EE11206

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ABSTRACT

“Necessity is the mother of invention. Energy crises is the cry of future”

The conventional sources of energy, the single most important pre-requisite for

power generation are depleting fast. The world is heading towards a global energy crisis

mostly from running out of these energy sources, decreasing the dependency on fossil

fuels is recommended. Yet, the sources of energy are infinite. The greatest task of present

day is to exploit the non-conventional energy sources for power generation. Of late, many

methods have been introduced for this purpose such as fuel cell technology, hydrogen

fuel, solar energy, tidal energy and wind energy. But these non-conventional sources do

not promise to meet the ever increasing energy demand.

The Nuclear Fusion energy will not only serve as an alternative but will also

prove to be the only source of energy in future. The principle of generating power

through nuclear fusion is elucidated in this paper. The huge amount of energy which is

obtained from fusion reaction is used to generate steam which drives the turbine and the

alternator coupled to the turbine generates electricity. The creation and confinement of

plasma and the advantages of this reactor is explained in this paper. Fusion research is

considered worth pursuing because it promises to be a widely available energy source

with essentially unlimited supply and manageable environmental impact. Especially in

India, which has the largest population of whom energy demands has to be met; we need

a technology that generates large amount of power with minimum input requirements.

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TABLE OF CONTENTS

1. The Nuclear Fusion Reaction……………………… 2

2. Creation of Plasma…………………………………. 2

3. Plasma Confinement……………………………….. 3Tokamak……………………………………….. 3

4. Heating of Plasma…………………………………... 5

5. Can Nuclear Fusion Plant Explode? ........................ 7

6. Leakage and containment of Radioactivity………… 7

7. Availability of Fuels…………………………………. 8

8. Advantages of Fusion………………………………... 9

CONCLUSION …………………………………………… 10

REFERANCE……………………………………………... 11

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from "The Fusion Quest" by T.K.Fowler, ISBN-0801854563

Inertial fusion involves the firing many times per second of high

energy particle or laser beams from all directions at tiny solid fuel pellets in a

reaction chamber. Material sputtered off the pellet by the high energy beams drives

a shock wave towards the pellet centre, raising its temperature and density. This

implosion leads to sufficient fusion reactions occurring to overcome the losses, and

a large amount of energy is released in a "micro-explosion". The resulting alpha

particles, neutrons, and radiation flow radially out towards the reaction chamber

walls. These are situated far enough (typically meters) away and built so as to be

able to withstand the loads.

PLASMA CONFINEMENT

Since a plasma consists of two types of charged particles, ions (+ve)

and electrons (-ve), magnetic fields can be used to isolate the plasma from the

vessel walls. In a magnetic field the particles readily spiral along the field lines but

diffuse only slowly across them. The most promising magnetic confinement

systems are toroidal (ring-shaped) and, of these, the most advanced is the Tokamak.

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The Tokamak

Schematic diagram of a Tokamak

In a Tokamak, plasma is heated in a toroidal vessel and confined away

from the vessel walls by magnetic fields.

The basic components of the Tokamak's magnetic confinement system are:-

• The toroidal field which is produced by coils surrounding the vacuum

vessel.

• The poloidal field produced by a current in the plasma; the plasma current is

induced by transformer action.

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Toroidal and poloidal fields of a Tokamak

The idea of using these reactions is that if the products of the reaction

can be made to slow down in the fusing medium, they can be used to help maintain

the reaction temperature, and if neutrons are produced they can escape the medium

to heat up the surrounding materials, and their coolants then used at high

temperature to generate electricity using a conventional steam or gas turbine.

The energy released is partitioned among the reaction products

inversely with their mass, and they carry it away as kinetic energy. The reactions

are difficult to achieve, because the nuclei have a positive electrical charge and

therefore strongly repel each other. This can be overcome if their kinetic energy is

large enough to bring them close enough that the (attractive) strong nuclear force

pulls the nuclei together.

HEATING OF PLASMA

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One such method is neutral injection heating. Fuel atoms are accelerated

as ions, neutralised by collisions with a gas, then cross the magnetic field, where

they are ionized by the plasma and trapped by the magnetic field. They then slow

down, transferring their energy to the plasma by collisions (mainly with electrons if

the beam particle energy is high enough), thus heating it.

Another method is radio frequency heating, which introduces

electromagnetic waves into the plasma. If an electromagnetic wave interacts with

particles of various velocities, some will be travelling slower than the wave, and

some faster. Usually more particles exist travelling a bit slower than the wave than a

bit faster, so electromagnetic waves will preferentially experience drag and be

damped by the plasma. This collision less (or Landau) damping, transfers energy

between the waves and the plasma particles. The energy is delivered to the plasma

by antennas or wave guides at the plasma edge. The frequencies are tuned so that

the energy is absorbed in the appropriate region of the plasma and by the

appropriate particles. The plasma has essentially three main "resonant" frequencies

where heating is most effective - at the electron and ion cyclotron frequencies, and

at the lower hybrid frequency. The first two are the frequencies at which the ions

and electrons orbit the magnetic field lines as they spiral round the torus. Waves at

the lower hybrid frequency propagate well in plasma which has electric fields and

magnetic fields perpendicular, typical of the plasma edge.

Both these additional heating systems (beams and radio frequency) can be

arranged to also impart momentum preferentially to the electrons relative to the

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ions.

CAN NUCLEAR FUSION PLANT EXPLODE?

The amount of fuel in the plasma at any time is about 1 gramme -

enough for a few seconds' reactions. The reaction process itself is a fine balance of

making an ultra-high vacuum, injecting only fuel into it, driving adequate currents

within it and in surrounding coils to contain it, and reaching sufficient density to be

able to heat it enough to raise fusion power to peak levels. If anything goes wrong

in any of these processes, the plasma hits the surrounding material walls, and the

resulting flood of impurities extinguishes the plasma. That is the challenge of

fusion. There can be local problems with all the energy concentrating on certain

surfaces, causing melting and damaging the investment, but there is no nuclear-

driven thermal runaway possible.

Certain accidents can release water coolant into the reaction chamber. If

there are hot surfaces nearby these can dissociate water into hydrogen and oxygen,

and explosive mixtures can result if care is not taken. Again, the energies are

enough to damage the investment, but not to cause sufficient damage to affect the

general public. The plant is designed with various lines of defense to avoid the

possibility of contamination outside the plant in the case of such hypothetical

accidents.

LEAKAGE AND CONTAINMENT OF RADIOACTIVITY

Analyses show that under normal operation the extra annual dose to the

most exposed individual is about 1% more than that of natural background

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radiation.

The DT fusion reaction creates helium, which is inert and harmless, and

neutrons, which can make surrounding materials radioactive for varying amounts of

time. Should these barriers fail, the plant is equipped with a ventilation system

with detritiation systems, able over time to clean the atmospheres

The first line of defense is the tokamak vacuum vessel itself which has

to be leak free in order to provide a sufficiently clean plasma to produce fusion.

Extensive safety analyses have been carried out and show that even

under even hypothetically possible accident conditions there will be no need for

evacuation of any of the population around the site.

After 100 years of post-operation radioactive decay, nuclear fusion

reactor will be left with about 6000t of waste. When packaged, that is equivalent to

a cube with about 10 m edges.

Nuclear fusion reactor waste is less biologically active than coal

power station waste 100 years after operation

AVAILABILITY OF FUELS

Deuterium is abundant as it can be extracted from all forms of water. If all the

world's electricity were to be provided by fusion power stations, Deuterium supplies

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would last for millions of years.

Tritium does not occur naturally and will be manufactured from Lithium within the

machine.

Lithium, the lightest metal, is plentiful in the earth's crust. If all the world's

electricity were to be provided by fusion, known reserves would last for at least

1000 years.

Once the reaction is established, even though it occurs between Deuterium and

Tritium, the consumables are Deuterium and Lithium.

ADVANTAGES OF FUSION

• A vast, new source of energy.

• Fuels are plentiful.

• Inherently safe since any malfunction results in a rapid shutdown.

• No atmospheric pollution leading to acid rain or "greenhouse" effect.

• Radioactivity of the reactor structure, caused by the neutrons, decays rapidly

and can be minimized by careful selection of low-activation materials.

• Provision for geological time-span disposal is not needed.

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CONCLUSION

The demand for energy is infinite. To meet the ever increasing demand

new energy technologies that are promising are essential. Especially in India, which

has the largest population of whom energy demands has to met, we need a

technology that generates large amount of power with minimum input requirements.

The concept of Fusion power promises to meet all the energy demand

of our country, and a country like India that is racing towards future at rapid rate,

this technology is not a big deal. Especially in the ongoing era where the world is

focusing on reducing environmental pollution, the fusion power being pollution less

could proof to be the only alternative to replacement for fossil fuels and to meet the

world energy demand.

Hence the study and advancement of the field of Nuclear Fusion

power is worth pursuing to make the world not just a better but a safer place to live.

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Reference:

The Fusion Quest by T.K.Fowler

www.ITER.org

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