The encryption of the program is underway

The financial difficulties of the reactor project thermonuclear Iter will take advantage of its competing alternative Hiper (High Power Laser Energy Research) Since a few weeks, the protagonists of this program that engages the CEA and CNRS are on war footing to boast assets: same objectives, schedule and chances of success, but for a much more competitive cost.

Hiper and Iter interested in the same issue: how to reproduce and control the energy mechanisms of stars on Earth The theory is known: in the heart of the Sun, hydrogen nuclei are able to merge with the high temperatures (15 million degrees). The reaction creates a helium nucleus and releases energy as neutron.

Two scenarios

To control this compromise between temperature, density and time during which the environment must be maintained under these conditions, physicists have devised two scenarios. Magnetic fusion is likely to be the most expensive: the reaction occurs in a superconducting magnet confining plasma at high temperatures (100 million degrees). There are introduced by two isotopes of hydrogen (deuterium and tritium). As in the stars, their merger produces a helium atom and a very energy neutron. It is the principle of Iter including the weakest link is the low density of fuel in the medium. Using a laser, inertial confinement fusion partially fixes the problem to Iter. Met millimetre beads of deuterium and tritium are excited by a localized power source. The heating of the envelope mechanically compressed gas, as in a bicycle pump. In the warmer central point (100 million degrees), a first atomic fusion occurs. The initial energy spreads to other nuclei, merging in turn and so on until chain reaction produces more energy than what was spent to initiate it.

Remains unknown: how much energy is required for ignition At least 1 megajoule, according to the calculation of the physicists who will soon have two demonstrators to validate their theory, in the United States (National Ignition Facility will there be first here laser fire in 2012) and Bordeaux where Laser Mega Joule, delivered in 2014 by the ECA, will issue enough power to boil two litres of water in one billionth of a second.

As for the Iter plasma, laser technology presents risks of instability, particularly because the probability of mixing between the fuel and material component the IMB, a multilayer complex alloys, glass and plastics. Hence the idea of separating the reaction in two separate operations: first compress the gas by a powerful laser beam, then heat the fuel by other more intense fire. "By combining two types of laser, should achieve a rapid and economical lighting", says François Amiranoff, Director of the laboratory for the use of intense lasers (Luli) and coordinator of the European project Hiper, who bet on these results.

Making tracks

To succeed this challenge, researchers need to uniformly distribute energy to all parts of the fuel ball, projecting a multitude of shooting laser at a high frequency. "We aim 1 kilojoules to a frequency of 10 Hz", details the specialist in plasma physics. A few days ago, his new laser Lucia took a first step in the race to achieve two shots per second (2 Hz) of an intensity of 7 joules. A result which, according to François Amiranoff, "is password to validate the preparatory phase of Hiper".

Started in 2009 with a budget of EUR 11 million, must be completed in one year with the definition of large scientific options. In addition to lasers, it remains to determine tracks for the economically acceptable manufacture of the fuel logs. Researchers must also draw the system that will position the fuel. It finally find materials can withstand prolonged Neutron fluxes.

Then follow scientific testing to develop the specifications of the loads of a préréacteur, then the construction of a prototype will help draw the architecture of the reactor. Optimistic goal of the calendar: 2035. The encryption of the program is underway. It should not exceed EUR 1 billion, or 10 of the Iter project.