The elusive dream, are we searching down a blind path?
Here is the thing the vast majority of people do not know. 40% of the energy released by our sun, Sol, comes from the very first step of the proton-proton fusion chain. That step involves in round numbers 1/10E+27 collisions between 2 protons leading to 1 proton decay into a neutron forming 1 deuterium nucleus and all other cases where the two protons succumb to electrostatic repulsion and split back apart. Pause and consider that fact for a minute, 40% of all the energy released by our sun comes from this 1/10E+27 reaction taking place several billion times each second.
Humans from the 1940's to today have focused nearly all our efforts on fusing higher and easier to accomplish steps in the PP chain that takes place in all low mass stars. For example at an effective temperature 1 million degrees Kelvin Deuterium and Protium (a naked hydrogen nucleus, a proton) fuse to form Helium-3, the lighter stable isotope of Helium. As a result of this reaction radiative bodies with a mass as low as 13 times that of Jupiter can achieve the threshold temperature to consume all the existing Deuterium in the super-Jovian body to form Helium-3 out of the their accumulated Protium and Deuterium until every Deuterium nucleus is consumed. From 13 times Jupiter to 80 times Jupiter in mass size this is the highest fusion threshold that a radiative body can achieve, but once the Deuterium is all consumed the body contracts further causing higher heating in the core. but not enough heat to pass the threshold for P-P fusion into Deuterium in that 1/10E+27 rate. Instead the body officially becomes a 'brown dwarf' and spend the rest of its undisturbed life cooling.
If the mass is around 81 times that of Jupiter or .075% the mass of Sol the contraction heating after the Deuterium supply is exhausted is just enough to initiate the P-P fusion at that 1/10E+27 rate and the radiative body is officially a 'star' because the second step in the chain is to fuse Deuterium and Protium into Helium-3, which is the definition used for 'fusion'. The very smallest Red Dwarf stars stop at this point. They can make Deuterium and they can make Helium-3 from that Deuterium because doing so is so easy even Brown Dwarves can manage that step, but adding more protons to make Helium-4 by a couple different methods is beyond their temperature/density threshold so over a period of hundreds of billions of years they will slowly convert their Protium primordial Hydrogen into Helium-3 and then simply stop fusing.
For humans trying to do fusion reactions on Earth the temperature/density issue is crucial because we can not manage to make and hold plasma at the same densities of the core region of even the smallest self sustaining red dwarf star. Typically our solution to this conundrum is to use a very low density plasma and heat it to extremely high temperatures compared to those at the core of the core of even a giant star, let alone a medium size dwarf like Sol. Having chosen to go this route we then concluded that fusing higher order nuclei from Deuterium was the best route to follow, however the energy to fuse Deuterium with deuterium is very high at the density we can achieve, on the order of 400 million Kelvin. The very core of Sol is only 13.8 million K in temperature and the core of Proxima Centauri, the closest red dwarf is about 4 million K.
Given that fusing Deuterium and Protium into He-3 is not only easier to accomplish that D*D fusion, D*P fusion yields on average 5.5 MeV of energy while D*D yields on average 3.6 MeV from three possible resulting nuclei. I think it is nuts we are are so committed to D*D or D*Tritium as fusion fuels. In large part this arose because D*D was the first successful Hydrogen Bomb reaction material and all current Hydrogen Bombs are D*T designs based on using Lithium metal as the precursor to Tritium.
Forget about the bombs and go back to fundamentals, a hydrogen plasma confinement system does not need to depend on bomb materials and in point of fact can get a better energy yield without producing excess neutrons by fusing P*D=He-3.
D*D=H-3(Tritium) + Proton + 4.0 MeV about half the time.
D*D=He-3 + Neutron + 3.25 MeV about half the time; Very Rarely D*D=He-4 + 23 MeV.
P*D=He-3 + 5.49 MeV fusion releases no neutrons or protons, just energy and a lot of it.
P*P=D + 1.44 MeV is exceedingly rare to the point that you need billions of collisions to get one successful decay. This isn't practical for human energy production but supplies 40% of our suns energy.
Although its potential to generate electricity at a commercial scale is several decades away, nuclear fusion can become a promising option to replace fossil fuels as the world's primary energy source and could have an important role to play in addressing climate change, participants agreed at an IAEA General Conference side event focused on the status of fusion energy research, with major players in attendance.
Despite the potential benefits to society from fusion, such as the abundance and accessibility of fuel, the carbon free footprint and the absence of high-level radioactive waste, its science remains one of the most challenging areas of experimental physics today: controlling thermonuclear fusion for energy production is a complex and challenging undertaking.
Moderating the discussion, Meera Venkatesh, Director of IAEA Division of Physical and Chemical Sciences, highlighted the difficulties facing fusion technology to make commercially-viable fusion power a reality. She pointed out that finding the right materials to construct the fusion reactor, and developing the mechanism that will be used to extract the enormous energy/heat that is emitted, are among the major tasks ahead. “The realization of fusion power reactors would be a landmark achievement, taking nuclear science and technology to a higher level,” she said.
ITER: Proving fusion technology on Earth
One major step toward reaching this goal is the ITER project, a 35-nation collaboration to design, build and operate an experimental reactor to achieve and sustain a fusion reaction for a short period of time. ITER will be the world’s largest tokamak, a donut-shaped configuration for the containment of the plasma, which is where the reaction — at temperatures hotter than the Sun — will take place.
ITER Director-General, Bernard Bigot, highlighted the extensive progress in manufacturing and construction, which is now more than 50% completed, with the first experiments scheduled by 2025.
“When we prove that fusion is a viable energy source, it will eventually replace burning fossil fuels, which are non-renewable and non-sustainable. Our mission is to provide a new option which is safe, sustainable and economically competitive. Fusion will be complementary with wind, solar and other renewable energies,” he said.
ITER is expected to produce about 500 megawatts of fusion power by the late 2030s, and will enable scientists to observe for the first time a burning plasma, the state when the energy produced by the fusion reaction is almost or completely sufficient to maintain the temperature of the plasma, so that the external heating can be strongly reduced or switched off altogether. Studying the fusion science and technology at ITER’s scale will enable optimization of the plants that follow while leading discoveries in plasma science and technology.
Wendelstein 7-X: A new twist
These efforts are complemented by the world’s largest stellarator — Wendelstein 7-X (W7-X) at Max Planck Institute for Plasma Physics (IPP) in Germany — an alternative to the tokamak as the reactor layout. It is a twisted racetrack-shaped configuration, which is inherently stable and able to operate the plasma in a steady state for greater lengths of time than the tokamak, but it is technically harder to design.
Although W7-X will not produce energy, its designers hope to prove that stellarators are also suitable for application in power plants and to demonstrate their capability to operate continuously. Such continuous mode will be essential for commercial operation of a fusion reactor.
Sibylle Günter, Scientific Director of IPP, highlighted the most recent results from the first high-performance plasma operation of W7-X, which has recently achieved the highest stellarator fusion triple product: the density, confinement time and plasma temperature used by researchers to measure the performance of a fusion plasma.
“This is an excellent value for a device of this size, and it makes us optimistic for our further work. In the future, we expect to run the machine for a longer time,” she said.
The fusion triple product has seen an increase of a factor of 100,000 in the last fifty years of fusion experimentation; another factor of five is needed to arrive at the level of performance required for a power plant. Some of the improvements in this product were the result of experimental fusion reactors becoming larger. Plasma takes longer to diffuse from the centre to the walls in a bigger reactor, and this extends the confinement time.
Günter added: “Size matters in terms of heat insulation. Based on our experience, I believe that ITER will perform even better than planned today.”
Let there be light
While large scale experiments such as ITER and W7-X continue, nearly two dozen start-ups are working on a variety of devices, fuels, and approaches, using new technologies. These start-ups are backed by venture capital funding.
Mila Aung-Thwin, director of the award-winning documentary about the quest for fusion energy, Let There Be Light, which was shown at the event, emphasized that in addition to public investments into fusion research, there is an increase in the number of new players working in the area of nuclear fusion. As an example, the movie shows fusion start-ups in Canada and the USA.
“It’s great that there are more private entities supporting innovation. Perhaps we are at the level of technology now where start-ups can compete with national labs and agencies, as they seem to be in space travel,” he said.
Bigot added: “These companies are trying to develop alternative options to ITER. Their investors want to make fusion a reality, and this demonstrates trust in fusion as a promising energy supply for the world in the middle and long term.”
Fusion Energy at the IAEA
The IAEA has been supporting the research and development work towards future nuclear fusion energy since the beginning, in the 1950s. The IAEA played an important role in the set-up of ITER, and continues to act as a central hub among Member States developing programme plans and initiating new R&D activities leading to various concepts of a demonstration fusion power plant (DEMO) through its DEMO Programme Workshop.
The IAEA is cooperating with the ITER Organization based on the IAEA-ITER Cooperation Agreement, and is playing an important bridging function between the 35 ITER members and the other IAEA Member States through its periodic series of Fusion Energy Conferences, Workshops and Technical Meetings, Coordinated Research Projects, and publishing the leading scientific journal in the field, Nuclear Fusion.
IAEA