How is it possible to achieve artificial nuclear fusion?

Typically, this reaction has a threshold temperature of about 200 million degrees

by Lorenzo Ciotti
How is it possible to achieve artificial nuclear fusion?

The most studied reaction for decades, to use the fusion in a reactor of a power station to produce electricity, is the deuterium-tritium fusion, because it is the one that requires the lowest temperature. Typically, this reaction has a threshold temperature of about 200 million degrees.

Actually, in technical jargon the temperature is expressed in kiloelectron volts: 200 million degrees are equal to 20 keV. The drawback of the standard D-T reaction, the coldest, is the production of very high energy neutrons: to give an idea, about 7 times the standard energy of a fast fission neutron, which corresponds to that produced by the fission reaction nuclear power of uranium 235.

The problem of fast neutrons is that, being devoid of charge, they cannot be confined by a magnetic field, but unlike neutrinos, neutrons interact very heavily with matter. Neutrons in particular tend to make steel, reinforced concrete, and other conventional structural materials radioactive, transforming the chemical elements they contain: the phenomenon is called neutron activation.

The presence of fast neutrons therefore makes it necessary to use very heavy shielding. This is one of the main problems for a deuterium-tritium reactor, such as ITER. Neutrons on the other hand are a source of heat inside the walls of the reactor, which is exploited in the production of electricity.

In addition, neutrons are used to produce tritium through neutron capture reactions of lithium, flowing behind walls of lithium plasma or a lithium-lead alloy in which the lead shields outward and helps to multiply fast neutrons, increasing the conversion rate of lithium to tritium.

How is it possible to achieve artificial nuclear fusion?

Starting from the experiments on the transmutation of nuclei by Ernest Rutherford, conducted at the beginning of the 20th century, the fusion of heavy isotopes of hydrogen in the laboratory was carried out for the first time by Mark Oliphant in 1932: in the same year James Chadwick discovered the neutron particle.

During the remainder of that decade the main cycle stages of nuclear fusion in stars were derived from Hans Bethe. Research into fusion for military purposes began in the early 1940s as part of the Manhattan Project, but this was not implemented until 1951.

Nuclear fusion was used for warfare for the first time on November 1, 1952, during of the explosion of the H-bomb called in slang Ivy Mike. Research into the development of controlled thermonuclear fusion for civilian purposes began systematically in the 1950s and continues today.

Among others, some projects are underway in 2021 with the aim of demonstrating the technology. On December 5, 2022, a group of researchers from the National Ignition Facility at the Lawrence Livermore National Laboratory carried out for the first time an inertial confinement fusion with a positive energy balance.

The 2.05 MJ supplied to the target in fact generated 3.15 MJ of power. However, 300 MJ of energy were needed to power the 192 lasers. The overall energy balance was therefore extremely negative. The research results were officially announced on December 13, 2022 in Washington.