seminar report on fusion power plant

7/31/2019 Seminar Report on Fusion Power Plant

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SEMINAR REPORT

ON

NUCLEAR TECHNOLOGYFUSION REACTORS

ByNAVIN SHUKLA

Roll no.-0616540031MECHANICAL 3 rd YEAR

Submitted to the department of Mechanical EngineeringIn partial fulfillment of the requirement

For the degree of Bachelor of technology

InMechanical Engineering

Kanpur Institute of Technology, A-1 Rooma, KanpurU.P.Technical University, Lucknow

April 2009, 14


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Table of Contents

1) Introduction2) Basic nuclear fusion technology3) Magnetic confinement (MFE)4) Inertial confinement (ICF)5) Plasma Heating

5.1 Ohmic Heating 5.2 Neutral-Beam Injection 5.3 Radio-frequency Heating

5.3.1) Induction5.3.2) Dielectric5.3.3) Microwave

6) Cold fusion7) Fusion history

8) Fusion power plant9) Joint European Torus (JET)9.1) Machine information9.2) Current status9.3) Remote handling

10) How to start a fire10.1) Produce plasma10.2) feed the coils10.3) Produce pulses

11) International Thermonuclear Experimental Reactor (ITER)11.1) Objective

11.2) Reactor overview11.3) Technical design11.4) Assessment of vacuum vessel

12) HiPER 12.1) Background12.2) Description12.3) Fast ignition and HiPER 12.4) Current status12.5) Assessing fusion power

13)Fusion advantages14) Conclusion

14.1) How fusion is safe?

14.2) fusion for the near future

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http://www.eoearth.org/article/Nuclear_fusion_power#Basic_fusion_technology%23Basic_fusion_technologyhttp://www.eoearth.org/article/Nuclear_fusion_power#Inertial_confinement_.28ICF.29%23Inertial_confinement_.28ICF.29http://www.eoearth.org/article/Nuclear_fusion_power#Plasma_Heating%23Plasma_Heatinghttp://www.eoearth.org/article/Nuclear_fusion_power#Ohmic_Heating%23Ohmic_Heatinghttp://www.eoearth.org/article/Nuclear_fusion_power#Neutral-Beam_Injection%23Neutral-Beam_Injectionhttp://www.eoearth.org/article/Nuclear_fusion_power#Radio-frequency_Heating%23Radio-frequency_Heatinghttp://www.eoearth.org/article/Nuclear_fusion_power#Joint_European_Torus_.28JET.29%23Joint_European_Torus_.28JET.29http://www.eoearth.org/article/Nuclear_fusion_power#Basic_fusion_technology%23Basic_fusion_technologyhttp://www.eoearth.org/article/Nuclear_fusion_power#Inertial_confinement_.28ICF.29%23Inertial_confinement_.28ICF.29http://www.eoearth.org/article/Nuclear_fusion_power#Plasma_Heating%23Plasma_Heatinghttp://www.eoearth.org/article/Nuclear_fusion_power#Ohmic_Heating%23Ohmic_Heatinghttp://www.eoearth.org/article/Nuclear_fusion_power#Neutral-Beam_Injection%23Neutral-Beam_Injectionhttp://www.eoearth.org/article/Nuclear_fusion_power#Radio-frequency_Heating%23Radio-frequency_Heatinghttp://www.eoearth.org/article/Nuclear_fusion_power#Joint_European_Torus_.28JET.29%23Joint_European_Torus_.28JET.29


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CERTIFICATE

It is to certify that the seminar report entitled NUCLEAR TECHNOLOGY ATOMIC FUSION which is submitted by NAVIN SHUKLA in partial fulfilment of the requirement for the award of degree B.Tech in department of Mechanical Engineering Of U.P. Technical University, is a record of candidate own work carried out by him under my/our supervision. The matter embodied in this thesis isoriginal and has not been submitted for the award of any other degree.

DATE: Head of Department

(MechanicalEngineering)

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ACKNOWLEDGEMENT It gives us a great sense of pleasure to present the report of the seminar undertaken during B.Tech third year. We owe special debt of gratitude to Mr. S.K.SONKAR , Department of mechanical engineering, Kanpur Institute of Technology; Kanpur for his constant support and guidance throughout the course of our work. His sincerity, thoroughness and perseverance have been a constant source of inspiration for us. It is only his cognizant efforts that our endeavours have seen light of the day.

We also take the opportunity to acknowledge to contribution of Mr. A.P.Mishra , Department of Mechanical Engineering, Kanpur Institute of Technology; Kanpur for his full support and assistanceduring the preparation of seminar report.

We also dont like to miss the opportunity to acknowledge the contribution of all faculty member of thedepartment for their kind assistance and cooperation during preparation of seminar report but not theleast, we acknowledge our friends for their contribution in the completion of the project.

Name: NAVIN SHUKLA

Roll NO.-0616540031

Date:

Signature:

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ABSTRACT

Nuclear reactions are capable of releasing huge quantities of energy. Such reactions can beachieved either by the nuclear fission (splitting) of elements of high atomic number or by the nuclear

fusion (joining) of elements with low atomic number. In astrophysics, fusion reactions power the starsand produce all but the lightest elements. The most efficient reaction to utilise fusion on earth is the DT

fusion reaction in which nuclei of the two Hydrogen isotopes Deuterium (D) and Tritium (T) are forced together to overcome the rejection due to their electric charge and to allow them to fuse due to the

strong nuclear binding force between them. The product of this reaction is a Helium nucleus and aneutron, both with very high kinetic energy.

Research in controlled nuclear fusion and its associated field plasma physics has progressed steadily for several decades and is now at a crossroad. The construction of a new international experimental machine ITER, to be built in worldwide international co-operation, has been decided. ITER aims to

prove the scientific and technological feasibility of fusion energy. With this machine and its goals,controlled nuclear fusion makes the decisive transition to a new area: from a time where plasma

physics and nuclear engineering were separate disciplines to a time where plasma physics and nuclear engineering will be intimately intertwined. With a foreseen power of 400 MW, ITER will produce 1.5 x1020 neutrons/s; equivalent to the number of neutrons/s produced by a 2.2 GWth fission reactor. Fusionwill need the nuclear engineering expertise. The paper introduces nuclear fusion from basic principlescommon to fusion and fission. The differences between fission and fusion, the reasons for them and theconsequences are pointed out. Different research lines were followed to achieve the conditions for a

self-sustaining controlled thermonuclear burn. Examples of major hurdles, which have been overcome,highlight the progress of research in magnetic confinement. Though challenges remain, ITER is likely to

show the feasibility of fusion energy. The promise of fusion energy opens up new perspectives and

opportunities for the development of fission energy and could lead to better boundary conditions for fission energy in the near future.

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1) Introduction

Even though renewable resources will probably be able to meet a greater proportion of the World's energyrequirements than they do at present, experts agree that they will not be able to satisfy the total demand. New energyoptions must therefore be developed - systems which are optimally safe, environment-friendly and economical.Controlled thermonuclear fusion is one of these rare options .

JET and ITER are fusion devices of the "tokamak" type. The JET Tokamak of the European Community, based in Abingdon (UK), is the largest and most powerful in the World.

Worldwide cooperation involving Europe, Japan, Russia, USA, China, South Korea and India have agreed tosite ITER (International Thermonuclear Experimental Reactor) at Cadarache in France. The start of construction will bein 2007 with construction time of about 10 years. Around 600 scientists, engineers, technicians and other personnel willwork on the device for approximately twenty years.

Fusion devices of "stellarator" type: TJ-II is being operated at Madrid and Wendelstein 7-X is being built atGriswold. Upon completion in 2012 the latter will be the world's largest experiment of the stellarator type.

Fusion powers the sun and stars as hydrogen atoms fuse together to form helium , and matter is converted intoenergy. Hydrogen , heated to very high temperatures , changes from a gas to plasma in which the negatively chargedelectrons are separated from the positively charged atomic nuclei (ions). Normally, fusion is not possible because the

positively charged nuclei naturally repel each other. But as the temperature increases the ions move faster, and theycollide at speeds high enough to overcome the normal repulsion. The nuclei can then fuse, causing a release of energy.

The overall reaction in the sun is "burning" hydrogen to make helium:

4 1H + 2 e --> 4He + 2 neutrinos + 6 photons

Each time this reaction occurs, 26 million electronvolts (MeV) of energy are released.

The Sun

In the sun, massive gravitational forces create the right conditions for this, but on Earth they are much harder

to achieve. Fusion fueldifferent isotopes of hydrogenmust be heated to extreme temperatures of some100 million degrees Celsius, and must be kept dense enough, and confined for long enough (at least onesecond), to trigger the energy release. The aim of the controlled fusion research program is to achieve"ignition", which occurs when enough fusion reactions take place for the process to become self-sustaining,with fresh fuel then being added to continue it.

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In principle, fusion has some extremely attractive features. The big advantage of fusion compared with fossil-fuel-based energy production is its relatively small fuel requirements. For the same amount of energy, fusionrequires about six orders of magnitude (~106) less fuel compared with chemical energy sources (coal, oil,etc.). A convenient way to think about this is to consider that the hydrogen in an ordinary cup of tap water contains the energy equivalent of a full tank of motor gasoline in an automobile. That is, the approximatelyone drop of heavy water in that cup could, through fusion, provide as much energy as 20 gallons of motor gasoline.

2) Nuclear fusion

The aim of fusion research is to utilize the energy source of the sun and stars here on earth: A fusion power plant is to derive energy from fusion of atomic nuclei. Under terrestrial conditions this can most rapidly be achievedwith the two hydrogen isotopes, deuterium and tritium. These fuse to form helium, thus releasing neutrons and large

quantities of energy:One gram of fuel could yield in a power plant 90 000 kilowatt-hours of energy, i. e. the combustion heat

derived from 11 tons of coal.The basic substances needed for the fusion process, viz. deuterium and lithium, from which tritium is produced

in the power plant, are available throughout the world in almost inexhaustible quantities. A cubic meter of water contains 34 grams of deuterium the energy equivalent of 300000 litters of oil. The oceans, the seas and lakes couldsupply enough deuterium for a 1000 reactors over a millions of years. With special conditions fusion needs an ignitiontemperature of 100 million degrees.

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With current technology, the reaction most readily feasible is between the nuclei of the two heavy forms (isotopes) of hydrogendeuterium (D) and tritium (T). Each D-T fusion event releases 17.6 MeV (2.8 x 10-12 joule, compared with200 MeV for uranium-235 (235U) fission). Deuterium occurs naturally in seawater (30 grams per cubic meter), whichmakes it very abundant relative to other energy resources. Tritium does not occur naturally and is radioactive, with ahalf-life of around 12 years. It can be made in a conventional nuclear reactor, or in the present context, bred in a fusionsystem from lithium. Lithium is found in large quantities (30 parts per million) in the Earth's crust and in weaker

concentrations in the sea. While the D-T reaction is the main focus of attention, long-term hopes are for a D-D reaction, but this requires much higher temperatures.

In a fusion reactor, the concept is that neutrons will be absorbed in a blanket containing lithium whichsurrounds the core. The lithium is then transformed into tritium and helium. The blanket must be thick enough (about 1 meter) to slow down the neutrons. This heats the blanket, and a coolant flowing through itthen transfers the heat away to produce steam which can be used to generate electricity by conventionalmethods. The difficulty has been to develop a device that can heat the D-T fuel to a high enough temperatureand confine it long enough so that more energy is released through fusion reactions than is used to get thereaction going.

At present, two different experimental approaches are being studied: fusion energy by magnetic confinement(MFE) and fusion by inertial confinement (ICF). The first method uses strong magnetic fields to trap the hot

plasma. The second involves compressing a hydrogen pellet by smashing it with strong lasers or particle beams.

3) Magnetic confinement (MFE)

In magnetic confinement (MFE), hundreds of cubic meters of D-T plasma at a density of less than amilligram per cubic meter are confined by a magnetic field at a few atmospheres pressure and heated tofusion temperature.

Magnetic fields are ideal for confining plasma because the electrical charges on the separated ions andelectrons mean that they follow the magnetic field lines. The aim is to prevent the particles from coming intocontact with the reactor walls as this will dissipate their heat and slow them down. The most effectivemagnetic configuration is toroidal, shaped like a thin doughnut, in which the magnetic field is curved aroundto form a closed loop. For proper confinement, this toroidal field must have superimposed upon it a

perpendicular field component (a poloidal field). The result is a magnetic field with force lines followingspiral (helical) paths, along and around which the plasma particles are guided. There are several types of toroidal confinement systems, the most important being tokamaks, stellarators and reversed field pinch (RFP)devices.

Scheme of the tokamak principle: arrangement of magnetic field coils and the resulting magnetic field thatconfines the plasma

The word tokamak means "toroidal chamber" in Russian. It is a magnetic fusion device that is in a shape of atorus (e.g., a doughnut). In a tokamak, the toroidal field is created by a series of coils evenly spaced aroundthe torus-shaped reactor, and the poloidal field is created by a strong electric current flowing through the

plasma. In a stellarator, the helical lines of force are produced by a series of coils which may themselves behelical in shape. But no current is induced in the plasma. RFP devices have the same toroidal and poloidalcomponents as a tokamak, but the current flowing through the plasma is much stronger and the direction of the toroidal field within the plasma is reversed.

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In tokamaks and RFP devices, the current flowing through the plasma also serves to heat it to a temperatureof about 10 million degrees Celsius. Beyond that, additional heating systems are needed to achieve thetemperatures necessary for fusion. In stellarators, these heating systems have to supply all the energy needed.

The tokamak (toroidalnya kamera ee magnetnaya katushkatorus-shaped magnetic chamber) was designedin 1951 by Soviet physicists Andrei Sakharov and Igor Tamm. Tokamaks operate within limited parametersoutside which sudden losses of energy confinement (disruptions) can occur, causing major thermal andmechanical stresses to the structure and walls. Nevertheless, it is considered the most promising design, andresearch is continuing on various tokamaks around the world, the two largest being the Joint European Torus(JET) in the UK and the tokamak fusion test reactor (TFTR) at Princeton in the USA.

Research is also being carried out on several types of stellarators. The biggest of these, the Large HelicalDevice at Japan's National Institute of Fusion Research, began operating in 1998. It is being used to study of the best magnetic configuration for plasma confinement. At Garching in Germany, plasma is created andheated by electromagnetic waves, and this work will be progressed in the W7-X stellerator, to be built at thenew German research center in Greifswald. Another stellarator, TJ-II, is under construction in Madrid, Spain.Because stellarators have no toroidal current, there are no disruptions and they can be operated continuously.The disadvantage is that, despite the stability, they do not confine the plasma so well.

RFP devices differ from tokamaks mainly in the spatial distribution of the toroidal magnetic field, which

changes sign at the edge of the plasma. The RFX machine in Padua, Italy is used to study the physical problems arising from the spontaneous reorganization of the magnetic field, an intrinsic feature of thisconfiguration.

4) Inertial confinement Fusion (ICF)

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In inertial confinement fusion (ICF), a newer line of research, laser or ion beams are focused very precisely onto the surface of a targeta sphere of D-T ice, a few millimeters in diameter. This evaporates or ionizes the outer layer of the material to form a plasma crown that expands, generating an inward-movingcompression front or implosion that heats up the inner layers of material. The core or central hot spot of thefuel may be compressed to one thousand times its liquid density, and ignition occurs when the coretemperature reaches about 100 million degrees Celsius. Thermonuclear combustion then spreads rapidlythrough the compressed fuel, producing several times more energy than was originally used to bombard thecapsule. The time required for these reactions to occur is limited by the inertia of the fuel (hence the name),

but is less than a microsecond. The aim is to produce repeated microexplosions.

Recent work at Osaka, Japan suggests that 'fast ignition' may be achieved at lower temperature with a secondvery intense laser pulse through a millimeter-high gold cone inside the compressed fuel, and timed tocoincide with the peak compression. This technique means that fuel compression is separated from hot spotgeneration with ignition, making the process more practical.

So far, most inertial confinement work has involved lasers, although their low energy makes it unlikely thatthey would be used in an actual fusion reactor. The world's most powerful laser fusion facility is the NOVA

at Lawrence Livermore Laboratory in the US, and declassified results show compressions to densities of upto 600 times that of the D-T liquid. Various light and heavy ion accelerator systems are also being studied,with a view to obtaining high particle densities.

5) Plasma Heating

In an operating fusion reactor, part of the energy generated will serve to maintain the plasmatemperature as fresh deuterium and tritium are introduced. However, in the startup of a reactor, either initiallyor after a temporary shutdown, the plasma will have to be heated to 100 million degrees Celsius. In currenttokamak (and other) magnetic fusion experiments, insufficient fusion energy is produced to maintain the

plasma temperature. Consequently, the devices operate in short pulses and the plasma must be heated afresh

in every pulse.

Glowing plasma inside a tokamak fusion test reactor

5.1) Ohmic Heating

Since the plasma is an electrical conductor, it is

possible to heat the plasma by passing a current throughit; in fact, the current that generates the poloidal field also heats the plasma. This is called ohmic (or resistive)heating; it is the same kind of heating that occurs in an electric light bulb or in an electric heater.

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The heat generated depends on the resistance of the plasma and the current. But as the temperature of heated plasma rises, the resistance decreases and the ohmic heating becomes less effective. It appears that themaximum plasma temperature attainable by ohmic heating in a tokamak is 20-30 million degrees Celsius. Toobtain still higher temperatures, additional heating methods must be used.

5.2) Neutral-Beam Injection

Neutral-beam injection involves the introduction of high-energy (neutral) atoms into the ohmically heated, magnetically confined plasma. The atoms are immediately ionized and are trapped by the magneticfield. The high-energy ions then transfer part of their energy to the plasma particles in repeated collisions,thus increasing the plasma temperature.

5.3) Radio-frequency heating

Radio frequency heating is the heating of materials by radio frequency (otherwise calledelectromagnetic) energy. This can be divided into 3 general categories as below. The term "radio frequency"is misleading - electromagnetic energy of any frequency is absorbed (and reflected) to a greater or lesser degree by all materials. In radio-frequency heating, high-frequency waves are generated by oscillators

outside the torus. If the waves have a particular frequency (or wavelength), their energy can be transferred tothe charged particles in the plasma, which in turn collide with other plasma particles, thus increasing thetemperature of the bulk plasma .The frequency used for any particular purpose will depend on many thingsand this is shown below.

In general, any material may accept electromagnetic energy but the degree to which that happens isdependent on;

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Frequency of the electromagnetic energy, Intensity of the electromagnetic energy, Proximity to the source of the electromagnetic energy, Conducting or non conducting material, Nature of the material (ie how lossy).

5.3.1) Induction Heating

Induction heating involves the heating of electrically conducting materials by electromagneticinduction. Currents are induced in the material and these currents cause heating. The frequency used mayvary from as low as mains frequency (50/60 Hz) to more than 10 MHz. Heating also occurs by hysteresis lossif the material has significant relative permeability (eg. Steel). Induction heating is generally a non-contact

process and usually consists of a coil in close proximity to but not touching the material to be heated (usuallya metal).

5.3.2) Dielectric Heating

Dielectric heating involves the heating of electrically insulating materials by dielectric loss . Voltageacross the material causes energy to be dissipated as the molecules attempt to line up with the continuouslychanging electric field. A common perception is that the molecules rub together, with the friction causingheat. This is not so. Friction is a macroscopic process and does not exist at the molecular level. The heat isgenerated solely by the inability of the molecules to line up with the electric field. Frequencies in the range of 10-100 MHz are necessary to perform dielectric heating. Dielectric heating is generally a contact process andusually consists of the material to be heated (usually a non-metal) sandwiched between metal plates forminga capacitor .

5.3.3) Microwave Heating

Microwave heating is actually a sub-category of dielectric heating in that insulating materials areheated primarily by dielectric loss. The difference is that of frequency. At frequencies above 100 MHz anelectromagnetic wave can be launched from a small dimension emitter and conveyed through space. Thematerial to be heated (a non-metal) can therefore be simply placed in the path of the waves and heating takes

place. It is a non-contact process. Typical domestic microwave ovens operate at 2.45 GHz.

6) Cold fusion

In 1989, spectacular claims were made for another approach, when two researchers, in USA and UK,claimed to have achieved fusion in a simple tabletop apparatus working at room temperature. Other experimenters failed to replicate this "cold fusion", however, and most of the scientific community no longer considers it a real phenomenon. Nevertheless, research continues. Cold fusion involves the electrolysis of heavy water using palladium electrodes on which deuterium nuclei are said to concentrate at very highdensities.

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7) Fusion history

Today, many countries take part in fusion research to some extent, led by the European Union, theUSA, Russia and Japan, with vigorous programs also under way in China, Brazil, Canada, and Korea.Initially, fusion research in the USA and USSR was linked to atomic weapons development, and it remained

classified until the 1958 Atoms for Peace conference in Geneva. Following a breakthrough with the Soviettokamak design, fusion research became big science in the 1970s. But the cost and complexity of the devicesinvolved increased to the point where international co-operation was the only way forward.

In 1978, the European Community (with Sweden and Switzerland) launched the JET project in the UK. JET produced its first plasma in 1983, and saw successful experiments using a D-T fuel mix in 1991. In the USA,the PLT tokamak at Princeton produced a plasma temperature of more than 60 million degrees in 1978 andD-T experiments began on the Tokamak Fusion Test Reactor (TFTR) there in 1993. In Japan, experimentshave been carried out since 1988 on the JT-60 Tokamak.

8) Fusion power plants

In the most likely scenario for a fusion power plant, a deuterium-tritium (D-T) mixture is admitted tothe evacuated reactor chamber and there ionized and heated to thermonuclear temperatures. The fuel is heldaway from the chamber walls by magnetic forces long enough for a useful number of reactions to take place.The charged helium nuclei which are formed give up energy of motion by colliding with newly injected cold

fuel atoms which are then ionized and heated, thus sustaining the fusion reaction. The neutrons, having nocharge, move in straight lines through the thin walls of the vacuum chamber with little loss of energy.

The neutrons and their 14 MeV of energy are absorbed in a "blanket" containing lithium which surrounds thefusion chamber. The neutrons' energy of motion is given up through many collisions with lithium nuclei, thuscreating heat that is removed by a heat exchanger which conveys it to a conventional steam electric plant.The neutrons themselves ultimately enter into nuclear reactions with lithium to generate tritium which isseparated and fed back into the reactor as a fuel.

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The inside of the thermo-nuclear fusion research reactor at JET is an environment hostile to human beings. In order to maintain and repair the reactor, as well as reconfigure it with new components before anynew series of fusion experiments, a bespoke Remote Handling system was developed at JET.

The design and operation of the Remote Handling system requires a myriad of different technologies, all of

which are also applicable to ITER, the next generation fusion research project.

1) Weight of the vacuum vessel: 100 tonnes

2) Weight of the toroidal field coils: 384 tonnes

3) Weight of the Iron Core: 2700 tonnes4) Wall material: Primarily carbon fibre composite, Beryllium coated.5) Plasma major radius: 2.96 m6) Plasma minor radius: 2.10 m (vertical), 1.25 m (horizontal)7) Flat top pulse length: 20 s

8) Toroidal magnetic field (on plasma axis): 3.45 T9) Plasma current: 3.2 MA (circular plasma), 4.8 MA (D-shape plasma)10) Lifetime of the plasma: 2060 s11) Auxiliary heating:12) Neutral beam injection heating 23 MW12) Radio frequency heating 15 MW Major diagnostics:1) Visible/infrared video cameras2) Numerous magnetic coils provide magnetic field, current and energymeasurements3) Thomson scattering spectroscopy provides electron temperature and electron

density profiles of the plasma4) Charge exchange spectroscopy provides impurity ion temperature, density androtation profiles5) Interferometers measure line integrated plasma density6) Electron cyclotron emission antennas fast, high resolution electron temperatureprofiles7) Visible/UV/X-ray spectrometers temperatures and densities8) Neutron spectroscopy Number of neutrons leaving the plasma relates directly tothe fusion power.9) Neutron energy relates to the ion velocity distribution and hence the fuelreactivity.10) Bolometers energy loss from the plasma11) Various material probes inserted into the plasma to take direct measurementsof flow rates and temperatures12) Soft X-ray cameras to examine MHD properties of plasmas13) Time resolved neutron yield monitor14) Hard X-ray monitors15) Electron Cyclotron Emission Spatial Scanners

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9.2) Current statusJET was originally set up by EURATOM with a discriminatory employment

system that allowed non-British staff to be employed with more than twice thesalaries of their British equivalents. The British staff eventually had this practicedeclared illegal, and substantial damages were paid at the end of 1999 to UKAEAstaff, and later to contractors. This was the immediate cause of the ending of EURATOMs operation of the facility.In December 1999 JET's international contract ended and the United Kingdom AtomicEnergy Authority (UKAEA) then took over managing the safety and operation of the

JET facilities on behalf of its European partners. From that time (2000), JET'sexperimental programme was then co-ordinated by the European FusionDevelopment Agreement (EFDA) Close Support Unit.

JET operated throughout 2003 culminating in experiments using small amounts of tritium. For most of 2004 it was shut down for a series of major upgrades increasingtotal available heating power to over 40 MW, enabling further studies relevant to thedevelopment of ITER to be undertaken. In the future it is possible that JET-EP(Enhanced Performance) will further increase the record for fusion power.In late September 2006, experimental campaign C16 was started. Its objective is tostudy ITER-like operation scenarios.

9 .3) Remote handling

9.3.1) Why do Remote Handling at JET?

JET is the worlds largest experiment on thermo-nuclear fusion, the energy producing process whichtakes place in the sun.

Over time, high-energy neutrons render all components and support structures of the reactor radioactive.Furthermore many plasma facing tiles are covered in Beryllium, which, if breathed in as dust, poses a further hazard to anyone working inside the reactor. Therefore, JET always placed great emphasis on its RemoteHandling group, to ensure a maximum of tasks can be carried out fully remotely.

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The JET machine is a complex device whose detailed configuration changes as the physics experimentalrequirements dictate. The Remote Handling system is required to fulfill two functions:

Repair of any system whose failure stops the experiment Modification of Torus components for new experiments

Experience shows that remote handling interventions achieve higher precision and introduce less impuritiesthan sending men inside the torus did in the past .

The basic remote maintenance work is undertaken by a dexterous, force-reflecting master-slave servo-manipulator (called the Mascot).The Mascot Slave unit is transported on the end of a 10 metre long articulated robot. The Mascot master station is driven by experienced operators situated in the Remote Handling Control Room .

To gain access to the inside of the torus, two of the eight main horizontal ports are reserved for Remote

Handling. A second articulated Boom works in parallel with the first to transfer components and tools between storage facilities outside the torus and the workplace within the torus. Both Booms are hyper-redundant multi-joint devices to allow them to snake their way through the narrow ports and around thetorus.

Other robots are designed for Ex-Vessel work, like the Telescopic Articulated Remote Mast (TARM), whichis suspended from the main 150 ton gantry crane .

9.3.2) Remote Handling shutdown Life Cycle

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The JET experimental reactor undergoes a planned refurbishment period (called a shutdown) typicallyevery 1 to 3 years. During this time plasma experiments are suspended, the torus is vented (i.e. the vacuum isended) and brought to normal atmospheric pressure just above room temperature. This is the time when the

Remote Handling equipment enters the torus to do planned refurbishment work.

However, the work to prepare a Remote Handling shutdown starts several years before then. First the plasma physicists think up a new series of fusion experiments and begin to design the new components required.Already at this stage the Remote Handling engineers are involved, to ensure that the design of all newcomponents is compatible with Remote Handling tooling.Then the Remote Handling design engineers at JET start to design tools and (if needed) robotic equipment suchas dedicated end-effectors, to assist in the installation of the new torus components.

At the same time Remote Handling operation engineers work out strategies of how to best achieve certain

installation tasks and develop the task logistics, procedures and teach-files. The new work procedures arederived at in a Virtual Reality simulation, and later tested and fine-tuned in a physical full-scale mockupfacility, using the real robotic equipment and the real Remote Handling tools, but mostly using dummycomponents.

10) How to start a fire?

Nowadays we dont use controlled fire directly in our houses, but we still take advantage of it: Fossilfuels are burned in power plants to produce the energy we need in our daily life. The predictions how long thereserves of fossil fuels will last differ, depending on who analyses the resources. One thing is certain: some day

fossil fuels will be exhausted. Therefore scientists and decision makers are looking for new energy resources.One of them could be the use of the fusion process that has been happening in the Sun for 4.5 billion years withtemperatures of 15 million degrees. To use this energy source on Earth physicists and engineers aim to reachtemperatures ten times higher than in the Sun. JET as a European fusion experiment can achieve these extremeconditions under which the process is investigated in detail to use it in future power plants.

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10.1) Firstly: Produce plasmaTo investigate the plasma state and later to harness energy with the man-made technology, the plasma

has to have a temperature of hundreds of millions of degrees Celsius. Plasma is composed of nuclei andelectrons moving independently from each other. JET is capable of producing a completely ionised gas.

Obtaining these extraordinary high temperatures requires extraordinarily powerful heating. This is done by Neutral Beam Injection Heating (NBI) and Radio Frequency Heating (RF). The total input power to thesesystems can be up to 250 megawatts. The installed output power is 55 megawatts of the radio frequency power.Powerful heating is also needed to sustain this temperature, otherwise the plasma would rapidly cool down dueto inevitable heat losses via radiation and heat convection or conduction.

Plasma and its heating

10.2) secondly: Feed the coils Plasma heating is not the biggest consumer of energy at JET. At the hundreds of million degreesCelsius needed, standard thermal insulation methods are totally inadequate. The reason tungsten is thematerial with the highest known melting point of 3,422 degree Celsius, which isnt at all sufficient to resistthe high temperature of the plasma. So to confine the plasma JET uses a magnetic confinement system tokeep the charged particles of the plasma away from the vessel wall and to protect it from the hot plasma.Unless the plasma is well insulated in the magnetic field, it can lose energy due to a temperature gradientfrom the vessel wall to the plasma centre of about one million degrees per centimetre. The well-definedmagnetic coils producing the strong magnetic fields need a significant amount of power. Under thecircumstances high currents normally required, electrical resistance of the coils causes significant losses of energy in form of heat. As a consequence they need to be water-cooled. The energy to do so is mostlydissipated to the atmosphere via special cooling towers. Some fusion experiments, like Tore Supra in France,LHD in Japan, EAST in China, KSTAR in South Korea,Wendelstein 7-X (under construction) in Germany,or the future experiment ITER use superconducting coils that avoid energy losses at the expense of runningthem at very low temperatures, around -270 degree Celsius, using liquid helium. These experiments will run

with higher energy efficiency by using superconducting coils .

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JET's coils and plasma

10.3) thirdly: Produce pulsesEvery individual experiment at JET lasts several tens of seconds. During experimental campaigns there

are some 30 experiments daily, which physicists call a pulse. Most of the JET power consumption isconcentrated in short bursts, which is quite demanding on the electricity grid and on electrical engineering ingeneral. Moreover, even during a single pulse, the power requirements are not constant the start-up needsmore power than the plateau, the sustaining phase. On one hand, the toroidal field coils are the largest singleload on JET. On the other hand, the poloidal field system has complex switching and control requirements. The

plasma is always in the move and after it has been created, its position and shape is feedback-controlled. Themagnetic field is continuously measured, and additional power is supplied to the vertical and horizontal

polemical field amplifiers according to plasma behaviour.

Running a JET pulse requires around 500 megawatts of power, of which more than a half is fed to the toroidalfield coils. Around 100 megawatts of power is needed to run the poloidal field sys tem. The rest of nearly150 megawatts runs the additional heating sources.

The energy conversion efficiencies of all heating systems limit the power the plasma receives. However, inmost JET pulses only part of these installed capacities is exploited, depending on experimental scenarios. Last

but not least, the plasma also gets a few megawatts of power from ohmic heating. Ohmic heating means electriccurrent induced in the plasma by the inner poloidal coils. In total, JET plasmas usually consume a few tens of megawatts and accumulate only a fraction of the consumed energy. The difference between input and outputdisappear via radiation, heat conduction and particle losses.

When the fire is lit in this way the real work has just begun: physicists explore the conditions under which the plasma will be able to produce energy in a future fusion power plant.

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JET's power loads

11) International Thermonuclear Experimental Reactor (ITER)ITER ( International Thermonuclear Experimental Reactor ) is an international tokamak

(magnetic confinement fusion) research/engineering proposal for an experimental project that will help tomake the transition from today's studies of plasma physics to future electricity-producing fusion power

plants. It will build on research done with devices such as DIII-D, EAST, KSTAR, TFTR, ASDEX Upgrade,Joint European Torus, JT-60, Tore Supra and T-15, and will be considerably larger than any of them.

ITER is designed to produce approximately 500 MW (500,000,000 watts) of fusion power sustained for up to1000 seconds (compared to JET's peak of 16 MW for less than a second) by the fusion of about 0.5 g of deuterium/tritium mixture in its approximately 840 m 3 reactor chamber. Although ITER is expected to

produce (in the form of heat) 5-10 times more energy than the amount consumed to heat up the plasma tofusion temperatures, the generated heat will not be used to generate any electricity.

According to the ITER consortium, fusion power offers the potential of "environmentally benign, widelyapplicable and essentially inexhaustible" electricity, properties that they believe will be needed as worldenergy demands increase while simultaneously greenhouse gas emissions must be reduced, justifying theexpensive research project.

ITER was originally an acronym for I nternational T hermonuclear E xperimental R eactor , but that title wasdropped due to the negative popular connotation of "thermonuclear," especially when in conjunction with"experimental". "Iter" also means "journey", "direction" or "way" in Latinand this double meaning reflectsITER's role in harnessing nuclear fusion as a peaceful power source.

11.1) Objectives

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The official objective of ITER is to "demonstrate the scientific and technological feasibility of fusionenergy for peaceful purposes". ITER has a number of specific objectives, all concerned with developing aviable fusion power reactor:

To momentarily produce ten times more thermal energy from fusion heating than is supplied byauxiliary heating (a Q value of 10).

To produce steady-state plasma with a Q value greater than 5. To maintain a fusion pulse for up to eight minutes. To ignite a 'burning' (self-sustaining) plasma. To develop technologies and processes needed for a fusion power plant including superconducting

magnets and remote handling (maintenance by robot). To verify tritium breeding concepts.

To refine neutron shield/heat conversion technology (most of energy in the D+T fusion reaction is released inthe form of fast neutrons).

11.2) Reactor overview

When deuterium and tritium fuse, two nuclei come together to form a helium nucleus (an alpha particle), and a high-energy neutron.

While in fact nearly all stable isotopes lighter on the periodic table than iron will fuse with some other isotope and release energy, deuterium and tritium are by far the most attractive for energy generation as theyrequire the lowest activation energy (thus lowest temperature) to do so.

All proto- and mid-life stars radiate enormous amounts of energy generated by fusion processes. Mass for mass, the deuterium-tritium fusion process releases roughly three times as much energy as uranium 235fission and millions of times more energy than a chemical reaction such as the burning of coal. It is the goal

of a fusion power plant to harness this energy to produce electricity.

The activation energy for fusion is so high because the protons in each nucleus will tend to strongly repel oneanother, as they each have the same positive charge. A heuristic for estimating reaction rates is that nucleimust be able to get within 100 femtometer (1 10 13 meter) of each other, where the nuclei are increasinglylikely to undergo quantum tunnelling past the electrostatic barrier and the turning point where the strongnuclear force and the electrostatic force are equally balanced, allowing them to fuse. In ITER, this distance of approach is made possible by high temperatures and magnetic confinement. High temperatures give thenuclei enough energy to overcome their electrostatic repulsion. For deuterium and tritium, the optimalreaction rates occur at temperatures on the order of 100,000,000 K. The plasma is heated to a hightemperature by ohmic heating (running a current through the plasma). Additional heating is applied usingneutral beam injection (which cross magnetic field lines without a net deflection and will not cause a largeelectromagnetic disruption) and radio frequency (RF) or microwave heating.

At such high temperatures, particles have a vast kinetic energy, and hence velocity. If unconfined, the particles will rapidly escape, taking the energy with them, cooling the plasma to the point where net energy isno longer produced. A successful reactor would need to contain the particles in a small enough volume for along enough time for much of the plasma to fuse. In ITER and many other magnetic confinement reactors,the plasma, a gas of charged particles, is confined using magnetic fields. A charged particle moving through

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a magnetic field experiences a force perpendicular to the direction of travel, resulting in centripetalacceleration, thereby confining it to move in a circle.

A solid confinement vessel is also needed, both to shield the magnets and other equipment from hightemperatures and energetic photons and particles, and to maintain a near-vacuum for the plasma to populate.The containment vessel is subjected to a barrage of very energetic particles, where electrons, ions, photons,alpha particles, and neutrons constantly bombard it and degrade the structure. The material must be designedto endure this environment so that a powerplant would be economical. Tests of such materials will be carriedout both at ITER and at IFMIF (International Fusion Materials Irradiation Facility).

Once fusion has begun, high energy neutrons will radiate from the reactive regions of the plasma, crossingmagnetic field lines easily due to charge neutrality. Since it is the neutrons that receive the majority of theenergy, they will be ITER's primary source of energy output. Ideally, alpha particles will expend their energyin the plasma, further heating it.

Beyond the inner wall of the containment vessel one of several test blanket modules will be placed. These aredesigned to slow and absorb neutrons in a reliable and efficient manner, limiting damage to the rest of thestructure, and breeding tritium from lithium and the incoming neutrons for fuel. Energy absorbed from thefast neutrons is extracted and passed into the primary coolant. This heat energy would then be used to power an electricity-generating turbine in a real power plant; however, in ITER this heat is not of scientific interest,and will be extracted and disposed.

11.3) Technical design

Selected facts: The central solenoid coil will use superconducting niobium-tin, to carry 46 kA and produce a field of 13.5 teslas. The 18 toroidal field coils will also use niobium-tin. At maximum field of 11.8T they will store 41 GJ (total?). They have been tested at a record 80 kA. Other lower field ITER magnets(PF and CC) will use niobium-titanium.

11.4) Assessment of the vacuum vessel

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ITER has decided to ask AIB-Vinotte International (an inspection organisation located in Belgiumand accredited by the French Nuclear Authorities ASN) to assess the confinement (vacuum) vessel, heart of the project, following the French Nuclear Regulatory requirements.

The Vacuum Vessel is the central part of the ITER machine: a double walled steel container in which the plasma is contained by means of magnetic fields.

The ITER Vacuum Vessel will be the biggest fusion furnace ever built. It will be twice as large and 16 timesas heavy as any previously manufactured fusion vessel: each of the nine torus shaped sectors will weighabout 450 tons. When all the shielding and port structures are included, this adds up to a total of 5,116 tons.Its external diameter will measure 19.4 m, the internal 6.5 m. Once assembled, the whole structure will be11.3 m high.

The primary function of the Vacuum Vessel is to provide a hermetically sealed plasma container. Its maincomponents are the main vessel, the port structures and the supporting system. The main vessel is a doublewalled structure with poloidal and toroidal stiffening ribs between 60 mm thick shells to reinforce the vesselstructure. These ribs also form the flow passages for the cooling water. The space between the double wallswill be filled with shield structures made of austenitic stainless steel which is corrosion resistant and does notconduct heat well. The inner surfaces of the vessel will be covered with blanket modules. These modules will

provide shielding from the high-energy neutrons produced by the fusion reactions and some will also be usedfor tritium breeding concepts.

The Vacuum Vessel has 18 upper, 17 equatorial and 9 lower ports that will be used for remote handlingoperations, diagnostic systems, neutral beam injections and vacuum pumping.

12) HiPER

The High Power laser Energy Research facility (HiPER ) is an experimental laser-driven inertial

confinement fusion (ICF) device undergoing preliminary design for possible construction in the EuropeanUnion starting around 2010. HiPER is the first experiment designed specifically to study the "fast ignition"approach to generating nuclear fusion, which uses much smaller lasers than conventional designs, yet

produces fusion power outputs of about the same magnitude. This offers a total "fusion gain" that is muchhigher than devices like the National Ignition Facility (NIF), and a reduction in construction costs of aboutten times

12.1) Background

Inertial confinement fusion (ICF) devices use "drivers" to rapidly heat the outer layers of a "target" inorder to compress it. The target is a small spherical pellet containing a few milligrams of fusion fuel,

typically a mix of deuterium and tritium. The heat of the laser burns the surface of the pellet into plasma,which explodes off the surface. The remaining portion of the target is driven inwards due to Newton's ThirdLaw, eventually collapsing into a small point of very high density. The rapid blow off also creates a shock wave that travels towards the center of the compressed fuel. When it reaches the center of the fuel and meetsthe shock from the other side of the target, the energy in the shock wave further heats and compresses thetiny volume around it. If the temperature and density of that small spot can be raised high enough, fusionreactions will occur.

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The fusion reactions release high-energy particles, some of which (primarily alpha particles) collide with thehigh density fuel around it and slow down. This heats the fuel further, and can potentially cause that fuel toundergo fusion as well. Given the right overall conditions of the compressed fuelhigh enough density andtemperaturethis heating process can result in a chain reaction, burning outward from the center where theshock wave started the reaction. This is a condition known as "ignition", which can lead to a significant

portion of the fuel in the target undergoing fusion, and the release of significant amounts of energy.

To date most ICF experiments have used lasers to heat the targets. Calculations show that the energy must bedelivered quickly in order to compress the core before it disassembles, as well as creating a suitable shock wave. The energy must also be focused extremely evenly across the target's outer surface in order to collapsethe fuel into a symmetric core. Although other "drivers" have been suggested, notably heavy ions driven in

particle accelerators, lasers are currently the only devices with the right combination of features.

12.2) Description

In the case of HiPER, the driver laser system is similar to existing systems like NIF, but considerablysmaller and less powerful. The driver consists of a number of "beamlines" containing Nd:glass laser amplifiers at one end of the building. Just prior to firing, the glass is "pumped" to a high-energy state with aseries of xenon flash tubes, causing a population inversion of the neodymium (Nd) atoms in the glass. Thisreadies them for amplification via stimulated emission when a small amount of laser light, generatedexternally in a fibre optic, is fed into the beamlines. The glass is not particularly effective at transferring

power into the beam, so in order to get as much power as possible back out the beam is reflected through theglass four times in a mirrored cavity, each time gaining more power. When this process is complete, aPockels cell "switches" the light out of the cavity. One problem for the HiPER project is that Nd: glass is nolonger being produced commercially, so a number of options need to be studied to ensure supply of theestimated 1,300 disks

.

From there, the laser light is fed into a very long spatial filter to clean up the resulting pulse. The filter isessentially a telescope that focuses the beam into a spot some distance away, where a small pinhole located atthe focal point cuts off any "stray" light caused by inhomogeneities in the laser beam. The beam then widensout until a second lens returns it to a straight beam again. It is the use of spatial filters that lead to the long

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beamlines seen in ICF laser devices. In the case of HiPER, the filters take up about 50% of the overall length.The beam width at exit of the driver system is about 40 cm 40 cm.

One of the problems encountered in previous experiments, notably the Shiva laser, was that the infrared light provided by the Nd: glass lasers (at ~1054 nm in vaco ) couples strongly with the electrons around the target,losing a considerable amount of energy that would otherwise heat the target itself. This is typically addressedthrough the use of an optical frequency multiplier, which can double or triple the frequency of the light, intothe green or ultraviolet, respectively. These higher frequencies interact less strongly with the electrons,

putting more power into the target. HiPER will use frequency tripling on the drivers.

When the amplification process is complete the laser light enters the experimental chamber, lying at one endof the building. Here it is reflected off of a series of deformable mirrors that help correct remainingimperfections in the wavefront, and then feeds them into the target chamber from all angles. Since the overalldistances from the ends of the beamlines to different points on the target chamber are different, delays areintroduced on the individual paths to ensure they all reach the center of the chamber at the same time, withinabout 10 ps. The target, a fusion fuel pellet about 1 mm in diameter in the case of HiPER, lies at the center of the chamber.

HiPER differs from most ICF devices in that it also includes a second set of lasers for directly heating thecompressed fuel. The heating pulse needs to be very short, about 10 to 20 ps long, but this is too short a timefor the amplifiers to work well. To solve this problem HiPER uses a technique known as chirped pulseamplification (CPA). CPA starts with a short pulse from a wide-bandwidth (multi-frequency) laser source, asopposed to the driver which uses a monochromatic (single-frequency) source. Light from this initial pulse issplit into different colors using a pair of diffraction gratings and optical delays. This "stretches" the pulse intoa chain several nanoseconds long. The pulse is then sent into the amplifiers as normal. When it exits the

beamlines it is recombined in a similar set of gratings to produce a single very short pulse. But because the pulse now has very high power, the gratings have to be large (approx 1 m) and sit in a vacuum. Additionallythe individual beams must be lower in power overall; the compression side of the system uses 40 beamlines

of about 5 kJ each to generate a total of 200 kJ, whereas the ignition side requires 24 beamlines of just under 3 kJ to generate a total of 70 kJ. The precise number and power of the beamlines are currently a subject of research. Frequency multiplication will also be used on the heaters, but it has not yet been decided whether touse doubling or tripling; the latter puts more power into the target, but is less efficient converting the light.As of 2007, the baseline design is based on doubling into the green.

12.3) Fast Ignition and HiPER

In traditional ICF devices the driver laser is used to compress the target to very high densities. Theshock wave created by this process further heats the compressed fuel when it collides in the center of thesphere. If the compression is symmetrical enough the increase in temperature can create conditions close tothe Lawson criterion, leading to significant fusion energy production. If the resulting fusion rate is highenough, the energy released in these reactions will heat the surrounding fuel to similar temperatures, causingthem to undergo fusion as well. In this case, known as "ignition", a significant portion of the fuel willundergo fusion and release large amounts of energy. Ignition is the basic goal of any fusion device.

The amount of laser energy needed to effectively compress the targets to ignition conditions has grownrapidly from early estimates. In the "early days" of ICF research in the 1970s it was believed that as little as1 kilojoules (kJ) would suffice, and a number of experimental lasers were built in order to reach these power levels. When they did, a series of problems, typically related to the homogeneity of the collapse, turned out to

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seriously disrupt the implosion symmetry and lead to much cooler core temperatures that originally expected.Through the 1980s the estimated energy required to reach ignition grew into the megajoule range, whichappeared to make ICF impractical for fusion energy production. For instance, the National Ignition Facility(NIF) uses about 330 MJ of electrical power to pump the driver lasers, and in the best case is expected to

produce about 20 MJ of fusion power output. Without dramatic gains in output, such a device would never bea practical energy source.

The fast ignition approach attempts to avoid these problems. Instead of using the shock wave to create theconditions needed for fusion above the ignition range, this approach directly heats the fuel. This is far moreefficient than the shock wave, which becomes less important. In HiPER, the compression provided by thedriver is "good", but not nearly that created by larger devices like NIF; HiPER's driver is about 200 kJ and

produces densities of about 300 g/cm. That's about one-third that of NIF, and about the same as generated bythe earlier NOVA laser of the 1980s. For comparison, lead is about 11 g/cm, so this still represents aconsiderable amount of compression, notably when one considers the target's interior contained light D-Tfuel around 0.1 g/cm.

Ignition is started by a very-short (~10 picoseconds) ultra-high-power (~70 kJ, 4 PW) laser pulse, aimed

through a hole in the plasma at the core. The light from this pulse interacts with the fuel, generating a shower of high-energy (3.5 MeV) relativistic electrons that are driven into the fuel. The electrons heat a spot on oneside of the dense core, and if this heating is localized enough it is expected to drive the area well beyondignition energies.

The overall efficiency of this approach is many times that of the conventional approach. In the case of NIFthe laser generates about 4 MJ of infrared power to create ignition that releases about 20 MJ of energy. Thiscorresponds to a "fusion gain" the ratio of input laser power to output fusion power of about 5. If oneuses the baseline assumptions for the current HiPER design, the two lasers (driver and heater) produce about270 kJ in total, yet generate 25 to 30 MJ, a gain of about 100. Considering a variety of losses, the actual gainis predicted to be around 72. Not only does this outperform NIF by a wide margin, the smaller lasers are

much less expensive to build as well. In terms of power-for-cost, HiPER is expected to be about an order of magnitude less expensive than conventional devices like NIF.

Compression is already a fairly well-understood problem, and HiPER is primarily interested in exploring the precise physics of the rapid heating process. It is not clear how quickly the electrons stop in the fuel load;while this is known for matter under normal pressures, it's not for the ultra-dense conditions of thecompressed fuel. To work efficiently, the electrons should stop in as short a distance as possible, in order torelease their energy into a small spot and thus raise the temperature (energy per unit volume) as high as

possible.

How to get the laser light onto that spot is also a matter for further research. One approach uses a short pulsefrom another laser to heat the plasma outside the dense "core", essentially burning a hole through it andexposing the dense fuel inside. This approach will be tested on the OMEGA-EP system in the US. Another approach, tested successfully on the GEKKO XII laser in Japan, uses a small gold cone that cuts though asmall area of the target shell; on heating no plasma is created in this area, leaving a hole that can be aimedinto by shining the laser into the inner surface of the cone. HiPER is currently planning on using the goldcone approach, but will likely study the burning solution as well.

12.4) Current Status

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In 2005 HiPER completed a preliminary study outlining possible approaches and arguments for itsconstruction. The report received positive reviews from the EC in July 2007, and moved onto a preparatorydesign phase in early 2008 with detailed designs for construction beginning in 2011 or 2012.

In parallel, the HiPER project also proposes to build smaller laser systems with higher repetition rates. Thehigh powered flash lamps used to pump the laser amplifier glass causes it to deform, and it cannot be firedagain until it cools off, which takes as long as a day. Additionally only a very small amount of the flash of white light generated by the tubes is of the right frequency to be absorbed by the Nd:glass and thus lead toamplification, in general only about 1 to 1.5% of the energy fed into the tubes ends up in the laser beam.

Key to avoiding these problems is replacing the flash lamps with more efficient pumps, typically based onlaser diodes. These are far more efficient at generating light from electricity, and thus run much cooler. Moreimportantly, the light they do generate is fairly monochromatic and can be tuned to frequencies that can beeasily absorbed. This means that much less power needs to be used to produce any particular amount of laser light, further reducing the overall amount of heat being generated. The improvement in efficiency can bedramatic; existing experimental devices operate at about 10% overall efficiency, and it is believed "near term" devices will improve this as high as 20%.

HiPER proposes to build a demonstrator diode-pump system producing 10 kJ at 1 Hz or 1 kJ at 10 Hzdepending on a design choice yet to be made. The best high-repetition lasers currently operating are muchsmaller; MERCURY at Livermore is about 70 J, HALNA in Japan at ~20 J, and LUCIA in France at ~100 J.HiPER's demonstrator would thus be between 10 and 1000 times as powerful as any of these.

In order to make a practical commercial power generator, the high-gain of a device like HiPER would haveto be combined with a high-repetition rate laser and a target chamber capable of extracting the power.Additional areas of research for post-HiPER devices include practical methods to carry the heat out of thetarget chamber for power production, protecting the device from the neutron flux generated by the fusionreactions, and the production of tritium from

12.5) Assessing fusion power

Fusion power plants has the potential to substantially reduce the environmental impacts of increasingworld electricity demands since, like nuclear fission power, they would make negligible contributions acidrain or the greenhouse effect compared to fossil fuels. Fusion power could easily satisfy the energy needsassociated with continued economic growth, given the ready availability of fuels. There would be no danger of a runaway fusion reaction as this is intrinsically impossible and any malfunction would result in a rapidshutdown of the plant.

However, although fusion generates no radioactive fission products or transuranic elements, and theunburned gases can be treated on site, there would a short-term radioactive waste problem due to activation

products. Some component materials will become radioactive during the lifetime of a nuclear reactor, due to bombardment with high-energy neutrons, and will eventually become radioactive waste. The volume of suchwaste would be similar to that due to activation products from a fission reactor. The radiotoxicity of thesewastes would be relatively short-lived compared with the actinides (long-lived alpha-emitting transuranicisotopes) from a fission reactor.

There are also other concerns, such as those first raised in 1973 by the American Association for theAdvancement of Science (AAAS). These include the hazard arising from an accident to the magnetic system.

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The total energy stored in the magnetic field would be similar to that of an average lightning bolt (100 billion joules, equivalent to about 45 tonnes of TNT). Attention was also drawn to the possibility of a lithium fire. Incontact with air or water, lithium burns spontaneously and could release many times that amount of energy.Safety of nuclear fusion is a major issue.

But the AAAS was most concerned about the release of tritium into the environment. It is radioactive andvery difficult to contain since it can penetrate concrete, rubber and some grades of steel. As an isotope of hydrogen it is easily incorporated into water, making the water itself weakly radioactive. With a half-life of 12.4 years, tritium remains a threat to health for over one hundred years after it is created, as a gas or inwater. It can be inhaled, absorbed through the skin or ingested. Inhaled tritium spreads throughout the softtissues and tritiated water mixes quickly with all the water in the body. The AAAS estimated that each fusionreactor could release up to 2x10 12 Bequerels of tritium a day during operation through routine leaks,assuming the best containment systemsmuch more in a year than the Three Mile Island accident releasedaltogether. Moreover, an accident would release even more. This is one reason why long-term hopes are for the deuterium-deuterium fusion process, dispensing with tritium.

Materials research and development will play a major role in determining fusion's future viability due to the

very high energetic neutron bombardment, thermal stress, and magnetic forces.

At this point in time the economics of fusion power are largely unknown. The capital costs are likely to belarge, given that a fusion power plant would be much larger in physical size and more complex than aconventional fission power plant. The levelized cost cost of electricity from current fission reactors is greater than that from fossil fuels and wind, so fusion must make significant progress on this front to compete infuture electricity markets.

Thus, while the scientific community has made enormous progress in our scientific understanding of fusion,as of yet there is no clearly identified route to an attractive commercial fusion power plant that will sell in theenergy marketplace of the 21st century and beyond. While fusion power clearly has much to offer if and

when the technology is eventually developed, the problems associated with it also need to be addressed if isto become a widely used future energy source.

13) Fusion advantages

Fusion power would provide much more energy for a given weight of fuel than any technologycurrently in use, and the fuel itself (primarily deuterium ) exists abundantly in the Earth's ocean: about 1 in6500 hydrogen atoms in seawater is deuterium. Although this may seem a low proportion (about 0.015%),

because nuclear fusion reactions are so much more energetic than chemical combustion and seawater iseasier to access and more plentiful than fossil fuels, some experts estimate that fusion could supply theworld's energy needs for millions of years.

An important aspect of fusion energy in contrast to many other energy sources is that the cost of productionis inelastic . The cost of wind energy, for example, goes up as the optimal locations are developed first, whilefurther generators must be sited in less ideal conditions. With fusion energy, the production cost will notincrease much, even if large numbers of plants are built. It has been suggested that even 100 times the currentenergy consumption of the world is possible.

Some problems which are expected to be an issue in this century such as fresh water shortages can actually be regarded merely as problems of energy supply. For example, in desalination plants, seawater can be

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purified through distillation or reverse osmosis. However, these processes are energy intensive. Even if thefirst fusion plants are not competitive with alternative sources, fusion could still become competitive if largescale desalination requires more power than the alternatives are able to provide.

Despite being technically non-renewable, fusion power has many of the benefits of long-term renewableenergy sources (such as being a sustainable energy supply compared to presently-utilized sources andemitting no greenhouse gases ) as well as some of the benefits of the much more limited energy sources ashydrocarbons and nuclear fission (without reprocessing ). Like these currently dominant energy sources,fusion could provide very high power-generation density and uninterrupted power delivery (due to the factthat it is not dependent on the weather , unlike wind and solar power).

In nutshell the advantages are;

The non - radioactive part of the fuel is abundant on a worldwide scale and practically inexhaustible.

The radioactive part of the fuel (tritium) is generated in the reactor itself and is burned producing He andneutrons.

The ash (He) is safe and non- radioactive.

The quantities of the fuel and ash are very small (a few hundreds of kilograms per year and reactor.)

The biological hazards presented by fusion waste are, after 10 years, one thousand times smaller than thoseassociated with fission waste.

14) Conclusion

14.1) How safe is Fusion?

The following explanation focusses on magnetic confinement of deuterium-tritium-fuelled plasmas,such as those in ITER, but similar or even stronger arguments apply also to other fuel combinations and tolaser fusion.

a) The fusion process is inherently safe.

Leak-tight confinement barriers are essential to produce fusion reactions. Equipment failure quickly leads to plasma extinguishment .

b) No chain reaction is involved and the reaction is thermally self-limiting.

. There is no danger of a large jump in plasma power output, since normal operation is close to pressurelimits which already maximise the number of fusion reactions that will occur. In ITER, because of experimental uncertainty, it is possible for the plasma to operate at somewhat (


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Achieving low loss burn conditions is a delicate matter and requires many conditions to be satisfied - thefailure or change of a single one enhances plasma energy losses and terminates the burn. Halting the fuellingquickly extinguishes the plasma. In ITER about 0.5 g of fuel is in the machine at any time, and thefuelling/exhaust rate is also about 0.5 g/s. Even if the exhaust fails, the plasma is quickly poisoned byimpurities, and extinguishes.

The power and energy densities in the reactor and plasma are low.

The main sources of energy which can damage ITER are pressurised coolant, chemical reactions (e.g. of leaking coolant and hot materials, or of hydrogen and air), heat from the fusion reaction in the plasma, andmagnetic energy in the coils. There are no large stores of chemicals or other energy sources able to cause

powerful explosions. ITER is designed such that its hardware avoids the unexpected release from energysources or mitigates the consequences of any such release to acceptable levels not only for the general public,to ensure the ultimate safety of the plant, but also for plant operators, to protect their investment. To help inthese respects, ITER has large heat transfer surfaces and heat sinks which transfer and absorb energy,maintaining low temperatures and avoiding melting of components. The same will be true in a power reactor,

but the margins needed for ITER should be able to be reduced, and the overall power density should be able

to be increased .

The reaction products are either absorbed in surrounding structural or tritium-breeding materials (neutrons),or are non-radioactive (helium).

In ITER nearly all materials around the plasma are to shield the surrounding equipment, whereas in a power reactor the bulk will breed tritium from lithium-containing materials, ready to burn it in the plasma.

Activated structural materials from neutron irradiation are not mobile except dust and corrosion productswhich form only a small fraction.

The neutrons produce activated waste materials. Dust is formed by sputtering from high energy particles inthe plasma hitting the surrounding material surfaces. Although not necessarily a problem itself, this dust can become contaminated with tritium. Coolant channels can become corroded, especially in high nuclear radiation fields, and the corrosion can dislodge and be freed if a coolant pipe breaks. In ITER the coolantchemical control system is capable of maintaining coatings of activated corrosion products well below 10 kg

per loop, with less than 60 g as loose material or ions in the coolant (these limits are used in accidentanalysis). In a power reactor this aspect will be further optimized.

Negligible operational environmental impact.

The potential risk to the local environment is limited and is reduced as low as judged reasonably achievable by the independent nuclear regulator in the country concerned.

Negligible long term environmental impact.

Neither the provision of fuel or plant hardware, nor its removal after use, places an intolerable and uncertain burden on current or future generations.

14.2) fusion for the near future

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Thanks to JET and other fusion experiments, major progress has been made towards developingfusion as a viable energy source, concludes Dr Robinson. Its time to move on a number of fronts, he says.We now have a good understanding of how the materials used in fusion plants might behave althoughfurther tests in a dedicated facility are still required, and we understand how to deal with the short-livedwaste products that fusion plants will produce. These short-lived waste products are the parts of the machinethat would be bombarded with neutrons from the fusion process, and so become radioactive. With carefulmaterial selection and recycling, these wastes would last for significantly less time than fission waste 30 to40 years compared with hundreds of years. Dr Robinson continues, When external costs are included, wehave calculated that fusion costs will be comparable with clean coal or any baseload renewable energytechnologies and if you take into account that there would be no need for environmental remediation withfusion, the economics of fusion become even more favourable.

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seminar report on fusion power plant

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