PASER; EINSTEIN'S LITTLE MACHINE
Posted on Wednesday, September 13, 2006 @ 23:20:44 UTC by vlad
|
|
PARTICLE ACCELERATION BY STIMULATED EMISSION OF RADIATION (PASER for short), a sort of particle analog of the laser process, has been demonstrated, for the first time, by a team of physicists from the Technion-Israel Institute of Technology using the accelerator facilities at the Brookhaven National Lab.
In a regular laser, photons traveling through an active medium (a body of excited atoms) will stimulate the atoms, through collisions, to surrender their energy in the form of additional emitted photons; this coherent process builds on itself until a large pulse of intense light exits the cavity in which the amplification takes place. In the new proof-of-principle PASER experiment, the active medium consists of a CO2 vapor, and instead of surrendering their energy in the form of stimulated photons, the atoms transfer their energy to a beam of electrons. The electrons stimulate the atoms into giving up their surplus energy through collisions. The electrons' energy is amplified in a coherent way; that is, the electrons are directly accelerated by a direct and coordinated quantum transfer of energy. Although millions of collisions are involved for each electron, no heat is generated. The transferred energy goes into an enhanced electron motion. One could say that here was a laser which produced no laser light, only a laser-like transfer of energy resulting in electron acceleration.
It should be said that the electrons began with an energy of 45 million electron volts (MeV) and absorbed only a modest energy of about 200 thousand electron volts (keV). The electrons, first accelerated in a conventional accelerator, were also exposed to a CO2 laser and also sent through a "wiggler" array of magnets; these actions served to carve a larger bunch of electrons into separate micro-bunches, which are timed and modulated in energy in order to more readily partake of the resonant PASER process in the CO2-filled resonant cavity a little farther along (see figures at http://www.aip.org/png/2006/268.htm). Being able to accelerate electrons with energy stored in individual atoms/molecules, a concept now demonstrated with the PASER, provides new opportunities since the accelerated electrons may prove to be significantly "cooler" (they are more collimated in velocity) than in some other prospective acceleration schemes, enabling in turn the secondary generation of high-quality x rays, which are an essential tool in nano-science. (Banna, Berezovsky, Schachter, Physical Review Letters, upcoming article.)
EINSTEIN'S LITTLE MACHINE. Albert Einstein was the ultimate theorist, having spun out mathematical explanations of space and time, gravity, atoms, and quantum phenomena. And yet Einstein also had his experimentalist side too. He grew up in a household where gadgets were all around (his father owned an electrical instrument factory), and he worked in a patent office where a parade of detailed engineering drawings came past his view every day. In fact he built several practical devices and took out numerous patents of his own. One of Einstein's creations, which he called his "Maschinchen," or little machine, sought to measure voltages at the level of 0.0005 volts. This sort of precision is easy to achieve nowadays but was not possible in 1907, when Einstein developed a contraption which took charge induced on a metal plate by a weak nearby potential and then stored it in a special accumulator; the effect of the small voltage signal could then be multiplied. Three known versions of this machine are known to exist, at least one of which was used in an experiment conducted by Walter Gerlach (who later worked on the Stern-Gerlach discovery of electron spin). Now, two scientists at the University of Ghent in Belgium have performed computer simulations to show in detail how the Maschinchen worked. Danny Segers (danny.segers@ugent.be) says that he and Jos Uyttenhove are building a replica to better explore Einstein's handiwork. (American Journal of Physics, August 2006)
--------
Source: PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics
News
Number 792 September 13, 2006 by Phillip F. Schewe, Ben Stein,
and
Davide Castelvecchi www.aip.org/pnu
|
| |
|
Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.
| |
Average Score: 5
Votes: 1
| |
|
