Page 31 - PEN eBook October 2025

SMART ENERGY SMART ENERGY

hydrogen nuclei (protons, H) ultimately combine to In this reaction, a nucleus of deuterium fuses with
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form a helium-4 nucleus ( He), releasing two positrons tritium ( H), a radioactive isotope of hydrogen, to
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(e⁺), two electron neutrinos (ν ), and a burst of energy: produce a helium-4 nucleus and a highly energetic
e
neutron:
4 H → He + 2e + 2ν + energy
+
4
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e
2 H + H → He + n + 17.6 MeV
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Each positron soon annihilates with an electron from
the surrounding plasma, releasing two 511-keV photons This single-step process releases 17.6 MeV, with 80.1%
per interaction—adding up to 1.022 MeV. Because two carried away by the fast neutron as kinetic energy
positrons are involved, the final energy is 2.044 MeV. (14.1 MeV). This reaction is favored because deuterium
Combined with the nuclear energy from the fusion and tritium fuse at comparatively lower
itself (~23.66 MeV), the total energy output per cycle is temperatures—about 100 million degrees
approximately 25.7 MeV. Celsius—which is significantly less demanding than a
hypothetical p-p terrestrial fusion, which would require
The reaction occurs at temperatures between 1 billion degrees Celsius.
4 million and 15 million degrees Celsius, significantly
lower than those needed in Earth-bound plants—close In October 2023, the Joint European Torus (JET)
to 100 million degrees Celsius but using a different tokamak set a new world record by producing
fuel. The immense gravitational pressure at the heart of 69.26 MJ (4.32 × 10 GeV) of fusion energy over
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a star compensates for the lower ignition temperatures. six seconds on a single pulse. This achievement
Modern Alchemy in and the product—helium-4 is 0.7% lighter than the four was powered by just 0.21 mg of D-T fuel, heated to
150 million degrees Celsius. The energy released
Due to the mass difference between the reactants
underscores the immense potential of fusion reactions.
the Tokamak: Taming protons—this energy can be calculated from Einstein’s is produced naturally in the upper atmosphere by
While deuterium is abundant in seawater, tritium
relation: ∆E = ∆m × c .
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Fusion Reactions with within the star from the p-p chain is about 26.73 MeV, cosmic rays. Because of its scarcity, researchers aim
The widely accepted value for the energy deposited
to generate tritium within the reactor itself. This is
achieved by bombarding lithium-6 and lithium-7 with
depending on the precise mass values and neutrino
SiC Shields accounting. neutrons released during the D-T fusion reaction.
These neutrons are absorbed and moderated by a thick
Every second, our sun fuses about 620 million tons of
blanket (one meter) of lithium surrounding the reactor
hydrogen into 616 million tons of helium, enabling life core, enabling continuous tritium breeding.
By Filippo Di Giovanni, contributing writer for Power Electronics News on our planet. WHAT IS A TOKAMAK?

The p-p chain involves three steps: A tokamak (a Russian acronym) is a reactor designed
In the spasmodic quest for an inexhaustible and clean Today’s fusion research initiatives, from Europe’s to achieve controlled thermonuclear fusion by
energy source, humanity has turned its gaze toward EUROfusion to MIT’s innovations in structural materials, ▶ Production of deuterium ( H) with emission of a confining hot plasma in a toroidal chamber using
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the stars, seeking to replicate the reactions powering are converging toward the vision of building reactors positron and a neutrino: intense magnetic fields, even 200,000× stronger than
them, including the sun. Nuclear fusion, touted as the that can sustain long-duration plasma and deliver Earth’s magnetic field. It combines two
gold standard of energy generation, promises a future net-positive energy. As these global experiments 1 H + H → H + e + ν e components—toroidal and poloidal—to create a twisted
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free from carbon emissions and resource scarcity. Yet push the boundaries of plasma physics and materials helical magnetic cage that keeps the plasma stable and
the path to harnessing stellar furnaces is fraught with science, SiC stands at the frontier, ready to help ▶ Fusion of deuterium to form helium-3 ( He) and away from the reactor walls. This configuration allows
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challenges, especially in the selection of materials that harness fusion energy. emission of a photon y: the plasma to reach the extreme temperatures and
can withstand the extreme conditions recreated on pressures for fusion reactions to occur.
Earth. HOW STARS LEVERAGE 2 H + H → He + y
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PROTON-PROTON FUSION REACTION Notable examples of experimental tokamaks include
Recent breakthroughs detailed in “Comprehensive In the sun, nuclear fusion transforms hydrogen atoms ▶ Final production of He and emissions of two the JET and the international ITER project.
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new insights on the potential use of SiC as into heavier elements, releasing immense amounts of protons:
plasma-facing materials in future fusion reactors,” energy. This occurs when two atomic nuclei are brought SiC IN FUSION REACTORS
have spotlighted silicon carbide as a transformative sufficiently close for the strong nuclear force to 3 He + He → He + H + H Following its formidable inroad into the power
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candidate. With its exceptional thermal resilience overcome their electrostatic repulsion, allowing them semiconductor market, SiC has emerged as highly
and low erosion rates, SiC is emerging as a modern to fuse and form a new nucleus. FUSION REACTIONS ON EARTH promising for fusion reactors, particularly as a
alchemical solution, transmuting the limitations of Instead of the p-p chain, fusion reactors leverage the plasma-facing material. Within the tokamak’s extreme
conventional materials into new possibilities for fusion The dominant fusion mechanism in solar-type stars deuterium-tritium (D-T) reaction, chosen for its high environment—defined by blistering temperatures,
reactor performance. is the proton-proton (p-p) chain reaction, whereby four energy yield and relatively lower ignition temperature. intense neutron flux, and powerful electromagnetic
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