This is hotter than the interior of our Sun, which is about 15 million degrees Kelvin, and also hotter than any previous temperature ever achieved on Earth, they say.
They don't know how they did it.
The feat was accomplished in the Z machine at Sandia National Laboratories.
"At first, we were disbelieving," said project leader Chris Deeney. "We repeated the experiment many times to make sure we had a true result."
Thermonuclear explosions are estimated to reach only tens to hundreds of millions of degrees Kelvin; other nuclear fusion experiments have achieved temperatures of about 500 million degrees Kelvin, said a spokesperson at the lab.
The achievement was detailed in the Feb. 24 issue of the journal Physical Review Letters.
The Z machine is the largest X-ray generator in the world. It』s designed to test materials under extreme temperatures and pressures. It works by releasing 20 million amps of electricity into a vertical array of very fine tungsten wires. The wires dissolve into a cloud of charged particles, a superheated gas called plasma.
A very strong magnetic field compresses the plasma into the thickness of a pencil lead. This causes the plasma to release energy in the form of X-rays, but the X-rays are usually only several million degrees.
Sandia researchers still aren』t sure how the machine achieved the new record. Part of it is probably due to the replacement of the tungsten steel wires with slightly thicker steel wires, which allow the plasma ions to travel faster and thus achieve higher temperatures.
One thing that puzzles scientists is that the high temperature was achieved after the plasma』s ions should have been losing energy and cooling. Also, when the high temperature was achieved, the Z machine was releasing more energy than was originally put in, something that usually occurs only in nuclear reactions.
Sandia consultant Malcolm Haines theorizes that some unknown energy source is involved, which is providing the machine with an extra jolt of energy just as the plasma ions are beginning to slow down.
Sandia National Laboratories is located by Albuquerque New Mexico and is part of the U.S. Department of Energy (DOE).作者: Adelyn 時間: 2006-3-21 04:50
[B]Bubbles Get Hotter than the Sun[/B]
By Michael Schirber
LiveScience Staff Writer
posted: 03 March 2005
06:55 am ET
Just as blowing up a bubble leads to a pop, so can shrinking it. Rapidly collapsing bubbles have long been known to reach astonishing temperatures.
Now scientists have measured just how hot. And they're surprised.
"When bubbles in a liquid get compressed, the insides get hot C very hot," said Ken Suslick of the University of Illinois at Urbana-Champaign. "The temperature we measured C about 20,000 degrees Kelvin [35,540 Fahrenheit] C is four times hotter than the surface of our Sun."
The bubbles are driven to form and collapse in a process called sonoluminescence, in which a liquid is blasted with high-frequency sound waves between 20 and 40 kilohertz (the highest pitch that humans can hear is about 20 kilohertz).
Inside a collapsing bubble, the temperature rises precipitously. Atoms and molecules collide with high-energy particles to create a fourth state of matter, called plasma. The process emits light.
But the heating is so brief and localized that it cannot be measured directly with a thermometer.
The emitted light, however, can be analyzed to determine the temperature of the imploding gas. Previous measurements of multiple-bubble sonoluminescence have found temperatures of 5,000 Kelvin, or 8,500 degrees Fahrenheit.
Suslick and his graduate student David Flannigan were able to measure the temperature of single bubbles, which are not disturbed by neighboring ones. The light from these isolated bubbles is bright enough to be seen by the naked eye.
The high temperatures, measured by Suslick and Flannigan, were partly expected from theory, but solid evidence has been lacking, said Detlef Lohse from the University of Twente, The Netherlands.
The new experiments "are a milestone in single-bubble sonoluminescence, as they constitute the first direct measurement of the temperature and the state of matter in a single bubble at collapse," said Lohse, who was not involved in the work.
The light that is seen is coming from the outer surface of the rapidly shrinking bubble. Inside this surface, the temperature is believed to be even higher. Some have predicted that in these extreme conditions nuclear fusion might occur, but no conclusive evidence has yet been found.
The recent results are reported in the March 3 issue of the journal [I]Nature[/I].作者: Adelyn 時間: 2006-3-21 04:51
[B]Simple Experiment Creates Surprising State of Matter[/B]
By Robert Roy Britt
LiveScience Managing Editor
posted: 06 December 2005
02:01 am ET
Physicists at the University of Chicago essentially dropped a marble into loosely packed sand, producing a jet of sand grains that briefly behaves like a special type of dense fluid.
They describe it as a novel state of matter.
"We're discovering a new type of fluid state that seems to exist in this combination of gas―air in this case―and a dense arrangement of particles," said lead researcher Heinrich Jaeger. "It's just a most amazing phenomenon."
[B]How it works[/B]
Strange states of matter are sometimes created in super-cold conditions approaching absolute zero. Things get weird there. But this experiment was done at room temperature.
[CENTER][B]Images at top are from a high-speed video of a granular jet produced by the impact of a marble into sand at atmospheric pressure. Bottom row is a les impressive jet created at reduced pressure.[/B] Images courtesy of Heinrich Jaeger, University of Chicago[/FONT][/CENTER]
"The jet acts like an ultra-cold, ultra-dense gas, not in terms of ambient temperature, but in terms of how we define temperature via the random motion of particles," Jaeger explained. "Inside the jet there is very, very little random motion."
Though announced yesterday, the phenomenon was first noted in 2001 in work by Sigurdur Thoroddsen and Amy Shen, who were then at the University of Illinois at Urbana-Champaign.
Jaeger encouraged his graduate student Andrew Flior to reproduce the experiment, and a group led by Detlef Lohse at the University of Twente in The Netherlands used high-speed video and computer simulations to suggest the jet was caused by gravity as material rushed in to fill the void left behind by the impacting object.
The researchers made X-ray images at 5,000 frames per second. They conclude that air compressed between the sand grains provides most of the energy to drive the jet, since the same experiment performed at artificially low air pressure does not produce a significant jet.
"The result is totally unexpected," said Lohse. "One would think that the effect of air would weaken the jet, but what is the case is just the opposite."
The jet is broken into two distinct segments, one solid and the other a stream of droplets.
"One of the biggest questions that we have still not solved is why this jet is so sharply delineated." Jaeger said. "Why are there these beautiful boundaries? Why isn't this whole thing just falling apart?"
[B]You can do it[/B]
The research was funded by the National Science Foundation and the Department of Energy.
The basics of the experiment can be repeated at home, though without all the government funding and a fancy X-ray imager you probably won't get the full effect.
Pour a cup of powdered sugar into another container to ensure it is loosely packed, Jaeger explains. Drop a marble into the cup. "Once you drop that marble in there, you see that jet emerging, but you have to look fast."
The discovery is detailed in the December issue of the journal [I]Nature Physics[/I].
