Fusion:Basic Principles, Current Progress and ITER Plans

MODIFIED FROM:

Mohamed Abdou

Distinguished Professor, Mechanical and Aerospace Engineering Department

Director, Center for Energy Science and Technology Advanced Research (CESTAR)

Director, Fusion Science and Technology Center

University of California Los Angeles (UCLA)

Plenary Talk presented at the 9th International Cairo Conference on Energy and Environment

What is Nuclear Fusion?

• Nuclear Fusion is the energy-producing process taking place in the core of the Sun and stars

• The core temperature of the Sun is about 15 million °C. At these temperatures hydrogen nuclei fuse to give Helium and Energy. The energy sustains life on Earth via sunlight

Energy Released by Nuclear Reactions

• Light nuclei (hydrogen, helium) release energy when they fuse (Nuclear Fusion)

• The product nuclei weigh less than the parent nuclei

• Heavy nuclei (Uranium) release energy when they split (Nuclear Fission)

• The product nuclei weigh less than the original nucleus

Energy Released by NuclearFusion and Fission

• Fusion reactions release much higher energies than Fission reactions

Fusion Reactions• Deuterium – from water

(0.02% of all hydrogen is heavy hydrogen or deuterium)

• Tritium – from lithium(a light metal common in the Earth’s crust)

Deuterium + Lithium → Helium + Energy

This fusion cycle (which has the fastest reaction rate) is of interest for Energy Production

Plasmas• A Plasma is an ionised gas. A mixture of positive ions

and negative electrons with overall charge neutrality• Plasmas constitute the 4th state of matter, obtained at

temperatures in excess of 100,000 degrees• Plasmas conduct electricity and heat

Self-Sustaining or ‘Ignited’ Plasmas• Deuterium – tritium fusion reaction:

D + T → 4He + n + Energy

The 4He nuclei (‘’ particles) carry about 20% of the energy and stay in the plasma. The other 80% is carried away by the neutrons and can be used to generate steam.

Plasmas become Self-sustaining or Ignited when there is enough power to balance losses from the plasma

• In stars plasma particles (including a’s) are confined mainly by gravity and high plasma densities achieved

• On Earth: – hot dense plasmas can be confined in Magnetic fields (Magnetic

Confinement Fusion)– superdense plasmas can be obtained by imploding solid deuterium-

tritium pellets (Inertial Confinement Fusion)

Fusion in the Sun

• Hydrogen fuses to form helium and 2 positrons and lots of energy.

Further fusion makes heavier elements (but not heavier than

iron in our sun – it’s too small…)

• Once Fe (iron) is reached, no more fusion can occur in stars up to about 5 – 10 times the size of our sun.

Larger Elements Than Iron

• There are lots of elements heavier than iron.• These are formed in supernovae.• Supernovae occur in extremely large stars

Generally speaking, they implode and then explode, sending these larger molecules across the universe.

• Later, gravity pulls them back together in large masses which can eventually become solar systems.

So, how do billions of atoms of one element get back together after being scattered across the

universe?

The answer is gravity first, then density.

By gravitational pull all of the elements come back to together in large masses (planetary nebulae which eventually become planets – take astronomy for the details.

In hot molten rock (which was present for developing planets), denser atoms sink to the center, less dense atoms stay near the surface.

Just as if you place oil and water in a container, the water ends up with the other water, and the oil with the other oil.

Core is Mostly Iron

• So, if the core is mostly iron and gold is more dense than iron, where is most of the gold on Earth?

• If gold is there, how have we found it in the crust?

• The answer is meteorites.