Accelerator step towards fusion

24 November 2009

A collaboration among DOE's Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory, and the Princeton Plasma Physics Laboratory (PPPL) called the Heavy Ion Fusion Science Virtual National Laboratory, headed by Grant Logan of Berkeley Lab’s Accelerator and Fusion Research Division (AFRD), is building an accelerator that will soon allow scientists access to warm dense matter in the laboratory.

“Most accelerators are built to boost relatively small bunches of particles to very high energies,” says Joe Kwan of AFRD, Project Manager of the Neutralized Drift Compression Experiment-II (NDCX-II). “To study warm dense matter, we need a different kind of accelerator, one that can deliver very high currents—a great many particles—in short pulses of moderate energy.”

NDCX II is a linac that operates on the principle of induction, as in a transformer. “The NDCX-II is like a string of transformers, where the beam itself acts as the second winding,” says Kwan. “A high-energy accelerator would send a particle beam through the target like a bullet through paper, but our beam of lithium ions is optimized to deposit most of its energy in the target itself, heating it instantly to warm dense matter.”

Livermore’s John Barnard, who with Ron Davidson of PPPL is a Deputy Director of the Virtual Lab, says, “The object is to reach the warm dense matter stage quickly, giving us time to measure its properties before it boils away.”

While warm dense matter is a field of study in itself, fusion energy is much on the minds of NDCX-II’s builders. “On the one hand, the U.S. is a major participant in ITER, the international tokamak project located in France that’s studying magnetic fusion,” says Logan. But the other major approach to controlled fusion is inertial confinement, in which a fuel capsule is hit by energetic “driver” beams from all directions, causing it to implode and then ignite in a miniature thermonuclar explosion.

Although Livermore’s National Ignition Facility (NIF) is an inertial confinement facility optimized for studying nuclear stockpile stewardship, not power production, Logan says, “NIF will be the first to demonstrate the scientific basis for inertial fusion energy through ignition, fusion, and energy production.”

But NIF’s big glass lasers can only deliver a few shots a day without active cooling. Power plants must operate near-continuously, and induction acceleration is projected to use energy far more efficiently than glass laser technology. Once the fundamentals of capsule ignition and implosion are understood at NIF, says Barnard, “we’ll be prepared to look at more practical questions for future drivers.”

Construction of NDCX-II began in July, aided by stimulus funding from the American Recovery and Reinvestment Act, and is expected to be completed in March of 2012 at a cost of only $11 million.




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