the Greenwald boundary has been torn down

the Greenwald boundary has been torn down
the Greenwald boundary has been torn down
  • ITER will be sized appropriately to minimize energy loss and maximize the probability of success

  • General Atomics has managed to stabilize plasma with a density 20% above the Greenwald limit

At Xataka we have spoken many times about the challenges that people who research in the field of nuclear fusion must overcome so that the first commercial reactors reach a good port. We have talked about the need to develop new types of steel capable of being minimally activated by the impact of high-energy neutrons; about how important it is to stabilize the plasma and control turbulence, etc.

However, so far we have only briefly touched on the reason why each new experimental nuclear fusion reactor is larger than the last. In fact, when you conclude your ITER assembly (International Thermonuclear Experimental Reactor), the fusion machine being built by an international consortium led by Europe in the French town of Cadarache, will be the largest experimental reactor on the face of the Earth. And it will not be, of course, by a whim of chance.

Nuclear fusion and the Greenwald limit

In experimental nuclear fusion reactors, such as ITER, scientists confine charged deuterium and tritium nuclei using a magnetic field. What happens is that no matter how powerful that field is, it always has a limit of intensity and when the particles are produced they acquire very varied energies. Some have a lot of energy, and others, however, acquire little energy. Reactor engineers are able to contain the average energy, but those particles that exceed that energy value have the ability to escape the magnetic field.

What scientists working on fusion pursue is that the energy that escapes is small enough so that a decreasing energy level does not occur within the reaction.

The problem is that if many particles escape, a lot of energy is lost and the fusion reaction cannot be sustained over time. Fortunately this challenge can be solved by modulating the magnetic fields and increasing plasma size. This is the reason why each experimental reactor is larger than the last. Scientists believe ITER is the appropriate size because the more particles there are around one that wants to escape, the more likely it is to hit another on its escape path and turn around, or give up its energy.

Ultimately, what scientists working on fusion pursue is that the energy that escapes is small enough so that a decreasing energy level does not occur within the reaction. This has already been achieved in JET, but it has been achieved for a short time because the effort cannot be maintained for a long time due to lack of size, looking at it very simplified. Be that as it may, good news has just occurred. And a research group from the American company General Atomics has published an article in Nature that makes a significant contribution in this area.

The Greenwald limit establishes the maximum density value that the fuel can reach inside the vacuum chamber of a nuclear fusion reactor. In theory, by exceeding this value inside a reactor tokamak disruption may occur, which is an event in which the plasma is destabilized, magnetic confinement is disrupted, and the fusion reaction ceases. A disruption can cause serious damage to the internal walls of the vacuum chamber depending on the energy of the particles that escape confinement and impact with them.

The Greenwald limit establishes the maximum density value that the fuel can reach inside the vacuum chamber of a nuclear fusion reactor.

Exceeding the Greenwald limit does not guarantee that a disruption will occur, but physicists and engineers who work with reactors tokamak Until now they considered this parameter a barrier that they could not ignore. The contribution made by General Atomics scientists is very relevant because they have managed to empirically prove working conditions that have allowed them to sustain the stability of the plasma with a density 20% above the Greenwald limit for 2.2 seconds.

In their experiment they used a reactor tokamak with a radius of 1.6 meters (ITER will have a radius of no less than 6.2 meters) and a gas containing deuterium nuclei (ITER fuel will incorporate both deuterium and tritium nuclei). As we have seen, it is very important that the density of the plasma is high enough to minimize the probability of occurrence. significant energy losses caused by particles that manage to escape magnetic confinement. And now the researchers who work with reactors tokamak They know that it is possible to exceed the Greenwald limit to work with the density required to sustain the fusion reaction. There is no doubt that it is great news.

Image | General Atomics

More information | Nature

In Xataka | If commercial nuclear fusion energy finally arrives, we will owe it largely to this reactor. And it is not ITER

 
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