HOW IT WORKS: Fusion Power

primitive man believed the Sun to be a huge ball of fire much like a great chunk of coal that would eventually burn itself out like a cold cinder in a few thousand years but in the 1920s astronomers changed all this they told us that it was nuclear energy that fired the Sun and stars our Sun is really a star not just an ordinary furnace sending out light and heat but a huge nuclear furnace that will burn and produce great amounts of radiant energy for millions and millions of years the Sun generates 90% of its energy in its core every second 564 million tons of hydrogen are converted to 560 million tons of helium the remaining 4 million tons radiates away each second as heat and light like the Sun light we saw streaming through our ceiling a moment ago the Sun will continue to burn itself at this rate for billions of years to come changing hydrogen to helium it does this by thermonuclear burning fusion if you will a process that literally is the ultimate source of energy in the universe in the Sun's core subatomic particles are racing about at incredible speeds creating a sort of atomic pudding as they rush about they bump into one another sometimes they bump hard enough so they can't pull apart again they fuse and some of their mass is changed to energy here on earth fusion researchers have been trying for 20 years to imitate the Sun the high temperatures in the Sun would burn any metal to a hot scalding gas everything we know of will melt by about 6,000 degrees Fahrenheit so we couldn't possibly put such fast-moving particles into a pot and cook them up and that's the crux of the fusion problem here on earth how to keep a group of hot particles in one place without a pot the fuel for fusion is in common water the heavy hydrogen that exists in all the world's oceans man figuratively lives on an ocean of energy here are two gallons of water there's a little less than a hundredth of an ounce of heavy hydrogen in here costing only a few cents to extract it from the water fusion reactions occurring in that quantity of fuel would produce the same heat energy as the combustion of 2 tons of coal or the burning of 300 gallons of gasoline one pound of fusion fuel would produce 40 million kilowatt hours of electricity enough electricity for 20,000 people for a year fusion researchers are trying to liberate some of the energy that holds the nucleus together remember we're working with charged particles a group of extremely high temperature particles called a plasma the fourth state of matter let's look at one of the more practical fusion reactions one that occurs more easily than any other this white ball represents a deuterium nucleus a form of hydrogen the most common element in the universe this red ball over here represents a nucleus of tritium another form of hydrogen when these particles are accelerated to high speeds and collide they fuse forming a single heavier unstable nucleus which quickly breaks apart at enormous speed forming a single neutron particle and the helium nucleus there is less mass at the end of this reaction than at the beginning this mass has not been lost it has been converted into kinetic energy when a nucleus of deuterium it's a nucleus of tritium they will fuse to form a single heavier unstable nucleus quickly springing apart with increased energy to form a single neutron and a nucleus of helium that's one possible fusion reaction Einstein's formula e equals MC squared tells us that mass and energy are equivalent there's another point to remember here a small part of the mass of any nucleus is present in the form of energy that binds the parts of the nucleus together it takes less energy to bind the nucleus formed after a fusion reaction than it did to bind the individual nuclei that collided to create that fusion reaction remember if an atom were the size of this room its nucleus would be no larger than this grain of sand normal atoms can get no closer than about a hundred millionth of an inch this is because their outer electrons would touch that may not seem like much space but it does keep the nuclei apart so we must ionize the atoms that's another way of saying stripping off their outer electrons now the nuclei can approach each other much more closely there is no protective screen of electrons keeping them apart the son uses its enormous gravitational pressures to squeeze the particles extremely close together but here on earth we cannot command such massive forces we must therefore turn to intense magnetic fields or to high-powered lasers to overcome the mutual repulsion of subatomic particles we must accelerate them to enormous speeds this means heat we must heat the particles hotter and hotter get them to move faster and faster if we can get them close enough together the nuclear force within the particles will take over and they will fuse making a plasma is easy every time we turn on a fluorescent light we make a plasma but as far as fusion researchers are concerned these plasmas are too cold our laboratory plasmas must approach 100 million degrees centigrade Fusion is heating and confinement preventing these hot particles from coming in contact with anything solid once a hot plasma touches anything it cools off it ceases to be a plasma the problem is not one of preserving the container but rather one of preserving the plasma here's a group of balls representing charged plasma particles they are more or less moving random with no particular direction to their motion when we apply a magnetic field of these charged particles their electrical charge forces them to spin or spiral along the lines of magnetic force the magnetic field has given the particles invisible backbones the negatively charged particles spiral in one direction the positively charged particles in the opposite direction as they travel on their helical paths the particles will occasionally collide with other particles when this occurs the particles scatter or jump from one field line to another eventually drifting out of the center of the magnetic field to diffuse to the walls of the container researchers have used a number of different shapes to confine plasma particles one of these shapes has been a magnetic mirror here's a hollow piece of straight plastic tube it's wrapped with electrical windings that create the magnetic field we pump most all of the air out then we inject our fuel into the tube apply an electrical potential and a magnetic field this field forces the charged particles toward the center of the tube creating a small diameter plasma about the size of a garden hose to prevent the particles from escaping out the ends of the container we place strong magnetic fields here at each end these strong magnetic fields act as mirrors as the particles approach the ends they face a more powerful magnetic field than the one in the middle this turns them around and they bounce back toward the other end in a kind of ping pong fashion we call these devices mirror machines despite all these considerations some particles do get lost out the ends now we can design a device that has no ends we can turn the ends of this tube upon themselves to form a circle a donut we call this shape of torus and many research bottles are of such shape including tokamaks theoretically now the particles should race around and around until they hit some other particles and fuse well it's just not that simple as fusion researchers have painfully discovered when we turn this straight tube into a torus you run into yet another problem we've compressed the magnetic lines of force much closer together on the inside of the torus making the field much stronger here on the inside wall that on the outside wall here since particles always seek the path of least resistance they will drift across the magnetic fields toward the outside wall and be lost man is trying to satisfy an age-old golden rule which dr. James tuck of Los Alamos once told us about no the golden rule if you want to make fusion power is this you have yourself a bottle it's got some density of particles / see see it's also got some temperature and it stays in the bottle for some time tall now it turns out that you spent some work in getting it up to this high temperature to cook up the contents of the bottle you spent them now then something comes out in the rate in the way of thermonuclear burning what you have to do is to ensure that there's more comes out then use point put in and lure a certain factor in producing fusion conditions we do have some flexibility we can hold a plasma at low densities for say one second or we can choose to hold the plasma at higher densities say a hundred times greater for only a hundredth of a second we must also heat the plasma to 100 to 150 million degrees now how can we achieve these incredible temperatures well we can use resistance heating to heat the plasma to about twenty million degrees centigrade this is the same principle that makes the wire in your toaster hot then we can compress the plasma into a smaller and smaller volume heating it to perhaps 50 million degrees centigrade at these temperatures the plasma begins to self heat to 100 to 150 million degrees centigrade heating does appear to be a major obstacle but not insurmountable 24 years of effort have produced plasmas that have buckled many that have kinked others that have fluted whipping around like a wild snake to eventually hit the walls and quench out still there's no fundamental reason why nuclear fusion is not achievable dr. Harold Firth of Princeton University when I came into this project almost 20 years ago there was a tremendous amount of soozee Azzam everyone was confident of success and the reason that mood then faltered for about a decade is that this enthusiasm was a kind of ignorant enthusiasm if you don't know the subject then being a good healthy cheerful red-blooded scientist you naturally enthusiastic so after this initial enthusiasm then came a decade of caution and skepticism and now after 20 years we are back through enthusiasm the important difference is that the present enthusiasm is based on information among the things that we know for certain are the following Fusion fuel is an essentially infinite supply and is available to all countries at negligible costs fusion will produce no noxious chemical combustion products and there will be absolutely no chance of a runaway reaction and fusion will not involve materials that could be stolen or used for clandestine purposes fusion will involve some radioactivity but in relatively small amounts in fusion power plants will be able to be sited essentially where we want possibly even inside of the cities where their energy can best be used finally our studies show that fusion power costs should be comparable with those that we have today fusion research and development problems are very complex we feel that we have a very good understanding of what those problems are and we are mounting a vigorous and expanding program to solve them later this decade we expect to achieve a major program milestone the creation of reactor light conditions in a hydrogen plasma at this laboratory fusion research started some 20 years ago and it seemed that one professional life can be equated to the many machines that he has worked on at the present time we're rather preoccupied with our latest device the print and large tourist the Princeton machine is a doughnut-shaped Taurus called a tokamak it's a significant step up in size confining a plasma that's about three feet across to demonstrate fusion the plasma must reach 100 million degrees these Princeton researchers hope to raise their plasma temperatures into the 20 to 50 million degree range push their confinement times up to a tenth of a second or so their biggest job keeping the plasma from shifting up or down from bulging or expanding not allowing the plasma to hit the walls of the container the performance of the Princeton machine promises to be a goldmine of information on the tokamak principle its success will tell fusion researchers just how big a step they must take toward the design of a large deuterium tritium burning machine our initial motivation for building or Mack the Oakridge tokamak was to find out how the doughnut shaped plasma cross-section behaves as it's made fatter and fatter or Mac has a cross-section of about 18 inches we began experiments in 1972 which confirmed our expectation that plasma confinement is indeed better in a larger device the second phase of our experiments began in 1973 when we started using neutral beams to heat the plasma to higher temperatures right now we have heated the plasma ions to a temperature of about 6 million degrees C and have confined the plasma for about a hundredth of a second we hope to increase these numbers much of our work at Oak Ridge and other fusion laboratories is aimed at determining scaling laws so that when we design and build fusion test reactors we'll have a better idea of plasma behavior in these large systems I've been at this game here in Livermore since 1953 that's over 20 years I've worked on several experiment including toy talk to X 1 to X 2 and now we're on the air with a new machine to X to B the Livermore Machine is the largest most advanced mirror device in the world a new heating system has been added pushing the temperature of the plasma to 40 million degrees the theory behind the mirror approach is to bounce the plasma particles back and forth many times before they are lost out the ends of the machine the plasma is now being held for about a thousandth of a second still too short a time the plasmas created are also still too thin and too cold but as larger and larger devices are built these Livermore researchers believe the energies and confinement times will improve ok great doesn't have much of an integral bit here in Los Alamos our main approach is pulsed high density systems compared to the toca MOX and mirror machine our plasma densities are a thousand times larger and our confinement times correspondingly 1,000 times smaller at Los Alamos the problems are not ones of temperature and density but ones of confinement the philosophy is to quickly shock heat the plasma diffusion temperatures and densities before it becomes lost early experiments in straight devices solved many technical problems but all suffered from the plasma leaking out the ends of the tube in 1974 researchers turned the device into a torus and losses currently the plasma has been successfully placed on a circle efforts are now concerned with stabilizing the plasma preventing it from jumping off the circle by use of feedback circuits we at general atomic are little bit different than most people working in tokamaks both tokamaks and Beverage are toroidal or doughnut shaped melodic potters dr. okawa and his colleagues at san diego are working with a unique non circular plasma this kidney shaped device achieves the same confinement times as other machines but uses 10 times less magnetic pressure this is an important cost savings in the design of a fusion power plant the non circular concept was proven with earlier experiments in smaller devices plans are now underway to construct a still larger machine the doublet 3 it will operate at temperatures of 50 million degrees since magnets are the major expense of a fusion reactor the doublet design promises to be the least expensive approach man's only successful method of producing fusion did not involve magnetic fields at all that was the hydrogen bomb that same principle could be used in a controlled manner using high-powered lasers here's how it works an ultra high-powered laser would fire its light beam at a very small pellet dropped into a target chamber the pellet would be hit from all sides at the same time its outer layers vaporizing away the inner core compressed the core of the pellet would be compressed and heated to fusion densities and temperatures before it could overcome its inertia and expand pellet after pellet would be dropped perhaps 10 a second each releasing as much energy as about 10 pounds of dynamite this energy could be used to heat the surrounding fluid hot enough to make steam the laser fusion reactor would be working like an internal combustion engine putt-putt pudding along the mini pellet would be quite small probably a hollow sphere about the width of a single human hair here are a million such pellets the challenge is to build a laser powerful enough and to manufacture a cheap suitable fuel pellet Computer Studies here at Livermore really gave impetus to laser fusion in 1961 we were able to show theoretically that you might be able to compress and heat a tiny pellet of deuterium tritium with a powerful laser beam and create a fusion event right now we're in the process of building a 10 kilojoules solid-state laser it'll be about a hundred yards long and will consist of an array of 20 laser beams these beams will all be focused on a pellet in a target chamber delivering more than 25 trillion watts of power in less than a billionth of a second lots of people ask us how we can design a laser fusion reactor that would ignite about ten of these small pellets every second time after time well it involves a lot of moderately sophisticated technology the theory is already fairly advanced meanwhile in the laboratory we have recently compressed and heated a pellet with a laser and released fusion energy to have a commercial laser fusion reactor we need to build a laser a thousand times more powerful than any laser presently available it's a difficult challenge the fusion reactors job whether laser or magnetic would be to draw the heat of the plasma off into a fluid circulating around the plasma chamber and then through primary and secondary heat exchanging systems the fusion heat would boil water creating steam to turn a conventional turbine and run a generator the outlook of the American fusion program is best characterized by artist dr. Robert Hirsch in the early 1980s we expect to create many thermal megawatts of fusion energy for the first time and in the late 1980s we are aimed at producing the first electrical power from fusion after we operate a fusion demonstration plant in the mid to late 1990s fusion should then become a commercial reality ready to begin to relieve our dependence on other energy sources as we start into the 21st century

Channel: DOCUMENTARY TUBE

Views: 601,354

Keywords: physics, theory, engineering

Id: LJZvFlo0iNs

Length: 26min 10sec (1570 seconds)

Published: Wed Apr 08 2015