Press District – a historic step for inertial integration

Can you first remind us of what nuclear fusion is?

There are two ways to generate energy from nuclear reactions.

First of all, there
nuclear fission, which includes the breaking of heavy atomic nuclei. This mechanism is used in nuclear power plants.

There is also
fusion, is an experimental phase reverse reaction, in which light nuclei, particularly the isotopes of hydrogen (deuterium and tritium) are grouped together over a very short distance, in order to generate thermonuclear energy. This reproduces the physical reaction that occurs in the core of stars. To get close enough to them and overcome the natural electrostatic repulsion between these cores, the material must be heated to several million degrees Celsius under very high pressure. Then the substance ionizes and forms a plasma.

What are the benefits of fusion to produce energy?

These fusion reactions can eventually produce renewable energy. In large quantities,
Without generating radioactive waste and greenhouse gas emissions. In addition, the isotopes of hydrogen used in fusion are present in large quantities on Earth and in a permanent manner.

We are talking here about inertial fusion. What is it about?

To maintain the necessary conditions for obtaining plasma, it is necessary to confine the substance,
Either by magnetic field at fairly reasonable densities for a sufficiently long time, either by
Laser inertial confinement at higher densities and in a much shorter time. Magnetic confinement fusion is tested as part of
ITER . project. Inertial fusion is being studied at the National Ignition Facility (NIF) and in France, at the Laser MégaJoule (LMJ), designed and produced by the Department of Military Applications (DAM) at CEA, at CEA-CESTA near Bordeaux.

Inertial fusion consists of
It supplies, by means of laser beams, a sufficient amount of energy to a very small amount of deuterium and tritium It is contained in a capsule with a diameter of a few millimeters. This capsule, or target, will be pressurized hard to heat it up and make it high density.

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External views of the integration goal. In the bottom image, we see a polymer bead filled with deuterium placed in the center of the transformation cavity. © CEA / DAM

There are two types of inertial fusion schemes. The so-called direct attack plan consists of direct impact on this capsule of hydrogen isotopes with laser beams.

Another scheme is to place the capsule in a centimeter-long metal cylinder. This cylinder has two entry holes for laser beams. These rays affect the inner surfaces of the cylinder and heat up the metal emitting X-rays, and these X-rays will compress the capsule, resulting in a fusion reaction. This is the inertial fusion scheme that operates in both the NIF and LMJ. At LMJ, we have projects very similar to those of NIF. In this area, we discuss the different measuring devices (diagnostics), goals and results obtained.

How is the nuclear fusion experiment conducted on August 8 at NIF such a major breakthrough?

this is
The experiment conducted at NIF is a huge step forwardBecause the American researchers who started laser experiments for more than 10 years, It is close to the ignition thresholdAnd
Either the moment we recover as much thermonuclear energy as what laser energy provided. The NIF 192 laser produced 1.9 megajoules and the Americans recovered 1.3 megajoules of thermonuclear energy. The yield is 0.7, very close to the gain of 1, the ignition threshold, a result that has not been obtained before. And so did the Americans
Proof of concept ability to achieve ignitionn.

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To produce energy economically and profitably, it would be necessary to perform this same experiment with a gain of not 1 but rather 10, in a repetitive and robust manner, say 10 similar experiments per second, 24 hours a day. But it does require a lot of preparation: We can currently imagine doing one or two a week at NIF, no more.

It is a very ambitious challenge. This is why the priority method for energy production remains magnetic confinement fusion through the ITER project.

Why can’t we run this experiment repeatedly yet?

This experience is from
Great complexity of implementation. There is a massive amount of lasers, 192 beams for NIF, which must be driven by strong focus limitations on the target. Each time, there are hundreds of optical components to tune in. Laser pulse durations are on the order of a few nanoseconds, or a few billionths of a second. The deuterium and tritium targets must be cooled significantly, to temperatures close to absolute zero, before they reach 100 million degrees Celsius during fusion. All of these upstream experiments are simulated with highly complex calculations running on the CEA/DAM supercomputers in Bruyères-le-Châtel.

What are the prospects for the future of energy production using inertial fusion?

We are currently at the proof-of-concept level and
I don’t think it’s possible to come up with something economically viable for a few decades. This will certainly mean increasing the number of beams and relying on other laser technology, so that we can produce the necessary energies.

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A hall laser du LMJ. © MS-BEVIEW / CEA

Does inertial fusion have other applications for NIF and LMJ other than energy production?

One of the main goals of the inertial fusion experiments, which are shared by the NIF and LMJ, is to contribute to
Ensuring the reliability of nuclear warheads for deterrence Either in the United States or in France. Inertial fusion allows temperatures and pressures to be restored to levels close to those encountered during nuclear tests, which were permanently discontinued in 1996 for France. The simulation software I supervise is based on both supercomputers and experimental means, such as LMJ or Valduc’s Epure radial stabilization. To this end, the Department of Defense funded this extraordinary installation, the LMJ.

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LMJ 3D diagram. © MS-BEVIEW / CEA


Since the launch of the LMJ program,
The Department of Defense has decided to allocate 20-25% of LMJ experience time to the international academic community. These basic research experiments make it possible to study astrophysical phenomena, for example the behavior of the cores of giant planets or the opacity of the sun. There is the same program for opening NIF.

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External view of the Megajoule laser © MS-BEVIEW / CEA

About the Laser Megajoule (LMJ)

LMJ is an unusual experimental installation, built at the CEA-CESTA Center (near Bordeaux). In the final configuration of the LMJ, 176 beams providing 1.3 megajoules of energy will be focused on a target placed in the center of the experimental chamber. Since its commissioning in 2014, the LMJ’s gradual increase in power has continued, in a consistent manner, between the laser power (starting the lasers) and the experimental system (about forty measurement or diagnostic systems will be installed on the run), as well as with the simulation software needs. At the end of 2019, for the first French experiments in inertial confinement nuclear fusion, 48 energy beams gave out 160 kilojoules.

Find out more: http://www-lmj.cea.fr

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