The story so far: Imagine creating an artificial sun on earth that can produce energy from the same process that gives us starlight and sunshine. Two recent achievements have taken us a step closer to this dream. China's Experimental Advanced Superconducting Tokamak (EAST) sustained the plasma at 70 million degrees Celsius for 1,056 seconds in January 2022. In February 2022, the Joint European Torus (JET) fusion experiment in Oxfordshire, U.K., produced 59 megajoules (MJ) of energy from thermonuclear fusion. These are dress rehearsals for the upcoming International Thermonuclear Experimental Reactor (ITER), a global experiment to generate 500 MW of power by fusing hydrogen atoms into helium atoms by 2035.
What is thermonuclear fusion?
In a thermonuclear fusion reaction, lighter atoms like those of hydrogen fuse to produce slightly heavier atoms like that of helium. The whole is greater than the sums; sometimes, the sums are greater than the whole. The mass of one hydrogen atom is 1.007825 Atomic Mass unit (AMU). When four hydrogen atoms are combined, it transmutes into a helium atom. The sum of the mass of four hydrogen atoms is 4.03130 AMU, while the mass of one helium atom is just 4.00268 AMU. As we know, matter is neither created nor destroyed; hence the mass difference 0.02862 AMU is converted into pure energy by way of Einstein's famous formula E=mc2.
If we fuse four grams of hydrogen into helium, about 0.0028 grams of mass would be converted to 2.6x10^11 joules; with that energy, we can light a 60-watt light bulb for over 100 years! 600 million tons of hydrogen are fused every second in the Sun, producing 596 million tons of helium. If one-thousandth of a gram of mass can create energy to power a 60W bulb for a hundred years, imagine the amount of energy the remaining four million tons of hydrogen unleash every second by the Sun.
What is the history of efforts to achieve nuclear fusion?
On March 24, 1951, then Argentinian president Juan Perón stunned the world by announcing the success of 'Proyecto Huemul' led by Nazi scientist Ronald Richter to harness energy from fusion. Not knowing that he had been tricked, he went on to say that the invention would bring “a greatness which today we cannot imagine”. People went on to believe that, with the technology at hand and two superpowers, the U.S. and USSR striving to one-up each other in technological progress, building the thermonuclear bomb were feasible, by harnessing energy from the fusion process. But this turned out to be science fiction. While the world wondered how a rural, backward Argentina could put together the technology, it soon became clear that Richter had pulled a fast one. Then in a politically precarious position, Perón had fallen for it.
But both the USSR and the U.S. stepped up their fusion research, not to be left behind. Soon, the Soviets came up with a viable design to kindle and sustain nuclear fusion—the Tokamak. Unlike the fission reactors, like the ones in Kalpakam and Koodankulam, the fusion reactors do not pose the dangers of a radioactive leak. Gram for gram, the thermonuclear power produces four million times more energy than burning coal. The only waste product is harmless helium.
“The Artificial Sun”: In stars such as the sun, hydrogen atoms combine to produce helium in the thermonuclear reaction and release immense energy in light and radiation. Ordinarily, the atoms cannot fuse. The like charges of the electron clouds surrounding the atoms would repulse and keep them at bay from coming too close. However, in the core of the stars, the temperature is some 15 million Kelvins. All the electrons are ripped away at these temperatures, forming what is known as plasma. Further, due to gravity, the pressure builds up 200 billion times greater than Earth's atmospheric pressure, making the density to become 150 times that of water. In this sizzling heat, intense pressure and dense core, the plasma of hydrogen fuse with each other to form helium, spewing colossal energy in the form of light and heat.
If only one can mimic the condition of the interior of the stars, we can artificially ignite fusion; and the fusion reactors which permits us to do so are Tokamaks.
What is the Tokamak?
If fusion has to occur, the first step has to be the creation of hot plasma. Heating a tiny pellet of hydrogen to millions of degrees and generating plasma is not that hard; lasers could do the job well. However, to keep the fiery plasma at millions of degrees from touching the container wall is another thing. Soviet physicists Igor Tamm and Andrei Sakharov conceptualised that if one can create a magnetic field in the shape of a torus — like a south Indian vada—then the scorching plasma could be contained in the invisible magnetic bottle. The scalding of the walls of the container could be prevented. Based upon this theory, an experimental reactor was built and demonstrated by a Soviet team led by Lev Artsimovich at the Kurchatov Institute, Moscow.
The Tokamak is an acronym for tongue-twisting Russian terms 'toroïdalnaïa kameras magnitnymi katushkami', which means "toroidal chamber with magnetic coils". Although alternative designs such as z-pinch and stellarator have been designed and tested, tokamaks are still the rage for achieving fusion.
The research on fusion commenced by being shrouded in the worrying secrecy of the Cold War. But the effort to harness energy from thermonuclear fusion today, thankfully, is a global collaborative effort. Thirty-five countries, including India, Russia, the United States, the United Kingdom, China, European Union, are collaborating to jointly build the largest Tokamak as part of the International Thermonuclear Experimental Reactor (ITER).
The idea germinated in 1985. After years of ups and downs since March 2020, the machine assembly is underway at Saint Paul-lez-Durance, southern France. With the installation of the Cryostat, a device to cool the reactor, covering the assembly is slated to be completed by 2025. If all goes well, the first plasma will be produced at the end of 2025 or early 2026. After testing and troubleshooting, energy production will commence in 2035.
The plant is expected to generate 500 MW power and consume 50 MW for its operation, resulting in a net 450 MW power generation. Although there are many experimental tokamaks worldwide, including one in India, none have demonstrated net energy production more than the input. Thus, the main task of the experimental ITER reactor is to get operational experience and train human resources. Scientists, engineers and technicians from all the 35 participating countries are working on the site learning along the way, hoping to lay the foundation for their own national fusion energy programmes.
What is the significance of the recent feats?
The ITER fusion reaction will use the isotopes of hydrogen called deuterium and tritium. Deuterium, also called heavy hydrogen, has a neutron and a proton in its nucleus. In contrast, ordinary hydrogen has only one proton. Tritium, another isotope of hydrogen, has two neutrons and one proton. To create plasma for fusion, the mixture of deuterium and tritium needs to be heated to temperatures 10 times hotter than the Sun's centre. Using strong magnets, the weltering plasma must be held in place, made to swill around, beams collide, fuse and release tremendous energy as heat. The heat must be removed from the reaction to boil water, produce steam and turn a turbine to generate electricity.
The plasma at high temperature needs to be sustained for a long time if commercial energy has to be obtained. One of the critical challenges in the Tokamak is the sudden appearance of plasma instabilities. We need to get experience and assess the probability of such disruptions and work out how we can manage them. Making plasma at higher and higher temperatures and sustaining it at that temperature for more and more time will provide insights on disruptions. The Chinese accomplishment of maintaining 2.8 times the Sun's temperature for 17 minutes is a milestone in this direction. For the first time, the Joint European Torus experiment used the tritium fuel mix, the same one that will power ITER. They could harvest one-third of the input energy as an output, a significant step from earlier results. The experimental results from this JET indicate that the models used to design ITER are robust, boosting our confidence in them. These experiments would help validate ITER's designs.
What about India vis-à-vis fusion?
Way back in 1955, in the first 'Atoms for Peace' meeting in Geneva, Homi J. Bhabha saw a future in energy coming from thermonuclear fusion. The Institute for Plasma Research (IPR) in Gandhinagar and the Hot Plasma Project at Saha Institute of Nuclear Physics (SINP), Kolkata, took the lead in nuclear fusion research in India.
T.V. Venkateswaran is Scientist F at Vigyan Prasar, Dept of Science and Technology