They generate a ‘burning plasma’, a new milestone in nuclear fusion

THE Nuclear fusion generates the light and heat of the stars, and on Earth could also be our sustainable energy source in the future. Unlike what happens in the fission reactions of current nuclear power plants, where an atomic nucleus is split into two lighter ones, in fusion reactions two light nuclei (usually deuterium and tritium, isotopes of hydrogen) come together to form another, heavier nucleus. and produce energy.

But recreating this process in the laboratory is a challenge, as it consumes much more energy than it obtains and several critical steps must be overcome. One of them is to get self heating of matter in a plasma state (not solid, liquid or gas) through nuclear fusion, and this week researchers at Lawrence Livermore National Laboratory (LLNL), in California (USA), report that they succeeded.

For the first time in a nuclear fusion research facility, the fuel was largely self-heated, a clear milestone on the way to proving that energy can be generated from fusion.

Chris Young (Lawrence Livermore National Laboratory)

According to a study published in the journal Naturegot a ‘burning plasma‘, in which nuclear fusion is the main source of heat to keep the fuel from deuterium-tritium in a plasma state hot enough to allow further fusion reactions.

“For the first time in a fusion research facility, the fuel mostly heated up,” one of the authors, a physicist Chris Young, which explains: “For fusion reactions to occur, the fuel needs to be very hot (about 100 million Fahrenheit) with some sort of external heat source, but in a hot plasma it is the fusion reactions themselves that heat the fuel. . plasma more than external heating”.

Therefore, the creation of an igneous plasma is a clear frame on the way to showing that energy can be generated from fusion, which would be relevant for the production of electricity”, emphasizes Young.

Plasma combustion was carried out in the installation National Ignition Facility (NIF) from the Californian laboratory using 192 laser beamswith which a capsule containing 200 micrograms of fuel deuterium-tritium thermonuclear reactor, reaching temperatures and pressures high enough to trigger self-heating fusion reactions.

In the ‘destiny bay’ of the NIF, which was also the engine room of the starship Enterprise in the movie ‘Star Trek: Into Darkness’, 192 laser beams converge at the center of this giant sphere to implode the tiny hydrogen isotope fuel capsule. . / Damien Jemison

The procedure used was Inertial Confinement Fusion (ICF)for its acronym in English), “where the ‘inertia’ of a shell of material that implodes by means of lasers is used, to confine and heat the fusion fuel inside”, explains the physicist, who confirms that the process very short: “In inertial confinement fusion, the plasma burns until a few hundred picoseconds (trillionth of a second, 10^-12 seconds)”.

Previous attempts to get hold of the fiery plasma have been limited by problems controlling its form and preventing it from altering the way laser beams deposit energy into it, but the improved experimental design What the LLNL scientists have achieved has made it possible to use capsules that can hold more fuel and absorb more energy, while maintaining plasma. The details of the system optimization are also published this week in the magazine Physical Nature.

Experiment design before (left) and after being improved (right). / Nigel Woolsey adapted from . Zylstra et al.

The yield generated in these experiments, where a maximum value of up to 170 kilojoules of energytriple that obtained in previous tests.

Two new milestones ahead

The authors consider this a milestone in nuclear fusion, but acknowledge that there is a long way to go before electricity can be produced on a commercial scale using this procedure.

“Building a reactor brings with it a large number of additional technical challenges, and our current focus is on the underlying science,” says Young, who anticipates that upcoming milestones include demonstrating fusion’s ‘ignition’ and then “gaining power”.

After plasma burning, the next steps with increasing difficulty will be ignition and energy gain.

Chris Young (Lawrence Livermore National Laboratory)

“On a burning plasma – explains – its conditions are such that the self-heating of alpha particles (protons and neutrons generated from tritium deuterium) in the plasma overcomes heating from external sources; but in one ignited plasma or on, the self-heating of these alpha particles is already so great that it far outweighs all energy losses in the fusion plasma, producing thermodynamic instability.”

The next step will be energy gain, “what happens when more energy is obtained from fusion than was supplied to create the fusion plasma. This point needs to be reached before nuclear fusion energy is commercially viable. Basically, the steps of increasing difficulty are plasma burning, ignition, and energy gain.”

Fire plasma of the future in ITER

The physicist clarifies that the concept of plasma burning is applicable to all approaches to nuclear fusion, although the path to achieve it can be through very different routes. In their case, they used inertial confinement with lasers, but there is also the option of magnetic fusion energy (MFE)where electromagnetic fields are used to confine and heat the plasma.

This last approach is followed in the ITER, the massive experimental facility being built, slowly but surely, in the south of France. Its objective is also to demonstrate that nuclear fusion can help solve the Earth’s energy problem and for that its promoters will generate a plasma that will circulate at 150 million degrees Celsius, caged inside a circular vacuum chamber by means of very powerful magnetic fields. .

ITER (which means ‘road’ in Latin) will be an experimental project and will not supply power to the grid, but its successor: DEMOone demo reactor which makes it possible to produce electricity from fusion processes. In both cases the components of the plasma will also be deuterium and tritium, which will react to generate helium and neutrons. They are the ones who will transfer their energy to generate electricity.

The IFMIF-DONES facility in Grenada will recreate the neutron irradiation conditions that will occur after fusion reactions, with the aim of validating materials found close to them, either in a reactor such as ITER or DEMO or in facilities similar to the NIF

José Aguilar (IFMIF-DONES)

But for this to be possible and profitable, it is necessary to develop materials able to resist high energy neutrons and high heat flux and the design with which this challenge will be approached is with IFMIF (International Facility for Irradiation of Fusion Materials). Its mission will be to generate a database of irradiated materials that will be used for the DEMO reactor, developing several phases, one of which includes an installation in Spain: IFMIF DONATIONS.

“This facility will recreate the neutron irradiation conditions that will occur after fusion reactions, with the aim of validating materials found close to them, whether in a fusion reactor like ITER or DEMO or similar facilities. similar for the different procedures”, he tells SINC José AguilarCoordinator of the IFMIF-DONES Technical Office.

Aguilar recalls that in 2017 the European Union decided that the location of the IFMIF-DONES in European territory would be carried out in Escuzar (Grenade)“and we are currently carrying out engineering work to prepare the start of the construction phase, with only official confirmation at European level remaining in the coming months.”