Talk:Nuclear fusion/Pompura paper

Controlled

Thermonuclear

Technology

By:

Mike Pompura

Seminole Community College

September 15, 2004

ENC 1101

Maria Brandon

Research Paper OUTLINE

Thesis:

Even with the extremely difficult conditions necessary to initiate and maintain a controlled

nuclear fusion reaction, the opportunity of having a viable energy source that will last for

millions of years continues to provide the main initiative for continuing research and

development in the field.

1:  Thermonuclear Theory A.	History and Background B.	 Lawson Criteria C.	Fuel Supply D.	Advantages as a Power Source

2:    Plasma containment A.	Inertial Confinement B.	Magnetic Confinement a.	Open Systems b.	Closed Systems

3:    Future Applications

4:    Because the fuel is available in almost unlimited supply, I believe that fusion energy

will become the major power source of the future long after the petroleum sources

have depleted and made the internal combustion engine obsolete. Not only is this

energy source “clean” and environmental-friendly it also has the potential for a

higher efficiency in the fuel utilization; nothing is wasted in the conversion process.

Mike Pompura Maria Brandon ENC-1101 9/15/04

CONTROLLED THERMONUCLEAR TECHNOLOGY

Nuclear fusion has been attained on the earth in the form of the hydrogen bomb. The

bomb is a form of uncontrolled fusion which has no practical value except to make large

holes in the ground quickly. Controlled fusion presents unique problems which scientists

have yet to solve. Once the problems are solved, fusion power promises to be a source

of energy that could be used for a variety of purposes.

The primary fuel for the fusion process is Deuterium which is abundant in seawater

“There is one Deuterium atom in every 6,500 ordinary hydrogen atoms of seawater. The Deuterium in one gallon of seawater has the fusion energy equivalent to 300 gallons

of gasoline, or the fusion energy available from a cubic mile of seawater has been

calculated to be the equivalent to the combustion of 5,700 billion barrels of crude oil –

the amount of 2.5 times the world’s entire oil reserves.”1  At the current rate of fuel oil

consumption the Deuterium in the oceans could last for 500,000,000 years. The

possibility of a low cost fuel in abundant supply provides a strong initiative for further

research and development in the field of thermonuclear energy.

Fusion reactions were first discovered with a particle accelerator when scientists

directed a beam of high speed neutrons into a target of frozen Deuterium. The energy

released from these experiments was far less than the energy required to initiate them,

but it did prove that the fusion process was actually possible. Project Sherwood

was the code name given to the experiments conducted into the fusion research during the

early 1950’s.

A thermonuclear reaction takes place when two nuclei fuse together to form a stable heavier

one, thereby releasing elementary particles and kinetic energy in the process. The nucleus

consists of protons and neutrons and it carries a positive electric charge which tends to repel

other nuclei. The greater number of protons in the nucleus relates directly to a stronger

repulsive force; therefore the lightest nuclei are the easiest ones to fuse. To overcome this

repulsive force a nucleus must have enough kinetic energy to fuse with another one. The kinetic

energy required to fuse atoms amounts to several thousand electron volts, but the energy

liberated in the fusion reaction totals in the million electron volt range. “One electron volt is the

energy that a singly charged particle gains in falling through a potential difference of one volt.”2

The usual way of accelerating atoms to sufficient kinetic energies for fusion reactionsis to heat

them, therefore the term thermonuclear is applied. Amoung the many ways to heat atoms are:

1: Electrical Currents 2: Magnetic Fields 3: Laser Beams

When matter is superheated to extreme temperatures the atoms are stripped of their electrons

and form positive ions. This cloud of ions and electrons is called a plasma. Two fields of

science that deal with plasmas are hydromagnetics and plasma physics. Plasma physics deals

with the physics of hot ionized gases and hydromagnetics deals with the dynamics of electrically

conducting fluids interacting with magnetic fields. The usual way of handling these plasmas is

to confine them in a magnetic field.

The Lawson Criterion was first proposed by the British scientist J.D. Lawson in 1956, and it

states that if a fusion reaction output is to exceed its input, the value (nT) must exceed a critical

number. The value “n” is measured in particles per cubic centimeter, and the value “T” is

measured in fractions of a second. “The nuclear energy released per unit time is proportional to

the product of the ion number density squared (n2), the nuclear reaction cross-section, and the

ion-ion collision velocity. The thermal energy supplied to this volume is proportional to the

product of the ion number density (n), the mean thermal energy, and the reciprocal of the

containment time (T), which is the average time that a hot Deuterium or Tritium nucleus spends

in the reacting region.”3 For a typical D-T reaction the value is 1014 at a temperature of 200

million degrees Kelvin. For a D-D reaction the value is 1016 at a temperature of 1,000 million

degrees Kelvin. The basic requirements for achieving useful power from a fusion reactor are to

heat the fuel to a high temperature, keep it free from impurities, squeeze it to an adequate

density, and hold the plasma together long enough. Fuel for the fusion reactor will most likely be one of four choices:

1.	Deuterium 2.	Tritium 3.	Helium 4.	Lithium

Deuterium and Tritium are isotopes of hydrogen. Deuterium has one proton and neutron in

its nucleus which is called a Deuteron; it is a stable isotope quite abundant in nature. Tritium has

one proton and two neutrons in its nucleus which is called a Triton. This isotope is radioactive

and rarely found in nature, but it can be easily produced by bombarding Lithium with neutrons.

Lithium is a metal which is quite abundant in nature. The stable isotope of Helium, He3, is

another possible fuel for fusion reactions. The most logical choice would be a combination of

Deuterium and Tritium because of their availability and ease of fusion.

Deuterium can easily be separated from ordinary hydrogen by the electrolysis of water. Tritium can easily be obtained from Lithium metal, alloys or salts. Lithium could be used as

blankets around the reactor core, liberating tritium as the neutron flux penetrated it.

Among the many advantages of a fusion reactor is the fact that only a very small amount of

fuel would be present in the reactor vessel at any given time, thereby eliminating the possibility

of a runaway explosion. The interior of the reactor vessel would be radioactive, but the waste

products would not. This would eliminate the problem of handling highly radioactive waste

disposal now common to all operational fission reactors.

The efficiency of the fusion power plant could be raised to 90% in certain fuel cycles that

would permit direct conversion of the plasma into electricity. Also, the fuel itself could not be

used to make an explosive device; one would first require a fissionable trigger to detonate the

fuel. Operating a fusion reactor would not require burning any oxygen or hydrocarbons, and it would not release carbon dioxide or other combustion products into the air. The only source of

problems would be from the Tritium. Tritium diffuses through most metallic containers, and is

difficult to contain. Routine release of Tritium would be necessary for operation of the reactor,

but it poses little serious threat as compared to fission reactor byproducts.

There are two general approaches to plasma containment; inertial and magnetic. Inertial

confinement is actually a misnomer since actual confinement does not occur. In theory, a dense

plasma is heated very rapidly by using lasers or particle beams. “Laser beams would first heat

the surface of a tiny Deuterium-Tritium pellet causing the material on the surface to blow off; the

inward counterforce would implode the remaining material causing a fusion reaction to occur.”4

Development of this type of research is still quite new compared to the applications of magnetic

confinement. The main hinderance is the power required for the laser beam. What is needed is a

million joules of energy delivered in less than a nano-second. Magnetic confinement of plasmas can be divided into open and closed systems. Magnetic

systems have been studied as early as the 1950’s. “In an open systems device the magnetic lines

depart from the plasma region rather than close in on themselves to form a loop.”5 The open

systems operate either on the mirror reflection principle, magnetic well, or theta pinch theory. The mirror reflection device is usually an open tube with a magnetic field which is weak in the

middle and strong at the ends, thus trapping the plasma in the center. The open systems tend to

leak plasma more readily than the closed systems although both operate on the principle of

magnetic confinement. The best conditions that these machines have indicated to date are a

plasma temperature of 200 million degrees Kelvin contained for .0001 second with a particle

density of only 108 ions per cubic centimeter.

Reactors operating on the open systems principle are susceptible to an inherent instability known as micro-instability, which renders them marginal for use in practical power production units. A modification was made to the mirror reflection device, and it was renamed the

magnetic well. With the well device, experiments have achieved ion densities in the 1013 range

with a containment time of .0003 second at a temperature of 200 million degrees Kelvin.

“In most theta pinch devices, a single turn coil is at each end of an open cylinder. A large

capacitor storage bank is rapidly discharged through the coil, thereby inducing an electric current

in the gas in a direction encircling the axis of the cylindrical volume. This direction is the 0

direction in the cylindrical coordinates, thereby giving rise to the name Theta Pinch.”6  This

electrical discharge serves to provide a magnetic field, ionize and heat the plasma, all in a micro-

second. The Z pinch device is similar to the theta pinch, but the difference lies in the direction of

the applied magnetic field.

In a closed system device the magnetic field closes in on itself, forming a circle. The usual

configuration for closed systems is the torus which looks like a donut. The closed systems can

be classified into three types:

1: Stellarators 2: Tokamaks 3: Internal Ring

The stellarator was first built in 1952 at Princeton University. Coils are built around the

torus, and are spaced at intervals. These coils produce a magnetic field which twists around the

central axis of the toroid. An electrical current is discharged into the plasma to heat it to high

temperatures. The best results from these machines has been a temperature of only 2 million

degrees Kelvin, which is not even close to the 200 million that is required; and an ion density of

1013 particles per cubic centimeter with a containment time of 50-4 second.

A more efficient and most promising closed system is known as the Tokamak, which was developed in Russia in 1968 by Lev Artsimovich. The windings on a tokamak are quite simple

compared to the stellarator, and serve only to create an external magnetic field. Because of this, tokamaks can be built to a higher aspect ratio which tends to stabilize the plasma and permit a

higher current discharge into the plasma for denser confinement. The aspect ratio is the minor

radius compared to the major radius of the torus, meaning they can be built to larger diameters.

Research at Princeton with a new type of tokamak known as the Adiabatic Toroidal

Compressor utilizing neutral particle injection, have achieved ion densities of 3013 at a

temperature of 20 million degrees Kelvin for .01 second. By using this device the plasma

density has increased to a large amount. Studies have concluded that more optimum conditions

can be available in building larger tokamaks. Another tokamak called ORMAK located at Oak

Ridge laboratory has achieved favorable results. The difference in ORMAK is the use of a

super-cooled transformer. The torus has two sets of coils around it which serve to center the

plasma. The transformer loops around the core of the torus and serves to heat the plasma. All of

this equipment sits in a large vacuum tank filled with liquid nitrogen.

The internal ring devices utilize a ring inside the torus for the purpose of achieving optimum

magnetic confining fields with excellent stability characteristics. These devices are only

considered as research tools and not possible fusion reactor prototypes. The internal ring tends

to conduct heat away from the plasma thus reducing the probability of achieving the required

temperatures.

Fusion reactors operating on the magnetic confinement principle will require a minimum

temperature of 200 million degrees Kelvin with an ion density of 1015 particles per cubic

centimeter for at least .1 second in order to undergo a successful fusion reaction process for the production of useful energy. A typical fusion reactor will probably use the D-T fuel cycle at first

since it is the easiest to undergo the fusion process. A lithium blanket would surround the

reactor core in order to absorb extraneous neutrons and release Tritium for the fusion process to

utilize. The lithium could also be used as a heat transfer medium, absorbing the fusion core heat

and transferring it to a heat exchanger to make steam for driving a turbogenerator. The

efficiency would be rated at only about 60%. By using other fuel cycles it would be possible to

directly convert the plasma stream into electrical current without the use of a turbogenerator;

thus increasing the efficiency closer to the 90% mark..

The reactor could be a mirror machine where some of the plasma could escape at one of the

open ends and be made to pass though electrostatic collectors which convert the ions and

electrons into direct current. Experiments at the Livermore laboratory have used the kinetic

energy of a 1,000 electron volt ion beam to directly convert it into electricity. These studies

prove that the theory will work and could be utilized on a larger scale. The fusion plasma can

also be considered a high temperature heat source that could be used for a variety of commercial

purposes. The plasma can also be used as a source of large amounts of ultraviolet radiation.

Among the many possible uses are:

1: Desalting of Water 2: Bulk Heating 3: Sterilization of Sewage/Waste 4: Ore/Mineral Processing for Aluminum/Steel 5: Reduction of toxic chemicals to their basic compounds 6: Direct Synthesis of Carbohydrates from carbon dioxide/water 7: Production of Hydrogen 10: The neutrons could be used to shorten the half-lives of radioactive wastes 11:  Production of fissionable reactor fuel from Thorium

Considerable progress has been made since the introduction of fusion research in 1952.

Plasma densities and temperatures have increased significantly, and the confinement times have

been shortened and improved, but there are still problems that are required to be resolved before

a practical fusion reactor can be built for the production of useable power. The reactor will

probably be a combination of machines now in development, using the advantages of each one.

Nuclear fusion releases more energy per pound than the fission process. There is 15 times

more energy available in fusing a gram of hydrogen than there is in fissioning a gram of

uranium. When hydrogen undergoes fusion it releases only .7% of its mass as energy. Further

possibilities of power production include the matter-antimatter reactions, which would release

100% of their mass as energy and is 140 times more powerful than fusion reactions. Sadly, this

reaction only occurs in nuclear physics labs and is very remote in terms of an energy source.

The fusion process is being developed now, and the fact that the fuel is almost inexhaustible

provides the strongest incentive for creating additional research and development in the field.

NOTES

1 U.S. Atomic Energy Commission, Atomic Energy Programs: 1972, Washinton, D.C.: GPO, 1972, p.66

2 “Fusion Principles”, Ecyclopedia Americana, 1977 ed. P.511.

3 Encyclopedia Americana, p.511

4 U.S. Atomic Energy Commision, Atomic Energy Programs: 1971. Washington, D.C. : GPO, 1971, p.73.

5 “Controlled Fusion”, Encyclopedia Americana, 1977 ed. P.513

6	Encyclopedia Americana, 1977, p.515

WORKS CITED

American Nuclear Society. Energy Alternatives. LaGrange, I11. 1981.

Asimov, Isaac. The Story of Nuclear Energy. Washington,D.C.: GPO, 1972.

Corliss, William. Direct Conversion of Energy. Washington,D.C.: GPO. 1964.

Glasstone, Samuel. Controlled Nuclear Fusion. Wasington,D.C.: GPO, 1968.

Jacobs, D.J. Sources of Tritium and its Behavior Upon Release to the Enviroment. Washington,D.C.: GPO. 1968.

Laquer, Henry, Cryogenics – The Uncommon Cold. Washiington,D.C.: GPO 1967.

Post, Richard. “Fusion Principles”. Encyclopedia Americana. Ed 1977.

Seaborg, Glenn. Peaceful Uses of Nuclear Energy. Washington,D.C.: GPO, 7/70.

Simon, Albert. “Controlled Nuclear Fusion”. Encyclopedia Americana. ed.1977.

U.S. Atomic Energy Commission. Fundamental Nuclear Energy Researcg-1970. Washington,D.C: GPO, 1970.

U.S Atomic Energy Commission. Fundamental Nuclear Energy Research-1971. Washington,D.C.: GPO. 1971

U.S. Atomic Energy Commission. Atomic Energy Programs. Washington,D.C.: GPO. 1972.