?INTERNATIONAL THERMONUCLEAR EXPERIMENTAL REACTOR (ITER) AND TOKAMAK
International thermonuclear experimental reactor or we also know it as ITER is a megaproject run by a number of countries to attain and harness the virtually limitless energy. Each project works on the basis of a principle and ITER works on the basis of nuclear fusion. When the universe was just about to start there was nothing but quark plasma and big bang fusion leads to some optimum temperature that was responsible for formation of lighter nuclei which further fuse for the formation of heavier nuclei. Now the question is how is this important for us?
NUCLEAR FUSION is the process which keeps a star burning, by burning means the unlimited energy of the stars is produced by fusion of smaller nuclei and formation of heavier nuclei. But how is this possible as we know that energy can neither be created nor be destroyed than from where is this energy get produced? Well when the mass of a formed nuclei is measured and its constituent nuclei’s mass are measured then it is realized that mass of formed nuclei is less than the constituent parts. But we also know that mass is always conserved. So nuclear pose a threat to both conservation of mass and energy till Albert Einstein pose his famous mass energy relation. Due to this relation the whole picture of the process got cleared. When nuclei fuse to form heavy nuclei may be due to friction some of the mass is converted to energy.
E = mc^2
So according to mass energy relation it is stated that energy and mass are interconvertible in stars at the time of nuclear fusion. This is the process that forms the basis of project. The nuclear fusion under experiment at ITER needs some special environmental conditions which are necessary for the process which are as follows :-
Very high temperature (to provoke high energy Collison)
Sufficient particle plasma density (to increase the likelihood of collison to occur)
And sufficient confinement time
HISTORY OF ITER
The idea of international joint experiment in fusion was launched in 1985 since then a number of scientists and engineers collaborated to the project. The countries that are contributed to ITER are China, The European union, India, Japan, Russia, Korea and United states of America. All these countries have been working together for 35 years to build and operate ITER.
One year later when ITER is formed an agreement was reached that the European union, Japan, the Soviet union and US will follow the design for the large fusion facility. The conceptual design for the project was started in 1988 and by 2001 the design of fully functional fusion facility was developed and approved by the members of the committee.
The people’s republic of China and republic of Korea later joined the project in 2003 followed by India in 2005. The biggest problem for establishing ITER is the place so later on all the members shook head on the place suggested by the European union. ITER is run by a government body, ITER council. It has the authority of overall direction of ITER organization. It can appoint the director-general and high ranking posts of ITER organization. It sets the budget of the ITER project and all the related resources. The ITER agreement was officially signed on 21st November 2006 by ministers of participating countries and the ITER organization was officially established on 24th October 2007.
SCIENCE BEHIND ITER PROJECT
The basic principle behind the ITER project is Nuclear Fusion, as it is responsible for burning stars it can be used to produce enormous amount of energy. Now the question that arises is that what is nuclear fusion and why is this thing important for ITER?
QUESTION 1: WHAT IS NUCLEAR FUSION?
Nuclear fusion is a process in which smaller nuclei fuses to form heavier nuclei and in this process fusion energy is released. But it is known that energy can neither be created nor be destroyed then from where you think this energy is produced, actually it is true that energy can neither be created nor be destroyed and same thing applies to mass. The problem was solved by one of the most genius minds of 20th century Albert Einstein that mass and energy are interconvertible then he proposed his famous energy mass relation which is
So, this solves the problem of how energy is produced by fusion. Actually, when two of the nuclei collide the friction leads to reduce mass of the resultant nuclei which converts into the energy and that energy is used by stars to keep themselves burning.
QUESTION 2: What is making it work?
Plasma physics is all behind the fusion in ITER project. As it is quite clear that environment plays a very important role in fusion process of ITER hence plasma is produced for fusion process. Plasma is an ionized state of matter similar to gas produced at a very high temperature. As the temperature of the machine is increased the electrons are released from the nuclei hence and leads to formation of ionized gas known as plasma. Plasma environment is very tenuous about one million times less dense than the air we breathe so it makes smaller particles to fuse and yield energy.
The conditions that needs to be fulfilled for making the ITER project work and are mandatory are as follow: –
Very high temperature: This is required so that the particles can fuse with energy and leads to an effective Collison.
Sufficient plasma density: This is required to increase the chances of collison of the particles.
Sufficient confinement time: To hold plasma so that it can expand in defined volume.
The fusion of particles is achieved in a machine named tokamak which contains and control the hot plasma by using its magnetic field.
So let’s understand this with a practical example, in case of fusion between deuterium and tritium the products that are formed are a helium particle, a neutron and great amounts of energy. In tokamak the magnetic field keeps a hold on the charged helium particles and confined them to the containment itself. On the other hand about 80% of the energy is taken by neutrons and electrically neutral they cannot be confined so they get absorbed by tokamak walls and their energy is converted to heat which is captured by cooling water in the vessels and got converted to steam which later can be used to move turbines to produce electricity.
QUESTION 3: Why deuterium and tritium are used in tokamak?
It is not wrong if different isotopes of lighter elements are used for achieving the fusion yet deuterium and tritium still manage to be most efficient in the process. Deuterium can be extracted from almost all the forms of water and is widely available element. It’s harmless and virtually inexhaustible so it is a good option for the project. Tritium on the other hand is very radioactive and found in trace amount on Earth but can be produced using the lithium which is a major component on the Earth. Now to solve the problem of tritium insufficient amount the idea of lithium blankets was proposed that helps to undergo a chain reaction that leads to formation of tritium soon after the fusion of deuterium and tritium. As we know high energy neutrons are released while the fusion process so which when targeted to a blanket of lithium around the walls can lead to production of one helium molecule and other tritium which can be used as a fuel a later. The blanket of lithium is known as breeding blanket as it can indefinitely produce fuel for the project.
QUESTION 4: How ITER is able to maintain the temperature of created plasma that high?
The required temperature for the process of fusion in tokamak is 150 million °C which is created by magnetic fields in the confinement. There are many techniques which have a combined effect on stabilizing the plasma temperature that high. Heating plasma can be done with two possible ways internally and externally. Internally the changing magnetic field is the reason for heating effect of plasma. The magnetic field by the process of induction produced high intensity electricity which when passed through the plasma gas makes ions and electrons highly energized and lead them to collide which produces the heating effect. This heating effect from high intensity current is known as ohmic heat. Paradoxically it is believed that as the temperature of the plasma increases the resistance as well as the heat reduces, so ohmic heating cannot be an effective way to create that high temperature.
Externally there are basically two methods to create that heating process which are:-Neutron beam injection
High intensity EM waves
Neutron beam injection is a process through which a large amount of energy is transferred into the core of tokamak, by shooting high energy particles into the plasma. Outside the machine particles are accelerated to some energy level which then passes through the ion beam neutralizer to remove charge from it. Now those high energy particles simply are targeted to the heart to plasma gas and that transfers high amount of energy to plasma particles by rapid collison. This technique is used to deliver million of watts of energy to the plasma particles.
Another way of achieving such high temperature is high energy EM waves. Scientists are planning to incorporate such waves to the plan of tokamak so that this temperature can be maintained. Just like microwaves in an oven these energy waves transfer heat and energy to the plasma particles which consequently leads to increase in its temperature and internal energy of particles.
ADVNATAGES OF FUSION
The most concerning problem for the physicist all over the world is that in search of an efficient way for conversion of different forms of energy they are harming the nature in one or the other way. The continuous upgradation of all kinds of power plant leads to simultaneous degradation of the environment in which we are living. The anthropogenic processes like global warming and the greenhouse effect are continuously increasing the Earth’s temperature. So, with this much problems to face why ITER is something on which physicist are drawing their attention. ITER project is based on fusion and for sure this project must have something to deal with large amount of problems
The following advantages makes the fusion worth using :-
Abundant energy: – The fusion process can produce energy about four times more than the energy produce in a chemical reaction. So, the baseload energy to all the industries and cities can be provided by fusion process.
Sustainability: – The most important requirement for any energy production plant is the fuel. Fuels for ITER plant are abundant in nature and can be recycled from those which are there in nature so the fuel for the process is quite excellent in amount.
No Carbon dioxide: – As already discussed the residual carbon dioxide is a major problem that is why a plant that is not producing it as it’s residual product can play a major role in changing the world
No long lived radioactive waste: – Obviously it is very hard to handle radioactive waste so this method is helpful as it produces no radioactive waste so it is easy to handle its residues.
No risk of meltdown: – Any nuclear leak cannot be possible in this machine. This is because it is difficult to meddle with the core of the plasma, if anything happens the plasma cools down and stops the reaction.
TOKAMAK –THE MACHINERY
All the conventional power plants in world simply convert the mechanical energy to electrical energy by simply converting heat into steam which moves the turbine to produce electrical energy. Similarly, in tokamak the heat is converted to steam which then focused on the turbine to make it move to produce electricity. To harness the nuclear energy from the fusion process tokamak was built by all the conventional methods.
QUESTION 1: How does the tokamak machinery works?
The tokamak is highly advanced machinery having many parts performing some major functions which together makes this process work. The tokamak has a doughnut shaped heart which is a complete vacuum. Inside the heart the gas becomes the plasma which provides the environment for the fusion process. In stars also the plasma provides the environment for the fusion process, as in tokamak. The word tokamak comes from a Russian word means a toroidal chamber of magnetic fields, in this machine a large amount of magnetic field is there that stimulates and maintain the plasmatic environment for the fusion.
The process of the tokamak is quite complex yet easy to understand, firstly the vacuum is created in the machine later magnetic field is created to control plasma which is followed by the involvement of the gaseous fuel.
QUESTION 2: What is ITER tokamak and what are its parts?
The ITER tokamak is a machine that is designed and manufactured for harnessing the energy produced by fusion of process. It is a cylindrical shaped machine having extreme design to control all the factors simultaneously to make fusion process work. It has many parts the major parts are as follows: –
The machine has a weight of about23000 tons and capacity of producing the energy of about 500 MW. The plasma temperature of the core is about 150 million °C which is about 10 times more than the core of sun.
Now we are going to take each and every part of the machine separately.
As it is already discussed that major part of magnets is to maintain the plasma in the tokamak, but the strength of the magnetization must be very high which is produced by cooling the magnets with helium in the range of 4 kelvin which makes a magnet superconducting. In a standard ITER machine about 10000 tons of magnets are used with about 51 Giga joules of energy. The only task of this magnetic energy is to confine, control, initiate and maintain plasma. Once the magnet becomes superconducting it serves a very important purpose as it can produce more magnetic field than any normal conventional counterpart. It can conduct high charge and is very easy to operate. These magnets are manufactured by niobium-tin or niobium-titanium.
Toroidal field system
Eighteen “D”- formed toroidal field magnets set around the vacuum vessel deliver an attractive field whose essential capacity is to limit the plasma particles. The toroidal field loops are intended to deliver an aggregate attractive vitality of 41 gigajoules and a greatest attractive field of 11.8 tesla. Weighing 310 tons each, and estimating 9 x 17 m, they are among the biggest parts of the ITER machine.
Poloidial field system
Six ring-formed poloidal field loops are arranged outside of the toroidal field magnet structure to shape the plasma and add to its dependability by “squeezing” it far from the dividers. The biggest loop has a distance across of 24 meters; the heaviest is 400 tons. The poloidal field loops are intended to create an aggregate attractive vitality of 4 gigajoules and a most extreme attractive field of 6 tesla.
The 440 blanket modules that completely cover the inner walls of the vacuum vessel protect the steel structure and the superconducting toroidal field magnets from the heat and high-energy neutrons produced by the fusion reactions. As the neutrons are slowed in the blanket, their kinetic energy is transformed into heat energy and collected by the water coolant. In a fusion power plant, this energy will be used for electrical power production.
Each blanket module measures 1 x 1.5 metres and weighs up to 4.6 tonnes. Over 180 design variants exist (related to the position of the modules in the vacuum vessel), but all have a detachable first wall that directly faces the plasma and removes the plasma heat load, and a main shield block that is designed for neutron shielding. The blanket modules also provide passageways for diagnostic viewing systems and plasma heating systems.
The ITER blanket, which covers a surface of 600 m², is one of the most critical and technically challenging components in ITER: together with the divertor it directly faces the hot plasma. Due to its unique physical properties (low plasma contamination, low fuel retention), beryllium has been chosen as the element to cover the first wall. The rest of the blanket modules will be made of high-strength copper and stainless steel.
ITER will be the first fusion device to operate with an actively cooled blanket. The cooling water—injected at 4 MPa and 70 °C—is designed to remove up to 736 MW of thermal power.
During later stages of ITER operation, some of the blanket modules will be replaced with specialized modules to test materials for tritium breeding concepts. A future fusion power plant producing large amounts of power will be required to breed all of its own tritium. ITER will test this essential concept of tritium self-sustainment.
The ITER examinations will occur inside the vacuum vessel, a hermetically fixed steel compartment that houses the combination responses and goes about as a first security regulation hindrance. In its donut molded load, or torus, the plasma particles winding around consistently without contacting the dividers.
The vacuum vessel gives a high-vacuum condition to the plasma, enhances radiation protecting and plasma solidness, goes about as the essential constrainment obstruction for radioactivity, and offers help for in-vessel parts, for example, the cover and the divertor. Cooling water coursing through the vessel’s twofold steel dividers will evacuate the warmth created amid task.
The ITER cryostat—the biggest hardened steel high-vacuum weight chamber at any point manufactured (16,000 m³)— gives the high vacuum, ultra-cool condition for the ITER vacuum vessel and the superconducting magnets.
About 30 meters wide and the same number of in tallness, the inward distance across of the cryostat (28 meters) has been controlled by the span of the biggest parts its encompasses: the two biggest poloidal field loops. Made from hardened steel, the cryostat weighs 3,850 tons. Its base area—1,250 tons—will be the single biggest heap of ITER Tokamak get together.
The cryostat has 23 infiltrations to permit access for support and also more than 200 entrances—some as vast as four meters in estimate—that give access to cooling frameworks, magnet feeders, assistant warming, diagnostics, and the expulsion of cover areas and parts of the divertorDIVERTOR
Arranged at the base of the vacuum vessel, the divertor separates warmth and powder delivered by the combination response, limits plasma defilement, and shields the encompassing dividers from warm and neutronic loads.
Each of the divertor’s 54 “tape congregations” has a supporting structure in hardened steel and three plasma-confronting parts: the internal and external vertical targets and the arch. The tape gatherings additionally have various demonstrative segments for plasma control and material science assessment and improvement.
The inward and external vertical targets are situated at the crossing point of attractive field lines where molecule siege will be especially extraordinary in ITER. As the high-vitality plasma particles strike the vertical focuses on, their dynamic vitality is changed into warm and the warmth is expelled by dynamic water cooling.