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How a Laser Fusion Experiment Unleashed an Energetic Burst of Optimism [1]
['Kenneth Chang']
Date: 2021-08-17
“The data is pretty obvious,” Dr. Glenzer said.
The improved fusion results also help the National Ignition Facility fulfill its primary use — to verify that nuclear weapons work. After the United States suspended underground nuclear testing in 1992, lab officials argued that some way was needed to verify the computer models that replaced testing.
Dr. Herrmann said that within 24 hours of the latest experiment, someone working on the program of modernizing nuclear weapons contacted the NIF team. “They’re interested in applying this to important questions that they have,” he said.
The center of the National Ignition Facility is the target chamber, a metal sphere 33 feet wide with gleaming diagnostic equipment radiating outward.
The laser complex fills a building with a footprint equal to three football fields. Each blast starts with a small laser pulse that is split via partly reflecting mirrors into 192 beams, then bounced back and forth through laser amplifiers before converging on a gold cylinder that is about the size and shape of a pencil eraser.
The laser beams enter at the top and bottom of the cylinder, vaporizing it. That generates an inward onslaught of X-rays that compresses a BB-size fuel pellet of carefully frozen deuterium and tritium, the heavier forms of hydrogen. In a brief moment, the imploding atoms fuse together.
Since the initial promising 2014 results, the NIF scientists have tinkered with the setup of the experiment. The capsules containing the hydrogen are now made of diamond instead of plastic — not because diamond is stronger but because it absorbs X-rays more readily. The scientists adjusted the design of the gold cylinder and the laser pulse to minimize instabilities.
The scientists now also have better diagnostic tools.
After years of only modest improvements, the combinations of modifications started paying off, and the calculations indicated that the Aug. 8 shot might triple what NIF had produced in the spring. Instead, the gain was a factor of eight, far more than had been predicted.
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[1] Url:
https://www.nytimes.com/2021/08/17/science/lasers-fusion-power-watts-earth.html
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