FUSION ENERGY BREAKTHROUGH IN U.S.

United States government officials announced on Tuesday that a federal facility had achieved a significant milestone in nuclear fusion research. Energy secretary Jennifer Granholm said the feat puts us on the path to “zero-carbon abundant fusion energy powering our society.”
Officials said the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL), California, had conducted a fusion test on December 5 that produced 153% as much energy as went into triggering it.
The NIF uses powerful lasers to heat and compress hydrogen nuclei. When the nuclei fuse, they release heat. When this heat is equal to or greater than the heat delivered to the container, the event is called ignition. The ratio of the output energy to the input delivered to the container is the gain.
In 2021, the NIF reported that it had achieved a gain of 0.72. Now, it has reportedly achieved ignition with a gain of 1.53 with a yield of 3 megajoules. “The recent results from the NIF are a major achievement on the road to fusion energy,” Matthew Zepf, professor at the Friedrich Schiller University Jena and a director of the Helmholtz Institute Jena, said.

Inertial confinement

Magnetic confinement and inertial confinement are two popular ways to achieve nuclear fusion. Magnetic confinement uses bespoke reactors in which a hydrogen plasma is heated to a high temperature and the nuclei are guided by strong magnetic fields to fuse. Its corresponding technology is considered to be more technologically mature than that of inertial confinement.
In the NIF’s setup, 192 high-power lasers fire pulses at a 2-mm-wide capsule inside a 1-cm-long cylinder called a hohlraum, in less than 10 billionths of a second. The capsule holds deuterium and tritium atoms. As the pulses strike the hohlraum’s insides, the latter heats up and releases X-rays, which heat the nuclei to millions of kelvin and compress them to billions of Earth-atmospheres.
The high temperature is required to energise the nuclei to overcome their mutual like-charges-repel repulsion. The technique is called inertial confinement because the nuclei’s inertia creates a short window between implosion and explosion in which nuclear forces dominate, fusing the nuclei.
When two hydrogen-2 nuclei fuse, they yield a helium-4 nucleus, a neutron and 17.6 MeV of energy according to the mass-energy equivalence.

‘Burning plasma’

For a fusion chain reaction, the energy released by the initial reaction needs to set the stage for more reactions. To this end, the NIF’s goal has been to create a “burning plasma”: when nuclei are encouraged to fuse not by the external heat source but by the heat of other reactions.
The NIF achieved this in 2021 with a gain of 0.72: 1.37 megajoules produced by the fusing nuclei versus 1.97 megajoules delivered by the lasers.
In August 2022, the facility reported it had produced a burning plasma that met the Lawson criterion: the heat generated was sufficient to potentially trigger other fusion reactions as well as offset heat loss during the reaction. Now, the facility has reportedly achieved a burning plasma that meets the Lawson criterion as well as a gain greater than 1.

Caveats

The NIF’s is a significant scientific achievement — but where energy is concerned, the important question is: what does it imply for practicable fusion?
After the NIF achieved a gain of 0.72 in 2021, the people in charge of the experiment tried thrice to repeat their feat. They failed — because the NIF fusion facility is a highly sophisticated system with tiny moving parts. Even small changes in input conditions, like microscopic bumps on the capsule, can lead to large variations in output.
So the NIF will need to reproduce its new results.
Second: For fusion to be truly gainful, the energy released by the reactions needs to be greater than the energy going into the lasers, about 300 megajoules, and not just the energy delivered to the hohlraum. This hasn’t yet been achieved.
“The energy transferred to the plasma is just about 1%, the rest is all lost in other processes,” said Shishir Deshpande, a professor at the Institute for Plasma Research, Gandhinagar.

SOURCE: THE HINDU, THE ECONOMIC TIMES, PIB

Post Views: 64