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1 / 2 Fusion Energy: `Yes We Can' by Laurence Hecht Editor-in-chief, 21st Century Science & Technology January 11, 2009
John Nuckolls, former director of Lawrence Livermore National Laboratory, has proposed a 10-year strategy for achieving laser fusion, which he said could be accomplished with 10 percent of President-elect Obama's $150-billion projected energy program. The contents of Dr. Nuckolls' proposal addresses issues of science not well-known to today's general public, but which should be better known.
In laser fusion, a tiny target
of deuterium, sometimes combined with tritium, is compressed by a shock wave which
is produced by focused laser beams. The shock causes the deuterium, a naturally occurring
isotope of hydrogen present in seawater, and tritium to combine, forming a nucleus
of helium and a neutron.
The mass of the resulting helium nucleus is less
than the component nuclei, and the mass difference is released as energy, according
to the famous equation E = mc2. The energy release per fusion is several times greater than that produced by the fission of a uranium nucleus, which is millions of times greater than the energy released by burning of a molecule of oil or natural gas.
The heat of fusion energy can thus drive electrical turbines with far greater efficacy than any known power source, and can also be utilized in a device known as the fusion torch, to break down raw ore and even garbage
into its constituent elements.
Dr. Nuckolls,
who led research on laser fusion at the national laboratory for many years, proposed
"four steps to fusion power." (1) build an efficient high-average power laser module,
a factory for producing laser targets, and a fusion chamber; (2) build a surged, heat capacity
inertial fusion energy system; (3)build a fusion engine; (4) build a fusion power plant.
Fusion energy by laser ignition, known more generally as inertial confinement, has already been repeatedly demonstrated, and was one of the leading paths being pursued when the national fusion energy program was effectively dismantled in the 1980s.
Nuckolls was addressing the means needed to develop a laboratory proof-of-principle demonstration into a commercially workable energy generation project.
Inertial
confinement production of fusion energy is related to the means by which a hydrogen
bomb is detonated, and thus emerged from the national laboratories as one of the peaceful
spin-offs of military research. In one method of laser fusion known as indirect drive, a
closed chamber known as a hohlraum is used to focus thermal x-rays produced by the
laser heating, which in turn can drive the nuclear fusion.
Indirect drive hohlraum targets
are used to simulate thermonuclear weapons tests. A key to the technique involves understanding the singularity which occurs upon formation of a shock wave.
Soviet research in the field was stimulated by study of the famous paper by
19th century mathematical physicist Bernhard Riemann, which had predicted the appearance
of sonic shock waves decades before their experimental verification.
Other methods of inertial confinement fusion do not require lasers. These include the Z-pinch, in which the vaporization of fine wires by an intense electrical current causes a 2 / 2 compression of the wire (Z-pinch) that produces x-rays which drive the fusion of the target.
In another method, recently proposed by Dr. Friedwardt Winterberg, the high-voltage discharge of an early type accelerator known as a Marx Generator
produces a very powerful instantaneous magnetic
field pressure which compresses a cone-shaped deuterium-tritium target, using an ingenious
geometry.
Dr. Nuckolls made his "Yes we can" proposal at the
annual meeting of Fusion Power Associates held in Livermore, Calif. Dec. 3-4, 2008,
where he and fellow fusion pioneer Richard F. Post were presented Special Awards for
their pioneering contributions to fusion energy development. Dr. Post, now 90-years-old,
was a leader in developing the other main branch of fusion power research known as
magnetic confinement.
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