New system regenerates the protective layer of the tokamak interior without turning it off

Researchers at the Princeton Plasma Physics Laboratory (PPPL) have shown that a system they developed to deliver boron powder to a fusion reactor reactor walls continuously protect and prevent plasma degradation. Its gradual contamination by tungsten is detrimental to the overall reaction and presents an obstacle to the construction of a practical one fusion reactor period.

The Nuclear fusion is a way to generate cheap, clean and safe energy. However, due to numerous technical difficulties, mankind has not yet managed to build a fusion reactor that produces more energy than is fed into it and sustain the reaction process for a long period of time.

In fusion reactors - the most common type is the tokamak - is increasing tungsten used. This is because this element is very resistant to high temperatures. That Plasma however, can damage the tungsten walls of the reactor, resulting in tungsten entering and contaminating the plasma. Boron protects the tungsten from negative effects and prevents it from entering the plasma. In addition, it absorbs unwanted elements such as Oxygen, which can enter the plasma from other sources. These elements can cool down the Plasmas and lead to a termination of the reaction.

Image Source: Wikipedia ; Which

We needed a way to use the reactor Lives to coat without that magnetic field of the tokamak The experiments were conducted at the W Environment in Steady-State Tokamak (WEST) operated by the French Alternative Energies and Atomic Energy Commission (CEA). WEST - whose first letter of the name from the chemical symbol for tungsten is derived - is one of the few tokamaks, whose walls are made entirely of tungsten. Also, this device is characterized by record-breaking long Response Times out. It was also chosen as a test site because its superconducting magnets are made of a material that will be used to build magnets for future fusion reactors.

Nuclear fusion (fusion reaction) is a process, which expires on the sun. It involves the merging of lighter elements with heavier ones, using large amounts of Energy be generated. Very high temperatures are required to perform the fusion. And it is precisely these high temperatures that present a major problem. They reach millions of degrees and pose a danger to the reactor's materials. For this reason, the refractory tungsten is coated with boron for protection. However, the conditions inside the reactor are extreme and the protective layer is wearing away. It needs to be reapplied. Therefore, a method had to be developed to restore the coating without having to shut down the reactor frequently. boron in one working tokamak contributing is like cleaning your apartment without interrupting your daily routine. This is very helpful because it means you don't have to spend extra time cleaning, explains CEA's Alberto Gallo vividly.

The device developed by the Americans is mounted on top of the tokamak. It uses precision actuatorsto move powder from the hoppers into the tokamak's vacuum chamber. The mechanism used makes it possible to precisely adjust the amount and speed of powder application. The device is versatile and can work not only with boron, but also with other materials. It will therefore also be useful in fusion reactors of other designs. That could be very useful in the future, says Bodner.

The results of the experiments surprised the developers of the device themselves. It turned out that the injected boron didn't just protect the tungsten. We found that throwing the powder in so that it was at a higher temperature increased confinement of the plasma, which favored the reaction, adds Bodner. This phenomenon was particularly helpful because it occurred without the occurrence of an unfavorable H mode occurred. This is a condition where plasma confinement increases significantly, causing edge plasma instability (ELMs - Edge Localized Modes) threatens. ELMs, in turn, lead to heat dissipation outside the plasma, which reduces the efficiency of the overall reaction and risks damaging reactor components. "It's great news that we're able to achieve plasma confinement as good as H-mode, but without going into H-mode and risking creating ELMs," enthuses Bodner.

For the near future, the scientists are planning experiments in which they want to test how much of the added boron actually causes a protective layer forms on the reactor walls. This knowledge will enable them to understand how the powder delivery system to optimize.