05/08/2024
An international research group led by the Institute for Plasma Science and Technology of the National Research Council (Cnr) in Milan has demonstrated that gamma rays produced in the deuterium-tritium nuclear reaction can provide an accurate and alternative method for measuring the power achieved in new fusion reactors. The study is the subject of two scientific articles published in Physical Review C and Physical Review Letters
An international research group led by the Institute for Plasma Science and Technology of the National Research Council of Italy (Cnr-Istp), based in Milan, contributes significantly to solving one of the biggest challenges related to the use of nuclear energy: measuring the power achieved in new fusion reactors based on the deuterium-tritium reaction.
To date, the only direct measurement technique for fusion power used in magnetic confinement reactors is to "count" the number of free neutrons generated by the fusion of the two hydrogen isotopes—deuterium and tritium—most commonly used as the fuel for the reaction. When these reactants fuse, the helium-5 nucleus formed decays into helium-4 and a free neutron with an energy of 14 MeV: the absolute count of these energetic neutrons provides a direct measurement of the rate of fusion reactions. However, this technique presents several difficulties: the emission and the transport of neutrons from an extended source like the tokamak, and their interaction with reactor materials, require the use of complicated simulation codes, as well as long and costly calibration campaigns to validate the codes.
Today, the Italian-led study—conducted by Cnr-Istp in collaboration with the Departments of Physics of the University of Milano-Bicocca and the University of Milan, the ENEA research center in Frascati, and other European institutions as part of the "GETART" project—identifies gamma rays emitted from the decay of helium-5 as a new and alternative method to measure such power. The study is the subject of two scientific articles published in Physical Review C and Physical Review Letters.
"The new method developed is based on the absolute measurement of two gamma rays with energies of about 13 MeV and 17 MeV, emitted in the decay of helium-5: from this measurement, never before carried out with sufficient accuracy, it was possible to determine the energies and relative intensities with which the two gamma rays are emitted. This gamma ray emission process has a relative probability (called branching ratio) much lower than that of 14 MeV neutron emission," explains Marica Rebai, a researcher at Cnr-Istp and first author of the paper published in Physical Review C.
Andrea Dal Molin and Davide Rigamonti are the first authors of the subsequent paper published in Physical Review Letters: "This result allowed us to determine, in a second study, the branching ratio of gamma-ray emission relative to neutron decay, which is one per 42,000 14 MeV neutrons produced, thus paving the way for the use of absolute gamma-ray measurement as a new alternative and complementary method to neutron measurements for determining the power achieved in new fusion reactors based on the deuterium-tritium reaction, such as ITER and SPARC," they add.
According to the project coordinator, Marco Tardocchi, a research director at Cnr-Istp: "Until now, the absence of a direct and alternative method to absolute neutron counting has been an obstacle to the independent validation of results obtained from ongoing experiments and the authorization of future commercial plants. This type of measurement based on absolute gamma-ray counting represents the only possible technique also in view of the use of future reactors based on alternative fuels that do not produce neutrons, for example, those based on the fusion of deuterium and helium-3 or proton and boron-11." The optimization of this measurement was preliminarily performed at the ENEA neutron generator “Frascati Neutron Generator” (FNG), one of the few in the world available for fusion research and other application sectors, including aerospace, automotive, physics and particle detectors. Entirely designed and built by ENEA at the Frascati Research Center, FNG is the most powerful 14 MeV neutron source in Europe.
The experiments were conducted at the Joint European Torus (JET) facility in the UK—the largest nuclear fusion experiment in the world—during the experimental campaign called DTE2, and were partly funded by the European consortium EUROfusion, of which Italy is a partner.
In addition to marking an important milestone for Italy in the international context, this research represents an effective example of collaboration between academia and research institutions. This is confirmed by the director of Cnr-Istp, Olga De Pascale, and the director of the Department of Physics of the University of Milano-Bicocca, Giuseppe Gorini: "This result is a source of pride for our country, and well represents the fruitful collaboration between university researchers, including young doctoral students, and Cnr, demonstrating once more how the link between universities and research bodies is vital for Italian research".
Per informazioni:
Marco Tardocchi
Cnr-Istp
marco.tardocchi@istp.cnr.it
02/66173-244-457
Ufficio stampa:
Francesca Gorini
Ufficio stampa Cnr
francesca.gorini@cnr.it
Responsabile Unità Ufficio stampa:
Emanuele Guerrini
emanuele.guerrini@cnr.it
ufficiostampa@cnr.it
06 4993 3383
Vedi anche:
- A. Dal Molin et al., "Measurement of the gamma-ray-to-neutron branching ratio for the deuterium-tritium reaction in magnetic confinement fusion plasmas," Phys. Rev. Lett. 133, 055102 (2024),
- M. Rebai et al., "First direct measurement of the spectrum emitted by the 3H(2H, ?)5He reaction and assessment of the ??1 and ??0 relative yields," Phys. Rev. C 110, 014625 (2024)