They call it an artificial sun because it is the same energy source our nearest star uses. It is one of science’s most promising breakthroughs and goes by the technical name of nuclear fusion—a virtually clean energy source that the major powers have been pursuing for decades. So much so that fifty years ago, the experts said that there were only fifty years left to achieve it.
It seems, however, that we are getting closer with China just breaking the record for the most prolonged nuclear fusion reaction—120 million degrees Celsius for 101 seconds.
In this article, we will talk about:
What is nuclear fusion or the artificial sun?
First of all, let’s explain what nuclear fusion is all about. Conventional nuclear power plants work by releasing energy from fission. That is, by “smashing” atoms. Enriched uranium bombarded with neutrons is used to initiate a nuclear chain reaction.
These plants have been in operation for more than half a century. In particular, the USSR opened the first nuclear power plant connected to the electricity grid in 1954. However, as the series on the Chernobyl disaster explained, they are not without risks.
On the one hand, there are uncontrolled chain reactions. While their consequences are catastrophic, this type of event is highly anomalous. The real problem with nuclear fission lies in the waste generated, which can maintain dangerous radioactivity levels for centuries.
In contrast, nuclear fusion or artificial sun offers the possibility of generating energy safely and with almost no waste. Due to its low carbon footprint, it could be a formidable tool against climate change.
How is this achieved? Essentially, by fusing two light nuclei into one heavy nucleus under high pressure and very high temperatures. This reaction also releases energy because the resulting nucleus has less mass than the initial two separate nuclei.
“The deuterium in one liter of seawater can produce the energy equivalent of three hundred liters of oil.”
Typically, the fuel used to create an artificial sun is based on deuterium and tritium isotopes. Deuterium can be extracted from seawater, while tritium is obtained from lithium. Both elements are abundant in absolute terms and practically infinite compared to uranium. For example, the deuterium in one liter of seawater can produce the energy equivalent of three hundred liters of oil.
Just to get an idea of the energy released in a fusion process, it is sufficient to note that a few grams of fuel can produce one terajoule—enough to cover one person’s energy needs in a developed country for six years.
Does nuclear fusion generate radioactive waste?
No. The fusion reaction also generates waste. Most of it is helium, an inert gas. However, a small amount of radioactive waste from tritium is also produced.
Fortunately, they decay much earlier than their fission counterparts. In particular, they can be reused or recycled in less than a hundred years.
Additionally, the neutron fluxes generated in the fusion process can affect the surrounding materials, which gradually become radioactive in the absence of shielding. Thus, shielding of reactor structures will be another crucial aspect.
How an artificial sun works
OK, so we already have our tritium and deuterium fuel, as well as the basic principle of operation. But how exactly does the process work? Well, here, when you move from theory to practice, the pitfalls begin.
As we have already mentioned, very high pressure and temperature must be applied. Enough to turn the fuel into an extremely hot plasma. The atoms must collide with each other at a temperature of at least one hundred million degrees Celsius and at a pressure sufficient to bring them so close together that the nuclear attraction force exceeds the electrical repulsion.
It would be like overcoming the repulsion of two magnets of the same polarity until they are glued together to draw a rough parallel.
To achieve these extreme conditions, magnetic fields and powerful laser beams are focused on the fuel. Once the ultra-hot plasma state is reached, the fuel must continue to be added and, at the same time, the high heat emission must be contained without destroying the reactor.
Of course, no material can withstand 100 million degrees Celsius without melting instantly. This is where plasma confinement comes into play, which is achieved by different types of reactors, as detailed at the end of the article.
Latest fusion breatkhroughs
As we mentioned initially, one of the latest breakthroughs in nuclear fusion has come from China. In May 2021, researchers at the Southwestern Institute of Physics (SWIP) in Chengdu, China, announced that their HL-2M reactor had broken all records in nuclear fusion testing.
While it is a complex process, the biggest challenge is not fusion itself, as numerous reactors have achieved it in recent years. The real challenge is sustaining it over time: few have managed to go beyond a few seconds.
And that is where the SWIP scientists have won the medal: they have reached 150 million degrees Celsius temperatures for 101 seconds. The previous record, held by South Korea, was 20 seconds.
The tokamak reactor has been dubbed the “artificial sun,” although in reality, it is ten times hotter than the sun’s core. All eyes are now focused on the most prominent international project: the ITER. This gigantic project involving 35 countries has just completed its first construction phase. If all goes well, the final reactor will generate 500 MW by 2035.
What are the most common fusion reactors?
Like HL-2M, ITER is a tokamak reactor, one of several designs currently being tested. The classification of fusion reactors is mainly defined by the types of plasma confinement and how the plasma is heated. As indicated by the International Nuclear Association, the following fusion technologies could be mentioned:
- Magnetic confinement
- Inertial confinement
- Magneto-inertial fusion (MTF)
- Hybrid fusion
This technique is the most common and consists of using powerful electromagnets to confine the plasma, which is heated utilizing an electric current and auxiliary systems such as microwaves or accelerated particles. The magnetic fields used are toroidal, a term derived from “torus,” a doughnut in mathematical terms.
This design stems from Russian physicists Sakharov and Tamm, who designed the first tokamak in 1951. Depending on the shape of the confinement chambers and the type of electromagnets, these fusion reactors can be divided into four types:
- Tokamak, the classic “doughnut” shaped reactor
- Reverse Field Magnetic Pinch (RFP)
- Compact toroids
This type of confinement is one of the most recent lines of research. Used by reactors such as the National Ignition Facility (NIF) in the US or First Light Fusion in the UK, it involves using hundreds of laser beams or creating shock waves to compress a fuel microcapsule.
In the case of NIF, 192 ultraviolet laser beams are projected onto a microcapsule of frozen deuterium and tritium.
So far, NIF has only achieved an ignition of a few billionths of a second, while the First Light Fusion project is still at an early stage of development.
Magneto-inertial fusion (MTF)
As the name suggests, these reactors combine toroidal reactors and inertial confinement features. The first proposals for this design date back to the 1970s, but MTF technology has only gained momentum in the last decade. Several companies are now working on experimental MTF reactors.
Like the tokamak, the plasma is confined employing a magnetic field. However, the heating is carried out by a series of giant pistons that generate a shock wave. You can see a model MTF reactor in action in this video.
This type of reactor combines a fission reactor covering the core where the fusion process occurs. In this way, the fusion generates neutrons that impact the fissile material layer surrounding the core.
The advantage of this type of technology is that it does not require plutonium or uranium isotopes U-235 to carry out fission but is capable of achieving fission with any uranium isotope. It can operate even with radioactive waste from fission reactors.
There would be no risk of an uncontrolled chain reaction, and less radioactive waste would be generated than in conventional fission. Incidentally, there would be a way to process existing waste and reduce its hazardousness.
The first design dates from 1977 and, like the tokamak, was the work of Soviet scientists. Of the four technologies mentioned, it has seen the most negligible experimental development. So far, one of the few significant breakthroughs has come from the Kurchatov Institute in Russia, which announced a preliminary design in 2020.
We will see one of these reactors fully operational within the next decade with any luck. Of course, while this artificial sun becomes a reality, we will continue to make use of the sun we already have, thanks to technologies such as photovoltaic cells. Along with wind, solar power today is the best guarantee for a transition to a more sustainable economy.