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New Measurement Method Enhances Fusion Power Analysis
Magnetic confinement fusion devices have emerged as pivotal technologies in the quest for controlled nuclear fusion, utilizing powerful magnetic fields to maintain the stability of hot plasmas. These innovations hold promise for advancing eco-friendly energy production strategies.
Effective operation of these devices is contingent on precise measurements of fusion power. Traditionally, this has been accomplished through absolute neutron counting, which quantifies the total neutron output during a plasma discharge, offering insights into reaction rates and yields.
A collaborative research initiative led by the Consiglio Nazionale delle Richerche (CNR-ISTP) and the University of Milano-Bicocca, along with global partners and under the leadership of Dr. Marco Tardocchi, has unveiled a novel measurement technique aimed at refining fusion power metrics.
This innovative approach, detailed in a study published in Physical Review Letters, investigates the gamma-ray-to-neutron branching ratio specifically in deuterium-tritium reactions.
According to Andrea Dal Molin, the lead author of the study, “Our project was initiated in the context of ITER, the forthcoming International Thermonuclear Experimental Reactor, which aims to validate the potential of generating electricity through nuclear fusion.” He emphasized that one of ITER’s major technical hurdles is the dual-method approach needed for fusion power assessment. The established method of absolute neutron counting, which is already in use in current experiments like the Joint European Torus (JET), needed to be complemented by a new method.
Dal Molin and his team sought to exploit the rare gamma rays emitted during the deuterium-tritium fusion process as an alternative measurement tool. Their approach involves measuring the emissions from two gamma rays that are a product of an excited 5He nucleus transitioning to lower energy states.
“The occurrence of this reaction channel is much less likely, with a probability of 2.4×10-5, compared to the neutron and alpha particle output,” noted co-author Davide Rigamonti. He added that this leads to a substantial neutron flux, which can create unwanted background interference during gamma-ray measurements. To mitigate these effects, developing an efficient neutron attenuator was crucial for the successful implementation of their method.
Through extensive research efforts, Dal Molin, Rigamonti, and their collaborators managed to pinpoint the energies and relative intensities of the gamma rays, which had previously remained uncharacterized. They then leveraged the absolute neutron count from the JET facility to calculate the gamma-ray-to-neutron branching ratio.
“Our precise determination of the gamma-ray-to-neutron branching ratio for the deuterium-tritium fusion reaction sets the stage for utilizing gamma-ray counting as an independent technique for fusion power measurement in upcoming fusion experiments,” Dal Molin stated. “This advance thus offers a vital tool for verifying results and enhancing measurement accuracy.”
This recent study represents significant progress in the capability to accurately gauge fusion power in future nuclear fusion initiatives. The methodology established for gauging the gamma-ray-to-neutron branching ratio may also be adaptable to other types of fusion reactions that do not produce neutrons, such as those involving proton-boron or deuterium-helium-3 reactions.
“There is currently a renewed interest in fusion energy research, driven by involvement from both public and private sectors,” Rigamonti added. “New tokamaks that are designed to operate with deuterium-tritium mixtures, like ITER, are being developed. Our objective is to incorporate this gamma-ray measurement technique for assessing fusion power in future magnetic confinement reactors.”
More information: A. Dal Molin et al, Measurement of the Gamma-Ray-to-Neutron Branching Ratio for the Deuterium-Tritium Reaction in Magnetic Confinement Fusion Plasmas, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.055102.
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phys.org