Technology: Laser-Cooled Neutral Plasma Created by Scientists - PressFrom - US
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TechnologyLaser-Cooled Neutral Plasma Created by Scientists

23:20  03 january  2019
23:20  03 january  2019 Source:   newsweek.com

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Plasma is one of the four fundamental states of matter, and was first described by chemist Irving Langmuir in the 1920s. Plasma can be artificially generated by heating or subjecting a neutral gas to

Plasmas are supposed to be hot. Hydrogen nuclei undergo fusion in the Sun because plasma You are going to email the following Really cool neutral plasmas Message Subject (Your Name) has forwarded a page to you from Science

Laser-Cooled Neutral Plasma Created by Scientists© Brandon Martin/Rice University

For the first time, scientists have created laser-cooled neutral plasma. The temperatures reached are around 50 times colder than that of deep space, with the plasma reaching -273C.

Normally we think of lasers as being used to heat things up. However, laser cooling is the opposite—using laser light to cool down a physical system. If scientists can work out how to cool atomic gases, it opens up the “ultracold world,” Tom Killian, of Rice University, told Newsweek. This, he said, would allow them to cool down atomic gasses to about a millionth of a degree above absolute zero, “where the bizarre laws of quantum mechanics take over,” he explains.

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Laser cooling refers to a number of techniques in which atomic and molecular samples are cooled down to near absolute zero. Laser cooling techniques rely on the fact that when an object (usually an atom) absorbs and re-emits a photon (a particle of light) its momentum changes.

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Killian, Thomas Langin and Grant Gormon, also of Rice University, worked out a way to apply the tricks of laser cooling to ions in a neutral plasma.  Plasma is one of the four fundamental states of matter, after solids, liquids and gases. It is often produced in extremely hot places—like the Sun, for example.

In their experiment, Langin used a set of 10 lasers of different wavelengths to cool the neutral plasma. They vaporized strontium metal with one set of lasers, which trapped and cooled a set of atoms. They then ionized the the ultracold gas with a second set. This second pulse converted the gas into a plasma, which expanded rapidly and then dissipated.

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A non- neutral plasma is a plasma for which the total charge is sufficiently different from zero, so that the electric field created by the un- neutralized charge plays an important or even dominant role in the plasma dynamics.

The plasma acceleration structures are created either using ultra-short laser pulses or energetic particle beams that are matched to the plasma parameters. Under normal conditions the plasma will be macroscopically neutral (or quasi- neutral ), an equal mix of electrons and ions in equilibrium.

"If an atom or ion is moving, and I have a laser beam opposing its motion, as it scatters photons from the beam it gets momentum kicks that slow it," Killian said in a statement. "The trick is to make sure that light is always scattered from a laser that opposes the particle's motion. If you do that, the particle slows and slows and slows."

By cooling down the neutral plasma, the researchers have opened up new possibilities for studying plasmas in extreme environments, such as inside white dwarf stars and in the center of Jupiter. Findings are published in the journalScience.

The immediate applications of this research are not yet clear. The team is now working to make even colder plasmas. “The ultimate limit, unless we discover some clever new tricks, is a temperature of about … about 100 times colder than we have demonstrated.” One of the limitations of the research is that the probe to measure temperatures can only go down so far.

“We have just started working with laser cooling,” he continued. We will try to push colder. We will try to develop new temperature probes to measure colder temperatures. It is predicted that if we cool far enough without letting the density get too low, the system will form a crystalline plasma, called a Wigner crystal. It is believed that ions in the center of a White dwarf star exist in this state.”

Killian said the main goal of laser cooling is to “explore the unknown,” adding that “the ‘frontier’ of cold has always been irresistible for physicists.”

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