laser systems take up most of the building, which is three soccer fields in size. A laser pulse with a duration of 15 nanoseconds , distributed over 192 beam lines, brings an energy of several mega joules into the evacuated target chamber . The fusion fuel, a mixture of the hydrogen isotopes deuterium and tritium , is located as a thin frozen layer (18  Kelvin ) on the inside of a 2 mm small spherical plastic capsule centrally in a small gold-plated metal cylinder. The two openings at the ends of the cylinder are each covered with two layers of thin film for thermal protection. The outer film heats up to 25 K due to the ambient radiation, enough to allow any remaining condensed air to evaporate in the vacuum of the chamber. However, the foils are permeable to the laser beams that aim past the capsule ( indirect drive ) onto the inner surface of the cylinder. Gold is black at the laser wavelength of 351 nm, so it completely absorbs the radiation. The laser energy thermalises within the pulse duration and fills the cylinder with X-rays ( cavity radiation ). The surface of the capsule turns into a rapidly expanding plasma . The recoil of the expansion accelerates the spherical shell to a speed of several 100 km / s. If it succeeds in reaching the center with sufficient symmetry, the ignition threshold is reached there at temperatures of 50 to 100 million Kelvin and a density that exceeds that of lead a hundred times, at which the fusion reaction continues to “burn” automatically. Then the fusion zone would migrate from the inside to the outside within a few 10  picoseconds ; about half of the material should fuse and release much more energy than was necessary for ignition.

State of the experiments

After the systems were put into operation in January 2010, a density and temperature were reached for the first time at the end of September 2010 at which the deuterium-tritium mixture reacts at all. At the end of 2013, it was possible to release more nuclear fusion energy than the approximately 10 kJ that had previously been introduced into the reaction zone by compression.

The test capacity of the system is limited, as each individual "shot" has to be prepared in a complex manner. In 2011 around 310 shots were carried out, around half of which were used for nuclear fusion research. The target chamber is made of 10 cm thick aluminum. In the event of a shot with a significant release of fast neutrons, it becomes radioactive; in particular, sodium-24 is produced, a beta and gamma emitter with a half-life of 15 hours. Several days of cooldown are then required before personnel can enter the chamber to prepare for the next shot.

In June 2016 was in a report to the Department of Energy associated National Nuclear Security Administration doubted scientific arguments whether the ignition of a fusion plasma can ever be achieved with NIF.

In 2017 it was possible to use the system to measure cross sections , which are important for understanding hydrogen burning in stars, under star-like conditions.

Goals of the experiments

In addition to the experiments as part of the Stockpile Stewardship Program to simulate nuclear weapon explosions as a replacement for the weapons tests previously carried out, the facility was also intended to be used for research into inertial fusion for peaceful energy generation. This is no longer mentioned in the meantime (2017). However, the results obtained from the measurements on the fundamentals of stellar astrophysics are reported.

Data from the NIF laser

  • Number of beam lines: 192
  • Aperture of the laser medium: 40 × 40 cm
  • Pump source: flashlights
  • Laser medium: Nd: glass (phosphate)
  • Fundamental wavelength: 1053 nm
  • Frequency tripled: wavelength 351 nm
  • Efficiency (pump light UV): 0.7%
  • Pulse energy per beam: 18.75 kJ
  • Focus (beam diameter at the target): 5 times the diffraction limit
  • Shot repetition rate: 4 to 6 pulses per day
  • Area of ​​the building: 230,000 sq ft, equivalent to approximately 21,368 m²
  • Planned costs and construction time (as of 1994): 1.2 billion US $, completion 2002
  • actual cost: $ 3.4 billion
  • Completion: May 2009
  • First "full system" shot with> 1 MJ: October 2010

literature

  • Philip Bethge: Disneyland for Physicists . In: Der Spiegel . No. 45 , 2009, p. 144 f . ( online ).

Web links

Commons : National Ignition Facility  - collection of pictures, videos and audio files

Individual evidence

  1. ^ NIC Conducts First Integrated Ignition Experiment ( February 21, 2013 memento in the Internet Archive ). Retrieved September 12, 2011
  2. ↑ A Big Laser Runs Into Trouble . NYT October 6, 2012, accessed October 11, 2012
  3. ↑ Report defines new path for NIF . optics.org, December 19, 2012.
  4. ^ Final Optics Assembly . ( Memento of February 16, 2013 in the Internet Archive ) NIF home.
  5. ↑ Sam Naghshineh: Deformable mirror and the National Ignition Facility , July 8, 2013.
  6. ^ LLNL: Targeting Ignition . In: Science & Technology Review , 6/2012.
  7. ↑ a b Fusion Energy: High-power Lasers for Clean Energy. (No longer available online.) In: NIF home. Archived from the original on October 25, 2013 ; Retrieved November 15, 2012 .
  8. ↑ Successful dress rehearsal for laser fusion . Heise Online News, accessed on February 11, 2010
  9. ^ 1st Successful Ignition Experiment at NIF. In: photonics.com. October 25, 2010. Retrieved October 28, 2010 .
  10. ↑ Fuel gain exceeding unity in an inertially confined fusion implosion . In: Nature , February 12, 2014.
  11. ^ Laser fusion near crucial milestone . In: Nature , March 7, 2012.
  12. ↑ Online book about the system ( Memento of May 2, 2012 in the Internet Archive ) p. 56
  13. ↑ D. Kramer: Article. In: Physics Today , June 2016
  14. ↑ a b D. T. Casey, DB Sayre u. a .: Thermonuclear reactions probed at stellar-core conditions with laser-based inertial-confinement fusion. In: Nature Physics. 2017, doi: 10.1038 / nphys4220 .
  15. ↑ Could This Lump Power the Planet? In: Newsweek , November 14, 2009.
  16. ↑ Michael Wiescher, Dieter Schneider: A stellar plasma on earth . In: Physik Journal , Vol. 18, 2019, Issue 4, pp. 29–34