A Bigger Bang for our Buck? A Look at the Naval Research Lab’s Laser Fusion Program

Most international fusion research to date has followed the tokamak model, which uses magnetic fields to heat and squeeze the hydrogen plasma: the United Kingdom’s Joint European Torus (JET), Japan’s JT-60, and the world’s largest tokamak, ITER, currently being assembled in France, are among the most well-known—and most expensive—fusion projects.

Inside the doughnut shaped JET tokamak

Some scientists in the U.S. have taken the inertial confinement fusion (ICF) route, using lasers to initiate a reaction like the fusion that takes place inside the sun or a hydrogen bomb. An ICF experiment is underway at the Lawrence Livermore National Laboratory’s National Ignition Facility (NIF). But another laser fusion facility exists, and it’s located right here in Washington.

Steve Obenschain’s team of researchers and developers at the Naval Research Lab’s (NRL) Laser Fusion Program are spearheading a directly driven target approach to inertial fusion energy using an intense array of krypton fluoride (KrF) lasers. KrF has the deepest UV light of all high energy ICF lasers and can provide the most uniform target illumination, qualities that could substantially help towards obtaining high target gains needed for future fusion power plants.

The direct drive approach directs laser beams straight to the tiny fuel pellet (usually made from a blend of two Hydrogen isotopes, deuterium and tritium), which the NRL team says is simpler and more efficient than indirect drive, in which the pellet is placed inside a cylindrical container, called a hohlraum, that converts the driver laser beams into x-rays to compress the fuel. The main disadvantage of indirect drive is that the hohlraum uses a considerable amount of energy to heat itself, significantly reducing the overall efficiency of laser-to-target energy transfer.

Completed in 1995, NRL’s Nike is the largest KrF laser facility being used for direct drive target experiments. NRL is using the adjoining Electra KrF laser facility to develop efficient and durable high-repetition rate technologies. Already capable of producing 90,000 continuous shots in a span of 10 hours (about 2.5 Hz), the Electra laser is expected to achieve the 5 Hz rate needed for fusion energy in the coming years.

The NRL team has made impressive progress in the development of direct drive IFE on relatively modest funds; NRL has requested $5 million for fiscal year 2012 to continue its experiments, compared to the University of Rochester’s $62.5 million request for its Omega facility and the $48 million Sandia National Laboratory’s Z facility has requested. NIF has cost more than $3.5 billion, and the US contributed nearly $80 million to ITER in fiscal year 2011, just a small fraction of its $7 billion total budget.

It’s clear that the technologies for clean energy don’t come cheap. But it’s important to continue funding R&D for these fusion projects, which are steadily making progress every day; if all goes well for the team at NRL, they could be just eight years away from using a full-scale KrF laser beam in a fusion test facility.

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