Waiting for ignition. New report says future research into inertial confinement fusion hinges on the ability of the National
Ignition Facility, a giant laser device in California, to create a burning plasma using tiny polished capsule filled with cryogenic (supercooled) hydrogen
Credit: Lawrence Livermore National Laboratory
The United States should embark on a coordinated national research program into inertial confinement fusion—but only after researchers successfully
demonstrate the scientific basis of the technology by creating a burning plasma in the laboratory, an expert panel assembled by the U.S. National Academies
recommends in a report released today. That conclusion will pile the pressure on the National
Ignition Facility (NIF), the $3.5 billion laser fusion project at the government's Lawrence Livermore National Laboratory in California. NIF, which was
completed in 2009, was supposed to have achieved ignition—a burning plasma that
produces at least as much energy as it consumes—by last year. Having missed that deadline, however, NIF is now awaiting a decision from Congress about its future funding. In the meantime, the U.S.
Department of Energy (DOE) asked the National Academies to explore what steps the United States should take to develop fusion power if NIF does eventually
Fusion aims to generate power by melding light nuclei together to make larger ones, a process during which some of the nuclear mass is converted into
energy. But creating fusion requires temperatures of more than 50 million°C and huge pressures. Inertial confinement fusion (ICF) seeks to create those
conditions by taking a tiny capsule of fusion fuel (typically a mixture of the hydrogen isotopes deuterium and tritium) and crushing it at high speed using
some form of "driver," such as lasers, particle beams, or magnetic pulses.
ICF has received piecemeal funding over the years from a variety of sources, but the majority has come from DOE's National Nuclear Security Administration
(NNSA), which manages nuclear weapons. For nearly 2 decades, NNSA has supported the construction and operation of NIF because ICF's miniature explosions
can aid weapons scientists who are trying to maintain the U.S. nuclear weapons stockpile. NIF has become the world's flagship for ICF, and today's report
says its ability to successfully create a burning plasma will be key to taking the next steps toward a prototype fusion power plant. "The achievement of
ignition on NIF should be an important trigger for the government to decide if it should launch a national coordinated [inertial fusion energy] program," says committee
co-chair Ronald Davidson of Princeton Plasma Physics Laboratory in New Jersey.
The Livermore lab has been heavily promoting its vision of the next step, dubbed Laser Inertial Fusion Energy (LIFE).
But the NAS committee favors a broad-based program that would give equal billing to alternative laser-based approaches from the University of Rochester in
New York and the Naval Research Laboratory, as well as a magnetic pulse system being explored by DOE's Sandia National Laboratory and a particle beam
system from Lawrence Berkeley National Laboratory. "If the government decides to go ahead, there should be a well thought out program to test approaches at
the appropriate scale," Davidson says. "But if a particular approach proves too expensive [to be commercial], one should be prepared to take it off at the
next exit ramp."
DOE's existing ICF program is already under pressure to broaden its scope because of the difficulty that NIF is having getting to ignition. The proposal
before Congress seeks funding to also pursue magnetic pulse fusion at Sandia and the rival laser technique called polar direct drive, which would be
performed on NIF. "We should do all we can to get more data on polar direct drive at NIF. It gets an order of magnitude more energy onto the target," says
Robert McCrory, director of the Laboratory for Laser Energetics at the University of Rochester.
The report also highlights the fact that while ICF researchers have focused most of their effort on developing drivers and demonstrating ignition, other
areas of research essential to commercial exploitation have received less attention. These include reaction chambers that can withstand repeated blasts for
years on end, lasers that can fire high-energy pulses many times per second, and techniques to manufacture the tiny target capsules—a commercial plant
may use more than a million per day. "To keep the cost of electricity low, there will need to be an R&D program to demonstrate the technology to
manufacture targets on an industrial scale cost-effectively," Davidson says.
It is unlikely, however, that such a program would start any time soon. Funding for fusion in general is extremely tight because of general government
budget-cutting and the high cost of the ITER fusion reactor project in France, of which the United States is a partner. (ITER uses a different approach,
called magnetic confinement fusion.) Nevertheless, ICF researchers would very much like to hear that starting pistol from NIF. "Until you demonstrate
ignition, you don't have a path to energy," McCrory says.
*Clarification 11:20 a.m., 21 February: Davidson thinks "the achievement of ignition on NIF should be an important trigger for the government to decide if it should launch a national coordinated
[inertial fusion energy]," not an ICF program, as initially reported.