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National Academy calls for fusion energy roadmap

08 Mar 2012

Interim report recommends making effective use of the National Ignition Facility to assess energy-generating potential.

A committee at the US National Academy of Sciences (NAS) has recommended that the National Ignition Facility (NIF) becomes a major part of a drive to assess the feasibility of inertial fusion as a practical source of energy.

At present, the 192-laser NIF is focused primarily on fundamental science and addressing technical issues related to stewardship of the country’s nuclear weapons stockpile – but in recent months the project’s senior management team have increasingly highlighted the energy-generating potential of the technology.

Now, an interim report based on the first four meetings of the Academy's Committee on the Prospects for Inertial Confinement Fusion Energy Systems has concluded that enough has been achieved to warrant significant further investigation.

“An intense national campaign is under way to achieve ignition conditions on the NIF, and there has been considerable initial technical progress towards this major goal, although progress has been slower than initially anticipated,” wrote the committee.

Its recommendation is that “planning should begin for making effective use of NIF as one of the major program elements in an assessment of the feasibility of inertial fusion energy”.

In its current guise, NIF is designed to deliver single, intense bursts of laser energy to a deuterium-tritium target. At the recent Photonics West conference, NIF’s director for laser fusion energy Mike Dunne said he was hopeful that fusion with energy gain (or “burn”) would be demonstrated for the first time this year.

However, NIF has not been designed as a practical source of energy. For that to happen, a deuterium-tritium target would need to be ignited many times per second, and although Dunne and NIF director Ed Moses have outlined ways in which streams of targets could be dropped into a chamber and ignited with a high-repetition-rate laser, these ideas remain at a very early stage.

Technology roadmap
In its report, the NAS committee highlighted that it was pleased to see that the inertial confinement community has begun a process to develop a consensus on critical issues and future activities geared towards fusion energy.

“This important effort should be encouraged, with the overall goal of developing options for a community-based roadmap for the development of inertial fusion as a practical energy source,” it wrote.

One of only two conclusions that the committee has reached so far is that it is too early to identify any particular type of laser or other technology as the preferred option to drive inertial confinement fusion in an energy plant.

NIF’s current design features flashlamp-pumped Nd:glass lasers that emit in the infrared and are up-converted to the ultraviolet region before being aimed at the target. Both Dunne and Moses have said previously that the rapid progress made in high-efficiency laser diodes since NIF was first built make these devices more obvious choices for a future fusion energy facility – with Moses having identified diode pumping of ytterbium-doped strontium fluoro-apatite (Yb:S-FAP) crystals as a strong candidate technology.

The NAS committee suggests that krypton fluoride excimer lasers – capable of direct ultraviolet emission and widely deployed in lithography stepper systems used by the semiconductor industry – might also be an option.

Its interim report is based on four initial committee meetings that took place in 2011, and was submitted to the National Research Council (NRC) for review back in August 2011. Following two subsequent meetings, NAS is set to publish its final report on the topic this summer.

The committee says that the interim report is aimed at assisting the US Department of Energy in planning its future-year budget requests for inertial fusion energy, while the final report is due to provide a full assessment of the prospects for the approach, with specific regard to cost targets and R&D objectives associated with developing a demonstration plant.

In last month’s FY2013 budget request, the DOE said that it intended to cut its spending on science related to “high energy density laboratory plasmas” (HEDLP), which covers inertial fusion energy, from the $24.7 million enacted in 2012 to $16.9 million. The department added that spending priorities would need to be reassessed, and that the final NAS/NRC study report would inform a competitive review of the program.

Mike Dunne interview with SPIE.TV:

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