The sun burns in a lab

Friday 30 April 2010

Scientists strike atoms with impossibly high energy levels  

imageWHAT has kept the sun burning bright for millions of years without fail could soon be within reach of human technology. Scientists have been working towards creating controlled nuclear fusion reactions in labs but simulating the sun is not child’s play.



All nuclei are positively-charged and the energy needed to overcome their repulsion for each other is immense. Scientists around the globe have been trying to strike nuclei with impossibly high energy levels. Once the nuclei fuse, however, tremendously higher amounts of energy are released. In an article published in Science on March 5, S H Glenzer and group at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory show they have been able to deliver more than 1 megajoule of laser energy to a target in billionths of a second.

This is 30 times the energy ever delivered in the world thus far. How and more importantly where they were able to achieve this feat transports one to the sets of a science-fiction movie. A 10-storey building sprawled across an area of three football fields, NIF houses 192 giant lasers. It is capable of focusing millions of joules of energy on tiny targets, creating conditions similar to stars and cores of planets.

Glenzer and team fired the 192 lasers simultaneously on a target called the “hohlraum”. An eraser-sized cylinder, it contains a tiny spherical target filled with deuterium and tritium, two isotopes of hydrogen. Inside the cylinder, the laser energy is converted to Xrays which compress the fuel until it is hotter than 111.11 million°C under pressures billions of times that on Earth. Such conditions force the hydrogen nuclei to convert into plasma—a unique state of matter in which fusion is achieved releasing million times more energy than what was needed initially.

This experiment is the first that did not turn unstable from the laser-plasma reaction. “Its significance is also in achieving the ignition point,” said Prabhat Ranjan, plasma physicist from Dhirubhai Ambani Institute of Information and Communication Technology in Gandhinagar. “A piece of paper can burn without needing the ignition source. The fusion reaction, too, should be able to sustain itself without an external supply of energy,” he added.

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