Wednesday, May 18

US scientists take a key step towards nuclear fusion, a source of clean and unlimited energy

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

But recreating this process in the lab is a challenge, since much more energy is consumed than is obtained, and several critical steps must be overcome. One of them is to achieve the self-heating of matter in a plasma state (it is neither solid, liquid nor gas) through nuclear fusion, and this week researchers from the Lawrence Livermore National Laboratory (LLNL), in California (USA), They report that they have succeeded.

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

Chris Young
(Lawrence Livermore National Laboratory)

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

“For the first time in a fusion research facility, the fuel has mostly self-heated”, one of the authors, physicist Chris Young, tells SINC, explaining: “For fusion reactions to take place, it is necessary heat the fuel a lot (to about 100 million Fahrenheit) with some kind of external heat source, but in a burning plasma it’s the fusion reactions themselves that heat the plasma more than that external heating.”

“The creation of a fiery plasma is therefore a clear milestone on the way to showing that energy can be generated from fusion, which would be relevant to the production of electricity,” says Young.

Plasma combustion was carried out at the Californian laboratory’s National Ignition Facility (NIF) using 192 laser beams, with which a capsule containing 200 micrograms of deuterium-tritium thermonuclear fuel was rapidly heated and compressed, reaching temperatures and pressures high enough to trigger the self-heating fusion reactions.

The procedure used has been inertial confinement fusion (ICF), “where the ‘inertia’ of a shell of material that is imploded by lasers is used to confine and heat the fusion fuel in its interior”, clarifies the physicist, who confirms that the process lasts very little: “In fusion by inertial confinement, the plasma burns up to a couple of hundred picoseconds (trillionth of a second, 10-12 seconds)”.

Previous attempts to capture the fiery plasma were limited by problems controlling its shape and preventing it from altering the way lasers deliver energy onto it, but improved experimental design by LLNL scientists has made it possible to use capsules that can hold more fuel and absorb more energy while maintaining plasma. The details of the optimization of the system are also published this week in the magazine Nature Physics.

The yield generated in these experiments, where a maximum value of up to 170 kilojoules of energy has been reached, triples that obtained in previous tests.

Two new milestones ahead

The authors consider this to be 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 huge number of additional technical challenges, and our current focus is on the underlying science,” says Young, who anticipates that the next milestones include demonstrating fusion ‘ignition’ and then the “energy gain”.

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

Chris Young
(Lawrence Livermore National Laboratory)

“In a fiery plasma,” he explains, “conditions are such that the self-heating of the alpha particles (protons and neutrons generated from tritium deuterium) in the plasma exceeds the heating from external sources; but in an ignited plasma, the self-heating of those alpha particles is already so large that it far outweighs all the energy losses in the fusion plasma, leading to thermodynamic instability.”

The next step will be energy gain, “which occurs when you get more energy out of fusion than you put into it to create the fusion plasma. You need to get to this point before nuclear fusion power is commercially available.” Basically, the steps of increasing difficulty are burning plasma, ignition, and energy gain.”

Future fiery plasma at ITER

The physicist clarifies that the concept of burning plasma is applicable to all approaches to nuclear fusion, although the way to reach it may be through very different routes. In their case, they have 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 latter approach is the one followed in the ITER, the huge experimental facility that is being built, slowly but surely, In the south of france. Its objective is also to demonstrate that nuclear fusion can help solve the energy problem on Earth and for this 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 feed energy into the grid, but its successor will: DEMO, a demonstration reactor that allows electricity to be produced 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. These are the ones that will transfer your energy for electricity generation.

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

“In this facility, the neutron irradiation conditions that will occur after the fusion reactions will be recreated, with the aim of validating the materials found near them, either in a fusion reactor such as ITER or DEMO or in similar facilities. to NIF, since the problem is similar for the different procedures”, José Aguilar, Coordinator of the IFMIF-DONES Technical Office, told SINC.

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