A new way to create a plasma of record temperature was tested at the Korean tokamak

(ORDO NEWS) — South Korean specialists in the field of plasma physics reported on another experiment that was carried out at the KSTAR facility before its modernization.

Nominally, it turned out to be a repetition of previous records, and for those who follow the successes in this area, the achieved parameters will not seem fantastic.

But a little closer examination of the report reveals that this is a rather interesting next step towards a full-scale commercial fusion reactor.

According to a publication in the peer-reviewed journal Nature , physicists in South Korea have been able to hold plasma at temperatures in excess of one hundred million kelvins for more than 20 seconds. The values ​​are impressive, but not record-breaking.

Previously, they have already been achieved on the same installation . And then in 2020 it was an unsurpassed result. But since then, the “man-made sun” in the Celestial Empire (Chinese experimental superconducting tokamak, EAST ) has shown higher temperatures and kept them longer.

The latest report still deserves attention. First, even a repetition of already achieved plasma parameters is a significant result. This does not always happen even with strict copying of the conditions of the previous experiment.

Secondly, the confident excess of the bar of 100 million kelvins is an important milestone in the development of thermonuclear energy.

This plasma temperature is considered to be the minimum required to start a self-sustaining fusion reaction in tokamaks (the threshold is different for other types of reactors). Finally, thirdly, the conditions of the new experiment are very different from the previous ones, and this is important.

From the point of view of the convenience of maintaining a thermonuclear reaction, tokamaks are not the best choice. There are options for settings that allow you to control the plasma better.

However, toroidal reactors are simpler and better studied, so that their prospects among all types of facilities for controlled thermonuclear fusion (CTF) are the most promising.

In addition, in terms of material consumption and chamber volume, they are almost optimal. However, a finite number of fuel atoms can be placed in a tokamak chamber.

Therefore, the efficiency of the reaction after involving the entire volume of deuterium and tritium into it can be raised only by increasing the temperature and keeping the plasma clean for as long as possible.

A new way to create a plasma of record temperature was tested at the Korean tokamak 2
KSTAR installation

It is polluted by a substance that evaporates or is knocked out by individual ions from the walls of the vacuum chamber of the reactor. These impurities, even in extremely small amounts, degrade the quality of the plasma – lower the temperature and lead to increased instability of its characteristics.

There are several methods for countering plasma contamination. The most common in magnetic containment installations is the “frontier traffic barrier” ( ETB ).

In fact, it is due to the design of tokamaks and is expressed in the fact that the movement of ions and electrons slows down in the outer region of the plasma bundle. It turns out that almost nothing gets to the walls of the vacuum chamber except for neutrons.

An alternative method not so much replaces ETB as complements it – this is the “internal transport barrier” ( ITB ). To implement it, a finer control of the plasma parameters is required so that its density is maximum in the central part of the reaction region.

Then the walls of the vacuum chamber reach an even smaller amount of matter. The Korean tokamak KSTAR ( Korea Superconducting Tokamak Advanced Research ) uses ITB, and in a modified implementation.

Moreover, for the latest experiments, during which it was possible to repeat the record, the FIRE method was used – improving the acceleration (heating) of the plasma by more precise control of fast ions.

Fast are those deuterium and tritium nuclei devoid of electrons that carry most of the reaction energy. Although they do not exceed 5% of the total volume of matter in the reactor, the contribution of such ions to the energy release can safely be called decisive.

The essence of the FIRE method is that due to the extremely precise control over the reaction parameters, fast ions are collected in the very center of the plasma bundle. Thus, a more complete use of ITB is realized , and the average temperature of the substance in the tokamak is also increased.

Now KSTAR is undergoing a significant upgrade so that scientists can continue their experiments. The problem is that the last experiment had to be stopped before the reactor showed the maximum result – the installation does not allow holding hot plasma for more than half a minute.

Moreover, part of this time is spent to enter the operating mode, so 100 million degrees lasted only a little longer than two tens of seconds.

Once the reactor is back online, it will be re-experimented to test the FIRE method. It was too easy for South Korean specialists to repeat their record, and now they are wondering if they have really developed a new way to increase the efficiency of the reaction, or is it luck.


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