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Working Science

World's Largest Fast-Growth Crystal

by Rosalind Schrempf, Pacific Northwest National Laboratory

The world's largest fast-growth crystal, weighing 701 pounds, has been grown at Lawrence Livermore National Laboratory (LLNL). The previous record size for such a crystal was 650 pounds.

Lab researcher Randy Floyd poses next to an array of giant fast-growth crystals grown at Lawrence Livermore National Laboratory

Lab researcher Randy Floyd poses next to an array of giant fast-growth crystals grown at Lawrence Livermore National Laboratory. Randy is measuring the dimensions of the world's largest (701 lb.) fast-growth crystal grown in a record 52 days.

The enormous crystal will be sliced into plates a half-inch thick and 16.5 inches square and used in the National Ignition Facility, a giant laser under construction at LLNL that will help maintain the safety and reliability of the nation's nuclear weapons stockpile.

The pyramid-shaped potassium dihydrogen phosphate (KDP) crystal measures approximately 26 inches by 21 inches by 23 inches high and could have grown even larger had scientists not run out of room in their growth tank.

In research led by Ruth Hawley-Fedder, the crystal was grown in a record 52 days using a special rapid-growth technique that delivers twice the yield originally projected.

The crystal-growing process begins by placing a fabricated, thumbnail-sized seed crystal inside a six-foot-high tank filled with nearly a metric ton of supersaturated KDP solution at a temperature of 160° F. The temperature is gradually decreased to maintain supersaturation as the growing crystal extracts salt from the solution.

The researchers achieved the record-size crystal by adding more salt to the solution though a device called a continuous filtration system, which helps maintain crystal quality. Using this system may enable scientists to produce even larger and higher quality crystals in the future.

The crystal plates will be used in the National Ignition Facility to convert the laser's infrared light beams to ultraviolet light just before the beams strike the laser target. The Facility will require as many as 600 crystal plates.

The large-scale rapid-growth crystal growing technique has been shared with commercial crystal suppliers who have already produced about half the required crystals. This technology is expected to save millions of dollars for both construction and later operation of the National Ignition Facility.

This work is supported in part by the Office of Basic Energy Sciences. Contact: Ruth Hawley-Fedder, Lawrence Livermore National Laboratory, hawleyfedder1@llnl.gov.

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