(Photo of the inside of a target chamber where scientists plans to create an artificial sun – Lawrence Livermore National Laboratory, California, U.S.A)
The Sun : Part 2 - Prospects of creating artificial Sun on Earth
Dr.Benu Chatterjee
Dynamism of the Sun is discussed in Part 1 of the current series. The present article is a basic review of the reasons, principles and possibility of creating systems that would simulate properties of the Sun so that similar amount of heat (and light) as from the Sun can be artificially generated on our Planet Earth .
1. Introduction
The need for a new energy source has never been more pressing in recent time. Global energy demand is expected to double by 2050, while the share coming from fossil fuels – currently 85% – needs to drop dramatically if we are to reduce carbon emissions and limit global warming. This is all happening at a time when fossil fuel supplies are dwindling and fears about global warming are forcing governments to seek clean energy sources. It has long been clear that the answer to the imminent huge social, economic and global problems lies in the technology of nuclear fusion that has many advantages over its more toxic cousin fission.
The light and warmth that we enjoy from the sun, a star 93 million miles away, are reminders of how well the fusion process works and the immense energy it creates at Sun’s core. Physicists have dreamed of producing cheap, safe and plentiful energy through atomic fusion since the 1950s. While it has seemed an impossible goal for nearly 100 years, scientists now believe that they are on brink of cracking one of the biggest problems in physics by controlling the power of nuclear fusion of hydrogen isotopes, the reaction that burns at the heart of the Sun.
The present article reviews the background knowledge of nuclear fusion (sec.2) and the prospects of creating artificial Sun on Earth by replicating the extreme conditions that exist in Sun’s core (sec.3). Obviously, any success of such endeavour is likely to provide all the energy required in the world. Appendices are added in this article to provide greater depth of information.
2. Background
2.1. Basics of nuclear fusion
The science is simple. The fusion process echoes the system that takes place in the energy- producing core of the sun. In Sun’s fusion process, the nuclei of isotopes of hydrogen namely deuterium with one extra neutron, and tritium, with two, fuse at a fiercely hot 15 million Celsius (°C) forming a state of matter known as plasma which is a mixture of protons and electrons from atomic nuclei. On achieving "plasma burn" in the super hot condition, the fusion process produces helium and spits out power in the form of a highly energetic neutron to provide the colossal energy in the core of Sun’s reactor. In order to initiate a self-sustaining reaction, generation of plasma requires extreme temperature and pressure in Sun’s core where the temperature is around 15 million 0C and an estimated pressure of 250 billion atmospheres generated from core's gravity.
For fusion to occur on Earth, a temperature of at least 100 million 0C is needed. This is six times hotter than the inside of natural fusion reactor of Sun’s core. This is needed because Earth’s lack of extreme pressure encountered inside the Sun, is someway compensated by the super hot Earth’s condition. Thus for an Earth’s device to replicate the Sun, it has to withstand temperatures as high as 100 million 0C and control a deuterium-tritium fusion reaction. Such a unit would be able to supply infinite, clean energy for human beings.
Scientists have been attempting to harness nuclear energy from fusion since Albert Einstein derived his famous equation in 1905 relating energy (E) to change in mass (∆m) times the square of speed of light (c^2), i.e E = ∆m*c^2. As the speed of light squared is a vast number, even a minuscule loss of mass during fusion would produce a massive amount of energy. In fact, Einstein’s equation raised the hope that an incredible amount of energy could be available if atoms are fused together. With Einstein’s theory put into practice, the amount of energy locked up in one gram of matter, for example, is enough to power 28,500 off 100-watt light bulbs for a year.
2.2 Fusion process requires severe conditions
An important condition for nuclear fusion on Earth is the requirement of super hot plasma. The question naturally arises as to why so much heat is needed to achieve nuclear fusion even for light elements such as hydrogen isotopes! This is because under the extreme high pressure and temperature, the atoms with protons in the nucleus are brought together close enough for the nuclear forces to overcome the electrostatic repulsion of similarly charged protons in the hydrogen isotopes. The extreme conditions of temperature and pressure of hot plasma would accelerate the atomic nuclei of hydrogen isotopes to get close enough at a super high speed force to initiate nuclear fusion. It is estimated that more energy would be released in the end than needed to start off nuclear fusion. The change of heat of reaction is negative i.e. the reaction is exothermic. And because it is exothermic, the fusion of light elements is self-sustaining given that there is enough energy to start the fusion process in the first place.
2.3 Feasibility of “cold” rather than conventional “super hot” fusion
The conventional fusion process, as explained above, requires extreme temperature and pressure. Although the scientists consider it a grand scientific challenge to explore the feasibility of creating such extreme conditions, they are naturally interested in a fusion process that can be conducted under much less severe condition. This is where the viability of a cold fusion process comes into consideration.
Although cold fusion is a theoretical possibility, the field was largely written off as pseudoscience in the late 1980s, when electrochemists Stanley Pons and Martin Fleischmann reported that their room-temperature electrolysis experiment had produced so much excess heat—as well as nuclear by-products like tritium—that only a nuclear reaction could be blamed. The attention led to a massive wave of cold-fusion experiments, but no one was able to replicate their heat anomaly. A review panel of the Department of Energy debunked the evidence, and met again in 2004 to draw the same conclusion.
2.4. Nuclear fusion in preference to fission
Both processes involve reactions that would release energy. The fission process is well known in nuclear weapon industry namely atom bomb. It involves splitting of atoms (uuranium is the primary fuel) into two or more smaller, lighter atoms using little energy. In contrast, fusion occurs naturally in stars like the Sun and involves two or more smaller atoms such as hydrogen or its isotopes (deuterium and tritium) fused together to create a larger, heavier atom such as helium..
So the question is why not utilize energy from fission rather than fusion which demands extreme condition! The answer is simple. This is because despite requiring severe conditions, the energy produced by fusion is far greater than that from fission. On a per mass, or per nucleon (proton + neutron) basis, fusion wins hands-down. For example, fusion of one gram of deuterium releases 10^12 J of energy, or 275 million kcal. In comparison, a fission process would generate a mere 20 million kcal per gram of 235U making the fusion process over ten times as potent.
Also, contrary to fission, the fusion process is not self perpetuating. This would mean that the risk of a meltdown is non-existent with fusion reactors unlike the disaster fission accidents with some meltdown of reactors, namely in Mile Island (1979), Chernobyl (1986) and Fukushima (2011). Also, fission generates deadly radioactive waste as a by-product compared to hardly any from a fusion process where the by-products are mainly helium and neutron. The advantages of fusion over fission are briefly described in the appendices.
2.5 System evaluation for fusion
The basic principles of creating artificial Sun on Earth for an answer to world’s impending energy shortage are considered in terms of fusion of hydrogen isotopes namely deuterium-tritium system. When the fusion reaction occurs in Sun’s core which acts as a giant ball of gas, a strong gravitational pressure (~ 250 billion atmospheres) and an extreme temperature (~15 million 0C) force the nuclei of hydrogen isotopes together to fuse. Here on Earth, any fusion reaction will have to take place only at a tiny fraction of the scale of the Sun, without the benefit of Sun’s gravity. So to force the nuclei of hydrogen isotopes together on Earth, engineers need to build a reactor that would withstand temperatures at least ten times higher that of the Sun – which means hundreds of millions of degrees.
An enormous amount of energy is expected to be generated from a deuterium-tritium fusion reaction in a super hot plasma at about 100 million 0C. Deuterium fuses with tritium creating helium-4 and freeing a neutron with enormous energy. There is a small amount of change in mass which appears as the kinetic energy of the products. Based on the kinetic relation E = Δm^c*2, one would expect an estimated released energy of 17.6 MeV as illustrated in the appendices.
The estimated amount of energy released in one single reaction i.e. 17.6 MeV is one of those baffling measurements only physicists use and understand. Translating that into more meaningful terms, about 3.5 billion i.e.3.5*10^12 of the above fusion reaction would be needed every single second to light a 10-watt, low energy lamp. That sounds a lot, but the fact that 1g (0.04 oz) of hydrogen contains 600,000 trillion i.e. 600,000 *10^18 atoms, implies a very little fuel has the potential of making a huge amount of fusion power. The resulting heat from fusion of massive amounts of deuterium and tritium could be used to generate steam to drive turbines that could in turn generate electricity.
3. Reality check outs in replicating Sun on Earth
If a device can be developed that can withstand temperatures as high as 100 million 0C and control a deuterium-tritium fusion reaction, it will be considered as though an "artificial sun" had been created on Earth that would be able to supply infinite, clean energy for human beings. By scorching with concentrated waves of radiation, scientists believe that it will be possible to harness such a vast amount of energy (in the form of photons) created via nuclear fusion - the same process as in Sun’s core. Basically, there are following two internationally well-known projects that are underway in an endeavour to create artificial Sun on Earth : 3.1 Work at National Ignition Facility (NIF) in Livermore, California, and
3.2 Project on International Thermonuclear Experimental Reactor (ITER) which is being constructed in Cadarache, Southern France. As the name suggests, it is an international joint programme between the European Union, India, Japan, China, Russia, South Korea and the United States. The European Union is contributing 45% of the 16 billion Euro cost with the other six participants contributing 9% each.
3.1 Work at NIF, Livermore, U.S.A
In the 1970's, scientists began experimenting with powerful laser beams to compress and heat the hydrogen isotopes to the point of fusion. Scientists at NIF plan to use laser beams to ignite a tiny man-made star of a pellet of frozen hydrogen isotopes inside a 32ft-wide laboratory reaction chamber. It is hoped that by triggering a thermonuclear reaction via fusion of hydrogen atoms, temperatures of more than 100 million 0C and pressures billions of times higher than those found anywhere else on Earth would be created. The amount of power thus produced would be massively greater than that of the laser beams. The explosion will produce at least 10 times the amount of energy used to create it. If successful, the experiment will mark the first step towards building a practical nuclear fusion power station and a source of almost limitless energy.
3.1.1 Mechanics of the process
A special capsule containing a pellet of frozen mixture of fuels namely deuterium and tritium, is prepared which must first ignite for fusion. On hitting the inside of the capsule with laser beams, high-energy X-rays are expected to generate within a few billionths of a second. This activity will compress the fuel pellet inside the capsule until its outer shell blows off. The rapid heating caused by the laser "driver" makes the outer layer of the capsule target to explode. This explosion of the fuel pellet shell is a very crucial step. This is because in keeping with Isaac Newton's Third Law (for every action there is an equal and opposite reaction), the remaining portion of the target is driven inwards. This is similar to a rocket-like implosion, causing compression of the fuel inside the capsule, and formation of a shock wave which further heats the fuel in the very centre. This sequence of events is expected to result in a self-sustaining burn known as ignition. The fuels namely hydrogen isotopes are compressed enough together to initiate nuclear fusion, releasing vast amounts of energy.
Scientists have already spent 11 years to develop the work. The tiresome task of adjusting and aiming the laser could take up to a year before they can successfully achieve fusion. Laser pulses will be fired that would last just a few billionths of a second to create conditions that are found in the interior of stars or exploding nuclear weapons. It is obvious that unless the targeting is right, the experiment will not work. The whole experiment will cost £1.2 billion!
3.1.2 Latest results
According to NIF, 192 laser beams were fired (that would boil two kettles of water in a few billionths of a second) on November 2, 2010 at the centre of the reactor by aiming at a glass target containing deuterium and tritium gas. The resulting release of energy was about 1.3 million joules (i.e. mega joule or MJ), which was a world record and the peak radiation temperature at the core was measured approximately 3.3million 0C (or six million degrees Fahrenheit) compared to about 15million 0C at Sun’s core. The result gave the scientists great confidence for a breakthrough so as to be able to achieve ignition conditions for deuterium-tritium fusion targets. This experiment although encouraging, was not 'live' in the sense that no self-sustaining fusion reaction was set off. However, this was just the first step, and further research and technological developments are needed to reach the final goal. NIF will be the first organisation where on using laser, the energy released from the fusion of fuel will exceed the laser energy used to produce the fusion reaction.
3.1.3 Construction of plant
Anticipating that self-sustaining fusion could be a reality, officials at NIF speculate that a prototype fusion reactor could be operational by 2020. And almost a quarter of the United States energy could be supplied from the fusion power by 2050.
Scientists will perform the experiment inside a structure that will cover an area of the size of three football grounds. A single infrared laser will be sent through almost a mile of lenses, mirrors and amplifiers to create a beam more than 10 billion times powerful than a household light bulb. Housed within a hanger-sized room that has to be pumped clear of dust to prevent impurities getting into the path of the beam, the laser will then be split into 192 separate beams, converted into ultraviolet light and focused into the centre of the hydrogen capsule. The inner wall of this capsule has an aluminium and concrete-coated target chamber. It is inside NIF's 130-ton target chamber where the neutrons fired by the 192 lasers stimulate the fusion reaction. The holes in the chamber which is 10 metres in diameter and covered in 30 cm thick concrete permits the 192 laser beams to enter the chamber.
As mentioned above, when the laser beams strike the inner walls of the capsule, high-energy X-rays will be generated within a few billionths of a second. The process is known as conducting inertial confinement fusion (ICF). The reactor eventually going live will generate unprecedented temperatures and pressures in the target materials that are held in a tiny glass ball. The temperature inside the chamber is expected to be more than 100 million degrees, creating pressures more than 100 billion times Earth's atmospheric pressure and thus nearly simulating conditions in the cores of stars like Sun.
3.2 ITER project in France
Impressive though they are, NIF project so far resembles big scale “lab” experiment. Any hope to achieve something like a commercial fusion process is now based on an international project namely ITER which is currently under construction in the South of France. Unlike laser-based approach at NIF, magnetic fields are used in ITER.
This is a groundbreaking largest scientific effort the world has ever known. The idea first conceived in 1987 was discussed and argued over several decades before finally being agreed in 2007 as a multinational cooperation between the European Union, China, India, Japan, South Korea, Russia and the US – in total, 34 countries representing more than half of world's population. If all goes according to plan, ITER could provide a large chunk of world’s future energy requirements.
3.2.1 Proposed plan
At the heart of a star, fusion occurs, as mentioned above, when hydrogen atoms fuse together under extreme heat and pressure to create a denser helium atom releasing, in the process a colossal amount of neutron energy. The unavailability of the prevailing extreme conditions of Sun’s core on Earth, prompted the physicists to develop a novel method of replicating Sun’s extreme conditions on Earth. The new system should not only provide a powerful heating facility to facilitate fusion, but also should have provisions to minimize any thermal losses by keeping the hot fuel particles of plasma away from the walls of the container. This is achieved by creating an artificial strong magnetic field in the form of a magnetic “cage” that would prevent the plasma particles from escaping. For the necessary energy production, this plasma has to be confined for a sufficiently long period for the fusion to occur.
3.2.2 Containment of plasma in Tokamak
Currently, the mostly developed configuration of a magnetic “cage” is called a Tokamak Reactor (as shown below) which is a Russian word for a torus/doughnut shaped magnetic containment chamber. It is one of the most researched techniques for controlling thermonuclear fusion power. According to the organisation’s website, ITER is based on the Tokamak concept of magnetic confinement, in which the plasma is contained in a doughnut-shaped vacuum vessel. The mixed fuel of hydrogen isotopes will be heated to temperatures in excess of 150 million 0C to form hot plasma that would start the fusion process. A super-hot cloud of hydrogen isotopes will rotate faster than the speed of sound while being bombarded with surges of electric current. Such activity will leave the hydrogen atoms ten times hotter than sun’s core for eventual fusion. Appendices provide more information about Tokamak.
Tokamak of today uses electromagnetism to confine plasma within the reactor and thereby preventing it from actually touching the walls of the reactor. The plasma is held in a doughnut-shaped reaction chamber of the Tokamak by using special coils that would deploy a powerful magnetic field causing the plasma particles to run around in spirals, without touching the wall of the chamber.
Currently, world’s largest and most powerful Tokamak is located at Culham Centre for Fusion Energy, U.K who is responsible for the Joint European Torus (JET) project. Since its inception, JET have come a long way in the past few decades by improving generation of few milliwatts in the 1970s to 16 megawatts (MW) from an input of 25MW (at about 64% output) in 1997. This encouraging progress has boosted confidence on the suitability of JET and hence Tokamak to deliver future power using deuterium-tritium fuel mix as a prospective commercial fusion process. However, in view of the lower output so far achieved, the fusion technology will have commercial attraction if the output can be improved by a near-constant tenfold power gain.
After more than 25 years of successful operation, JET although is still at the forefront of fusion research, a very important factor for ITER requires it to be scaled up. The system and materials for ITER need to be twice the size of JET along with a number of design improvements. JET is, however, closely involved in testing plasma physics, and assisting with the design and construction of ITER.
3.2.3 Construction of the plant
If plasma is ITER's heart, magnets are its skeleton. Containment of superhot, charged plasma in a huge magnetic field implies the need for several largest magnets in the world. The biggest of these are the poloidal field coils, which will run horizontally around the reactor's torus at its widest point (see diagram). At 25 metres across and weighing 400 tonnes, the magnetic coils (niobium-titanium alloy) are too large to be transported, so instead these are being built on site.
ITER is a very most complex machine eventually weighing 23,000 tons and will be as big as sixty football fields. Inside a monolithic building will be a nuclear reactor that will hopefully reduce our reliance on fossil fuels. When construction is complete, the pit will host a 73-metre-high machine (240 feet) that will attempt to create boundless energy by fusing hydrogen nuclei together, in much the same way as nuclear fusion occurs in stars like our Sun .On completion, a 60-mrtre-high building will be the centrepiece of a 39-building compound. It will house fusion of hydrogen isotopes in a doughnut-shaped Tokamak which is, of course, the heart of ITER.
Once installed, the enormous magnetic coils of a niobium-titanium alloy will be cooled to around 4 degrees above absolute zero, that's about -269 °C, until they become superconductors. This is necessary to limit energy consumption. It also means that some of the coldest objects on the planet will be just a few metres from one of the hottest systems in the universe - ITER's plasma.
3.2.4 Time scale
ITER project is expected to last 30 years of which 10 years being allotted for construction and 20 years for experimentation. Ground was broken on the construction site in 2008 and it is predicted that they will start building the reactor itself in 2015. Once completed, it should generate about 10 times more energy than it consumes for up to about 8–10 minutes. Even that, which will be a major achievement, will be far short of generating fusion power year after year. But it's a start!
Additionally, because fusion energy won't be ready for decades, even if it works, other low-carbon energy sources must still be pursued in the short-term at least. These issues, plus the logistics of dealing with multiple nations with their own fluctuating domestic budget constraints, mean that the site won't be ready for the first set of experiments until 2020. Even then, they will just be testing the reactor and its equipment. The first proper fusion tests between deuterium (abundant in sea water) and tritium (to be made from lithium) are unlikely to take place until 2028. If ITER is successful in its proof of principle mission, the plants are expected to operate from about 2040 - around 25 years away when the energy generated for electricity production will be used and stored.
3.2.5 Future outlook of ITER
Fusion is the goal of ITER whose proposed mission is to demonstrate the feasibility of a fusion reactor that can operate without negative impact to the environment or to surrounding ecosystems. Whether pinched or punched, the process of fusion, the same that powers the Sun and many other stars in the galaxy, provides hope for enormous energy at arm's length. If all goes to plan, the physicists hope to prove that they can produce ten times as much energy as required to heat the plasma to the required temperature to sustain fusion. However, because ITER is the first reactor of its kind, there are no plans as yet to use the excess energy to create electricity. The plan is to use 50 MW (in heating the plasma and cooling the reactor), and get 500 MW out. And that is a big gamble. This is because so far, the world's biggest Tokamak at JET only managed to achieve a 16 MW output with a 25 MW input at about 64% output in 1997. Undoubtedly, scaling up is an extremely important factor for Tokamak at ITER. With this in mind, ITER with twice the size of JET, as well as featuring a number of design improvements should theoretically be able to deliver an even greater output to input power ratio perhaps in the range of gigawatts.
If all goes well within the next 10 years or so, the system will be switched on when the particles inside the giant ringed-doughnut-shaped device of Tokamak will ramp up to 200 million 0C. The plasma thus generated will be contained by superconducting magnets cooled to -269 0C. This plasma will be hotter than Sun’s surface, resulting in the first sustained power-producing fusion reactor in the world, which could pave the way for further reactors that could produce terawatts of power with no radioactive waste for the next 30 million years, give or take.
However, because of so many cooks in the kitchen, ITER’s progress is fraught with power plays and controversies. Despite the seductive promise of finally getting a supply of electricity that's "too cheap to meter", the long wait to readiness and the fact that the technology remains unproven, means that many politicians are hesitant or even hostile to tolerate the expensive project.
Also, the project since its inception has run into a number of obstacles. For example, there have been number of challenges for the designers, the budget of 5 billion Euros has trebled, the scale of the reactor has been halved, and completion date has been pushed back. But despite the difficulties, some progress is being made. The parts are being manufactured and tested by the participating nations, many of whom hope to develop the necessary expertise to compete in any new fusion energy market that would be expected to follow a successful outcome at ITER.
4. Final comments
Scientists endeavour to create a mini-sun on Earth in a breakthrough project that could provide an endless supply of cheap, clean energy. It is like tapping into the real solar energy as fusion is the source of all energy in the world. Besides exciting physics being involved in such project, there are huge social, economic and global problems that it can help to solve.
Controlled nuclear fusion is seen as an efficient way to generate infinite, clean energy to offset the dearth of fossil fuels such as gas, oil and coal. Scientists and engineers are trying to create a giant star on Earth by simulating the chemical reactions at Sun’s core in order to produce energy in the most insane way imaginable. The consequences of the possibility of replicating the Sun on Earth would be spectacular. An era of genuinely cheap energy – both environmentally and financially, would have far reaching implications for everything from poverty reduction to conflict easement. It’s exciting to think that the next generation could in some way be fusion powered
5. Little dream
Scientists believe that having our own sun to fulfill the need of our energy for the next hundred years may not necessarily be an impossible dream! Maybe in future we can solve energy crisis by developing our own artificial sun. More time and support are all that scientists need to make this "nearly ideal energy source" a reality. Then again, claims that net fusion power is just around the corner have been made for decades.
Appendices
A. Features in favour of fusion over fission
1) Meltdown of reactor
The fusion process itself cannot go into a situation of runaway chain reaction as is possible in fission reactors that can trigger a “meltdown”. There are plenty of examples namely Three Mile Island (1979), Chernobyl (1986) and Fukushima (2011) where fission reactors melt down the reactors to various severities. Besides blatant fear mongering, the true extent of the damages inflicted by each event remain unknown. The risk of a meltdown is non-existent with fusion reactors. Once atomic fusion starts, the heat produced will keep the core hot. The fusion process unlike fission is not self perpetuating. The plasma involved in fusion requires a fiercely high temperature to sustain fusion within the reactor. If something causes the fusion reaction to go out of balance, the process stops within seconds with immediate cease of reaction, making the fusion process far safer. A meltdown is thus physically impossible. Replacing fission reactors with fusion reactors would be humanity’s way of taking the first step from a Type 0 civilization to a Type 1 civilization on the Kardashev scale. With the advancement of science, fusion reactors compared with traditional fission reactors are thus currently safer, cleaner and relatively green i.e. friendly to the environment.
2) Quality of radioactive by-product
A fission process unlike fusion unfortunately creates deadly radioactive waste as a by-product. In contrast, a fusion power plant is carbon free, and produces considerably lower amounts and less difficult-to-store toxic, radioactive by-products if any. This is because the by-products from fusion of hydrogen isotopes are mainly helium gas and neutron.
3) Availability of fuels
The most attractive part of the fusion process is that not only a small amount of fuel is required, but is also readily available. The fuels such as deuterium and tritium are relatively abundant on Earth. Deuterium is found in seawater (since one water molecule is made of one oxygen and two hydrogen atoms) and in fact there is one atom in every 5000 atoms of hydrogen in seawater is deuterium. This means that there is a vast supply of deuterium as heavy water that could be used for fusion. Tritium can be extracted from the metal lithium, a common element in soil. Thus, fusion energy would be beneficial to both the environment and the economy.
B. Calculation of fusion energy
In mass-energy equivalence concept in physics, mass and energy are considered to be the same thing i.e. a unit of mass is convertible to one electronvolt or eV. It is a common practice in particle physics where units of mass and energy are often interchanged to express mass in units of eV/c^2, where c is the speed of light in vacuum (from E = ∆m*c^2 ). Since 1 eV = 1.602 * 10^ -19 J, one can write the mass equivalent of 1 eV/c^2 as 1eV/c^2 = 1.602 *10^-19 (J)/ (2.997 * 10^8)^2 (m^2/s^2) = 1.783 *10^-36 J/ (m^2/s^2). This can be alternately expressed as 1.78*10^-36 kg since kg = J/ (m^2/s^2). Therefore, 1 kg = 1/ 1.78*10^-36 eV/c^2.
The masses of atoms and subatomic particles are extremely small. It is therefore convenient to define a new unit as the atomic mass unit – written as a.m.u or simply as u. One atomic mass unit is defined as one twelfth of the mass of one atom of the carbon 12 isotope. Number of atoms per one mole of any element is Avogadro’s number/constant which is 6.022 * 10^23. Therefore, 6.022*10^23 atoms are present per 1 mole of a substance or in exactly 12g of carbon-12isotope. Therefore, weight of 1 atom of carbon is
12g/ (6.022*10^23) = 1.99*10^-23g.
Since 1 u is one twelfth of the mass of one atom of carbon-12 isotope,
1 u = 1/12*(19.92*10-27) kg = 1.66*10^-27 kg, From the above relation,
1u =1 amu = 1.66*10^-27 / (1.78** 10^-36) eV/c^2 = 0.932 * 10^9 eV/c^2 = 932 Mev/c^2 (i.e. 932 million electron volts). (1 MeV = 1.6*10^-19 J and is equivalent to 0.00107 amu via E = mc².) On fusion, the gained energy is reflected in the mass difference ∆m between the fusion fuels and the products. The fusion products have less mass, and the energy gained amounts to
E = ∆m*c^2. For the calculation of the energy released on fusion of 1 deuterium atom with 1 tritium atom producing 1 helium atom and 1 neutron, following data on atomic mass are used :
Atomic mass of D = 2.0124 amu
Atomic mass of T = 3.0138 amu
Atomic mass of He = 3.9993 amu
Atomic mass of neutron = 1.0080 amu
Total mass of reactants is 2.0124+ 3.0138 =5.0262 amu, while that of products is 3.9993 + 1.008 = 5.0073 amu. Therefore, loss in mass is 5.0262 – 5.0073 = 0.0189 amu which is equivalent to 0.0189 * 932 = 17.6 MeV/c^2. Since neutron in the product has only one fourth of the mass of a helium atom, it carries away four times as much kinetic energy as the helium. This results in energy associated with helium and neutron as 3.5 MeV and 14.1 MeV respectively (as illustrated in sketch 3 above). Thus a fusion energy of 17.6 MeV is released when one deuterium nucleus fuses with one tritium nucleus creating a helium nucleus and a neutron : 2 1H + 3 1H →4 2He (3.5 MeV) +10 n (14.1 MeV).
C. Brief account of Tokomak
There are currently around 30 known Tokamak reactors in operation around the globe; the majority of them scattered across Europe, Russia and China. Surprisingly, such a device can harness energy using the same mechanism [on a much smaller scale] as on the Sun.
C.1 Principles of Tokamak
The initial design was first theorized by Russian physicist Oleg Lavrentiev in the 1950s, but it wasn’t until a few years later that two Russian physicists— Igor Tamm and Andrei Sakharov—invented what is now known as a Tokamak (though their device is still based on Oleg’s initial idea).
Not only the torus shape of the Tokamak is crucial in achieving the proper plasma containment, but it also allows magnetic field lines inside the torus to be manipulated in a helical shape created by a combination of a toroidal and poloidal magnetic field. The helical shape is attained in the following way. Electromagnets surrounding the torus create a toroidal field (simply put, a toroidal field is a magnetic field traveling in circles around the torus). Similarly, electromagnets are used inside the torus to induce a poloidal field (it is generated by the electrical flow of plasma) which travels in circles orthogonal to the toroidal field, resulting in the required helical shape.
At a fiercely hot 150 million °C, deuterium with one extra neutron, and tritium, with two, will form, as mentioned earlier, a state of matter known as a plasma, in which their nuclei fuse together to form helium. When they achieve "plasma burn", they will spit out power in the form of a highly energetic neutron.
C.2 Working of Tokamak
The Tokamak creates energy by absorbing large amounts of high energy neutrons. These neutrons are created by the heated plasma spinning around the reactor. Because these neutrons are neutrally charged, they are no longer held in the plasma stream by the magnetic fields, and continue outwards until they are stopped by the inner walls of the reactor. The heat from these neutrons is then converted into energy; however, a lot is lost in the process due to cooling. The neutrons yield so much energy, they could actually melt the walls of the reactor, which is obviously not a good omen. So to prevent this happening in destroying the system, a cryogenic cooling process is introduced by utilizing a mixture of liquid helium and liquid hydrogen. Both the superconducting magnetic coils and reactor walls are thus protected when combined with ceramic plates.
Today, fusion reactions occur in Tokamaks where gas of hydrogen isotopes is pumped into a vacuum chamber of the Tokamak, and electricity flows through the centre (the doughnut's hole). The gas becomes charged and is heated to the point when they lose electrons to form plasma which is then locked inside the vacuum chamber by powerful suspended magnetic fields (which are created by massive superconducting electromagnetic coils of a niobium-titnium alloy). The fields compress the hydrogen plasma, mimicking the pressure of Sun's core. Radio and microwaves are fired into the plasma to raise its temperature, and at around 100 million 0C fusion occurs. The main barrier to a sustained reaction, other than the high cost of the electricity needed to heat the chamber, is to find a material which can withstand that much heat for more than a few seconds. It is interesting to note an amusing story from Culham Centre where the amount of electricity to create the necessary magnetic field was so high that the National Grid had to be told for them to okay for the Centre to go ahead for a trial run of JET.
C.3 Possible hazards withTokamak
Though fusion is much cleaner than fission, it will still produce some radioactive and toxic materials. Most of this comes from the high-energy neutrons that gradually embed themselves in the walls of the torus, creating atoms such as cobalt-60. Tritium is also radioactive (with a half-life of 12 years), while beryllium used to line the torus is toxic. The entire site must, of course, finally conform to France's strict nuclear safety laws. The matter is further complicated by the fact that the site at Cadarache in France is moderately seismically active which would mean the buildings need to be supported on something like rubber pads to protect them from earthquakes.
C.4 Problem of heating Tokamak
Even though the technology has been around for quite some time and has proven to be effective, it does not come without constraints. The biggest problem involves heating the plasma. In order to reach its operating temperature, the plasma must be heated to 10 keV which is equivalent to about 100 million 0C. The various methods of heating the plasma range from applying magnetic compression to bombarding the plasma with high-frequency microwaves.
The Sun : Part 2 - Prospects of creating artificial Sun on Earth
Dr.Benu Chatterjee
Dynamism of the Sun is discussed in Part 1 of the current series. The present article is a basic review of the reasons, principles and possibility of creating systems that would simulate properties of the Sun so that similar amount of heat (and light) as from the Sun can be artificially generated on our Planet Earth .
1. Introduction
The need for a new energy source has never been more pressing in recent time. Global energy demand is expected to double by 2050, while the share coming from fossil fuels – currently 85% – needs to drop dramatically if we are to reduce carbon emissions and limit global warming. This is all happening at a time when fossil fuel supplies are dwindling and fears about global warming are forcing governments to seek clean energy sources. It has long been clear that the answer to the imminent huge social, economic and global problems lies in the technology of nuclear fusion that has many advantages over its more toxic cousin fission.
The light and warmth that we enjoy from the sun, a star 93 million miles away, are reminders of how well the fusion process works and the immense energy it creates at Sun’s core. Physicists have dreamed of producing cheap, safe and plentiful energy through atomic fusion since the 1950s. While it has seemed an impossible goal for nearly 100 years, scientists now believe that they are on brink of cracking one of the biggest problems in physics by controlling the power of nuclear fusion of hydrogen isotopes, the reaction that burns at the heart of the Sun.
The present article reviews the background knowledge of nuclear fusion (sec.2) and the prospects of creating artificial Sun on Earth by replicating the extreme conditions that exist in Sun’s core (sec.3). Obviously, any success of such endeavour is likely to provide all the energy required in the world. Appendices are added in this article to provide greater depth of information.
2. Background
2.1. Basics of nuclear fusion
The science is simple. The fusion process echoes the system that takes place in the energy- producing core of the sun. In Sun’s fusion process, the nuclei of isotopes of hydrogen namely deuterium with one extra neutron, and tritium, with two, fuse at a fiercely hot 15 million Celsius (°C) forming a state of matter known as plasma which is a mixture of protons and electrons from atomic nuclei. On achieving "plasma burn" in the super hot condition, the fusion process produces helium and spits out power in the form of a highly energetic neutron to provide the colossal energy in the core of Sun’s reactor. In order to initiate a self-sustaining reaction, generation of plasma requires extreme temperature and pressure in Sun’s core where the temperature is around 15 million 0C and an estimated pressure of 250 billion atmospheres generated from core's gravity.
For fusion to occur on Earth, a temperature of at least 100 million 0C is needed. This is six times hotter than the inside of natural fusion reactor of Sun’s core. This is needed because Earth’s lack of extreme pressure encountered inside the Sun, is someway compensated by the super hot Earth’s condition. Thus for an Earth’s device to replicate the Sun, it has to withstand temperatures as high as 100 million 0C and control a deuterium-tritium fusion reaction. Such a unit would be able to supply infinite, clean energy for human beings.
Scientists have been attempting to harness nuclear energy from fusion since Albert Einstein derived his famous equation in 1905 relating energy (E) to change in mass (∆m) times the square of speed of light (c^2), i.e E = ∆m*c^2. As the speed of light squared is a vast number, even a minuscule loss of mass during fusion would produce a massive amount of energy. In fact, Einstein’s equation raised the hope that an incredible amount of energy could be available if atoms are fused together. With Einstein’s theory put into practice, the amount of energy locked up in one gram of matter, for example, is enough to power 28,500 off 100-watt light bulbs for a year.
2.2 Fusion process requires severe conditions
An important condition for nuclear fusion on Earth is the requirement of super hot plasma. The question naturally arises as to why so much heat is needed to achieve nuclear fusion even for light elements such as hydrogen isotopes! This is because under the extreme high pressure and temperature, the atoms with protons in the nucleus are brought together close enough for the nuclear forces to overcome the electrostatic repulsion of similarly charged protons in the hydrogen isotopes. The extreme conditions of temperature and pressure of hot plasma would accelerate the atomic nuclei of hydrogen isotopes to get close enough at a super high speed force to initiate nuclear fusion. It is estimated that more energy would be released in the end than needed to start off nuclear fusion. The change of heat of reaction is negative i.e. the reaction is exothermic. And because it is exothermic, the fusion of light elements is self-sustaining given that there is enough energy to start the fusion process in the first place.
2.3 Feasibility of “cold” rather than conventional “super hot” fusion
The conventional fusion process, as explained above, requires extreme temperature and pressure. Although the scientists consider it a grand scientific challenge to explore the feasibility of creating such extreme conditions, they are naturally interested in a fusion process that can be conducted under much less severe condition. This is where the viability of a cold fusion process comes into consideration.
Although cold fusion is a theoretical possibility, the field was largely written off as pseudoscience in the late 1980s, when electrochemists Stanley Pons and Martin Fleischmann reported that their room-temperature electrolysis experiment had produced so much excess heat—as well as nuclear by-products like tritium—that only a nuclear reaction could be blamed. The attention led to a massive wave of cold-fusion experiments, but no one was able to replicate their heat anomaly. A review panel of the Department of Energy debunked the evidence, and met again in 2004 to draw the same conclusion.
2.4. Nuclear fusion in preference to fission
Both processes involve reactions that would release energy. The fission process is well known in nuclear weapon industry namely atom bomb. It involves splitting of atoms (uuranium is the primary fuel) into two or more smaller, lighter atoms using little energy. In contrast, fusion occurs naturally in stars like the Sun and involves two or more smaller atoms such as hydrogen or its isotopes (deuterium and tritium) fused together to create a larger, heavier atom such as helium..
So the question is why not utilize energy from fission rather than fusion which demands extreme condition! The answer is simple. This is because despite requiring severe conditions, the energy produced by fusion is far greater than that from fission. On a per mass, or per nucleon (proton + neutron) basis, fusion wins hands-down. For example, fusion of one gram of deuterium releases 10^12 J of energy, or 275 million kcal. In comparison, a fission process would generate a mere 20 million kcal per gram of 235U making the fusion process over ten times as potent.
Also, contrary to fission, the fusion process is not self perpetuating. This would mean that the risk of a meltdown is non-existent with fusion reactors unlike the disaster fission accidents with some meltdown of reactors, namely in Mile Island (1979), Chernobyl (1986) and Fukushima (2011). Also, fission generates deadly radioactive waste as a by-product compared to hardly any from a fusion process where the by-products are mainly helium and neutron. The advantages of fusion over fission are briefly described in the appendices.
2.5 System evaluation for fusion
The basic principles of creating artificial Sun on Earth for an answer to world’s impending energy shortage are considered in terms of fusion of hydrogen isotopes namely deuterium-tritium system. When the fusion reaction occurs in Sun’s core which acts as a giant ball of gas, a strong gravitational pressure (~ 250 billion atmospheres) and an extreme temperature (~15 million 0C) force the nuclei of hydrogen isotopes together to fuse. Here on Earth, any fusion reaction will have to take place only at a tiny fraction of the scale of the Sun, without the benefit of Sun’s gravity. So to force the nuclei of hydrogen isotopes together on Earth, engineers need to build a reactor that would withstand temperatures at least ten times higher that of the Sun – which means hundreds of millions of degrees.
An enormous amount of energy is expected to be generated from a deuterium-tritium fusion reaction in a super hot plasma at about 100 million 0C. Deuterium fuses with tritium creating helium-4 and freeing a neutron with enormous energy. There is a small amount of change in mass which appears as the kinetic energy of the products. Based on the kinetic relation E = Δm^c*2, one would expect an estimated released energy of 17.6 MeV as illustrated in the appendices.
The estimated amount of energy released in one single reaction i.e. 17.6 MeV is one of those baffling measurements only physicists use and understand. Translating that into more meaningful terms, about 3.5 billion i.e.3.5*10^12 of the above fusion reaction would be needed every single second to light a 10-watt, low energy lamp. That sounds a lot, but the fact that 1g (0.04 oz) of hydrogen contains 600,000 trillion i.e. 600,000 *10^18 atoms, implies a very little fuel has the potential of making a huge amount of fusion power. The resulting heat from fusion of massive amounts of deuterium and tritium could be used to generate steam to drive turbines that could in turn generate electricity.
3. Reality check outs in replicating Sun on Earth
If a device can be developed that can withstand temperatures as high as 100 million 0C and control a deuterium-tritium fusion reaction, it will be considered as though an "artificial sun" had been created on Earth that would be able to supply infinite, clean energy for human beings. By scorching with concentrated waves of radiation, scientists believe that it will be possible to harness such a vast amount of energy (in the form of photons) created via nuclear fusion - the same process as in Sun’s core. Basically, there are following two internationally well-known projects that are underway in an endeavour to create artificial Sun on Earth : 3.1 Work at National Ignition Facility (NIF) in Livermore, California, and
3.2 Project on International Thermonuclear Experimental Reactor (ITER) which is being constructed in Cadarache, Southern France. As the name suggests, it is an international joint programme between the European Union, India, Japan, China, Russia, South Korea and the United States. The European Union is contributing 45% of the 16 billion Euro cost with the other six participants contributing 9% each.
3.1 Work at NIF, Livermore, U.S.A
In the 1970's, scientists began experimenting with powerful laser beams to compress and heat the hydrogen isotopes to the point of fusion. Scientists at NIF plan to use laser beams to ignite a tiny man-made star of a pellet of frozen hydrogen isotopes inside a 32ft-wide laboratory reaction chamber. It is hoped that by triggering a thermonuclear reaction via fusion of hydrogen atoms, temperatures of more than 100 million 0C and pressures billions of times higher than those found anywhere else on Earth would be created. The amount of power thus produced would be massively greater than that of the laser beams. The explosion will produce at least 10 times the amount of energy used to create it. If successful, the experiment will mark the first step towards building a practical nuclear fusion power station and a source of almost limitless energy.
3.1.1 Mechanics of the process
A special capsule containing a pellet of frozen mixture of fuels namely deuterium and tritium, is prepared which must first ignite for fusion. On hitting the inside of the capsule with laser beams, high-energy X-rays are expected to generate within a few billionths of a second. This activity will compress the fuel pellet inside the capsule until its outer shell blows off. The rapid heating caused by the laser "driver" makes the outer layer of the capsule target to explode. This explosion of the fuel pellet shell is a very crucial step. This is because in keeping with Isaac Newton's Third Law (for every action there is an equal and opposite reaction), the remaining portion of the target is driven inwards. This is similar to a rocket-like implosion, causing compression of the fuel inside the capsule, and formation of a shock wave which further heats the fuel in the very centre. This sequence of events is expected to result in a self-sustaining burn known as ignition. The fuels namely hydrogen isotopes are compressed enough together to initiate nuclear fusion, releasing vast amounts of energy.
Scientists have already spent 11 years to develop the work. The tiresome task of adjusting and aiming the laser could take up to a year before they can successfully achieve fusion. Laser pulses will be fired that would last just a few billionths of a second to create conditions that are found in the interior of stars or exploding nuclear weapons. It is obvious that unless the targeting is right, the experiment will not work. The whole experiment will cost £1.2 billion!
3.1.2 Latest results
According to NIF, 192 laser beams were fired (that would boil two kettles of water in a few billionths of a second) on November 2, 2010 at the centre of the reactor by aiming at a glass target containing deuterium and tritium gas. The resulting release of energy was about 1.3 million joules (i.e. mega joule or MJ), which was a world record and the peak radiation temperature at the core was measured approximately 3.3million 0C (or six million degrees Fahrenheit) compared to about 15million 0C at Sun’s core. The result gave the scientists great confidence for a breakthrough so as to be able to achieve ignition conditions for deuterium-tritium fusion targets. This experiment although encouraging, was not 'live' in the sense that no self-sustaining fusion reaction was set off. However, this was just the first step, and further research and technological developments are needed to reach the final goal. NIF will be the first organisation where on using laser, the energy released from the fusion of fuel will exceed the laser energy used to produce the fusion reaction.
3.1.3 Construction of plant
Anticipating that self-sustaining fusion could be a reality, officials at NIF speculate that a prototype fusion reactor could be operational by 2020. And almost a quarter of the United States energy could be supplied from the fusion power by 2050.
Scientists will perform the experiment inside a structure that will cover an area of the size of three football grounds. A single infrared laser will be sent through almost a mile of lenses, mirrors and amplifiers to create a beam more than 10 billion times powerful than a household light bulb. Housed within a hanger-sized room that has to be pumped clear of dust to prevent impurities getting into the path of the beam, the laser will then be split into 192 separate beams, converted into ultraviolet light and focused into the centre of the hydrogen capsule. The inner wall of this capsule has an aluminium and concrete-coated target chamber. It is inside NIF's 130-ton target chamber where the neutrons fired by the 192 lasers stimulate the fusion reaction. The holes in the chamber which is 10 metres in diameter and covered in 30 cm thick concrete permits the 192 laser beams to enter the chamber.
As mentioned above, when the laser beams strike the inner walls of the capsule, high-energy X-rays will be generated within a few billionths of a second. The process is known as conducting inertial confinement fusion (ICF). The reactor eventually going live will generate unprecedented temperatures and pressures in the target materials that are held in a tiny glass ball. The temperature inside the chamber is expected to be more than 100 million degrees, creating pressures more than 100 billion times Earth's atmospheric pressure and thus nearly simulating conditions in the cores of stars like Sun.
3.2 ITER project in France
Impressive though they are, NIF project so far resembles big scale “lab” experiment. Any hope to achieve something like a commercial fusion process is now based on an international project namely ITER which is currently under construction in the South of France. Unlike laser-based approach at NIF, magnetic fields are used in ITER.
This is a groundbreaking largest scientific effort the world has ever known. The idea first conceived in 1987 was discussed and argued over several decades before finally being agreed in 2007 as a multinational cooperation between the European Union, China, India, Japan, South Korea, Russia and the US – in total, 34 countries representing more than half of world's population. If all goes according to plan, ITER could provide a large chunk of world’s future energy requirements.
3.2.1 Proposed plan
At the heart of a star, fusion occurs, as mentioned above, when hydrogen atoms fuse together under extreme heat and pressure to create a denser helium atom releasing, in the process a colossal amount of neutron energy. The unavailability of the prevailing extreme conditions of Sun’s core on Earth, prompted the physicists to develop a novel method of replicating Sun’s extreme conditions on Earth. The new system should not only provide a powerful heating facility to facilitate fusion, but also should have provisions to minimize any thermal losses by keeping the hot fuel particles of plasma away from the walls of the container. This is achieved by creating an artificial strong magnetic field in the form of a magnetic “cage” that would prevent the plasma particles from escaping. For the necessary energy production, this plasma has to be confined for a sufficiently long period for the fusion to occur.
3.2.2 Containment of plasma in Tokamak
Currently, the mostly developed configuration of a magnetic “cage” is called a Tokamak Reactor (as shown below) which is a Russian word for a torus/doughnut shaped magnetic containment chamber. It is one of the most researched techniques for controlling thermonuclear fusion power. According to the organisation’s website, ITER is based on the Tokamak concept of magnetic confinement, in which the plasma is contained in a doughnut-shaped vacuum vessel. The mixed fuel of hydrogen isotopes will be heated to temperatures in excess of 150 million 0C to form hot plasma that would start the fusion process. A super-hot cloud of hydrogen isotopes will rotate faster than the speed of sound while being bombarded with surges of electric current. Such activity will leave the hydrogen atoms ten times hotter than sun’s core for eventual fusion. Appendices provide more information about Tokamak.
Tokamak of today uses electromagnetism to confine plasma within the reactor and thereby preventing it from actually touching the walls of the reactor. The plasma is held in a doughnut-shaped reaction chamber of the Tokamak by using special coils that would deploy a powerful magnetic field causing the plasma particles to run around in spirals, without touching the wall of the chamber.
Currently, world’s largest and most powerful Tokamak is located at Culham Centre for Fusion Energy, U.K who is responsible for the Joint European Torus (JET) project. Since its inception, JET have come a long way in the past few decades by improving generation of few milliwatts in the 1970s to 16 megawatts (MW) from an input of 25MW (at about 64% output) in 1997. This encouraging progress has boosted confidence on the suitability of JET and hence Tokamak to deliver future power using deuterium-tritium fuel mix as a prospective commercial fusion process. However, in view of the lower output so far achieved, the fusion technology will have commercial attraction if the output can be improved by a near-constant tenfold power gain.
After more than 25 years of successful operation, JET although is still at the forefront of fusion research, a very important factor for ITER requires it to be scaled up. The system and materials for ITER need to be twice the size of JET along with a number of design improvements. JET is, however, closely involved in testing plasma physics, and assisting with the design and construction of ITER.
3.2.3 Construction of the plant
If plasma is ITER's heart, magnets are its skeleton. Containment of superhot, charged plasma in a huge magnetic field implies the need for several largest magnets in the world. The biggest of these are the poloidal field coils, which will run horizontally around the reactor's torus at its widest point (see diagram). At 25 metres across and weighing 400 tonnes, the magnetic coils (niobium-titanium alloy) are too large to be transported, so instead these are being built on site.
ITER is a very most complex machine eventually weighing 23,000 tons and will be as big as sixty football fields. Inside a monolithic building will be a nuclear reactor that will hopefully reduce our reliance on fossil fuels. When construction is complete, the pit will host a 73-metre-high machine (240 feet) that will attempt to create boundless energy by fusing hydrogen nuclei together, in much the same way as nuclear fusion occurs in stars like our Sun .On completion, a 60-mrtre-high building will be the centrepiece of a 39-building compound. It will house fusion of hydrogen isotopes in a doughnut-shaped Tokamak which is, of course, the heart of ITER.
Once installed, the enormous magnetic coils of a niobium-titanium alloy will be cooled to around 4 degrees above absolute zero, that's about -269 °C, until they become superconductors. This is necessary to limit energy consumption. It also means that some of the coldest objects on the planet will be just a few metres from one of the hottest systems in the universe - ITER's plasma.
3.2.4 Time scale
ITER project is expected to last 30 years of which 10 years being allotted for construction and 20 years for experimentation. Ground was broken on the construction site in 2008 and it is predicted that they will start building the reactor itself in 2015. Once completed, it should generate about 10 times more energy than it consumes for up to about 8–10 minutes. Even that, which will be a major achievement, will be far short of generating fusion power year after year. But it's a start!
Additionally, because fusion energy won't be ready for decades, even if it works, other low-carbon energy sources must still be pursued in the short-term at least. These issues, plus the logistics of dealing with multiple nations with their own fluctuating domestic budget constraints, mean that the site won't be ready for the first set of experiments until 2020. Even then, they will just be testing the reactor and its equipment. The first proper fusion tests between deuterium (abundant in sea water) and tritium (to be made from lithium) are unlikely to take place until 2028. If ITER is successful in its proof of principle mission, the plants are expected to operate from about 2040 - around 25 years away when the energy generated for electricity production will be used and stored.
3.2.5 Future outlook of ITER
Fusion is the goal of ITER whose proposed mission is to demonstrate the feasibility of a fusion reactor that can operate without negative impact to the environment or to surrounding ecosystems. Whether pinched or punched, the process of fusion, the same that powers the Sun and many other stars in the galaxy, provides hope for enormous energy at arm's length. If all goes to plan, the physicists hope to prove that they can produce ten times as much energy as required to heat the plasma to the required temperature to sustain fusion. However, because ITER is the first reactor of its kind, there are no plans as yet to use the excess energy to create electricity. The plan is to use 50 MW (in heating the plasma and cooling the reactor), and get 500 MW out. And that is a big gamble. This is because so far, the world's biggest Tokamak at JET only managed to achieve a 16 MW output with a 25 MW input at about 64% output in 1997. Undoubtedly, scaling up is an extremely important factor for Tokamak at ITER. With this in mind, ITER with twice the size of JET, as well as featuring a number of design improvements should theoretically be able to deliver an even greater output to input power ratio perhaps in the range of gigawatts.
If all goes well within the next 10 years or so, the system will be switched on when the particles inside the giant ringed-doughnut-shaped device of Tokamak will ramp up to 200 million 0C. The plasma thus generated will be contained by superconducting magnets cooled to -269 0C. This plasma will be hotter than Sun’s surface, resulting in the first sustained power-producing fusion reactor in the world, which could pave the way for further reactors that could produce terawatts of power with no radioactive waste for the next 30 million years, give or take.
However, because of so many cooks in the kitchen, ITER’s progress is fraught with power plays and controversies. Despite the seductive promise of finally getting a supply of electricity that's "too cheap to meter", the long wait to readiness and the fact that the technology remains unproven, means that many politicians are hesitant or even hostile to tolerate the expensive project.
Also, the project since its inception has run into a number of obstacles. For example, there have been number of challenges for the designers, the budget of 5 billion Euros has trebled, the scale of the reactor has been halved, and completion date has been pushed back. But despite the difficulties, some progress is being made. The parts are being manufactured and tested by the participating nations, many of whom hope to develop the necessary expertise to compete in any new fusion energy market that would be expected to follow a successful outcome at ITER.
4. Final comments
Scientists endeavour to create a mini-sun on Earth in a breakthrough project that could provide an endless supply of cheap, clean energy. It is like tapping into the real solar energy as fusion is the source of all energy in the world. Besides exciting physics being involved in such project, there are huge social, economic and global problems that it can help to solve.
Controlled nuclear fusion is seen as an efficient way to generate infinite, clean energy to offset the dearth of fossil fuels such as gas, oil and coal. Scientists and engineers are trying to create a giant star on Earth by simulating the chemical reactions at Sun’s core in order to produce energy in the most insane way imaginable. The consequences of the possibility of replicating the Sun on Earth would be spectacular. An era of genuinely cheap energy – both environmentally and financially, would have far reaching implications for everything from poverty reduction to conflict easement. It’s exciting to think that the next generation could in some way be fusion powered
5. Little dream
Scientists believe that having our own sun to fulfill the need of our energy for the next hundred years may not necessarily be an impossible dream! Maybe in future we can solve energy crisis by developing our own artificial sun. More time and support are all that scientists need to make this "nearly ideal energy source" a reality. Then again, claims that net fusion power is just around the corner have been made for decades.
Appendices
A. Features in favour of fusion over fission
1) Meltdown of reactor
The fusion process itself cannot go into a situation of runaway chain reaction as is possible in fission reactors that can trigger a “meltdown”. There are plenty of examples namely Three Mile Island (1979), Chernobyl (1986) and Fukushima (2011) where fission reactors melt down the reactors to various severities. Besides blatant fear mongering, the true extent of the damages inflicted by each event remain unknown. The risk of a meltdown is non-existent with fusion reactors. Once atomic fusion starts, the heat produced will keep the core hot. The fusion process unlike fission is not self perpetuating. The plasma involved in fusion requires a fiercely high temperature to sustain fusion within the reactor. If something causes the fusion reaction to go out of balance, the process stops within seconds with immediate cease of reaction, making the fusion process far safer. A meltdown is thus physically impossible. Replacing fission reactors with fusion reactors would be humanity’s way of taking the first step from a Type 0 civilization to a Type 1 civilization on the Kardashev scale. With the advancement of science, fusion reactors compared with traditional fission reactors are thus currently safer, cleaner and relatively green i.e. friendly to the environment.
2) Quality of radioactive by-product
A fission process unlike fusion unfortunately creates deadly radioactive waste as a by-product. In contrast, a fusion power plant is carbon free, and produces considerably lower amounts and less difficult-to-store toxic, radioactive by-products if any. This is because the by-products from fusion of hydrogen isotopes are mainly helium gas and neutron.
3) Availability of fuels
The most attractive part of the fusion process is that not only a small amount of fuel is required, but is also readily available. The fuels such as deuterium and tritium are relatively abundant on Earth. Deuterium is found in seawater (since one water molecule is made of one oxygen and two hydrogen atoms) and in fact there is one atom in every 5000 atoms of hydrogen in seawater is deuterium. This means that there is a vast supply of deuterium as heavy water that could be used for fusion. Tritium can be extracted from the metal lithium, a common element in soil. Thus, fusion energy would be beneficial to both the environment and the economy.
B. Calculation of fusion energy
In mass-energy equivalence concept in physics, mass and energy are considered to be the same thing i.e. a unit of mass is convertible to one electronvolt or eV. It is a common practice in particle physics where units of mass and energy are often interchanged to express mass in units of eV/c^2, where c is the speed of light in vacuum (from E = ∆m*c^2 ). Since 1 eV = 1.602 * 10^ -19 J, one can write the mass equivalent of 1 eV/c^2 as 1eV/c^2 = 1.602 *10^-19 (J)/ (2.997 * 10^8)^2 (m^2/s^2) = 1.783 *10^-36 J/ (m^2/s^2). This can be alternately expressed as 1.78*10^-36 kg since kg = J/ (m^2/s^2). Therefore, 1 kg = 1/ 1.78*10^-36 eV/c^2.
The masses of atoms and subatomic particles are extremely small. It is therefore convenient to define a new unit as the atomic mass unit – written as a.m.u or simply as u. One atomic mass unit is defined as one twelfth of the mass of one atom of the carbon 12 isotope. Number of atoms per one mole of any element is Avogadro’s number/constant which is 6.022 * 10^23. Therefore, 6.022*10^23 atoms are present per 1 mole of a substance or in exactly 12g of carbon-12isotope. Therefore, weight of 1 atom of carbon is
12g/ (6.022*10^23) = 1.99*10^-23g.
Since 1 u is one twelfth of the mass of one atom of carbon-12 isotope,
1 u = 1/12*(19.92*10-27) kg = 1.66*10^-27 kg, From the above relation,
1u =1 amu = 1.66*10^-27 / (1.78** 10^-36) eV/c^2 = 0.932 * 10^9 eV/c^2 = 932 Mev/c^2 (i.e. 932 million electron volts). (1 MeV = 1.6*10^-19 J and is equivalent to 0.00107 amu via E = mc².) On fusion, the gained energy is reflected in the mass difference ∆m between the fusion fuels and the products. The fusion products have less mass, and the energy gained amounts to
E = ∆m*c^2. For the calculation of the energy released on fusion of 1 deuterium atom with 1 tritium atom producing 1 helium atom and 1 neutron, following data on atomic mass are used :
Atomic mass of D = 2.0124 amu
Atomic mass of T = 3.0138 amu
Atomic mass of He = 3.9993 amu
Atomic mass of neutron = 1.0080 amu
Total mass of reactants is 2.0124+ 3.0138 =5.0262 amu, while that of products is 3.9993 + 1.008 = 5.0073 amu. Therefore, loss in mass is 5.0262 – 5.0073 = 0.0189 amu which is equivalent to 0.0189 * 932 = 17.6 MeV/c^2. Since neutron in the product has only one fourth of the mass of a helium atom, it carries away four times as much kinetic energy as the helium. This results in energy associated with helium and neutron as 3.5 MeV and 14.1 MeV respectively (as illustrated in sketch 3 above). Thus a fusion energy of 17.6 MeV is released when one deuterium nucleus fuses with one tritium nucleus creating a helium nucleus and a neutron : 2 1H + 3 1H →4 2He (3.5 MeV) +10 n (14.1 MeV).
C. Brief account of Tokomak
There are currently around 30 known Tokamak reactors in operation around the globe; the majority of them scattered across Europe, Russia and China. Surprisingly, such a device can harness energy using the same mechanism [on a much smaller scale] as on the Sun.
C.1 Principles of Tokamak
The initial design was first theorized by Russian physicist Oleg Lavrentiev in the 1950s, but it wasn’t until a few years later that two Russian physicists— Igor Tamm and Andrei Sakharov—invented what is now known as a Tokamak (though their device is still based on Oleg’s initial idea).
Not only the torus shape of the Tokamak is crucial in achieving the proper plasma containment, but it also allows magnetic field lines inside the torus to be manipulated in a helical shape created by a combination of a toroidal and poloidal magnetic field. The helical shape is attained in the following way. Electromagnets surrounding the torus create a toroidal field (simply put, a toroidal field is a magnetic field traveling in circles around the torus). Similarly, electromagnets are used inside the torus to induce a poloidal field (it is generated by the electrical flow of plasma) which travels in circles orthogonal to the toroidal field, resulting in the required helical shape.
At a fiercely hot 150 million °C, deuterium with one extra neutron, and tritium, with two, will form, as mentioned earlier, a state of matter known as a plasma, in which their nuclei fuse together to form helium. When they achieve "plasma burn", they will spit out power in the form of a highly energetic neutron.
C.2 Working of Tokamak
The Tokamak creates energy by absorbing large amounts of high energy neutrons. These neutrons are created by the heated plasma spinning around the reactor. Because these neutrons are neutrally charged, they are no longer held in the plasma stream by the magnetic fields, and continue outwards until they are stopped by the inner walls of the reactor. The heat from these neutrons is then converted into energy; however, a lot is lost in the process due to cooling. The neutrons yield so much energy, they could actually melt the walls of the reactor, which is obviously not a good omen. So to prevent this happening in destroying the system, a cryogenic cooling process is introduced by utilizing a mixture of liquid helium and liquid hydrogen. Both the superconducting magnetic coils and reactor walls are thus protected when combined with ceramic plates.
Today, fusion reactions occur in Tokamaks where gas of hydrogen isotopes is pumped into a vacuum chamber of the Tokamak, and electricity flows through the centre (the doughnut's hole). The gas becomes charged and is heated to the point when they lose electrons to form plasma which is then locked inside the vacuum chamber by powerful suspended magnetic fields (which are created by massive superconducting electromagnetic coils of a niobium-titnium alloy). The fields compress the hydrogen plasma, mimicking the pressure of Sun's core. Radio and microwaves are fired into the plasma to raise its temperature, and at around 100 million 0C fusion occurs. The main barrier to a sustained reaction, other than the high cost of the electricity needed to heat the chamber, is to find a material which can withstand that much heat for more than a few seconds. It is interesting to note an amusing story from Culham Centre where the amount of electricity to create the necessary magnetic field was so high that the National Grid had to be told for them to okay for the Centre to go ahead for a trial run of JET.
C.3 Possible hazards withTokamak
Though fusion is much cleaner than fission, it will still produce some radioactive and toxic materials. Most of this comes from the high-energy neutrons that gradually embed themselves in the walls of the torus, creating atoms such as cobalt-60. Tritium is also radioactive (with a half-life of 12 years), while beryllium used to line the torus is toxic. The entire site must, of course, finally conform to France's strict nuclear safety laws. The matter is further complicated by the fact that the site at Cadarache in France is moderately seismically active which would mean the buildings need to be supported on something like rubber pads to protect them from earthquakes.
C.4 Problem of heating Tokamak
Even though the technology has been around for quite some time and has proven to be effective, it does not come without constraints. The biggest problem involves heating the plasma. In order to reach its operating temperature, the plasma must be heated to 10 keV which is equivalent to about 100 million 0C. The various methods of heating the plasma range from applying magnetic compression to bombarding the plasma with high-frequency microwaves.