A Collaborative National Center for Fusion & Plasma Research

Fusion Basics

What is Plasma?

Plasma is a state of matter along with solids, liquids and gases. It consists of a partially-ionized gas, containing ions, electrons, and neutral atoms.

So what does that mean?

In a plasma, some electrons are freed from their atoms, allowing current  and electricity to flow.  In fact, one of the few naturally-occurring plasmas found here on Earth is lightning!

Can you think of other plasmas?

  • Fluorescent light bulbs contain mercury plasma.
  • Stars, such as the sun are hot balls of plasma.
  • Aurora Borealis  and Aurora Australis
  • Fusion reactors, like NSTX, use plasma to fuse atoms to make energy.
  • Plasma displays use small cells of plasma to illuminate images.

What is Fusion?

Light atoms like hydrogen (one proton and one neutron) can fuse together so tightly that they release energy.  This will only happen if the two positively charged nuclei get close enough that they overcome the electric force pushing them apart.  When the nuclei get close enough, the force that binds protons and neutrons together, the strong force, takes over and pulls the nuclei even closer together.

The sun’s core is a natural fusion reactor. Before the sun formed, it was a cloud of gas mostly made up of hydrogen and some helium.  At some point, the cloud became so massive that gravity caused it to collapse in on itself and it formed a star. Numerous collisions in the core of the sun freed electrons from ions, forming a plasma state. Fusion began in the sun when collisions between ions became so frequent that the ions got close enough to fuse together.

The sun uses gravity to get its nuclei close enough and hot enough to start fusion. On Earth, researchers are trying to build fusion reactors of their own. They try to get atoms close enough by maximizing the number of ions in a small region and the amount of time that they stay close together.  In order to do that, reactors get heated to temperatures much hotter than the core of the sun (>100, 000, 000 °C) which converts hydrogen gas into a hydrogen plasma. Strong magnetic fields or high-powered lasers then confine the plasma into a small controllable region where fusion can happen.

Tokamak-style fusion reactors, like NSTX, pump most of the extracted energy into fast neutrons which can be collected in a lithium bath.  The heated lithium runs heats a tank of water which then powers a steam engine.

Further Reading

Please check out these online sources for more information about fusion and fusion-related topics:

U.S. Department of Energy
Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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