Fusion Power
"Man-made fusion power resembles natural fusion power, i.e. solar power"
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions, such as those that occur in the sun. To fuse on our sun, nuclei need to collide with each other at very high temperatures, exceeding 10 million degrees Celsius, to enable them to overcome their mutual electrical repulsion [IAEA, 2021]. But making this process work smoothly & continuously in such a high-temperature condition is an immense challenge [AC, 2022].
Fusion reactions occur when two or more atomic nuclei come close enough for long enough that the nuclear force pulling them together exceeds the electrostatic force pushing them apart, fusing them into heavier nuclei. The process releases energy because the total mass of the resulting single nucleus is less than the mass of the two original nuclei: the leftover mass becomes energy [EG, 2023].
Unlike nuclear fission, nuclear fusion is a naturally occurring reaction (e.g., in the center of a star). Figure 1 shows the Deuterium (D) and Tritium (T) fusion reaction, which produces a helium nucleus (alpha particle), a neutron, and energy.
Research
Research into fusion reactors began in the 1940s, but as of 2023, no device has reached net power. In the decades scientists have been experimenting with fusion reactions, they had not until now been able to create one that produces more energy than it consumes. Most designs aim to heat their fuel to around 100 million degrees Celsius, which presents a major challenge in producing a successful design.
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Fusible or Fissionable?
Hydrogen & Helium are in general more fusible, while heavier elements, such as Uranium, Thorium, and Plutonium, are more fissionable.
Advantages over fission power
As a source of power, nuclear fusion has a number of potential advantages compared to fission, including i) reduced radioactivity in operation, ii) little high-level nuclear waste (the process doesn't result in byproducts like spent rods), iii) ample fuel supplies, and iv) increased safety.
Breakeven
A fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state. Q = 1 condition, when the power being released by the fusion reactions equals the required heating power, is referred to as “breakeven”.
On Dec 5 2022, a team at LLNL’s National Ignition Facility (NIF) ran a fusion experiment that produced more energy from a fusion reaction than the laser energy used to drive it: 2.05 MJ of laser energy was directed to the target, which released 3.15 MJ of fusion energy.
The burst output of 192 laser beams focused on a tiny diamond sphere the size of a peppercorn to generate a shock wave that pushed hydrogen atoms close enough together to fuse. While the energy released from this fusion was greater than the laser energy that hit the peppercorn sized target, the overall energy balance is a net loss and is not ready to be scaled up [AC, 2022].
Figure 1: Nuclear fusion reaction
