what is fusion? - general atomicsfusioned.gat.com/images/pdf/what_is_fusion.pdf · what is fusion?...

WHAT IS FUSION? Fusion is the process that powers the sun and the stars. It is the reaction in which two atoms of hydrogen combine together, or fuse, to form an atom of helium. In the process some of the mass of the hydrogen is converted into energy. The easiest fusion reaction to make happen is combining deuterium (or “heavy hydrogen) with tritium (or “heavy-heavy hydrogen”) to make helium and a neutron. Deuterium is plentifully available in ordinary water. Tritium can be produced by combining the fusion neutron with the abundant light metal lithium. Thus fusion has the potential to be an inexhaustible source of energy. To make fusion happen, the atoms of hydrogen must be heated to very high temperatures (100 million degrees) so they are ionized (forming a plasma) and have sufficient energy to fuse, and then be held together i.e. confined, long enough for fusion to occur. The sun and stars do this by gravity. More practical approaches on earth are magnetic confinement, where a strong magnetic field holds the ionized atoms together while they are heated by microwaves or other energy sources, and inertial confinement, where a tiny pellet of frozen hydrogen is compressed and heated by an intense energy beam, such as a laser, so quickly that fusion occurs before the atoms can fly apart. Who cares? Scientists have sought to make fusion work on earth for over 40 years. If we are successful, we will have an energy source that is inexhaustible. One out of every 6500 atoms of hydrogen in ordinary water is deuterium, giving a gallon of water the energy content of 300 gallons of gasoline. In addition, fusion would be environmentally friendly, producing no combustion products or greenhouse gases. While fusion is a nuclear process, the products of the fusion reaction (helium and a neutron) are not radioactive, and with proper design a fusion power plant would be passively safe, and would produce no long-lived radioactive waste. Design studies show that electricity from fusion should be about the same cost as present day sources. We’re getting close! While fusion sounds simple, the details are difficult and exacting. Heating, compressing and confining hydrogen plasmas at 100 million degrees is a significant challenge. A lot of science and engineering had to be learned to get fusion to where we are today. Both magnetic and inertial fusion pro- grams expect to build their next experiments that will reach ignition and produce more energy than they consume shortly after the year 2000. If all goes well, commercial application should be possible by about 2020, providing humankind a safe, clean, inexhaustible energy source for the future. Achieved (DD) ITER Power Plant TFTR TFTR/JET JET JT–60U TFTR JET/TFTR DIII–D DIII Alcator C PDX 1,000 Fusion Power MW th kW th W th 100 10 1,000 100 10 1,000 100 10 1 PLT 1970 Alcator C: Massachusetts Institute of Technology DIII & DIII–D: General Atomics Tokamak Experiment ITER: International Thermonuclear Experiment Reactor JET: Joint European Torus JT–60U: Japanese Tokamak Experiment TFTR: Princeton Plasma Physics Laboratory PDX: Princeton Divertor Project PLT: Princeton Large Tokamak 1980 1990 2000 2010 Achieved (DT) Projected (DT) House Light Bulb E=mc 2 Deuterium Helium Neutron Tritium D T n n P P n n He n P n n P Fusion Fusion Magnetic Confinement Magnetic Field Inertial Confinement Gravitational Confinement Sun Fuel Pellet Intense Energy Beams + - Nucleus Electron

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Page 1: WHAT IS FUSION? - General Atomicsfusioned.gat.com/images/pdf/what_is_fusion.pdf · WHAT IS FUSION? Fusion isthe process that powers the sun and the stars. ... Confinement Magnetic

To make fusion happen, the atoms of hydrogen must be heated tovery high temperatures (100 million degrees) so they are ionized(forming a plasma) and have sufficient energy to fuse, and then be held

together i.e. confined,long enough for fusionto occur. The sun andstars do this by gravity.More practical approaches on earth are magnetic confinement, where a strong magnetic field holds the ionizedatoms together while they are heated by microwaves or otherenergy sources, and inertial confinement, where a tiny pellet offrozen hydrogen is compressed and heated by an intense energybeam, such as a laser, so quickly that fusion occurs before theatoms can fly apart.

Who cares? Scientists have sought to make fusion work onearth for over 40 years. If we are successful, we will have anenergy source that is inexhaustible. One out of every 6500atoms of hydrogen in ordinary water is deuterium, giving a

gallon of water the energy content of 300 gallons of gasoline. In addition, fusion would be environmentallyfriendly, producing no combustion products or greenhouse gases. While fusion is a nuclear process, the products of the fusion reaction (helium and a neutron) are not radioactive, and with proper design a fusion power plant would be passively safe, and wouldproduce no long-lived radioactive waste. Designstudies show that electricity from fusion shouldbe about the same cost as present day sources.

We’re getting close! While fusion soundssimple, the details are difficult and exacting.Heating, compressing and confining hydrogenplasmas at 100 million degrees is a significantchallenge. A lot of science and engineeringhad to be learned to get fusion to where we aretoday. Both magnetic and inertial fusion pro-grams expect to build their next experimentsthat will reach ignition and produce more energythan they consume shortly after the year 2000.If all goes well, commercial application shouldbe possible by about 2020, providinghumankind a safe, clean, inexhaustible energysource for the future.

Achieved (DD)

ITER PowerPlant

TFTRTFTR/JET

JET

JT–60UTFTRJET/TFTR

DIII–DDIII

Alcator C

PDX

1,000

FusionPower

MWth

kWth