At the Lawrence Livermore National Laboratory in the USA, construction has been completed of the world's most powerful laser – the National Ignition Facility. $3.5 billion was spent on the needs of the project, and building the laser took 12 years.
The facility, the size of a football field, consists of 192 independent laser emitters which during the experiments will direct their beams simultaneously at a target a few centimetres across. In one thousandth of a second a beam will travel about 300 m. The pulse energy will reach 1.8 million J. Scientists expect the temperature and the pressure at the target to come close to the values in the Sun's core.
The superlaser will be used for peaceful purposes as well as military ones. In particular, the US Air Force will use it to test the fitness of nuclear warheads made decades ago. Among the peaceful applications of the laser scientists name astrophysical experiments, in which the processes going on inside stars and planets will be modelled, and research into the possibilities of nuclear fusion. In the words of Edward Moses, the head of the project, “experiments of this level will be carried out for the first time in the whole history of science”.
It should be recalled that thermonuclear fusion reactions were discovered more than 70 years ago. In 1934 George Gamow, an American physicist of Russian origin, put forward the idea that nuclear reactions proceeding at high temperature could be a source of energy able to keep stars hot for billions of years. The detailed theory of nuclear reactions in stars was extended by the Nobel laureate Hans Bethe in 1938. In these reactions more complex nuclei of other elements — helium, lithium, boron, carbon — are synthesised from hydrogen nuclei. And since they are formed at high temperature, these reactions are called thermonuclear fusion.
Thermonuclear fusion reactions are carried out in facilities of different types: some, the so-called tokamaks (from “toroidal chamber with a magnetic coil”), hold the plasma inside a closed loop by means of magnets. In the largest tokamak, JET, built by the European Union in Great Britain, the power of the thermonuclear reaction already reaches 16,000 kW, returning about 40% of the energy put into the plasma.
Facilities of the other type use superpowerful laser beams, which are directed at a target of thermonuclear fuel from all sides. This is a mixture of deuterium with tritium, cooled below the melting temperature of hydrogen (−263 °C).