Covering a cylinder with a magnetic coil triples its energy output during a nuclear fusion test

(a) Sketch of the magnetized NIF hohlraum constructed from AuTa₄ with solenoid coil to carry current. (b) X-ray entrainment measured through one of the LEHs and incident laser powers for magnetized and unmagnetized AuTa₄ hohlraum and two unmagnetized Au hohlraums. “BF” refers to “BigFoot”, the name of the previous ignition design. Credit: Physical examination letters (2022). DOI: 10.1103/PhysRevLett.129.195002

A team of researchers working at the National Ignition Facility, part of Lawrence Livermore National Laboratory, have found that covering a bottle containing a small amount of hydrogen with a magnetic coil and firing lasers at it triples its energy output – another step towards the development of nuclear fusion as a source of energy.

In their article published in the journal Physical examination lettersthe team, which has members from multiple facilities in the US, one in the UK and one in Japan, describes upgrading their setup to accommodate the introduction of the magnetic coil.

Last year, a team working at the same facility announced that they had come closer to carrying out a nuclear fusion test than anyone so far. Unfortunately, they could not repeat their results. Since that time, the team has revisited their original design, looking for ways to improve it.

The original design involved firing 192 laser beams at a tiny cylinder containing a tiny sphere of hydrogen in its center. This created X-rays that heated the sphere until its atoms began to fuse together. Some of the design improvements involved changing the size of the holes through which the lasers pass, but these only resulted in minor changes.

Looking for a better solution, the team looked at previous research and found several studies that had shown, through simulation, that enclosing a cylinder in a magnetic field should significantly increase energy production.

Putting the suggestion into practice, the researchers had to modify the cylinder – originally it was gold. Placing it in a strong magnetic field would create an electric current strong enough to tear the cylinder apart. So they made a new one from an alloy of gold and tantalum. They also changed the gas from hydrogen to deuterium (another type of hydrogen) and then covered the entire work with a tesla magnetic field using a coil. Then they turned on the lasers. The researchers saw an immediate improvement: the hot spot of the sphere increased by 40% and the energy production tripled.

The work marks a step towards the ultimate goal: the creation of a fusion reactor capable of producing more energy than was put into it.

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