New theoretical framework will prevent our fusion reactors from flourishing

Physicists at Princeton University's Princeton Plasma Physics Laboratory (PPPL) at Forrestal Campus, New Jersey, may have finally solved a long-standing problem in physics: how to tame fusion for the production of energy. Their work lays the foundation necessary to stabilize plasma temperature and density levels in fusion reactors, a problem that has plagued past efforts in this field.

Wild and Energetic

Plasma is one of the four natural states of matter. This may seem confusing since we all think that they are gases, liquids or solids, but there is a good explanation for this: Plasma is a state of matter so violent and energetic that it does not matter. simply does not exist freely on Earth.

Think of plasma as a soup, only instead of vegetables, it is full of protons and electrons (basically very energized hydrogen atoms) that mix to create l '. helium. . For a less culinary explanation, see here. This process requires a lot of energy to start – you need to heat the hydrogen to about 100 million degrees Celsius – but will generate monumental amounts of energy if you manage to make it work.

So it's easy to understand why Fusion is often hailed as the harbinger of infinite, free energy for everyone – never. So far, we've been able to recreate plasma in fusion reactors – donut-shaped tokamaks or funky stellarators, for example – but we have not found a way to keep this soup alive yet. charged particles

One of the biggest obstacles we have encountered is that plasma in fusion reactors tends to fluctuate tremendously in terms of temperature and density. Such turbulence is very dangerous because any projection of a leaking plasma will cross the wall of a reactor like a lightsaber through the butter. Faced with such probabilities, researchers have no choice but to stop the experimental reactions before they go wild

Plasma confined in the tokamak MAST at Fusion Energy Culham Center in the United Kingdom. Lines of magnetic fields that combine to act as an invisible bottle for plasma
Image credits ITER / CCFE

The most frustrating thing is that we know what we must do, but not how do it. We must contain the plasma in an orderly fashion and keep the reaction long enough for it to become positive at net energy, ie it generates more energy. energy that we do not inject.

The stars can take advantage of their mbad to support the plasma plays well, but we do not have this luxury. Instead, we use mbadively powerful magnetic fields (about 20,000 times stronger than those of the Earth) to drive away from the walls of the reactor

Going With the Flow

This is here that intervenes the present document. Plasma fluxes (like those inside the stars) have been shown to be very stable over time, with no dangerous turbulence. We did not know how to circulate the plasma in this way, but PPPL researchers report that it's a mechanism called magnetic flux pumping forcing the flux to the heart of the plasma to remain stable .

The team ran, magnetic flux pumping can take place in hybrid scenarios – a mix of standard flow regimes currently known from theoretical and experimental models. These standard diets include high containment mode (H mode) and low containment mode (L mode).

In L mode, an electrically balanced scenario – that is, it has a perfect ratio between positive charge and negative charge – particles – formed at lower temperatures, turbulence allows the plasma to evacuate some of its energy. The L mode is unstable because the high temperature plasma at the core is projected to the surface, destabilizing the reaction. If this mode can be overridden and the reaction goes into H mode, the overall plasma body temperature is increased and the reaction stabilizes. The H mode is an energy imbalanced mode, but the plasma is kept stable and confined by the electric fields that it generates itself (T. Kobayashi et al., Nature 2016).

In a hybrid scenario, however, the flux is maintained ordered only at the plasma core. This generates an effect similar to that found in the interior of the Earth, reports the team, where the solid iron core acts as a "mixer", generating a magnetic field. The interactions between this field, the one applied by the generator, and the two types of plasma flux stabilize the reaction.

Even better, this mechanism of magnetic flux pumping is self-regulating, as shown by the simulations. If the mixer becomes too strong, the plasma current falls just below the point where it would become out of whack.

And, best of all, the authors suggest that ITER – widely regarded as the most ambitious nuclear fusion project currently being built in Provence, France – can be adapted to experiment with the development of pumping magnetic flux using the same material that he uses to heat the plasma.

The article "Pumping magnetic flux in 3D nonlinear magnetohydrodynamic simulations" was published in the review Plasma Physics .

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