A second-generation approach to controlled
fusion power involves combining helium-3 (
32He) and
deuterium (
21H). This reaction produces a
helium-4ion (
42He) (like an
alpha particle, but of different origin) and a high-energy
proton (positively charged hydrogen ion) (
11p). The most important potential advantage of this fusion reaction for power production as well as other applications lies in its compatibility with the use of
electrostatic fields to control fuel
ions and the fusion protons. Protons, as positively charged particles, can be converted directly into
electricity, through use of
solid-stateconversion materials as well as other techniques. Potential conversion efficiencies of 70% may be possible, as there is no need to convert proton energy to heat in order to drive a
turbine-powered
electrical generator[citation needed].
There have been many claims about the capabilities of helium-3 power plants. According to proponents, fusion power plants operating on
deuteriumand helium-3 would offer lower capital and
operating costs than their competitors due to less technical complexity, higher conversion efficiency, smaller size, the absence of radioactive fuel, no air or water
pollution, and only low-level
radioactive waste disposal requirements. Recent estimates suggest that about $6 billion in
investment capital will be required to develop and construct the first helium-3 fusion
power plant. Financial breakeven at today's wholesale
electricity prices (5 US cents per
kilowatt-hour) would occur after five 1-
gigawatt plants were on line, replacing old conventional plants or meeting new demand.
[53]
The reality is not so clear-cut. The most advanced fusion programs in the world are
inertial confinement fusion (such as
National Ignition Facility) and
magnetic confinement fusion (such as
ITER and other
tokamaks). In the case of the former, there is no solid roadmap to power generation. In the case of the latter, commercial power generation is not expected until around 2050.
[54] In both cases, the type of fusion discussed is the simplest: D-T fusion. The reason for this is the very low
Coulomb barrier for this reaction; for D+
3He, the barrier is much higher, and it is even higher for
3He–
3He. The immense cost of reactors like
ITER and
National Ignition Facility are largely due to their immense size, yet to scale up to higher plasma temperatures would require reactors far larger still. The 14.7 MeV proton and 3.6 MeV alpha particle from D–
3He fusion, plus the higher conversion efficiency, means that more electricity is obtained per kilogram than with D-T fusion (17.6 MeV), but not that much more. As a further downside, the rates of reaction for
helium-3 fusion reactions are not particularly high, requiring a reactor that is larger still or more reactors to produce the same amount of electricity.
To attempt to work around this problem of massively large power plants that may not even be economical with D-T fusion, let alone the far more challenging D–
3He fusion, a number of other reactors have been proposed – the
Fusor,
Polywell,
Focus fusion, and many more, though many of these concepts have fundamental problems with achieving a net energy gain, and generally attempt to achieve fusion in thermal disequilibrium, something that could potentially prove impossible,
[55] and consequently, these long-shot programs tend to have trouble garnering funding despite their low budgets. Unlike the "big", "hot" fusion systems, however, if such systems were to work, they could scale to the higher barrier "
aneutronic" fuels, and therefore their proponents tend to promote
p-B fusion, which requires no exotic fuels like helium-3.