Fusion Reactor Size
Date: Around 1993
What are the limits to the size of a fusion reactor? I have read
Sci-Fi stories that include the hero carrying a portable generator and heard
rumors about a (discontinued) experimental fusion aircraft. I would guess
that you must have a certain mass to keep the reaction going, but what is the
The basic process of a fusion reactor has no real minimum mass.
But the complex equipment required to keep it going and make itefficient is
enormous. (With present technology) The basic process just needs a few atoms
of tritium or deuterium. It is the equipment that brings the atoms together
at high velocity or heats them to high temperature that is complicated and
bulky. This is quite different from a fission reaction, where a minimum mass,
called the critical mass, is needed. I think the experimental nuclear
airplane used a fission reactor. A typical critical mass for a fission
reaction would be several kilograms. This would be very portable, if it was
not for the shielding needed to keep from frying everybody in the vicinity.
Plus, you need cooling and heat exchangers to use the heat that is produced.
Both fusion and fission reactors put out heat as their primary method of
Actually, so far no fusion experiment has produced any more power
than went into heating the stuff up in the first place. That means that not
only do we not have portable generators, we do not have ANY fusion reactors
that actually produce power. There is actually a proverbial "20 year" effect
involved - reactors planned for 20 years in the future should finally be
producing power, maybe even commercially. Unfortunately, it hss sort of been
that way for the past 30 years or so.
Click here to return to the Physics Archives
Update: June 2012