What Matters: August 2008
An Overlooked Solution to the Global Energy Crisis
By Gary J. Linford '62
Fusion powers stars including the sun. Image: NASA.
MIT's publicly announced energy initiatives glaringly undervalue the thermonuclear fusion of hydrogen and helium, which use the virtually inexhaustible resources of deuterium, lithium, and (lunar) He3. Gram for gram, fusion of plentiful lighter elements releases ten billion times as much energy as combusting gasoline with oxygen, without producing any greenhouse gases. Thermonuclear fusion powers the Sun, and we have already made it work here on Earth, although few people outside the field know about this work. As fossil fuel supplies are obviously limited, we do have a profound need to bring fusion power plants on line ASAP.
Detractors argue that we don't know how to make fusion work on Earth. These folks evidently don't remember that Edward Teller demonstrated deuterium/tritium (D/T) inertial confinement fusion (ICF) via the reaction D + T → He4 + 14.2 MeV neutron here, on Earth, at more than full scale way back in 1952. Many called this ICF demonstration the "hydrogen bomb" because Edward needed a fission device to heat a capsule of D/T to the 200-million-degree ignition temperature. However, laser-initiated ICF research achieved >50x liquid D/T density at temperatures of 200 million degrees more than a decade ago. Although the U.S. is withdrawing (again) from the European Union's magnetic confinement ITER project in France, the single shot/day Nd:glass ICF National Ignition Facility at the Lawrence Livermore National Laboratory (LLNL) is nearing completion. Design studies funded by the Department of Energy (DoE) for Prometheus ICF with krypton-fluoride (KrF) laser or heavy ion (HI) ignited ICF power plants were completed in 1992 and released in 1994 for international publication.
Fusion power plant designers choose D/T because it is the
easiest fusion fuel to ignite. By
heating a D/T capsule to 200 million degrees while compressing the fuel to 100x
liquid density, all in a few billionths of a second, the strong force
overpowers the electrostatic repulsion of the two protons, and D/T fuses into
helium plus a fast neutron. Pulsed laser
or HI beams can do this job nicely. In
the Prometheus thermonuclear power
plant design, frozen D/T fuel pellets are injected at a 5 Hz rate into each
fusion reaction cylinder. Pulsed KrF laser
or HI beams heat and compress the hydrogen fuel pellets in a few nanoseconds,
releasing 109 J per pulse corresponding to an average power of 5 GW
of fusion power/cylinder assuming an individual pellet "gain" of
200x. With a 20-cylinder system, a 100
Hz Prometheus plant could produce 100,000,000 kW of fusion power—compare that
with an unsteady 100 kW wind turbine.
The cylinder walls of each reaction chamber incorporate lithium to
capture the 14.2 MeV neutrons (n) via the reaction Li6 + n →
Li7 →
He4 + T, a process that replaces the tritium used in the primary
fusion reaction while releasing heat. This
fusion heat is then used to produce steam to drive turbine generators. Each pair of reactions yields 2.8 picojoules,
consumes 3.3x10-24 g of deuterium and 10-23 g of lithium,
while producing 1.3x10-23 g of non-radioactive He4 "ash." Lithium and deuterium are also not
radioactive. The process is inherently safe owing to the small amount of D/T in
each fuel capsule. If something goes
wrong, the ICF reactor simply shuts down.
MIT's seminal role in laser fusion began back in 1962 when newly arrived
Charles Townes HM, a 1961 Nobel laureate in physics for inventing the laser, encouraged
an MIT student (me) to demonstrate as part of an undergraduate physics thesis that
high-power lasers can be focused down to dimensions of the order of a
wavelength of light, turning an incident energy density of 1 J/cm2
into 200 million J/cm2, thereby opening the doors to use pulsed lasers
to achieve hydrogen thermonuclear fusion. Edward Teller no longer needed
a fission device to reach D/T fusion ignition temperatures. By 2008, the
DoE and its predecessors have collectively spent $10 billion to demonstrate
(successfully) laser fusion of D/T. The physics has been proven, and the
time is ripe to engineer reliable power plant subsystems.
A single pickup truck can deliver sufficient deuterium and lithium to equal the energy output associated with combusting 25,000 railroad cars filled with coal. The two 1992 Prometheus fusion power plant designs featured innovative uses of non-linear optics to combine KrF laser beams for the laser ignition system and implemented advanced accelerator concepts, self-pinched HI beams with superconducting storage rings for the heavy ion ignition system. The full-scale development of two competing ICF ignition systems was proposed by the Prometheus designers to insure that at least one could qualify for meeting the demanding requirements of reliable ICF power plants.
Despite the promise of the Prometheus ICF power plant technologies, during the Clinton administrations Prometheus was not moved into the hardware development phase. Instead, the scientific teams working on ICF power plants were disbanded. Back in 2006, when oil was less than $100/barrel, the Bush-Cheney administration ignored a suggestion made by Senator Michael Enzi (R-WY) to establish a new national laboratory to perfect the delayed ICF power plant technologies. Evidently bringing workable fusion power plants on line is not a priority of our government. But why has MIT today seemed to have lost track of the remarkable 1962 foresight of Charles Townes under whose direction the crucial focusability of high power pulsed lasers was first demonstrated?
Given the successful subscale demonstrations of laser ICF in the U.S., what will be our excuse in 2028 when other nations of the world are selling turnkey ICF power plants to solve the global energy crisis while simultaneously improving their global balance of payments?
About the Author
Gary J. Linford '62 received an SB in physics at MIT as an Alfred P. Sloan Scholar and a PhD in laser physics from the University of Utah. He was a scientist in the laser technology department at Hughes Aircraft from 1963 to 1972, the laser amplifier group leader at Lawrence Livermore National Laboratory from 1973 to 1982, guest scientist at two Max Planck Institutes in Germany in 1978-79 and 1982-83, department manager/chief scientist at TRW from 1983 to 1996, and senior scientist at Pfeifer Science Associates from 1996 to 2008. He managed the ICF ignition system team for the Prometheus ICF power plant design (1990-1994) and has nine laser-related patents pending with three granted. He is married to Dr. Shirley J. Pfeifer.
What Matters is a guest opinion column written by a different MIT alumnus or alumna. The views expressed are entirely those of the author and do not necessarily represent the views of the Alumni Association or MIT. Interested in writing a column? Email whatmatters@mit.edu.
