Using magnetic fields and thermonuclear hydrogen plasmas to solve the energy crisis and global warming

ITER reactor

Schematic of the ITER fusion reactor currently being built in Cadarache, France, by a collaboration of 34 countries to establish by about 2025 whether fusion of hydrogen isotopes obtained from sea water and lithium will solve the global energy crisis and global warming crisis in politically and environmentally acceptable ways. The person standing in the lower right corner of the figure gives a sense of the reactor's size.

The human race is currently faced with the daunting technological challenge of producing enough energy to support a growing population of over seven billion people in an environmentally, economically, and politically acceptable way that is also sustainable over hundreds of years.

A promising way to solve this challenge is to generate energy by the fusion of the positively-charged nuclei of the hydrogen isotopes deuterium and tritium. Enough deuterium is available in the ocean to sustain a population of eight or more billion people for thousands of years, and the waste products of a fusion reactor are small amounts of helium gas (which is inert and so harmless), modest amounts of short-lived radioactive substances, and heat which is used to generate electricity. Fusion reactors can not undergo a melt-down like a fission reactor, and fusion reactors do not produce nuclear wastes that can be used to make nuclear weapons.

Building a fusion device is a great scientific and technological challenge that draws on all areas of physics, but especially on ideas discussed in Physics 162 related to electric and magnetic fields. The idea is to use ultracold superconducting magnets (at about ten degees above absolute zero) to generate strong magnetic fields that act as a "bottle" that will confine a superhot (300,000,000 K!) plasma of electrons and of positively charged deuterium and tritium nuclei in a toroidal region so that the nuclei, through their large speeds, can overcome their electrical repulsion and so approach each other closely enough (about one proton diameter) to undergo fusion that produces He nuclei and neutrons with an excess of energy. The kinetic energy of the fusion products is used to heat water to produce steam that turns turbines to generate the electricity used by people and by industry. The electricity is produced by taking advantange of one of the fundamental laws of electrodynamics, Faraday's law, which describes mathematically how a time-varying magnetic field produces an electric field that can drive currents in wires.

The challenge of heating an initially room-temperature gas of hydrogen to 300,000,000 K in a controlled way itself requires multiple applications of Physics 162 ideas: using Faraday's law to create an enormous axial electrical current to start the heating of the plasma, shining high-intensity microwaves that are tuned to resonant frequencies of the gyrating electrons and nuclei, and using electric fields to accelerate deuterium and tritium nuclei close to the speed of light, and then shooting the resulting high-intensity high-energy neutral beam into the plasma to heat the plasma and fuel it. In turn, measuring the electric and magnetic fields of the plasma by various devices gives important information about what the plasma is doing as it undergoes fusion.

Despite the enormous attraction of fusion and despite a world-wide collaboration that has lasted over fifty years and that has cost tens of billions of dollars, a working reactor has not yet been successfully designed. The main difficulty again involves 162 physics: the rapid motion of the charged nuclei and electrons (the latter move at about one hundredth the speed of light!) constitutes an electrical current that creates a substantial magnetic field. This field, when combined with the magnetic field generated by the external superconducting magnets, can open up "holes" in the magnetic bottle that causes the entire plasma to leak out within a few microseconds, bringing fusion to a halt. It is a difficult physics and math problem to determine how to adjust the hundreds of magnets in real time to compensate for the magnetic field generated by the complex plasma dynamics and so keep the plasma confined for sustained energy generation.

162 Home Page       Department of Physics