Where does fusion occur?
Solar/Stellar fusion
Why does the sun really shine? Fusion! They Might Be Giants breaks it down for you.
The most obvious example of natural fusion is our own sun. Fusion reactions in the sun give off energy mostly in the forms of visible and infrared light (heat). It is a self-sustaining process, meaning that the products of the reaction can fuel the next reaction, lasting for billions of years until its supply of fuel (primarily hydrogen and helium) runs out. The sun's large mass has enough gravity to create the high-pressure environment necessary for fusion to occur.
As you will read later in the site, Hans Bethe published a paper in 1938 that explained how stars like the sun fuse hydrogen into helium.
Laboratory-based fusion
Scientists have been working across international lines to research fusion since the early 20th century to unlock mysteries in outer space and efficiently provide electricity to the world.
The zeta-pinch system was invented in 1946 by George Paget Thomson and Moses Blackman and is commonly referred to as the "Z-pinch," was the earliest attempt to create fusion in a lab. It operated by confining the plasma using the Lorentz force, which states that when a current is run in the same direction through two conductors, they will be pulled toward each other, which will confine the plasma. The plasma created in Z-pinch devices was unexpectedly unstable, and this issue was not resolved until the previously classified UK project ZETA. Upon examination by US scientists, the measurements taken from ZETA were proven to be inaccurate (fusion had not actually occurred), and the Z-pinch fell out of favor.
The American answer to ZETA and the Z-pinch was a more toroidal machine called the Stellarator. Invented by Lyman Spitzer in 1950 at the Princeton Plasma Physics Laboratory, it uses a solenoid, or a long spiraled wire, bent into a ring to confine the plasma. However, the shape of the plasma allowed particles to drift out of the confinement area, so Spitzer twisted one end of the solenoid 180 degrees to make a figure 8 shape, and bent the figure 8 so that no coils would touch. This reduces the net force on a particle whether it's traveling on the inner or outer curve of the plasma. The Stellarator fell out of popularity in the 1970's when the tokamak design proved to be more successful.
Today, researchers are focusing on the tokamak as the most efficient machine for creating fusion. Proposed by Soviet researchers Andrei Sakharov and Igor Tamm, its name is an acronym for a Russian phrase meaning "toroidal chamber with axial magnetic field." It uses magnetic coils to create a magnetic field 100,000x that of the Earth to confine the plasma and levitate it away from the cooling walls of the tokamak. There are over 180 tokamaks constructed today. The largest tokamak project is the International Thermonuclear Experiment Reactor (ITER), based in Southern France; its mission is to finally dispel the notion that fusion is always fifty years away and use the technology for efficient electricity production. An interactive diagram of its components can be found on the ITER website (iter.org).
Nuclear weapons
Nuclear science is not entirely constructive- it is perhaps most widely known for its use in bombs and weaponry.
The Manhattan Project, headed by J. Robert Oppenheimer and Major General Leslie Groves, led to the development of the first atomic bombs (they utilized fission) that were dropped on Hiroshima and Nagasaki. From there, the "arms race" between the USSR and USA took off: both sides engaged in extensive testing of powerful nuclear weapons. Initially dreamed up by Enrico Fermi and Edward Teller, these newer weapons ignited with fission, which triggered the fusion cycle with the tremendous amount of energy it released.
The Manhattan Project, headed by J. Robert Oppenheimer and Major General Leslie Groves, led to the development of the first atomic bombs (they utilized fission) that were dropped on Hiroshima and Nagasaki. From there, the "arms race" between the USSR and USA took off: both sides engaged in extensive testing of powerful nuclear weapons. Initially dreamed up by Enrico Fermi and Edward Teller, these newer weapons ignited with fission, which triggered the fusion cycle with the tremendous amount of energy it released.
Today, nuclear weapons have proliferated to such an extent that they are proving to be one of the biggest threats to national security across the globe. With extremist governments such as those of Iran and North Korea alleging that they possess nuclear power, international organizations are stepping in to prevent nuclear war from breaking out. Treaties such as the Nuclear Non-Proliferation Treaty and UN Security Council sanctions are working to prevent mass destruction and maintain peace.