NIST Light Source Illuminates Plasma Of Experimental Reactor

Source:

http://www.sciencedaily.com/releases/2007/10/071011161327.htm

Science Daily — Using a device that can turn a tiny piece of laboratory space into an ion cloud as hot as those found in a nuclear fusion reactor, physicists at the National Institute of Standards and Technology are helping to develop one of the most exotic “yardsticks” on earth, an instrument to monitor conditions in the plasma of an experimental fusion reactor. Their measurement tool also is used in incandescent light bulbs–it’s the element tungsten.
The intended beneficiary of this research is ITER, a multinational project to build the world’s most advanced fusion test reactor. ITER, now under construction in Cadarache, France, will operate at high power in near-steady-state conditions, incorporate essential fusion energy technologies and demonstrate safe operation of a fusion power system. It will be a tokamak machine, in which a hot—250 million degrees Celsius—plasma of hydrogen isotope ions, magnetically confined in a huge toroidal shape, will fuse to form helium nuclei and generate considerable amounts of energy, much the same way energy is generated in the sun.
One major issue is how to measure accurately the temperature and density of the plasma, both of which must reach critical values to maintain the fusion process. Any conventional instrument would be incinerated almost instantly. The usual solution would be to use spectroscopy: monitor the amount and wavelengths of light emitted by the process to deduce the state of the plasma. But light comes from electrons as they change their energies, and at tokamak temperatures the hydrogen and helium nuclei are completely ionized -- no electrons left. The answer is to look at a heavier element, one not completely ionized at 250 million degrees, and the handy one is tungsten. The metal with the highest melting point, tungsten is used for critical structures in the walls of the tokamak torus, so some tungsten atoms always are present in the plasma.
To gather accurate data on the spectrum of highly ionized tungsten, as it would be in the tokamak, NIST physicists use an electron beam ion trap (EBIT), a laboratory instrument which uses a tightly focused electron beam to create, trap and probe highly charged ions. An ion sample in the EBIT is tiny—a glowing thread about the width of a human hair and two to three centimeters long -- but within that area the EBIT can produce particle collisions with similar energies to those that occur in a fusion plasma or a star.
In a pair of papers,* the NIST researchers uncovered previously unrecognized features of the tungsten spectrum, effects only seen at the extreme temperatures that produce highly charged ions. The NIST team has reported several previously unknown spectral lines for tungsten atoms with 39 to 47 of their 74 electrons removed. One particularly significant discovery was that an anomalously strong spectral line that appears at about the energies of an ITER tokamak is in fact a superposition of two different lines that result from electron interactions that, under more conventional plasma conditions, are too insignificant to show up.
Team member John Gillaspy observes, “That’s part of the fascination of these highly charged ions. Things become very strange and bizarre. Things that are normally weak become amplified, and some of the rules of thumb and scaling laws that you learned in graduate school break down when you get into this regime.” The team has proposed a possible new fusion plasma diagnostic based on their measurements of the superimposed lines and supporting theoretical and computational analyses.
Articles: * Yu. Ralchenko. Density dependence of the forbidden lines in Ni-like tungsten. J. Phys. B: At. Mol. Opt. Phys. 40 (2007) F175-F180
Yu. Ralchenko, J. Reader, J.M. Pomeroy, J.N. Tan and J.D. Gillaspy. Spectra of W(39+)-W(47+) in the 12-20 nm region observed with an EBIT light source. J. Phys. B: At. Mol. Opt.Phys. 40 (2007) 3861-3875.
Note: This story has been adapted from material provided by National Institute of Standards and Technology.

Fausto Intilla
www.oloscience.com

Physicist Defends Einstein's Theory And 'Speed Of Gravity' Measurement

Source:

http://www.sciencedaily.com/releases/2007/10/071003130816.htm

Science Daily — Scientists have attempted to disprove Albert Einstein's theory of general relativity for the better part of a century. After testing and confirming Einstein's prediction in 2002 that gravity moves at the speed of light, a professor at the University of Missouri-Columbia has spent the past five years defending the result, as well as his own innovative experimental techniques for measuring the speed of propagation of the tiny ripples of space-time known as gravitational waves.
Sergei Kopeikin, associate professor of physics and astronomy in the College of Arts and Science, believes that his latest article, "Gravimagnetism, causality, and aberration of gravity in the gravitational light-ray deflection experiments" published along with Edward Fomalont from the National Radio Astronomical Observatory, arrives at a consensus in the continuing debate that has divided the scientific community.
An experiment conducted by Fomalont and Kopeikin five years ago found that the gravity force of Jupiter and light travel at the same speed, which validates Einstein's suggestion that gravity and electromagnetic field properties, are governed by the same principle of special relativity with a single fundamental speed. In observing the gravitational deflection of light caused by motion of Jupiter in space, Kopeikin concluded that mass currents cause non-stationary gravimagnetic fields to form in accordance with Einstein's point of view.
Einstein believed that in order to measure any property of gravity, one has to use test particles. "By observing the motion of the particles under influence of the gravity force, one can then extract properties of the gravitational field," Kopeikin said. "Particles without mass -- such as photons -- are particularly useful because they always propagate with constant speed of light irrespectively of the reference frame used for observations."
"The property of gravity tested in the experiment with Jupiter also is called causality. Causality denotes the relationship between one event (cause) and another event (effect), which is the consequence (result) of the first. In the case of the speed of gravity experiment, the cause is the event of the gravitational perturbation of photon by Jupiter, and the effect is the event of detection of this gravitational perturbation by an observer.
"The two events are separated by a certain interval of time which can be measured as Jupiter moves, and compared with an independently-measured interval of time taken by photon to propagate from Jupiter to the observer. The experiment found that two intervals of time for gravity and light coincide up to 20 percent. Therefore, the gravitational field cannot act faster than light propagates."
Other physicists argue that the Fomalont-Kopeikin experiment measured nothing else but the speed of light. "This point of view stems from the belief that the time-dependent perturbation of the gravitational field of a uniformly moving Jupiter is too small to detect," Kopeikin said. "However, our research article clearly demonstrates that this belief is based on insufficient mathematical exploration of the rich nature of the Einstein field equations and a misunderstanding of the physical laws of interaction of light and gravity in curved space-time."
The research paper that discusses the gravimagnetic field appears in the October edition of Journal of General Relativity and Gravitation.
Note: This story has been adapted from material provided by University of Missouri-Columbia.

Fausto Intilla
www.oloscience.com

Gamma Ray Lasers? Positronium Created In The Lab

Source:

http://www.sciencedaily.com/releases/2007/09/070912154633.htm

Science Daily — Physicists at UC Riverside have created molecular positronium, an entirely new object in the laboratory. Briefly stable, each molecule is made up of a pair of electrons and a pair of their antiparticles, called positrons.

The research paves the way for studying multi-positronium interactions -- useful for generating coherent gamma radiation -- and could one day help develop fusion power generation as well as directed energy weapons such as gamma-ray lasers. It also could help explain how the observable universe ended up with so much more matter than "antimatter."
The researchers made the positronium molecules by firing intense bursts of positrons into a thin film of porous silica, which is the chemical name for the mineral quartz. Upon slowing down in silica, the positrons were captured by ordinary electrons to form positronium atoms.
Positronium atoms, by nature, are extremely short-lived. But those positronium atoms that stuck to the internal pore surfaces of silica, the way dirt particles might cling to the inside surface of the holes in a sponge, lived long enough to interact with one another to form molecules of positronium, the physicists found.
"Silica acts in effect like a useful cage, trapping positronium atoms," said David Cassidy, the lead author of the research paper and an assistant researcher working in the laboratory of Allen Mills, a professor of physics, the research paper's coauthor. "This is the first step in our experiments. What we hope to achieve next is to get many more of the positronium atoms to interact simultaneously with one another -- not just two positronium atoms at a time."
When an electron meets a positron, their mutual annihilation may ensue or positronium, a briefly stable, hydrogen-like atom, may be formed. The stability of a positronium atom is threatened again when the atom collides with another positronium atom. Such a collision of two positronium atoms can result in their annihilation, accompanied by the production of a powerful and energetic type of electromagnetic radiation called gamma radiation, or the creation of a molecule of positronium, the kind Cassidy and Mills observed in their lab.
"Their research is giving us new ways to understand matter and antimatter," said Clifford M. Surko, a professor of physics at UC San Diego, who was not involved in the research. "It also provides novel techniques to create even larger collections of antimatter that will likely lead to new science and, potentially, to important new technologies."
Matter, the "stuff" that every known object is made of, and antimatter cannot co-exist close to each other for more than a very small measure of time because they annihilate each other to release enormous amounts of energy in the form of gamma radiation. The apparent asymmetry of matter and antimatter in the visible universe is an unsolved problem in physics.
Currently, antimatter finds use in medicine where it helps identify diseases with the Positron Emission Tomography or PET scan.
Cassidy and Mills plan to work next on using a more intense positron source to generate a "Bose-Einstein condensate" of positronium -- a collection of positronium atoms that are in the same quantum state, allowing for more interactions and gamma radiation. According to them, such a condensate would be necessary for the development of a gamma-ray laser.
Study results appear in the Sept. 13 issue of Nature.
Their research was funded by the National Science Foundation.
Note: This story has been adapted from a news release issued by University of California - Riverside.

Fausto Intilla

www.oloscience.com